U.S. Department of 

Transportation

Federal Railroad 

Administration

Application of Welded Steel Sandwich Panels 

for Tank Car Shell Impact Protection 

Office of Research

and Development

Washington, DC 20590

DOT/FRA/ORD-13/19 Final Report

April 2013
NOTICE

This document is disseminated under the sponsorship of the 

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report.
i

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

April 2013

3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE

Application of Welded Steel Sandwich Panels for Tank Car Shell Impact Protection

5. FUNDING NUMBERS

DTFR53-00-C-00012 Task 

Order 264 6. AUTHOR(S) and FRA COTR

Michael E. Carolan, David Y. Jeong, Benjamin Perlman, Yellapu V. Murty, Shannon 

Namboodri, Bob Kurtz, R.K. Elzey, Satima Anankitpaiboon, Lucy Tunna, and Robert Fries

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

John A. Volpe National Transportation Systems Center

55 Broadway

Cambridge, MA 02142

Cellular Materials International, Inc.

1200 Five Springs Road, Suite 201

Charlottesville, VA 22902

Transportation Technology Center, Inc.

55500 DOT Road

Pueblo, CO 81001

8. PERFORMING ORGANIZATION 

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Research and Development

Washington, DC 20590

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

DOT/FRA/ORD-13/19

11. SUPPLEMENTARY NOTES

Program Manager: Francisco González III

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

This report describes research conducted to examine the application of sandwich structure technology to provide protection 

against the threat of an indenter striking the side or shell of a tank car in the event of an accident. This research was conducted in 

two phases over a 3-year period. Testing and analysis of flat, welded steel sandwich panels was conducted in the initial phase of 

the research. Based on the observations and results from that initial phase, a curved, welded steel sandwich panel was designed 

and built to protect the side or shell of a decommissioned liquid chlorine tank car during a full-scale impact test. Although the 

protective panel experienced severe damage, the commodity-carrying tank experienced only permanent deformation and did not 

puncture.

14. SUBJECT TERMS

Tank car, impact, protective panel

15. NUMBER OF PAGES

76

16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

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OF THIS PAGE

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19. SECURITY CLASSIFICATION

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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18

298-102
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2)

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2)

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2)

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 7 8 9 10 11 12 13

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Contents

Executive Summary........................................................................................................................ 1

1. Introduction............................................................................................................................ 3

1.1 Research Objectives......................................................................................................... 6

1.2 Sandwich Panels .............................................................................................................. 7

1.3 Previous Test Series......................................................................................................... 7

1.3.1 Preproduction Compression Testing at CMI ............................................................. 8

1.3.2 Uniaxial Compression Testing at ATLSS................................................................ 11

1.3.3 Three-point Bend Testing at ATLSS ....................................................................... 14

2. Manufacturing Considerations............................................................................................. 22

2.1 Materials ........................................................................................................................ 22

2.2 Welding.......................................................................................................................... 24

3. Full-Scale Impact Testing at TTC........................................................................................ 28

3.1 Overall Approach and Objectives.................................................................................. 28

3.2 Protective Panel Design, Material Selection, and Manufacturing ................................. 28

3.3 Indenter Modification .................................................................................................... 31

3.4 Test Setup....................................................................................................................... 32

3.5 Instrumentation .............................................................................................................. 34

3.5.1 Ram Car Accelerometers and Speed Sensors.......................................................... 35

3.5.2 Tank Car Pressure Transducers ............................................................................... 36

3.5.3 Speed Sensors .......................................................................................................... 36

3.5.4 Real-Time Photography and Targets....................................................................... 36

3.5.5 Special Considerations for Protecting Equipment ................................................... 39

3.5.6 Data Acquisition ...................................................................................................... 39

3.6 Test Results and Observations....................................................................................... 40

4. Summary.............................................................................................................................. 49

5. Discussion............................................................................................................................ 51

6. References............................................................................................................................ 54

Appendix A. Estimates of Labor, Material, and Capital Equipment for Manufacturing.............. 55

Appendix B. Protective Panel Attachments to Tank Car.............................................................. 65

Abbreviations and Acronyms ....................................................................................................... 68
iv

Illustrations

Figure 1. Schematic of Full-Scale Shell Impact Test Setup ........................................................... 5

Figure 2. Research Framework....................................................................................................... 6

Figure 3. Sandwich Panel with Components Identified.................................................................. 7

Figure 4. Confluence of Full-Scale and Component Level Tests................................................... 8

Figure 5. Load versus Position for Diamond Panel (Left) and Round-Tube Panel (Right) ........... 9

Figure 6. Photos of Diamond Panel during Crushing..................................................................... 9

Figure 7. Photos of Round-Tube Panel during Crushing.............................................................. 10

Figure 8. Drawing of Recommended Round Tube Core Design to Prevent Lateral Movement.. 10

Figure 9. 3-Inch 4130 Pipe Sample with Tubes Welded Together............................................... 11

Figure 10. Photos of Manufactured Panels for Uniaxial Compression Tests............................... 13

Figure 11. Load versus Displacement Curves for Round-Tube and Diamond Core Panels......... 14

Figure 12. Photos of Panels for Three-Point Bend Testing .......................................................... 16

Figure 13. Photo of Panel in Three-Point Bend Setup.................................................................. 17

Figure 14. Deformation of Panel No. 0047-20 and Corresponding Load-Displacement Curve .. 18

Figure 15. Deformation of Panel No. 0047-21 and Corresponding Load-Displacement Curve .. 19

Figure 16. Deformation of Panel No. 0047-17 and Corresponding Load-Displacement Curve .. 20

Figure 17. Panel in Three-Point Bend Test with Bubble Wrap to Estimate Load Transfer Area 21

Figure 18. Single (Left) and Double (Right) GMAW-P Plug Welds to 1-Inch Pipe.................... 25

Figure 19. Average Load at Failure for Various Welds................................................................ 26

Figure 20. Load to Failure for Various Weld Configurations at 4-Inch, 8-Inch and 12-Inch 

Spacing.................................................................................................................................. 27

Figure 21. Manufacturing Panel for Impact Test on Concave Fixture (Left) and Convex Fixture 

(Right)................................................................................................................................... 30

Figure 22. Protective Panel........................................................................................................... 31

Figure 23. Modification of 6-Inch by 6-Inch Indenter.................................................................. 31

Figure 24. Photos of Indenter Cap on 6-Inch by 6-Inch Indenter................................................. 32

Figure 25. Test Setup – View from East (Left) Side .................................................................... 32

Figure 26. Skid System................................................................................................................. 33

Figure 27. Welded Beam Connecting the Tank Car to the Skid System...................................... 33

Figure 28. Test Setup – View from West (Right) Side................................................................. 34

Figure 29. Accelerometer Locations on Ram Car ........................................................................ 35

Figure 30. Top View of Camera Setup ......................................................................................... 36

Figure 31. Side View of Camera Setup ........................................................................................ 37

Figure 32. Side View of Target Locations on Ram Car ............................................................... 37

Figure 33. Top View of Target Locations on Ram Car................................................................ 38

Figure 34. Side View of Target Locations on Tank Car and Protective Panel............................. 38

Figure 35. Top View of Target Locations on Tank Car ............................................................... 39

Figure 36. Protective Shell for Onboard HS Camera ................................................................... 39

Figure 37. Series of Images Showing Side Impact Progression ................................................... 40

Figure 38. Tank Car and Panel after Impact................................................................................. 41

Figure 39. Damage on Protective Panel – Impact Side ................................................................ 42

Figure 40. Damage on Protective Panel – Left and Right Sides................................................... 42

Figure 41. Damage on Back of Protective Panel .......................................................................... 43

Figure 42. Dent in the Jacket ........................................................................................................ 43
v

Figure 43. Deformation of Commodity Tank............................................................................... 44

Figure 44. Surface Crack on the Tank Car ................................................................................... 44

Figure 45. Tank Car Placement after Impact................................................................................ 45

Figure 46. Ram Car Acceleration ................................................................................................. 45

Figure 47. Ram Car Force............................................................................................................. 46

Figure 48. Ram Car Speed during Impact .................................................................................... 46

Figure 49. Ram Car Longitudinal Travel...................................................................................... 47

Figure 50. Kinetic Energy versus Time ........................................................................................ 48

Figure 51. Ram Car Force versus Distance .................................................................................. 48

Figure 52. Schematic of Protective Panel used in Full-scale Impact Test.................................... 49

Figure 53. Impact Scenarios with Equivalent Kinetic Energy...................................................... 51

Figure 54. Various tank car coverage strategies........................................................................... 55

Figure 55. Railroad Tank Car Protective Panel and Mounting Strap Processing......................... 57

Figure 56. Demonstration of Attachment Scheme........................................................................ 58

Figure 57. Stud Weld after Tensile Test (left) and Bend Test (right)........................................... 65

Figure 58. Cross Section of Weld................................................................................................. 66

Figure 59. HAZ in TC128-B Steel................................................................................................ 66

Figure 60. HAZ in Stud Bolt Region............................................................................................ 66

Figure 61. Microstructure of Stud Bolt......................................................................................... 66
vi

Tables

Table 1. Recent Railroad Hazmat Accidents.................................................................................. 3

Table 2. Panel Details for Quasi-Static Compression Tests......................................................... 12

Table 3. GMAW-P Welding Parameters...................................................................................... 12

Table 4. Panel Details for Three-Point Bend Tests....................................................................... 16

Table 5. Minimum Mechanical Properties of Steels Considered ................................................. 22

Table 6. Average Mechanical Properties of as Received Tubes and Face Sheets........................ 23

Table 7. Summary of Different Welding Methods....................................................................... 24

Table 8. Summary of Previous Full-Scale Shell Impact Tests ..................................................... 28

Table 9. Tensile Test Results for Considered Materials............................................................... 29

Table 10. Instrumentation Summary............................................................................................. 34

Table 11. Ram Car Accelerometers.............................................................................................. 35

Table 12. Pressure Transducers .................................................................................................... 36

Table 13. Summary of Full-scale Tank Car Shell Impact Tests Conducted at TTC .................... 52

Table 14. Cost Estimates for Panel and Mounting Hardware....................................................... 59

Table 15. Labor Estimate for Panel Manufacturing...................................................................... 61

Table 16. Labor Estimate for Mounting Strap Manufacturing ..................................................... 62

Table 17. Detailed Material Cost and Weight Calculations ......................................................... 62

Table 18. Projected Capital Equipment Requirements for Protective Panel Manufacturing ....... 63

Table 19. Options for Tank Car Coverage.................................................................................... 64
1

Executive Summary

One of the objectives of research sponsored by the Federal Railroad Administration (FRA) 

Office of Research and Development is to improve the transportation safety of railroad tank cars 

carrying hazardous materials (hazmat). This objective can be accomplished by investing 

resources to improve either the track infrastructure or the equipment. The focus of this report is 

the latter.

This report describes research conducted to examine the application of sandwich structure 

technology to provide protection against the threat of an indenter striking the side or shell of a 

tank car in the event of an accident. The principal advantages of sandwich structures are their 

ability to dissipate impact energy and to redistribute the impact force. The research program was 

conducted in two phases. The initial phase of research entailed the testing and analysis of flat, 

welded steel sandwich panels with different core geometries and face sheet arrangements. This 

research included the selection of materials based on mechanical properties such as yield 

strength, ultimate tensile strength, and ductility. Various manufacturing processes such as 

welding practices were considered in the development and application of sandwich structure 

technology for shell protection purposes. The research conducted in the initial phase of the 

program is described in detail in a previous report.

Based on the observations and results from the initial stages of research, a curved, welded steel 

sandwich panel was designed and built to protect the side of a decommissioned liquid chlorine 

tank car during a full-scale impact test. Moreover, the full-scale tank car shell impact test

represented the culmination of the three-year research effort sponsored by FRA’s Office of 

Research and Development.

Several organizations contributed to the overall research effort. The John A. Volpe National 

Transportation Systems Center (Volpe Center) provided technical support by conducting 

analytical studies, designing various tests to generate technical information to develop the 

protective panel, and helping to guide the overall research effort. Cellular Materials 

International, Inc. (CMI) was under contract with FRA to provide expertise on sandwich panels 

concerning such aspects as manufacturing development, fabrication processes, and evaluation of 

material properties. Transportation Technology Center, Inc. (TTCI) prepared for and conducted 

the full-scale impact test.

In the full-scale impact test conducted at the completion of this research program, a 

DOT105J500W specification tank car was filled with water to an outage of 10 percent and was

pressurized to 100 psi. A 6-foot by 6-foot protective panel weighing approximately 900 pounds

was attached to the side of the tank car. The location of the panel covered the longitudinal center 

of the tank at its equator. A ram car weighing 295,725 pounds impacted the center of the panel 

at a speed of 17.8 miles per hour (mph), which corresponds to more than 3 million foot-pounds 

of kinetic energy. The impact was made using an indenter with a 12-inch by 12-inch footprint. 

Although the protective panel experienced severe damage, the commodity-carrying tank 

experienced only permanent deformation and did not puncture.
2

Using a 6-foot by 6-foot curved panel to protect the side of a tank car is similar to using a halfheight shield to protect the end or the head of a tank car. Given the dramatically improved safety 

performance of tank cars after head protection requirements were instituted, this similarity led to 

the idea of using protective panels based on sandwich structure technology to retrofit existing 

tank cars against the threat of side of shell impacts. A possible strategy to optimize the costs, 

risks, and benefits associated with shell protection might be partial protection of the tank. For 

example, some benefit balanced against cost and risk could be realized from protecting only the 

bottom half of the tank since accident statistics indicate that shell punctures are more likely to 

occur along the lower half of the tank. Partial protection schemes are outlined in Appendix A.

One area that remains open in terms of applying sandwich structure technology to protect 

railroad tank cars against shell puncture is how to effectively attach the protective panel to the 

tank structure. The attachments would need to be compliant or flexible in order to mitigate 

localized failures. Various concepts are outlined in Appendix B of this report, but ultimately the 

expertise and the experience of tank car manufacturers will be required to develop an appropriate 

design.

Absorbing and dissipating 3 million foot-pounds of energy represents a formidable challenge 

because the design of such a system is constrained by the maximum allowable weight and 

clearance standards for rail cars. The effect of weight and space budgets on designs to improve 

the safety performance of tank cars is discussed in previous work [6]. The protective panel 

designed and built for the full-scale impact test weighed approximately 900 pounds. If such 

panels covered the entire tank car shell, the resulting shell protection system would be well 

within weight and space limitations for tank cars built to 286,000-pound gross weights. The 

observations and results from the research described in this report suggest that sandwich 

structure technology can, in principle, be applied to provide protection to the tank car shell in the 

event of a shell impact. Moreover, protection against puncture is essential for tank cars carrying 

those materials with the greatest potential to harm humans and the environment if released.
3

1. Introduction

Approximately two million shipments of hazmat are made by rail in North America annually [1]. 

Rail is recognized as the safest mode of transportation for moving large quantities of hazmat 

over large distances. Most rail-hauled hazmat shipments are carried in tank cars.1 A review of 

accident statistics indicates that the safety performance of railroad tank cars has improved 

significantly over the past 25 years [2]. The improved safety trend is attributed to long-term 

research sponsored by the industry and the government regulatory agencies in North America, 

specifically the Federal Railroad Administration (FRA) and Transport Canada. Moreover, this 

research led to the development of thermal protection systems, double-shelf couplers, largecapacity pressure relief valves, and head protection. Subsequently, safety regulations were 

instituted to require these design features for particular tank cars depending on the commodity 

being transported.

However, accidents involving the release of hazmat from rail cars can result in property damage,

environmental damage, evacuation of nearby population, injuries, and fatalities. Furthermore, 

the severity of some recent accidents involving the release of hazardous materials has raised 

attention about the crashworthiness of railroad tank cars under accident loading conditions. 

Table 1 lists some railroad hazmat accidents over the last decade. In five of the accidents listed 

in the table, the probable cause of the derailment was determined to be either a broken rail (New 

Brighton, PA; Oneida, NY; and Arcadia, OH) or a failure at a rail joint (Minot, ND, and 

Painesville, OH). In the two most recent cases (Tiskilwa, IL, and Columbus, OH), probable 

cause has yet to be determined because investigations by the National Transportation Safety 

Board (NTSB) are ongoing.

Table 1. Recent Railroad Hazmat Accidents

Location Date

Minot, ND January 18, 2002

Macdona, TX June 29, 2004

Graniteville, SC January 5, 2005

Anding, MS July 10, 2005

Texarkana, AR October 15, 2005

New Brighton, PA October 20, 2006

Shepherdsville, KY January 16, 2007

Oneida, NY March 12, 2007

Painesville, OH October 10, 2007

Cherry Valley, IL June 19, 2009

Arcadia, OH February 6, 2011

Tiskilwa, IL October 17, 2011

Columbus, OH July 11, 2012

 1 Some railroad-hauled hazmat is also carried in covered hopper cars, intermodal containers, and piggyback trailers.
4

The hazmat accidents listed at the beginning of Table 1 (specifically, Minot, ND; Macdona, TX;

and Graniteville, SC) involved releases of toxic inhalation hazard (TIH) materials such as 

chlorine and anhydrous ammonia. But since the Painesville, OH, accident of October 2007 and 

the most recent accident in Columbus, OH, in July 2012, general-purpose cars carrying 

flammable materials such as ethanol have been breached. Moreover, data obtained from the 

Universal Machine Language Equipment Register (UMLER) in October 2011 indicate that 

general-purpose tank cars with DOT111 specification represent about two-thirds of the total tank 

car fleet, whereas pressure cars with DOT105 and DOT112 specifications represent less than 

one-fifth of the overall population.

2

Improving the safety of hazmat transportation by rail can be accomplished by investing resources 

in either the track or the equipment. Track-related improvements include upgrading the 

infrastructure and mandating more frequent maintenance and inspection programs, whereas 

equipment improvements entail the development of safety features pertaining to the rolling 

stock. The focus of this report is on the latter.

In general, accidental loss of hazmat lading from railroad tank cars occurs from four sources: (1) 

releases from head impacts, (2) releases from shell or side impacts, (3) releases from top fittings, 

and (4) releases from bottom fittings. Accident statistics collected on tank cars carrying TIH

materials suggest that while less than half of all releases are caused by failures in the head and 

shell, such failures account for 85 percent of the total gallons of lost lading [3]. Tank cars 

carrying TIH require safety features such as head shields to protect against the threat of a head 

impact. At the present time, however, a similar design feature to protect the tank against the 

threat of a shell or side impact has not yet been developed.

This report describes basic research to explore the application of welded steel sandwich panels as 

a means to provide protection to tank cars in the event of an impacting object striking the shell 

(i.e., side) of the tank. The research was conducted over a three-year span and was sponsored by 

the FRA Office of Research and Development. Several organizations made contributions to the 

research project. The John A. Volpe National Transportation Systems Center (Volpe Center) 

provided technical support by conducting analytical studies, designing various test series ranging 

from the component-level to the full-scale impact test, and helping to guide the overall research 

effort. Cellular Materials International, Inc. (CMI) was under contract with FRA to provide 

expertise concerning certain aspects of sandwich panels, such as manufacturing development, 

fabrication processes, and evaluations of material properties. The culmination of the research 

project was a full-scale shell impact test performed by Transportation Technology Center, Inc. 

(TTCI) in Pueblo, CO. The full-scale test demonstrated that a 6-foot by 6-foot protective 

sandwich panel made with 3-inch tubular cores could successfully protect a DOT105J500W 

specification tank car (filled to 10 percent outage and an internal pressure of 100 psi) against a 

shell or side impact from a 12-inch by 12-inch indenter mounted on a ram car weighing 295,725 

pounds and travelling at a speed of 17.8 miles per hour (mph). Figure 1 shows a schematic of 

the test setup in which the tank car with the protective panel is positioned against a barrier on one 

side and struck by the ram car on the other.

 2 UMLER data from October 2011 indicates that the North American tank car fleet consisted of a total of 314,561 

tank cars, at that time. Of this total population, 212,373 were DOT111 specification cars; 34,474 were DOT112 

cars; and 26,087 were DOT105 cars.
5

Figure 1. Schematic of Full-Scale Shell Impact Test Setup 

Section 1 of this report describes the objectives of the basic research and summarizes the 

research activities leading up to the conduct of the full-scale shell impact test. In previously

performed research activities, component-level testing was conducted to examine the 

performance of various sandwich panel designs under quasi-static loading conditions, 

specifically uniaxial compression and three-point bending. Comparisons between these test 

results and companion analyses were reported previously [4,5]. Moreover, the selection of the 

sandwich panel design used in the full-scale impact test was based on the results of these

component-level tests.

Section 2 of this report discusses manufacturing considerations regarding the construction of 

welded steel sandwich panels to protect the commodity-carrying tank from an impacting object. 

Such considerations include the selection of core geometry, selection of material for the core and 

the face sheets, and welding procedure to build the protective panel. The availability of the 

materials in certain thicknesses and shapes was a significant factor in the selection process.

Section 3 provides the specific details of the full-scale impact test. This section also includes a 

description of the selected panel design, material selection, and manufacturing processes. This 

section also describes a retrofit to modify the indenter that was mounted onto the ram car. A 

previous full-scale shell impact test that was performed to puncture the commodity-carrying tank 

used an indenter with a 6-inch by 6-inch footprint. CMI designed the retrofit, which entailed the

use of a steel cap reinforced by gussets to cover the existing indenter and create a 12-inch by 12-

inch footprint at the impact surface.

Section 4 summarizes the research results. Section 5 discusses the implications of the overall 

research effort. The potential use of sandwich structures as a retrofit to existing railroads tank 

cars as a protection system against the threat of shell puncture is considered.
6

The appendices of this report give detailed information regarding the manufacture of the 

protective panel that was developed for the full-scale shell impact test. This manufacturing 

information provided by CMI includes estimates of labor, material, and capital equipment

needed to build similar panels. In addition, options for the level of protection, in terms of 

coverage of the tank shell, are detailed. Finally, concepts or methods to attach the protective 

panel to existing tank cars are outlined.

1.1 Research Objectives

Over the past several decades, the Government and the railroad industry have sponsored research 

to improve the safety of railroad tank cars. This research led to the development of thermal 

protection, double-shelf couplers, large-capacity pressure relief valves, and head shields. In 

2007, shortly after the occurrence of a series of train accidents involving the release of TIH

materials, research efforts focused on understanding the structural performance of tank cars 

under accident loading conditions [2]. An objective of this research was to develop more 

effective strategies for maintaining tank structural integrity under accident loading conditions. 

The framework used in this research to evaluate potentially improved designs is shown in Figure 

2. 

Figure 2. Research Framework 

Given the space and weight limitations of existing tank cars, innovative use of materials to 

develop safety design features was also considered as an objective. One of the technologies 

identified to improve the puncture resistance of tank cars is the engineered metal sandwich 

structure [6]. Engineered metal sandwich structures offer several characteristics that appeared 

attractive for the purpose of increasing the puncture resistance of tank cars. The engineered 

metal sandwich structure can be fabricated in a variety of core geometries and from a variety of 

materials. Because sandwich structures can be made of commercial, off-the-shelf metal sheets

and structural shapes, a wide variety of geometries are achievable using similar fabrication 

techniques. Additionally, sandwich structures were thought to offer the potential to be 

constructed with a rounded (nonplanar) form that would conform to the side of the tank shell. 
7

1.2 Sandwich Panels

Sandwich structures are generally composed of two face sheets separated by a geometric core. 

In the traditional design of sandwich structures, the separation of the face sheets by the core 

increases the area moment of inertia of the panel, which produces a higher bending stiffness-toweight ratio than solid or monolithic plates containing the same volume of metal. The face 

sheets carry almost all of the bending and in-plane loads while the core carries the shear load to 

prevent the face sheets from sliding past one another. Although sandwich panels may be 

fabricated from a variety of materials, steel panels were considered in this research program. 

This program focused on readily-available materials (e.g. off-the-shelf metal sheets and tubes) 

that offered a high degree of manufacturability. An exemplar sandwich panel featuring tubular 

cores is shown in Figure 3.

Figure 3. Sandwich Panel with Components Identified 

In the event of a collision or impact scenario, welded steel sandwich panels provide puncture 

protection to the commodity-carrying tank through load blunting and energy absorption.

Blunting means that the impact load is distributed over a larger area of the tank with respect to 

the indenter footprint, effectively increasing the energy needed to puncture the tank. Protective 

panels also work to absorb the collision energy. By absorbing energy in an external structure, 

the energy demands placed on the tank shell are reduced. Indeed, the load-blunting and energyabsorption capabilities of sandwich panels depend on the core shape or geometry, as well as the 

materials used for the panel.

1.3 Previous Test Series

The remainder of this section summarizes testing related to shell puncture protection conducted 

prior to the full-scale impact test of the tank car equipped with a protective panel. Figure 4

compares the previous tests with the full-scale impact test with the protective panel. The 

previous tests are categorized in the figure as full-scale shell impact tests on tank cars designed 

to carry liquid chlorine, a TIH material, and component-level, quasi-static tests on flat sandwich 

panels. The full-scale tests provided technical information on the structural behavior of tank cars 

under shell impact loading. Results and analyses of the previous full-scale impact tests have 

been described previously [14]. The component-level tests generated technical information on 

the deformation behavior of sandwich panels under specific and controlled loading conditions. 

In each of these previous tests, the research framework shown in Figure 2 was followed to 

confirm, verify, and validate analytical results and establish confidence and credibility in the 

modeling activities.
8

Figure 4. Confluence of Full-Scale and Component Level Tests

1.3.1 Preproduction Compression Testing at CMI

CMI manufactured and tested a series of panels to develop cost-effective manufacturing 

techniques and to provide data to assist in selecting panel designs for testing. Examples of the 

preproduction panels are outlined below. Larger samples were manufactured to identify suitable 

manufacturing practices for various core configurations. The smaller compression samples were 

tested using a 250-kip compression tester.

2-foot by 2-foot panels

A set of 2-foot by 2-foot panels with X-cores, tubular cores, and square tube cores with 

variations in thickness were manufactured. The goal of this exercise was to establish 

manufacturing methods to produce robust performance for each core topology. The various 

welding processes studied included resistance spot welding, gas metal arc welding – pulsed spray 

transfer mode (GMAW-P), and plasma welding. To reduce the heat affected area, and hence the 

distortion, intermittent plug or GMAW-P welding was studied in detail. 

Small Test Panels

The compression testing was conducted on a series of 4-inch by 4-inch panels with 1⁄4-inch

Domex face sheets and 2-inch diameter 1⁄8-inch wall thickness 1010 pipe. For comparison, 

panels with 2.875-inch by 7.86-inch long square tubes were fabricated and crushed. Each of the 

panels was welded differently to develop fabrication techniques and characterize the effect of 

welding geometries on panel performance. The panels were compression tested using a 250-kip 

compression tester at the Virginia Transportation Research Council (VTRC) facility in 

Charlottesville. Data, including force and displacement, were collected for the first 1 inch of 

displacement. However, the panels were crushed beyond 1 inch. 
9

One of the key outcomes of this prefabrication study was that it provided insight into the 

crushing behavior of the panels. The crushing behavior of the round tube cores is very different 

from the square tube cores. The contrast is structural response is shown in Figure 5. The square 

tube oriented to form a diamond core exhibits a comparatively high initial strength, but once 

failure occurs, the panel loses all strength. Figure 6 illustrates how the diamond core crushes

nonuniformly. In comparison, when the sandwich panels with round tubes crush, there is an 

initial steep rise in load followed by a gradual plateau. Following this plateau, the core exhibits a 

steep rise in load. Once it reaches the peak load, the core collapses and the force drops. When 

the load is first applied, the tubes are squeezed at the top and bottom and move outward. As the 

tube is forced outward, it meets with resistance from the adjacent tubes. As a result, the round 

tubes begin to square off (see Figure 7). The first threshold is the load at which the round tubes 

take a square cross section. Once the tubes can no longer move outward, the load increases as 

the squared tubes begin to crush. The second plateau is the load at which the squared tubes 

begin to collapse.

Figure 5. Load versus Position for Diamond Panel (Left) and Round-Tube Panel (Right)

 

Figure 6. Photos of Diamond Panel during Crushing

0

20000

40000

60000

80000

100000

120000

140000

0 0.5 1 1.5 2 2.5

Position (inch)

Load (pounds)

Sample #13

0

20000

40000

60000

80000

100000

120000

140000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Position (inch)

Load (pounds)
10

Figure 7. Photos of Round-Tube Panel during Crushing

The following observations were made from the preproduction compression testing of the small 

sandwich panel samples:

• Round tube cores have a different crushing behavior than square tubes or X-core.

• Testing speed did not affect panel compression behavior within the limits investigated.

• The load to crush a panel with the face sheets plug welded to the core was greater than 

the load needed to crush a panel in which the core was welded together but the face 

sheets were not welded to the core.

• When the pipes were stitched welded together, the load versus displacement response 

was more linear and there were not two thresholds.

• If not constrained, the cores will move laterally during compression.

To prevent lateral movement of the round tubes, it was recommended that two half tubes be 

welded on each end of the panel such that a panel with five tubes would have four tubes in the 

center and a tube cut in half lengthwise on each end, as shown in Figure 8.

Figure 8. Drawing of Recommended Round Tube Core Design to Prevent Lateral 

Movement

4.5-inch by 9-inch Panels

Compression tests were performed on 4.5-inch by 9-inch samples using 3-inch OD tube with 

various welding geometries. The face sheets were 1⁄4-inch Domex and the tube used, due to its 

availability, was 4130. The deformation patterns of the samples with the tubes with and without 

welds between them were almost identical; however, the compression data indicated that the 

sample made with the tubes welded together was significantly stronger. Regardless of whether 

the tubes were welded together or not, the 4130 tubes fractured at the bend lines (see Figure 9). 

In previous tests, 1010 tubes of the same dimension bent but did not crack in compression. 

Although 1010 tubes had a lower tensile strength than the 4130 tubes, the cores with 1010 tubes 

exhibited a greater crush resistance (i.e., the force to crush the panel a given distance was 

greater). Based on these and follow-up analyses, and due to the difficulty of welding 4130, 

1010 steel was selected as the core material for the test panels.

 
11

 

Figure 9. 3-Inch 4130 Pipe Sample with Tubes Welded Together

1.3.2 Uniaxial Compression Testing at ATLSS

Using the information obtained from the panel prefabrication study and test data, as well as 

Volpe’s finite element analysis on selected designs, fourteen panels were selected for testing 

under uniaxial compression at Lehigh University’s Fritz Engineering Lab. The objective of the 

tests was to measure the force versus displacement behavior of the sandwich panels when 

subjected to uniform loading on the face sheet. Because the top and bottom face sheets were 

loaded uniformly, the test results reflect the core compression behavior. These tests were 

employed to determine the mode of crushing for the various core types and to compare 

manufacturing techniques.

Core Designs and Manufacturing

All fourteen panels were manufactured by CMI and tested at Lehigh University. Three core 

designs were selected for panel fabrication: round tube core, X-core, and diamond core (i.e., 

square tube rotated 45 degrees). The specifics (materials, weld types, sizes) of the eight designs 

used for these panels are shown in Table 2. Two panels of the P1, P2, P3, P4, X1, and X2 

designs were manufactured. One of each set of panels was manually welded and the second one 

in each set was robotically welded. To examine variation in fabrication, the 6-inch by 24-inch

diamond core test articles (D1 and D2) were manufactured with and without stitch welds. 

However, one panel (D2) has the core elements welded together and the other (D1) does not. All 

core to core welds were done manually for the diamond panel and the 2-inch round tube panel. 

The welding parameters are shown in Table 3. Photos of some of the manufactured panels are 

shown in Figure 10. Note that there was no post heat treatment done to the panels after panel 

manufacturing. The weld procedures and the material used do not require such treatments.

Split Tube
12

Table 2. Panel Details for Quasi-Static Compression Tests

P1 P2 P3 P4 X1 X2 D1 D2

Panel Number 0047-01

0047-02

0047-03

0047-04

0047-05

0047-06

0047-07

0047-08

0047-09

0047-10

0047-11

0047-12

0047-13 0047-14

Core Round 

Tube

Round 

Tube

Round 

Tube

Round 

Tube

X-Core X-Core Diamond Diamond

Face sheet 

thickness

0.25” 0.25” 0.25” 0.25” 0.25” 0.25” 0.25” 0.25”

Face sheet 

material

100XF 100XF 100XF 100XF 100XF 100XF 100XF 100XF

Core Height 5” 3” 2” 2” 5” 5” 2.62” 2.62”

Core Thickness 0.125” 0.125” 0.125” 0.125” 0.125” 0.125” 0.125” 0.125”

Core Density 7.8% 12.5% 18% 18% 7% 7% 13% 13%

Core Material 1010 1010 1010 1010 1010 1010 1010 1010

Panel Width 5 cores

25”

8 cores

24”

12 cores

24”

12 cores

24”

5 hats

27”

5 hats

27”

9 cores

24”

9 cores

24”

Panel Depth 6” 6” 6” 6” 6” 6” 6” 6”

Weld Type Slot/Skip Slot/Skip Slot/Skip Slot/Skip & 

Stitch b/n 

core 

elements

Spot Slot and 

Spot

Slot and 

Skip

Slot/Skip 

and Stitch 

b/n core 

elements

No. of panels 2 2 2 2 2 2 1 1

Manufacturing 

Comments

3/8”x 1” 

slots; 2 

welds/core 

per side; 1 

panel 

manually 

and 1 

panel 

robotically 

welded

3/8”x 1” 

slots; 2 

welds/core 

per side; 1 

panel 

manually 

and 1 

panel 

robotically 

welded

3/8”x 1” 

slots; 2 

welds/core 

per side; 1 

panel 

manually 

and 1 

panel 

robotically 

welded

3/8”x 1” 

slots; 2 

welds/core 

per side; 1 

panel 

manually 

and 1 

panel 

robotically 

welded; 

1⁄4”x1” 

stitch 

welds b/n 

core 

elements

3/8” RSW 

speed 4” 

apart for 

core and 

face sheet 

welds

3/8”x 1” 

slots; 2 

welds/core 

per side; 

3/8” RSW 

spaced 4” 

apart for 

core welds; 

1 panel 

manually 

and 1 

panel 

robotically 

welded

3/8”x 1” 

slots; 2 

welds/core 

per side; 

robotically 

welded

3/8”x 1” 

slots; 2 

welds/core 

per side; 

1⁄4”x 1” 

stitch 

welds b/n 

core 

elements; 

robotically 

welded

Table 3. GMAW-P Welding Parameters

Process Volts Amps

Robotic 16 150

Manual 20 130

Filler Wire ER70S-3

Gas 92% Argon/8% CO2
13

6”x2’x5” Pipe Round Tube Core Test Article (P1) 6”x2’x3” Round Tube Core Test Article (P2)

6”x2’x2” Round Tube Core Test Article (P3) 6”x2’ X-Core Shell Test Article (X1)

6”x2’ Diamond Core Test Article (D2)

Figure 10. Photos of Manufactured Panels for Uniaxial Compression Tests

Observations

The panels were placed on a flat block in a 5,000-kip Baldwin compression testing machine at 

Lehigh University’s Fritz Engineering Laboratory. A movable test head was positioned slightly 

above the block at the top of the panel and moved down at 0.2 inch per minute. This speed was 

selected to determine quasi-static material deformation behavior avoiding any strain rate effects. 

The displacement of the top plate was measured by two string potentiometers mounted between 

the fixed and moveable heads of the universal testing machine. Each panel was compressed to 

approximately 50 percent of its original height. The applied load was recorded and two video 

cameras documented the tests in progress. 
14

Load versus displacement curves for two sandwich panels subjected to uniform uniaxial 

compression are shown in Figure 11. The peak or maximum load is considered the crushing 

load. The crushing load for the panel with the 2-inch round-tube core is 615 kips. The crushing 

load for the panel with the diamond core is 398 kips, or about 35 percent lower than the crushing 

load for the round-tube core panel.

CMI 0047-07: 2-inch Round-Tube Core CMI 0047-13: Diamond (2” Square) Core

Figure 11. Load versus Displacement Curves for Round-Tube and Diamond Core Panels

The following observations were made from these uniaxial compression test series:

• Each core (i.e. round tube, diamond, and X-core) exhibited a different characteristic 

crushing behavior.

• The load-displacement results for the round tube and diamond core geometry were 

repeatable between samples.

• The X-core panels had the lowest repeatability in terms of load versus displacement 

behavior and crushed shape. The variability may be due to failures in welds in the Xcore panels.

• The X-core samples with spot welding exhibited the lowest crush load.

• The round tubes contacted each other immediately upon crushing and began to deform 

plastically into a square cross-section. 

• For the round-tube core panels, the load to crush the 2-inch round-tube cores was greater 

than the load to crush the 3-inch tube or 5-inch tube core.

• Because the tube thickness was the same for all panels, the 2-inch tube core panel had the 

highest core density.

• For most cores, the friction between the support blocks in testing prevented lateral 

movement of the core. However, the load to crush the 2-inch round tube core was 

sufficient to overcome this friction and the tubes shifted laterally.

1.3.3 Three-point Bend Testing at ATLSS

The second set of component tests performed in this program was a three-point bend test where 

the loading would cause large deformation of the face sheet and not solely crush the cores. For 

Displacement (inches)

0.0 0.5 1.0 1.5 2.0 2.5

Load (kips)

0

100

200

300

400

500

600

700

Displacement (inches)

0.0 0.5 1.0 1.5 2.0 2.5

Load (kips)

0

100

200

300

400

500

600

700
15

this set of tests, the X-core and 5-inch round tube core were eliminated from the test protocol due 

primarily to their relatively low crush force once the initial peak was overcome. The 2-inch

round tube core was eliminated due to the amount of welding necessary to assemble the panel 

and the difficulty in predicting the lateral shift of the 2-inch round tubes during compression. 

Based on their performance under uniaxial compression and on their manufacturability, core 

geometries selected to be included in three-point bend testing were the 3-inch round tube core 

and the 2-inch square diamond core. 

A total of sixteen panels, 18 inches deep by 48 inches wide, were manufactured and tested. The 

manufacturing and design variables of the panels included the core type (round or square), solid 

or strip face sheets, manual or robotic welding, and orientation of core elements with respect to 

supports. Eight panels were constructed using the conventional solid top and bottom face sheets. 

Six panels were manufactured using strips instead of solid face sheets in an effort to prevent 

propagation of a crack along the perimeter of an impacting object. Such a crack would allow the 

impacting object to tear through the panel without engaging the panel’s structure outside of the 

impact area. Two panels were built using a solid face sheet on one side and a face sheet 

consisting of strips on the other. The test panel cores were either 0.125-inch wall 3-inch OD 

1010 steel round tubes or 0.125-inch wall 2-inch OD square tubes. Each square tube was rotated 

45 degrees to create a diamond core configuration. In all panels, the face sheets were 0.118-inch

100XF steel. The orientation of the cores was either in the long 48-inch direction or the shorter 

18-inch short direction. If the panel had a strip face sheet, the strips would be perpendicular to 

the length of the core elements. Panels constructed with tubes oriented in the 18-inch short 

direction were placed in the test fixture with the cores parallel to the test supports, as depicted in 

Figure 13. The panels with core oriented in the 48-inch longitudinal direction were positioned in 

the test fixture with tubes perpendicular to the supports. The design specifics of the panels are 

provided in Table 4.

The strip and solid face sheets were plug welded to the cores using 3⁄8-inch by 1-inch plug welds. 

The strips were 3 in wide and had 3-inch spacing between them. The welds were spaced at 6-

inch intervals along the core elements for all panels. The weld spacing normal to the core 

elements was 3 inches for the pipe core elements and 2.67 inches for the diamond core elements. 

Figure 12 shows photographs of panels with the strip face sheets and with the solid face sheets.
16

Table 4. Panel Details for Three-Point Bend Tests

Serial 

Number

Core Core Orientation 

Relative to 

Supports

Face Sheet Type Weld Type Weight 

(lb)

0047-19 Round Tube Parallel Solid Manual 139.5

0047-15 Diamond Parallel Solid Manual 139.5

0047-26 Round Tube Parallel Strip Robotic 111.0

0047-24 Diamond Parallel Strip Robotic 111.5

0047-21 Round Tube Perpendicular Solid Manual 141.0

0047-17 Diamond Perpendicular Solid Manual 140.0

0047-25 Round Tube Perpendicular Strip Robotic 110.5

0047-23 Diamond Perpendicular Strip Robotic 109.5

0047-29 Diamond Perpendicular Solid & Strip Manual 126.0

0047-20 Round Tube Parallel Solid Robotic 139.5

0047-16 Diamond Parallel Solid Robotic 139.5

0047-28 Diamond Parallel Strip Manual 109.0

0047-22 Round Tube Perpendicular Solid Robotic 142.5

0047-18 Diamond Perpendicular Solid Robotic 137.0

0047-27 Diamond Perpendicular Strip Manual 110.0

0047-30 Diamond Perpendicular Solid & Strip Manual 126.0

Strip Face Sheets Solid Face Sheets

Figure 12. Photos of Panels for Three-Point Bend Testing

The three-point bend tests were conducted on the Baldwin compression tester at Lehigh 

University, which was used in the previous test series. In order to apply the bending load, CMI 

designed and manufactured a fixture and load application block to accommodate the panels in 

the testing machine, as shown in Figure 13. The fixture consisted of two 4-inch round solid bars 

which were welded parallel to each other with 24-inch center-to-center spacing. The round bars 

were welded to a 1-inch plate supported by small pieces of steel that acted to resist deflection of 

the round bars during the compression tests. This fixture was placed on the bottom platen of the 

compression tester and each panel was centered on top of the two 4-inch bars. 
17

 

Figure 13. Photo of Panel in Three-Point Bend Setup

An approximate cubic steel load application block was manufactured by welding together 1-inch 

steel plates. It was machined to have a 12-inch by 12-inch contact area with 1-inch radius 

corners. The block was tapered to a 13-inch width at the top to facilitate removal of the block 

from the panels after testing. The load application block was centered over the panel and was 

attached to a 1-inch plate that was in turn bolted to the top platen of the compression tester. 

The initial test protocol was to bend and deform the panels with the ram traveling at 0.25 inch 

per minute until the top face sheet moved downward approximately 3 in or until it reached the 

top of the 4-inch diameter round bars of the bottom fixture. At Lehigh, the test protocol was 

modified so that the ram traveled approximately 6 inches until the panels were deformed almost 

completely, with the load application block nearly in contact with the bottom test fixture. 

Changing the protocol to cause more severe deformation allowed observation of the crush 

behavior to a completely flat state. 

Figure 14 shows the bending behavior of panel number 0047-20, which has solid face sheets and 

pipes parallel to the supports. The corresponding load displacement curve is also shown in the 

figure. Figure 15 shows the bending behavior of panel number 0047-21, which also has solid 

face sheets, but in this case the pipes are perpendicular to the supports. Figure 16 illustrates the 

bending behavior of panel number 0047-17, which has solid face sheets and diamond core 

perpendicular to the supports. In some tests, bubble wrap was placed under the panel, as shown 

in Figure 17, in order to estimate the area over which the load was transferred. Although the 

indenter was 12-inch by 12-inch, the bubble wrap indicated that the load was distributed over a 

larger area.

Load Application 

Test Fixture
18

Figure 14. Deformation of Panel No. 0047-20 and Corresponding Load-Displacement 

Curve

Displacement (inches)

0 1 2 3 4 5 6

Load (kips)

0

50

100

150

200

250

300

350

400
19

Figure 15. Deformation of Panel No. 0047-21 and Corresponding Load-Displacement 

Curve

Displacement (inches)

0 1 2 3 4 5 6

Load (kips)

0

50

100

150

200

250

300

350

400
20

Figure 16. Deformation of Panel No. 0047-17 and Corresponding Load-Displacement

Curve

Displacement (inches)

0 1 2 3 4 5 6

Load (kips)

0

50

100

150

200

250

300

350

400
21

Figure 17. Panel in Three-Point Bend Test with Bubble Wrap to Estimate Load Transfer 

Area

The following observations were made from the three-point bend tests:

• Panels with the core perpendicular to the supports require more force to deform than 

panels with the core oriented parallel to the supports.

• When the core elements are parallel to the supports, the elements are able to move past 

each other so that only the face sheet provides initial bending strength.

• Panels with solid face sheets are stiffer than similar panels with strip face sheets. The 

panels with solid face sheets require a greater force to deform.

• The strip face sheets did not crack in the diamond core panels with perpendicular 

orientation, but the solid face sheets did.

• Localized crushing of the pipe cores was observed in three locations: under the load 

application block and above each of the two supports, whereas localized crushing of the 

diamond cores was observed only under the load application block.

• The loaded area, as measured by the bubble wrap test, was approximately 50 percent 

greater than the 12-inch by 12-inch surface area of the indenter.
22

2. Manufacturing Considerations

FRA awarded a Small Business Innovation Research (SBIR) contract to CMI to design and 

manufacture test articles for the research project. CMI’s experience in fabricating steel sandwich 

structures and developing manufacturing plans for other platforms was applied to develop 

economical manufacturing processes and welding techniques for railroad tank car application.

2.1 Materials

The typical steel used for the tank car construction is TC128-B steel. This steel is not 

manufactured in the thin gauges needed for sandwich construction. In addition, TC128-B

requires a stress relieving treatment after welding. Therefore, CMI considered alternative steels

for the protective panels. The objective was to locate a commercially available steel composition 

that has high tensile strength (around100 ksi) and ductility around 30 percent in terms of linear 

elongation. High strength low alloy (HSLA) steels provide increased strength over conventional 

carbon steels; therefore, this group of steels was considered. HSLA steels are identified by their 

mechanical properties, not composition. Because they are much stronger and tougher than 

ordinary carbon steels, they are typically used in applications such as car and truck fabrication, 

bridge design, street lighting poles, oil storage tanks, and earth moving equipment where 

strength-to-weight ratio is important. These steels are typically highly formable and weldable 

and are resistant to corrosion, which is important for long-term use. The mechanical properties 

of the HSLA steels considered and other steels that surfaced as a result of this investigation are

listed in Table 5.

Table 5. Minimum Mechanical Properties of Steels Considered

(All values are minimum except where the ranges were provided by the manufacturer) 

Tensile 

Strength 

(ksi)

Yield 

Strength 

(ksi)

Elongation 

(%)

Typical Applications

AISI 4130 [7] 81 52 28

Structural and aircraft tubing, bicycle 

frames, clutch and flywheel 

components, roll cages

AISI 1010 [8] 52 44 20

Structural and vehicle components 

including body, fender, pans, washers, 

rivets, brushings, and nails

Modified 1010* [9] 72.1 61.7 38

HSLA50 [10] 60 50 20 Truck frames, brackets, crane booms, 

rail cars, ship construction, towers

Domex 100XF [11] 110 100 15

Trailers, construction and agricultural 

equipment, crane booms, vehicle 

frames and chassis

TC128-B [12] 81 – 101 50 19 -22 Railroad tank cars

Boron Steel* [13] 214 169 5-6 Vehicles

* Not readily available in tubes required for program
23

The 100XF HSLA material is far superior in strength compared with TC128-B and does not need 

to be stress relieved subsequent to welding. Therefore, CMI investigated this steel for the 

protection panels. Because various core geometries were being considered in this research 

program, one consideration during material selection was the availability of different tubular 

forms made of the same material. Although HSLA 100XF grades are available in flat sheet and 

tubular form, the tubular forms in the size ranges of interest could not be located at any vendor, 

nor through other channels, including major steel mills. The modified 1010 steel is also not 

available commercially. The standard AISI 1010 steel composition is readily available in all 

tubular shapes of interest to our program. Accordingly, this material was selected as the core 

material for the initial compression tests. AISI 4130 was also utilized as the core material for 

initial compression testing due to its availability. However, the 4130 chrome-moly pipe is 

difficult to weld. It requires preheat prior to welding and has a propensity for developing weld 

cracks and a weak heat affected zone (HAZ), both of which result in low fatigue resistance. The 

higher carbon content and martensitic structure of this metal are contributing factors to its poor 

weld ability. As a result, this material was not considered for this study. The Domex 100 XF 

was selected for face sheet material.

Thielsch Engineering performed mechanical testing of the as received tubes and face sheets. The 

average mechanical properties, with standard deviation in parentheses, of five samples of each 

material are summarized in Table 6. The minimum values for 1010 steel are 44 ksi for yield 

strength, 52 ksi for tensile strength, and 20 percent for elongation.

Table 6. Average Mechanical Properties of as Received Tubes and Face Sheets

Material Ultimate 

Tensile 

Strength (ksi)

Yield Strength,

0.2% offset 

(ksi)

Elongation 

in 1 inch (%)

5" diameter x 0.125" wall x 6" long 4130 

Steel Round Pipe 118 (1.4) 97.5 (2.5) 17.8 (0.45)

5" diameter x 0.125" wall x 6" long 1010 

Steel Round Pipe 52 (0.27) 37 (1.2) 38.7 (0.91)

3" diameter x 0.125" wall x 6" long 1010 

Steel Round Pipe 54 (0.42) 43 (0.6) 35.1 (1.3)

2" diameter x 0.125" wall x 6" long 1010 

Steel Round Pipe 63 (0.42) 52 (1.3) 32.3 (0.45)

2" diameter x 0.125" wall x 6" long 1010 

Steel Square Pipe 71 (0.96) 60.5 (2.0) 21.9 (0.42)

1/4" x 8" x 10 Domex Plate 113 (0.84) 101 (1.1) 17.8* (0.27)

Note: All ductile failures

* Elongation in 2 inches

Examination of the measured data shows significant variation in mechanical properties among 

the samples tested from the same 1010 steel grade. This can be attributed to the manufacturing 

process used for each batch of steel from which the specific tubes were produced. Each tube 

diameter is produced from a different batch of steel which may respond to subsequent 

mechanical working differently. The final strength of the material depends on the mechanical 
24

work experienced by each batch of steel prior to tube welding and the amount of post cold 

drawing done after tube welding. The tubes used for this study are welded and then cold drawn. 

2.2 Welding

Many different welding methods were considered for fabricating the panels. The criteria for 

selecting a welding method were as follows: strength of the weld, distortion (determined by heat 

input), maximum gap, processing time, equipment cost, post processing, and ability to automate 

the process. CMI worked with Edison Welding Institute (EWI) to analyze different welding 

processes. A summary of the processes considered is shown in Table 7.

Table 7. Summary of Different Welding Methods

Plasma 

Key Hole 

Weld w/ 

Cold Wire

2 Wire 

Tandem 

GMAW

Plasma 

GMAW

Laser/G

MAW

GMAW-P 

Plug Weld

Resistance 

Spot/Double

Process Speed –

in/min 20–30 100–160 20–30 150–200 N/A

2 welds/10 

Sec

Equipment Cost $40K $40K $50K $1,000K $10K $35K

Preprocessing Need a slot Need a hole

Maximum Gap Very Small Better Better Better Better None

Can It Be 

Mechanized? Yes Yes Yes Yes Yes Yes

Distortion (Heat 

Input kJ/in ) 40–50 25 40–50 10–15 Local Low

Plasma welding, laser welding, Gas Metal Arc Welding (GMAW), Pulsed GMAW-P, Resistance 

Spot Welding, and hybrid welding techniques that employ a combination of weld practices are 

among the processes that appeared amenable to welding thin-gauge materials incorporating 

various automation methods. Both plasma welding and plasma/GMAW hybrid welding 

processes generate intense heat input leading to higher heat distortion. Laser/GMAW, which is 

superior to all the other processes considered, is highly sophisticated and not readily available for 

routine manufacturing. The upfront equipment costs are very high compared with other 

processes considered herein. The GMAW welding process is a widely used welding method. 

Several advances have been made to improve this process in recent years. The heat input for this 

process can be controlled by the welding method used. One preferred method to minimize and 

precisely control the heat input without compromising weld efficiency is to pulse the arc. This 

process coupled with plug welding, GMAW-P, in contrast to a continuous weld, is expected to 

create minimum distortion and lower cost. This process can be readily adopted with minimum 

investment. The resistance spot welding process is another weld process that is widely used for 

very thin gauge materials and is being adopted for moderate thickness material. Both the 

GMAW-P and resistance spot welding equipment were available in house. Therefore, these two 

processes were selected for initial weld trials.

Several test welds were made using GMAW-P plug welding and resistance spot welding. Both 

flat plate-to-plate and flat plate-to-pipe welds were evaluated. A 0.25-inch Domex plate was 

welded to either 0.118-inch Domex flat plate or 1010 steel pipe with similar wall thickness.
25

Tensile tests were conducted on both the plate-to-plate and plate-to-pipe assembly that had been 

welded with these two processes. Both single and double plug welds, spaced 1 inch apart, were 

tested in plate-to-plate and plate-to-pipe combination. Duplicate samples were welded using 

resistance spot welding. All the weld samples were tested at CMI. The plug weld samples failed 

outside the weld with the exception of the single plug weld to the plate, which sheared in the 

weld. The single plug welds to pipe actually pulled material out of the pipe such that failure 

occurred in the 1010 pipe. One such failure is shown in Figure 18. The double plug weld to pipe 

forced the failure to occur in the Domex plate (see Figure 18). However, the strength of the weld 

was not as high as the plate-to-plate weld. 

 

Figure 18. Single (Left) and Double (Right) GMAW-P Plug Welds to 1-Inch Pipe 

Subsequently, samples with different plug weld configurations were tested to identify differences 

in weld strength based on plug hole geometry. Two 1⁄4-inch Domex plates were welded together 

using a resistance spot weld and Pulsed Gas Metal Arc Welding (GMAW-P) plug welds with 

various geometries. The average results of two tensile tests for each weld technique and 

geometry are shown in Figure 19. As was expected, due to its overall larger weld area, the 1⁄2-

inch by 11⁄2-inch plug weld exhibited the greatest strength. However, if the load per square inch 

of weld is compared rather than total load, the 1⁄2-inch round plug welds exhibited superior 

strength.
26

Figure 19. Average Load at Failure for Various Welds 

The total processing time, including preparation and welding times, was estimated for each weld 

configuration. Although resistance spot welding appeared to be the most cost effective method, 

technical issues precluded it from being a viable candidate; therefore, GMAW-P plug welding 

was down-selected to manufacture the panels. The optimal weld spacing between plug welds 

was then investigated. Tensile tests on Domex strips were conducted for various plug sizes and 

spacing and the average loads at failure for two samples of each configuration are shown in 

Figure 20. In these tests, the top plate was 0.25 inch and the bottom plate was 0.118 inch. Both 

plates were 4 inches wide and 18 inches long.

0

5000

10000

15000

20000

25000

30000

35000

1/2" Round

1/2" Round

w/Countersink

1/2" X 1" Oval

1/2" X 1 1/2" Oval

3/8" X 1" Oval

Spot

Load at Failure (pounds)
27

Figure 20. Load to Failure for Various Weld Configurations at 4-Inch, 8-Inch and 12-Inch

Spacing

The spacing between welds in the range of 4 to 12 inches had little effect on the total load to 

failure for any of the weld configurations. Welds spaced greater than 12 inches apart will not 

provide enough support for the face sheet in the event of an impact from an object with a small 

area but large amount of kinetic energy. Although the 1⁄2-inch by 11⁄2-inch plug welds were the 

strongest weld, the round tubes do not have sufficient area in contact with the face sheet to 

accommodate a 1⁄2-inch wide weld. Therefore, 3⁄8-inch by 11⁄2-inch plug welds spaced 8 inches

apart on a core element were the down-selected welding procedure for the final panels. 

 

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

1/2" Rd - 4"

Spacing

1/2" Rd - 8"

Spacing

1/2" Rd -

12"

Spacing

1/2" X 1" -

4" Spacing

1/2" X 1" -

8" Spacing

1/2" X 1" -

12"

Spacing

1/2" X 1.5"

- 4"

Spacing

1/2" X 1.5"

- 12"

Spacing

3/8" X 1" -

4" Spacing

3/8" X 1" -

8" Spacing

3/8" X 1" -

12"

Spacing

Lbs Force

The Base Material Failed Before Weld

The Base Material Failed Before The Welds
28

3. Full-Scale Impact Testing at TTC

One curved protective panel manufactured by CMI was installed on the shell of a 

decommissioned tank car and impact tested at the Transportation Technology Center (TTC) 

located in Pueblo, CO. This section describes (1) the approach and objectives of the full-scale 

test, (2) details of the protective panel including material selection and manufacturing processes, 

(3) a retrofit of the indenter to accommodate a larger impact footprint, (4) details of the test setup 

including instrumentation, and (5) test results and observations. 

3.1 Overall Approach and Objectives

Two full-scale shell impact tests, which have been reported in previous publications, e.g. [14],

were conducted previously at TTC and are summarized in Table 8. The basic protocol in these 

tests was kept the same. A decommissioned tank car was initially standing against a rigid wall. 

The tank car was oriented such that the shell of the car was perpendicular to a railroad track that 

terminated at the wall. A ram car with an indenter protruding from its leading end was set in 

motion on the track and would strike the standing tank car on its shell. However, the indenter 

size and the impact speed were varied. Consequently, the intended objectives and outcomes of 

these two tests were different. In the first full-scale impact test, the commodity tank experienced 

plastic deformation without puncture. In the second test, the commodity tank punctured.

Table 8. Summary of Previous Full-Scale Shell Impact Tests

Impact 

Speed 

(mph)

Indenter Dimensions Outcome

Width

(inches)

Height

(inches)

Edge Radii 

(inch)

Test 1 14.0 17 23 1 Permanent deformation, 

no puncture

Test 2 15.1 6 6 1⁄2 Puncture

For the full-scale test with a protective panel, the objective was to demonstrate that tank integrity 

can be maintained at an impact speed higher than the previous tests. 

3.2 Protective Panel Design, Material Selection, and Manufacturing

Based on the uniaxial compression and three-point bend testing performed in previous segments 

of the research program, the preferred design for the impact test was a square-tube (i.e. diamond 

core) sandwich panel. Because the protective panel is intended to be used against the shell of a 

tank car, the panel was designed to have a curved radius that conformed to the shell of the tank. 

However, due to the difficulty of manufacturing a curved panel with square tubes, alternative 

core designs, including cores with round tubes, square tubes with flattened corner faces, and Xcore, were considered. Based on lower manufacturing cost and better performance, the design 

selected for the impact test on the tank car was a sandwich panel with a core manufactured with 

3-inch round tubes. 
29

Material selection for the panel was based on material properties and availability. A search to 

identify an alloy similar to 1010 steel with strength approaching Domex 100XF with higher 

ductility for the face sheet material was carried out. The Domex 100 XF is a low-alloy steel with 

yield strength of 100 ksi, tensile strength of 110 ksi, and elongation of 16 percent. The 1010 

steel is a plain-carbon steel with the following minimum properties: yield strength of 44 ksi, 

tensile strength of 52 ksi, and elongation of 20 percent. For the core, the objective was to select 

the smallest thickness tube that could be easily welded. This criteria led to the selection of 3-

inch O.D. tubes with a 0.083-inch thickness and a 1010 face sheet with a 0.125-inch thickness.

Table 9 lists the average tensile properties measured from tensile tests conducted using three 

samples of each material. The numbers in parentheses represent the standard deviation for each 

tensile property. The tensile tests were conducted in accordance with ASTM A370 [15] and 

ASTM E8 [16]. The Domex sheet was included for comparison since this material was utilized 

in previous phases of the research program.

Table 9. Tensile Test Results for Considered Materials

Ultimate Tensile 

Strength (ksi)

Yield 

Strength 

(ksi)

Elongation 

(in 2 inches) 

(%)

Reduction in 

Area (%)

0.118” Domex Sheet – L 119 (1.5) 106 (2.1) 17 (0.5) 68 (0.87)

0.118” Domex Sheet – T 126 (0.58) 116 (1.0) 14 (0.29) 60 (2.0)

0.083” 1010 Tube - L 67.7 (1.4) 58.2 (2.8) 22 (2.75) 70 (5.0)

0.120” 1010 Tube – L 60.7 (0.29) 48.7 (0.76) 26 (0.29) 74 (1.5)

0.120” 1010 Sheet – L 47.8 (0.38) 29.2 (0.2) 40 (1.89) 84 (2.5)

0.120” 1010 Sheet - T 47.9 (0.45) 30.3 (1.05) 40 (0.76) 87 (1.2)

NOTES: L = Longitudinal, T = Transverse

The specifications of the protective panel manufactured by CMI for the full-scale impact test are

as follows:

• Panel Size: Approximately 72-inch by 72-inch

• Radius of Curvature: 55.4 inches

• Core selection: 3-inch O.D. 1010 Pipe Cores

– Core material: Carbon Round Electric weld ASTM A513 Type 1

– Core thickness: 0.083 inches

• Face sheet selection

– Face sheet material: ASTM A1010 CS Type B hot rolled

– Face sheet thickness: 0.120 inch

– Strip face sheet inside, solid face sheet outside

The panel covered an area of the tank car shell that was approximately 6 feet (length) by 6 feet 

(height). This size of panel was selected for several reasons. While a larger panel would provide 

protection over a larger portion of the tank shell, pretest simulations indicated that larger panels 

had an increased likelihood of material failure occurring directly beneath the impactor. Because 

of this localized failure, a large panel would offer little load distribution before the impactor

struck the shell of the tank. At the opposite end of the size spectrum, a panel that is only slightly 

larger than the impacting object would offer very little ability to blunt the impacting object 
30

owing to the small size of the panel. Additionally, more small-sized panels than large-size 

panels would be needed to protect the entire shell surface of the tank. The selected panel size 

was seen as a reasonable size for manufacturing, handling, and installation without being so large 

as to result in highly localized failure.

In order to fabricate a curved panel with the 55.4-inch radius, two mating fixtures were built on 

which to fabricate the panel. The concave fixture consisted of five concave supports with a 55.4-

inch radius spaced 16 inches apart. In Figure 21, the two fixtures are shown in photos of the 

panel being built.

 

Figure 21. Manufacturing Panel for Impact Test on Concave Fixture (Left) and Convex 

Fixture (Right)

A series of slots for plug welding, 3⁄8 inches wide by 1 inch long, were laser cut on the solid face 

sheet and strip face sheet pieces, then the face sheets were rolled to the correct radius. The 3-

inch tubes were placed on the concave fixture and tack welded together. The 3-inch wide strip 

face sheets, with 3-inch spacing between them, were then manually plug welded to the tubes 

using GMAW-P. The panel was then flipped and placed on a convex fixture so that the outer 

solid face sheet could be plug welded to the tubes. The plug welds were spaced 6 inches apart 

along the length of the tubes. The tubes were not stitch welded together because it resulted in 

asymmetrical deformation under loading, as shown in previous tests. The panel weighed 

approximately 900 pounds, with an estimated core relative density of 22.5 percent. Figure 22

shows photographs of the completed protective panel prior to it being attached to the tank car.
31

Figure 22. Protective Panel

3.3 Indenter Modification

As shown in Table 8, the previous full-scale tank car impact testing used a 6-inch by 6-inch 

indenter. CMI built a cap that was placed over the existing 6-inch by 6-inch indenter in order to 

adjust its impact footprint. Figure 23 shows schematics of the retrofit cap. The cap face was 

made with A514 steel. The sides of the cap and the gussets were made with A36 steel. The weld 

filler was ER110S-1. This modification resulted in a 12-inch by 12-inch indenter with a 1-inch 

radius. Figure 24 shows photographs of the retrofitted indenter. There are no welds between the 

12-inch by 12-inch cap and the 6-inch by 6-inch indenter. That is, contact is the only load 

transfer mechanism. The cap was designed to be removed to permit the 6-inch by 6-inch 

indenter to be utilized for any potential future testing programs.

Figure 23. Modification of 6-Inch by 6-Inch Indenter

White: Existing 6”x6” indenter

Green: 12”x12” retrofit 2.5” thick impact face

2” gusset

18” 
32

 

Figure 24. Photos of Indenter Cap on 6-Inch by 6-Inch Indenter

3.4 Test Setup

The tank car used in the full-scale testing was a decommissioned DOT105J500W that was 

previously used in service to carry liquid chlorine. Figure 25 shows a photograph of the test 

setup used in the impact test. The tank car with the protective panel was positioned with one 

side against a 3-inch steel plate attached to a concrete retaining wall, perpendicular to the track

that the ram car (shown at right) would travel on. The commodity-carrying tank was insulated 

with approximately 4 inches of fiberglass and ceramic fiber insulation. The fiberglass and 

insulation were covered by a thin steel outer jacket. The jacket and thermal protection were kept 

intact for the test, with the panel installed outside of the jacket. The tank car was filled 90

percent with water and then pressurized to 100 psi.

Figure 25. Test Setup – View from East (Left) Side

The wheels of the tank car were removed and replaced with heavy rectangular tube assemblies. 

This test car was then placed on two skids, shown in Figure 26. Four short I-beam sections 

connected the tank body bolster and skids (Figure 27). The tank car with the skids was placed on 

1-inch steel plates laid on the ground. The resulting skid system was designed to minimize the 

test car rollback and to allow the tank car and skids to slide on the steel plates during the impact. 
33

Figure 26. Skid System

Figure 27. Welded Beam Connecting the Tank Car to the Skid System

The protective panel was hung in the front and outside of the tank car outer jacket from the 

manhole using a cable that ran through the sixth tube. An additional cable with slack was used 

on the seventh tube to prevent the panel from falling to the ground in the event that the first cable 

broke. The panel hung freely against the tank car outer jacket to allow the panel to deflect freely 

during the impact. The panel hanging against the tank is shown in Figure 28. 
34

Figure 28. Test Setup – View from West (Right) Side

Welding the panel to the jacket was considered as an attachment option, but it was believed that 

this would result in an overly-stiff support condition. If the panel was not able to flex in 

response to the impact, the panel would likely experience highly-localized puncture around the 

perimeter of the impactor head. This localized failure would prevent the panel from distributing 

the impact load over an area of the tank shell larger than the impactor. The selected mounting 

attachment scheme was intentionally chosen to permit the panel to flex and deform in response 

to the striking impactor. Because of the irregularity of the outer jacket, the panel did not rest 

uniformly against the tank car. There was an approximately 1-inch gap between the panel and 

the car at both of its ends along the radius. The panel and car rested with no gaps at their 

centerlines and almost 2 feet above and below that area.

3.5 Instrumentation

Eleven accelerometers and two speed sensors were installed on the ram car. Two pressure 

transducers measured tank pressure at the pressure relief valves on the tank car. Three highspeed (HS) cameras and four high-definition (HD) video cameras documented the impact. Table 

10 summarizes the types of instrumentation and the channel counts.

Table 10. Instrumentation Summary

Type of Instrumentation Channel Count

Accelerometers 11

Speed Sensors 2

Pressure Transducers 2

Total Data Channels 15

Digital Video 7 Cameras

(3 HS and 4 HD)
35

3.5.1 Ram Car Accelerometers and Speed Sensors 

Triaxial accelerometers were placed at the two ends and at the center along the ram car 

centerline. Two longitudinal accelerometers were placed on the left and right sides of the middle 

of the ram car. There were a total of 11 accelerometers installed on the ram car. The typical 

scale factor calibration error for the accelerometers used was 2 percent. There were two speed 

sensors installed on the ram car, one on the left and one on the right. Figure 29 illustrates the 

sensor locations. Table 11 shows the details of the accelerometers installed on the ram car. 

Figure 29. Accelerometer Locations on Ram Car

Table 11. Ram Car Accelerometers

Channel Name Sensor Description Range

BA1CX Leading end, Centerline, X Accelerometer 100g

BA1CY Leading end, Centerline, Y Accelerometer 100g

BA1CZ Leading, Centerline, Z Accelerometer 100g

BA2LX Middle, Left Side X Accelerometer 100g

BA2CX Middle, Centerline, X Accelerometer 50g

BA2CY Middle, Centerline, Y Accelerometer 50g

BA2CZ Middle, Centerline, Z Accelerometer 50g

BA2RX Middle, Right Side X Accelerometer 100g

BA3CX Trailing end, Centerline, X Accelerometer 200g

BA3CY Trailing end, Centerline, Y Accelerometer 100g

BA3CZ Trailing end, Centerline, Z Accelerometer 200g

BA3CX, BA3CY, BA3CZ BA2CX, BA2CY, BA2CZ BA1CX, BA1CY, BA1CZ 10 ft

30 ft

60 ft
36

3.5.2 Tank Car Pressure Transducers

Two pressure transducers were attached to the pressure relief valves on the manway to measure 

the internal pressure in the tank during the impact. Table 12 lists the pressure transducers.

Table 12. Pressure Transducers

Channel Name Sensor Description Range

(psi)

TRP1 Low-range pressure transducer 600

TRP2 High-range pressure transducer 1,200

3.5.3 Speed Sensors

Redundant speed sensors measured the impact speed of the ram car when it was within 12 inches

of the impact point. The speed traps used reflector-based sensors. The ground-based reflectors

were separated by a known distance, and vehicle-based light sensors were triggered as the ram 

car passed over the reflectors. The last reflector was within 10 inches of the impact point. The 

time interval between passing the reflectors was recorded. Speed was then calculated from 

distance and time. The backup speed measurement was recorded with a handheld radar gun.

3.5.4 Real-Time Photography and Targets

Three HS and four real-time HD video cameras documented the impact event. Figure 30 and 

Figure 31 show schematics of the camera position setup. All HS cameras are crashworthy and 

rated for peak accelerations of 100 g. 

Figure 30. Top View of Camera Setup

HS1 – Straight 

Side View

HD1 – Top View

HD2 –

Isometric View 

(Bridge)

HS2 –

Isometric View

HD3 For Redundancy–

Isometric View (Bridge) 

HD4 –Pan
37

Figure 31. Side View of Camera Setup

The ram car, the protective panel, and the impact barrier were painted light gray. The tip of the 

indenter was painted red. High-contrast targets were applied to the ram car, the indenter, the 

protective panel, and at select ground reference points to aid in video analysis, should video 

analysis be necessary. Figure 32 through Figure 35 show the target locations on the ram car and 

on the tank car with the protective panel.

Figure 32. Side View of Target Locations on Ram Car

HD1 – Top View

HS3 – Onboard 

Overhead View
38

Figure 33. Top View of Target Locations on Ram Car

Figure 34. Side View of Target Locations on Tank Car and Protective Panel
39

Figure 35. Top View of Target Locations on Tank Car

3.5.5 Special Considerations for Protecting Equipment

Shielding was provided for all external instrumentation near the point of impact. The intent was 

to provide protection from high-velocity liquid in case the tank ruptured. For sensors such as 

accelerometers, welded or bolted shields were used. For cameras near the impact zone, highstrength clear plastic shells, like the one shown in Figure 36, were used. 

Figure 36. Protective Shell for Onboard HS Camera

3.5.6 Data Acquisition

A set of 8-channel battery-powered onboard data acquisition systems recorded data from 

instrumentation mounted on the ram car. These systems provided excitation to the 

instrumentation, analog antialiasing filtering of the signals, analog-to-digital conversion, and 

recording of each data stream. A similar set of ground-based data acquisition systems recorded 

data from the pressure transducers on the tank car.
40

The data acquisition systems were GMH Engineering DataBRICK Model II units [17]. Data 

acquisition complied with the appropriate sections of SAE J211/1 [18]. Data from each channel 

was antialias filtered at 1,735 hertz (Hz) and then sampled and recorded at 12,800 Hz. Data 

recorded on the DataBRICK units were synchronized to time zero at initial impact. The time 

reference came from closure of tape switches installed on the front of the test vehicle. Each 

DataBRICK unit is ruggedized for shock loading up to at least 100 g. Onboard battery power 

was provided by GMH Engineering in the form of 1.7 A-hr 14.4 Volt NiCad Packs. Tape 

Switches, Inc., provided the model 1201-131-A tape switches for event initial contact. 

Software in the DataBRICK units was used to preset zero levels for all acceleration channels. 

The DataBRICK units were set to record 1 second of data before the initial impact and 4 seconds

of data after the initial impact. 

3.6 Test Results and Observations

The test car was impacted by a 12-inch by 12-inch square indenter attached to a moving ram car

with a total weight of 295,725 pounds. The ram car was released by a locomotive from rest at 

1,600 feet away from the impact barrier. The track was inclined so that the ram car picked up 

speed as it traveled toward the standing tank car. The speed of the ram car when it struck the test 

car was 17.8 mph. The impact location was the center of the side of the tank car and the panel.

Figure 37 shows a series of still images taken from video of the impact test. This image shows 

the progress of the ram car as it strikes the panel-equipped car, causes deformation of the car, 

and is eventually propelled backward following rebound of the tank car.

Preimpact During Impact Postimpact

Figure 37. Series of Images Showing Side Impact Progression

 

The ram caused significant deformation to both the protective panel and the tank shell. The tank 

was both deformed and displaced by the impact. The tank did not puncture during this test, but 

successfully withstood the impact with its lading intact. The ram car was eventually propelled 

backward (i.e. opposite its initial direction of travel) as the tank car recovered elastically 

following the collision. Figure 38 shows a photograph of the tank car with the protective panel 

after impact. The spacing between targets on the side of the shell is indicated on this figure.
41

Figure 38. Tank Car and Panel after Impact

The ram car had air brakes that were designed to activate 2 seconds after the ram impacted the 

tank car to assure that the ram car did not rebound off the tank car, move up the incline, and then 

roll back into the tank car a second time. The test car bounced back 112 feet before the 

automatic brakes were tripped.

The test parameters for the 105J500W tank car were:

• Tank car number DCLX3050

• Tank car LT WT (empty) 81,700 pounds

• Outage 10% 

• Tank capacity 17,445 gal

• Fill fluid water

• Internal pressure 100 psi

• Tank car height (center to top of rail) 64.5 in.

The test parameters for the ram car were:

• Ram car weight 295,725 pounds

• Ram car initial speed 17.8 mph

• Indenter height (center to top of rail) 65.25 in.

• Ram car energy (derived) 3.13 million foot-pounds

The ambient conditions at the time of test were:

• Wind speed 5 mph NNE

• Ambient temperature 50°F

• Humidity 74%

• Barometric pressure 29.53 inches Hg

When the panel was impacted, the center of the panel crushed inward and the left and right edges 

of the panel buckled and pulled away from the tank car. The front face sheet stretched in an area 

from the left to right edge of the panel and approximately 1 foot above and below the impact. In 
42

some of the area that stretched and buckled, the plug welds on the top face sheet failed, and the 

front face sheet tore at the edges of the indenter, as seen in Figure 39. 

Figure 39. Damage on Protective Panel – Impact Side

The round pipes crushed in the area beneath the indenter—so much so that the walls of the pipes 

were touching and one severed near the edge of the impact. The outer core, on the left and right 

edges of the panel, deformed but the deformation was not as severe as it was in the center of the 

panel. On the edges, the pipes became oblong and some had a flattened edge adjacent to the tank 

car. Figure 40 shows the deformation of the panel from the side views. 

Figure 40. Damage on Protective Panel – Left and Right Sides

The back of the panel was bowed, which is shown in Figure 41. Some of the strips that made up 

the back face sheet tore at the edges of the indenter. The back of the pipes beneath the indenter 

were flattened. 

Plug 

Welds
43

Figure 41. Damage on Back of Protective Panel

Damage to the steel jacket was exposed after removing the protective panel from the side of the 

tank (Figure 42). This figure also shows the spacing between targets on the side of the tank 

shell.

Figure 42. Dent in the Jacket

After removing the steel jacket and the insulation, damage to the commodity-carrying tank was 

observed in the form of permanent dent without puncture (Figure 43). Moreover, there were no 

visible signs that water had leaked. The permanent dent in the commodity-carrying tank was 

approximately 11.5 inches deep and at least 160 inches long.
44

Figure 43. Deformation of Commodity Tank 

The center of the indenter impacted the panel directly over a weld seam on the tank car—this 

represents a worst case scenario. In the bottom section of the tank car, along the weld, there was 

some indication that the weld was beginning to fail in the HAZ area. Furthermore, a surface 

crack was found in the weld seam (Figure 44). 

Figure 44. Surface Crack on the Tank Car

During the impact, the tank car was pressed between the ram car and the retaining wall. Once 

the ram car’s forward motion had stopped, the tank car began to recover some of its elastic 

energy. This caused both the tank car and the ram car to rebound away from the retaining wall. 

The tank car rebounded during the impact and left more than 12 inches between the tank car and 

the impact barrier following the test (Figure 45).
45

Figure 45. Tank Car Placement after Impact

Instrumentation on the ram car provided data for calculation of the ram force and ram car energy. 

Signals from three ram car longitudinal accelerometers, BA2CX, BA2LX, and BA2RX were 

averaged to obtain the ram car acceleration (Figure 46). These acceleration signals were filtered 

with a Butterworth 4-pole phaseless low-pass filter that had a corner frequency of 100 Hz. 

Maximum deceleration was approximately 6.0 g, as shown in Figure 46. In the figure, a time of 

0 seconds corresponds to the initial contact between ram face and protective panel.

Figure 46. Ram Car Acceleration

Longitudinal force on the ram car was calculated as the product of ram car mass and 

acceleration. Figure 47 shows ram car force as a function of time. The longitudinal force on the 

ram car was produced by the moving ram contact with the tank car. The maximum force was 

approximately 1.8 million pounds.
46

Figure 47. Ram Car Force

The ram car’s velocity was computed by integrating and averaging the three acceleration signals 

identified above. The initial speed of the ram car (just prior to impact) was measured 

independent of the accelerometers. Figure 48 shows the velocity versus time behavior for the 

ram car. The ram car had an initial speed of 17.8 mph and a rebound speed of 9.3 mph. The 

calculated initial and rebound speed agreed with the data from the speed sensors and the speed 

gun. 

Figure 48. Ram Car Speed during Impact

Ram car longitudinal travel was computed by twice integrating the three acceleration signals. 

Figure 49 is a plot of the ram car longitudinal travel versus time. The ram made initial contact 

with the protective panel at a time of 0 seconds. This corresponds to a ram car longitudinal 
47

travel distance of 0 inches. This figure shows the maximum indentation of 47.41 inches, which 

agreed with the analysis of the side-view HS video. Following removal of the jacket and 

insulation, the permanent indentation in the tank was found to be approximately 11.5 inches 

deep.

Figure 49. Ram Car Longitudinal Travel

Ram car kinetic energy was computed from the following equation:

Based upon the mass of the ram car and an impact speed of 17.8 mph, the kinetic energy of the 

ram car at the time of impact was calculated as 3.13 million foot-pounds. Figure 50 shows a plot 

of kinetic energy versus time for the ram car from a time prior to impact through rebound of the 

ram car. The kinetic energy of the ram car decreases as the ram is slowed during the impact,

reaching a minimum value of 0 foot-pounds at the time of maximum indentation. As the ram car 

begins to accelerate backward by elastic recovery of the tank car, the kinetic energy begins to 

climb. As the ram car is propelled backward from the tank car it has a kinetic energy of 

approximately 0.85 million foot-pounds. The difference between initial and final kinetic energy 

of the ram car is approximately 2.28 million foot-pounds. This energy corresponds to the energy 

that was dissipated by the tank car and protective panel.
48

Figure 50. Kinetic Energy versus Time

Figure 51 shows the ram car force versus travel distance. The maximum force imparted to the 

ram car occurs at the period of maximum forward travel. As the ram car is forced backward, the 

force decreases until the ram has separated from the tank car and is moving backward along the 

track.

Figure 51. Ram Car Force versus Distance
49

4. Summary

This report describes research conducted over a three-year span in which sandwich structure 

technology was investigated as a means to provide protection to railroad tank cars against the 

threat of an object impacting the side of the tank. This research may be divided into two phases. 

The first phase was basic research with the objectives to: (1) examine fabrication and 

manufacturing issues associated with sandwich structures, (2) observe the deformation behavior 

of flat, welded steel sandwich panels under quasi-static loading, (3) confirm analytical and 

computational modeling efforts, and (4) rank and select candidate core geometries for dynamic 

impact testing. Fabrication and manufacturing issues were material selection for the sandwich 

panel components (face sheets and core geometries) as well as welding processes to build the 

panels. Focus was given to off-the-shelf materials because of their availability in the desired 

quantities. Flat, welded steel sandwich panels with candidate cores and materials were subjected 

to two types of quasi-static loading conditions: (1) uniaxial compression, and (2) bending with 

an indenter. Observations and results from these tests were described in a previous report [4]. 

This report also included computational analyses to complement the testing effort.

The second phase of research was the design of a curved, welded steel sandwich panel to protect 

an actual railroad tank car during a full-scale impact test. Based on the observations and results 

of the basic research phase, a curved sandwich panel was built with 3-inch OD pipe cores, a solid 

outer face sheet, and strips for the inner face sheet. As shown in Figure 52, the panel measured 

approximately 6 feet by 6 feet. The core material was ASTM A513 steel with a thickness of 

0.086 inches. The face sheet material was ASTM A1010 with a thickness of 0.120 inch. The 

cores were attached to the face sheets by gas metal arc welding (GMAW). The protective panel 

weighed approximately 900 pounds.

Figure 52. Schematic of Protective Panel used in Full-scale Impact Test
50

The protective panel was hung in front and outside of a decommissioned tank car, which was 

braced against a concrete barrier. The tank car and panel were struck by a 12” x 12” indenter 

mounted to a ram car moving with an initial kinetic energy of approximately 3.13 million footpounds. The impact resulted in permanent deformation to both the protective panel and the tank 

car. However, the tank car did not puncture and all lading (water) was contained throughout the 

impact. The ram car was propelled backward following the impact at a speed of approximately 

9.3 mph.
51

5. Discussion

In a collision event, momentum or kinetic energy is transferred from the moving object to other 

initially stationary objects in the overall system. In the full-scale shell impact test described in 

this report, the exchange of momentum or kinetic energy occurs among the various system 

components that include the protective panel, the outer jacket, the commodity-carrying tank, and 

the lading inside the tank.

The sandwich construction of the protective panel is designed to dissipate the kinetic energy and 

to distribute the impact load over a larger footprint than that of the indenter. Moreover, the 

compliance or flexibility of the sandwich panel allows for appreciable energy loss, in terms of 

dissipation and absorption. The energy loss is manifested through damage in the form of 

creating fracture surfaces or permanent deformation. In the full-scale test, for example, fractures 

of the welds and breaking of the strip face sheets were observed in the protective panel after 

impact. In addition, permanent deformation of the outer jacket and the commodity tank were 

also observed.

In the full-scale impact test described in Section 3, the ram car weight was 295,725 pounds and 

the impact speed was 17.8 mph. The corresponding kinetic energy is more than 3 million footpounds. In an attempt to envision the magnitude of this level of energy, Figure 53 shows other 

collision scenarios that generate the same level of kinetic energy. That is, a passenger car 

(assumed to weigh 160,000 pounds) traveling at 24.2 mph produces the same kinetic energy as 

the ram car impacting the tank car with the protective panel in the full-scale test. Similarly, an 

empty tank car (assumed to weigh 81,700 pounds) moving at a speed of 33.9 mph also translates 

to the same level of kinetic energy.

Figure 53. Impact Scenarios with Equivalent Kinetic Energy
52

Table 13 indicates that the impact speed achieved in the most recent test (i.e. 17.8 mph) is the 

highest impact speed of the three full-scale tank car impact tests conducted at TTC. The table 

also indicates that the indenter dimensions in each of the tests were different. Therefore, in 

addition to ram car weight and impact speed, another key factor that affects the likelihood of 

whether the commodity-carrying tank will puncture in the event of an impact is the size of the 

indenter. Damage from relatively small indenters is highly localized, and is concentrated near 

the corners of the indenter face. For relatively larger indenters, the overall tank “system” is 

engaged to help dissipate the kinetic energy from impact. Finite element simulations of fullscale tank car shell impacts such as those conducted at TTC suggest that the distinction between 

relatively small and large indenters is in the range between the 6-inch by 6-inch and the 12-inch 

by 12-inch indenters.

Table 13. Summary of Full-scale Tank Car Shell Impact Tests Conducted at TTC

Impact 

Speed 

(mph)

Indenter Dimensions Outcome

Width

(inches)

Height

(inches)

Edge Radii 

(inch)

Test 1 14.0 17 23 1 Permanent deformation, 

no puncture

Test 2 15.1 6 6 1⁄2 Puncture

Test 3* 17.8 12 12 1 Permanent deformation, 

no puncture

* With protective panel

Referring to Figure 52, the protective panel used in the most recent full-scale test covered an area 

of the tank car shell approximately six feet in length by six feet in height. The size of the panel 

was selected for several reasons. While a larger panel would provide protection over a larger

portion of the tank shell, pretest finite element simulations suggested that larger panels had an 

increased likelihood of material failure occurring directly beneath the indenter. Because of this 

localized failure, a large panel would offer little load distribution before the indenter strikes the 

shell of the tank. At the opposite end of the size spectrum, a panel that is only slightly larger 

than the impacting object would offer very little ability to blunt the impacting object owing to the 

small size of the panel. Additionally, if the protection scheme were envisioned to cover the 

entire shell surface of the tank, a smaller panel would require more instances to be installed. The 

selected panel size was seen as a reasonable size for manufacturing, handling, and installation 

without being so large as to result in highly localized failure.

Using a 6-foot by 6-foot curved panel to protect the side of a tank car resembles using a halfheight shield to protect the end or the head of a tank car. Given the dramatically improved safety 

performance of tank cars after head protection requirements were instituted, this resemblance 

leads to the notion of using protective panels based on sandwich structure technology to retrofit 

existing tank cars against the threat of side of shell impacts. A possible strategy to optimize the 

costs, risks, and benefits associated with shell protection might be partial protection of the tank. 

For example, some benefit, balanced against cost and risk, could be realized from protecting only 
53

the bottom half of the tank since accident statistics indicate that shell punctures are more likely to 

occur along the lower half of the tank. Partial protection schemes are outlined in Appendix A.

One area that remains open in terms of applying sandwich structure technology to protect 

railroad tank cars against shell puncture is how to effectively attach the protective panel to the 

tank structure. The attachments would need to be compliant or flexible in order to mitigate 

localized failures. Various concepts are outlined in Appendix B of this report, but ultimately the 

expertise and the experience of tank car manufacturers will be required to develop an appropriate 

design.

Absorbing and dissipating 3 million foot-pounds of energy represents a formidable challenge 

because the design of such a system is constrained by the maximum allowable weight and 

clearance standards for rail cars. The effect of weight and space budgets on designs to improve 

the safety performance of tank cars has been discussed in previous work [6]. The protective 

panel designed and built for the full-scale impact test weighed approximately 900 pounds. If 

such panels covered the entire tank car shell, the resulting shell protection system would be 

within weight and space limitations for tank cars built to 286,000-pound gross weights. The 

observations and results from the research described in this report suggest that sandwich 

structure technology can, in principle, be applied to provide protection to the tank car shell in the 

event of a shell impact. Moreover, protection against puncture is essential for tank cars carrying 

those materials with the greatest potential to harm humans and the environment if released.
54

6. References

1. Bureau of Explosives (BOE), Annual Report of Hazardous Materials Transported by Rail: 

Calendar Year 2011. Association of American Railroads, Washington, D.C. (2012).

2. Tyrell, D., Jeong, D., Jacobsen, K., Martinez, E., “Improved Tank Car Safety Research,” 

Proceedings of the 2007 ASME Rail Transportation Division Fall Technical Conference, 

RTDF2007-46013, Chicago, IL, September 2007.

3. Treichel, T., “List of Accident-Caused Releases of Toxic Inhalation Hazard (TIH) Materials 

from Tank Cars, 1965-2005,” RSI-AAR Railroad Tank Car Safety Research and Test 

Project, Report No, RA 06-05 (2006)

4. Jeong, D.Y., Carolan, M.E., Perlman, A.B., Tang, Y.H., “Deformation Behavior of Welded 

Steel Sandwich Panels Under Quasi-Static Loading,” Volpe National Transportation Systems 

Center Final Report, DOT/FRA/ORD-11/06, March 2011.

5. Carolan, M.E., Jeong, D.Y., Perlman, A.B., Tang, Y.H., “Deformation Behavior of Welded 

Steel Sandwich Panels Under Quasi-Static Loading,” Proceedings of the ASME/ASCE/IEEE 

2011 Joint Rail Conference, JRC2011-56054, Pueblo, CO, March 2011.

6. Tyrell, D., Jacobsen, K., Talamini, B., Carolan, M., “Developing Strategies for Maintaining 

Tank Car Integrity During Train Accidents,” Proceedings of the 2007 ASME Rail 

Transportation Division Fall Technical Conference, RTDF2007-46015, Chicago, IL, 

September 2007.

7. http://www.efunda.com/materials/alloys/alloy_home/show_alloy_found.cfm?ID=AISI_4130

&show_prop=all&Page_Title=AISI%204130

8. http://www.efunda.com/materials/alloys/carbon_steels/show_carbon.cfm?ID=AISI_1010&pr

op=all&Page_Title=AISI%201010

9. Jones, J., Quote from Weldedtube (2008)

10. http://www.leecosteel.com/products/high-strength-low-alloy-structural/hsla-structuralquality/a656-hsla-steel.html

11. http://www.ssab.com/Global/Domex/Datasheets/en/444_Domex%20100%20XF.pdf

12. Association of American Railroads, AAR Manual of Standards and Recommended Practices 

and Specifications for Tank Cars, M-1002, Appendix M.

13. Abernathy, M., Quote from Bull Moose Tube (2008)

14. Tang, Y.H., Yu, H., Gordon, J.E., Priante, M., Jeong, D.Y., Tyrell, D.C., Perlman, A.B., 

“Analyses of full-scale tank car shell impact tests,” Proceedings of the 2007 ASME Rail 

Transportation Division Fall Technical Conference, RTDF2007-46010, Chicago, IL, 

September 2007.

15. ASTM Standard A370, “Standard Test Methods and Definitions for Mechanical Testing of 

Steel Products,” ASTM International, West Conshohocken, PA, 2012 www.astm.org.

16. ASTM Standard E8, “Standard Test Method for Tension Testing of Metallic Materials,”

ASTM International, West Conshohocken, PA, 2011 www.astm.org.

17. GMH Engineering. (1996). DataBRICK Data Acquisition System Reference Manual. Orem, 

UT.

18. SAE International. (1995 March). SAE J211/1, Instrumentation for Impact Test—Part 1

Electronic Instrumentation. Warrendale, PA.

19. Treichel, T., “Specific Locations of Damage and Lading Losses on Tank Heads and Shells,” 

RSI-AAR Railroad Tank Car Safety Research and Test Project Report RA-06-04 (2007).
55

Appendix A. Estimates of Labor, Material and Capital Equipment for 

Manufacturing

In an effort to develop a framework to estimate the cost of side protection panels for railroad 

tank cars, CMI performed an analysis of the manufacturing costs and capital investments 

required to produce panels in annual volumes of 10k, 20k, and 40k in order to highlight any 

value of large-scale production. 

The study also captured the projected costs for various retrofit panel strategies covering varying 

portions of the sides of a rail car; all of the sides (100 percent), all but the section around the 

manway (86 percent), only the bottom (50 percent) and only sections adjacent to the wheels (33

percent). The schematics shown in Figure 54 are representative of the locations on the tank shell 

in which accident data have been collected [19]. Moreover, the accident data indicate that the 

bottom half of the tank is more likely to be impacted and punctured than the top.

Figure 54. Various tank car coverage strategies

Panel Design Assumptions

Costs were estimated for panels designed and constructed the same way that they were 

manufactured for the test performed at the Transportation Technology Center, using a solid cold 

rolled 1010 carbon steel 0.120-inch thick front face sheet, standard 3-inch diameter tube with a 

0.086-inch wall thickness, and a series of 3-inch wide 1010 steel 0.120-inch thick strips spaced 6

inches apart on the back. The tubes are attached to the front face sheet using GMAW plug welds 

every three inches and to the rear strips using GMAW plug welds with the same spacing. The 

tubes are not welded to each other. Some non-structural tack welding between the tubes is used 

during assembly to facilitate the manufacturing process. 

In a full-scale production environment, it is assumed that the panels would likely be retrofitted to 

the tank cars in the same facility in which they were manufactured; however, this study 

concentrates on the manufacturing of the protective panels and their attachment systems only. 

Because carbon steel corrodes easily, a coating process was included in the study. Conventional 

spray painting will not provide adequate corrosion protection due to geometry of the tube core. 

The coating process included for this cost study could be either the addition of a protective layer 

of paint using a full immersion dip coating process or a galvanizing line. Both coating systems 

are assumed to require similar capital investment and direct labor content. 
56

For the purpose of this analysis, it is further assumed that the panels are all the same size. A 

number of panel dimensions were considered, and it was decided that the optimum panel size 

would be approximately 7.5 feet by 6.25 feet. At this panel size, a standard CNC punch press 

can be used to cut the plug weld holes in the front face sheet, and the weight of the panel would 

be approximately 800 pounds which can be manipulated with conventional material handling 

equipment. With panels of this size, twelve panels would cover each side of a tank car. 

Panel Manufacturing Assumptions

Figure 55 shows a flow chart representing the manufacturing process described in this section.

The 1010 steel front face sheet material and tubes would be received from the mill cut to size. 

The rear strips would be cut in-house from a 3-inch wide coil of 1010 steel. The holes for plug 

welding would be cut into the front face sheet using a CNC punch. The rear strips would have 

plug holes punched on a progressive die during the process in which the strip material is 

straightened and cut to length. The tubes would be degreased prior to assembly to facilitate 

joining and make finishing of the assembly easier later in the production cycle. Both the face 

sheet and the rear strips would be rolled to the required curvature using a three roller mill large 

enough to accommodate a 7.5-foot wide face sheet.

Custom-made fixturing would be used during welding. These fixtures would be on tracks so that 

they could be moved in and out of the robotic welding cell. All setup would be done on the 

fixtures while they are outside the welding cell. Once the setup is completed, the parts would be 

moved into the cell for joining and then moved back out for additional setup. The first weld 

fixture would be designed to accept the tubular core and to position the rear strips accurately. Its 

surface would be concave with a radius that when the tubes and strips were loaded would 

achieve the required curvature of the inside, train car side, of the assembly. Both the tubes and 

strips would be loaded on the fixture manually with the assistance of a jib crane. The tubes 

would be tacked to each other in the assembly area using manual welding to reduce movement 

during robotic plug welding. When the assembly was ready for welding, it would be moved into 

the weld cell where two welding robots would plug weld the strips to the tubes. The plug 

welding of the assembly is the most time-intensive portion of the manufacturing operation. As 

currently designed, the panel will require 360 plug welds to attach the strips to the tubes which, 

using two robots simultaneously, would take approximately 24 minutes. Once welding is 

completed, the assembly still on the weld fixture would be moved out of the weld cell. A bridge 

crane would then be used to take the assembly off of the concave fixture, turn it over, and 

position it on a convex fixture. Using the overhead crane again, the front face sheet would be 

positioned on top of the assembly. The fixture and assembly would then be moved back into a 

robotic welding cell where two robots would plug weld the face sheet to the tubes using another 

360 welds, which again would require 24 minutes. All plug welding would be done using 

GMAW. The final step in the panel manufacturing process would be cleaning and coating the 

panels with a protective layer to inhibit corrosion. Because the tubes would need corrosion 

protection on their inside surface, the coating method requires complete immersion of the panel 

in the coating. Dip painting or galvanizing are two potential methods that have similar capital 

and direct labor costs. 
57

Figure 55. Railroad Tank Car Protective Panel and Mounting Strap Processing
58

Panel Attachment Assumptions

Ideally, the panels should be attached to the railroad tank car with minimal or no rework of the 

tank car itself, a goal that could be realized by employing a series of bands around the tank car to 

which the panels are “attached”. One series of bands would be wrapped around the car over the 

existing steel jacket which currently protects the insulation layer. These bands would be 

positioned so that the panels could be “attached” to them by stud welding the panels to the straps 

or forming hooks into the straps, Figure 56. The panels would be hung on these mounting 

configurations and then held in place by a second set of straps which would be wrapped around 

the tank car overtop the protective panels. At each location at which the curved sides of the 

protective panels would abut one another, wider straps would be employed. These wider straps 

would be used to secure the edges of two panels. This is not illustrated in Figure 56.

The straps would be manufactured using 1010 steel coil stock 0.1875-inch thick and 6 inches

wide. The strap material would be straightened, cut to size, and then rolled to the desired 

curvature. These straps would have holes punched in their ends. The ends would then be bent 

90 degrees using a press brake so that a tensioning bolt could be used to tighten them to the tank 

car. If the hook method were used, the hooks would be formed at the same time that the punch 

pierced the holes in the ends. Figure 56 illustrates the proposed hook method to attach panels to 

the tank cars. If studs are used, the studs would be attached after the ends were formed. Because 

the mounting strap cost using either method would be similar and the cost of these straps is not 

significant, all cost projections assume using the stud welded straps. 

 

 

Figure 56. Demonstration of Attachment Scheme
59

Costing Assumptions

Calculations for the costs of the panels have been based on the following assumptions:

Railroad Tank Car 

Tank Length – Assume 3-Foot Deep Heads 43.901 feet

Length of Tank to be Protected 37.901 feet

Tank Width 8.375 feet

Car Width w/ 4-Inch Insulation 9.042 feet

Tank Wall Thickness 0.777 inches

1010 Carbon Steel Cost 0.850 $/pound

Regular Core Tube Cost 1.500 $/foot

Individual Panel Width 6.30 feet

Individual Panel Height-Circumference 7.52 feet 

Panel & Mounting Strap Information

Outer Face Sheet 0.120 inches

Pipe Diameter 3.00 inches

Pipe Wall 0.083 inches

Pipe Weight per Foot 2.599 pound/foot

Inner Face Sheet – Strips 0.120 inches

Mounting Strap – Inner 0.1875 inches

Mounting Strap – Outer 0.1875 inches

Cost Estimates

Estimated costs were projected for manufacturing tube core tank car protective panels measuring 

7.5 feet by 6.25 feet with required mounting hardware at production rates of 10,000, 20,000, and 

40,000 panels per year. In addition, estimates were generated for the capital investment required 

to support these annual production volumes (Table 14). Although panels and mounting straps 

would be sold and used in multiple quantities and not sold individually, the cost of one panel 

would be approximately $885 and the average cost of a mounting strap would be $184.

Table 14. Cost Estimates for Panel and Mounting Hardware

10,000 Panels 

per Year

20,000 Panels 

per Year

40,000 Panels 

per Year

Panel Materials $13,395 $12,725 $12,343

Mounting Straps $1,274 $1,210 $1,174

Manufacturing Labor @ $20 per Hour $3,106 $3,044 $2,983

Burden – 120% of Labor $3,727 $3,653 $3,580

Margin – 5% $1,075 $1,032 $1,004

Estimated Panel and Mounting Hardware per Car $22,577 $21,664 $21,084

Capital Investment $2,779,750 $3,666,650 $5,832,475

Breakeven – Panels 2,586 3,554 5,809

Breakeven – Months of Production 16 11 9
60

Labor costs will be relatively inelastic as production volumes increase. Most of the available 

manufacturing economies of scale will have already been achieved at the 10,000-panel per year 

level. For this reason, a manufacturing volume increase to 20,000 and 40,000 panels per year 

will represent only a minor efficiency improvement, a 2-percent drop in labor cost each time the 

volumes double. Increased volume will have a slightly greater impact on the material costs. A 

5-percent decrease in material cost has been assumed if production increases from 10,000 to 

20,000 panels per year and an additional 3 percent if the volume increases to 40,000 panels. 

Detailed labor, material, and capital equipment cost estimates are provided below.
61

Table 15. Labor Estimate for Panel Manufacturing

Plug Weld Both Sides & Use Robot 

Panel Size – 6.3’ x 7.5’ w/ 3" Tube

Minutes To 

Complete 

Step

Minutes per 

Piece

Pieces per 

Panel

People 

Required

Minutes per 

Panel

Rear Face Sheet - Strips - 12 per Panel

Receive Coil 3" Wide, 120" Thick 1010 Steel 

Coil 712’ Long 30 3.75 1 1 4

(One Coil = Strips for 8 Panels )

Load Coil on Line and Set Up 30 3.75 1 2 8

Straighten, Punch, and Shear Strips 1 1 12 1 12

Roll to Required Curvature 3 3 12 1 36

Front Face Sheet 

Receive 60 Pieces 30 0.5 1 1 1

Set Up Face Sheet on Punch Press 6 6 1 2 12

Punch Slots – One Every 6"~360 Slots 0.05 0.05 360 1 18

Roll to Required Curvature 20 20 1 2 40

Tube

Receive 1200 Pieces 60 0.05 30 1 2

Degrease, Clean, Dry, and Move to Line 1 1 30 1 30

Assembly Plug Weld

Position Tube 1 1 30 2 60

Lay Strips 1 1 12 2 24

Tack Tube – Both Sides 0.25 0.25 60 1 15

Plug Weld the Strips w/ 2 Robots 0.067 2 12 1 24

Flip Panel 5 5 1 2 10

Place and Line Up Front Face Sheet 10 10 1 2 20

Tack Face Sheet to Tubes 0.25 0.25 60 1 15

Plug Weld Face Sheet to Tubes (2 Robots) 0.067 24 1 1 24

Remove Assembly 10 10 1 1 10

Clean & Dip

Dip Assembly in Cleaning Solution 5 5 1 1 5

Coat Assembly 20 20 1 1 20

Total 388 Minutes

6.47 Hours
62

Table 16. Labor Estimate for Mounting Strap Manufacturing

Assumes Using Straps with Weld Studs

Minutes to 

Complete 

Step

Minutes per 

Piece

Pieces per 

Panel

People 

Required

Minutes per 

Panel

Straps

Receive 10 Coils 12" Wide 0.1875" Thick 1010 

Steel Coil 150’ Long (One Coil = 6 Strips )149 6 1 10 1 10

Load Coil On Line and Set Up 15 2.5 10 1 25

Receive 10 Coils 6" Wide 0.1875" Thick 1010 

Steel Coil 150’ Long (One Coil = 6 Strips) 6 1 4 1 4

Load Coil on Line and Set Up 15 2.5 4 2 20

Straighten, Punch, and Shear Strips 0.5 1 14 1 14

Roll to Required Curvature 1 1 14 1 14

Form Ends 1 1 28 1 28

Total 115 Minutes

1.92 Hours

Table 17. Detailed Material Cost and Weight Calculations

Height 

(Top to 

Bottom)

Width

(Side to 

Side)

Thickness Studs Pcs Total 

Weight

Waste Cost

Ft Ft In Qty @ $1 

each

Panel – Each

Top Face Sheets 7.52 6.32 0.120 234 0.00% $199

Bottom Face Sheets – Strips 6.58 0.25 0.120 13 105 5.00% $84

Core Tube 6.32 0.25 28 460 0.00% $265

Totals 799 $558

Straps – Each

Straps against the Tank – Single 0.50 28.41 0.1875 12 67 5.00% $71

Straps against the Tank – Double 1.00 28.41 0.1875 24 133 5.00% $143

Outer Strap – Single 0.50 29.98 0.1875 58 5.00% $51

Outer Strap – Double 1.00 29.98 0.1875 115 5.00% $103
63

Table 18. Projected Capital Equipment Requirements for Protective Panel Manufacturing

Process Part Processed Equi pment Des cri pti on Ba s e Cos t

Freight & 

Setup Tota l Cos t 

Qty of 

Ma chi nes $ Qty of Ma chi nes $ Qty of Ma chi nes $

Feed Stri ps

Rea r Fa ce / Hol d Down 

Straps Payoff $500 $500

3 $1,500 3 $1,500 3 $1,500

Coi l Feed

Rea r Fa ce / Hol d Down 

Straps Coi l Feeder $6,000 $6,000

1 $6,000 1 $6,000 1 $6,000

Stra i ghte n Coi l

Rea r Fa ce / Hol d Down 

Straps Cooper Weymouth 6" $4,950 $1,000 $5,950 1 $5,950 1 $5,950 1 $5,950

Punch Hol es - 

Strips Rea r Fa ce Model PM2-20 Minster $24,500 $6,125 $30,625 1 $30,625 1 $30,625 1 $30,625

Shear

Rea r Fa ce / Hol d Down 

Straps Small Shear $15,000 $3,750 $18,750 1 $18,750 1 $18,750 1 $18,750

Roll

 Face Sheets / Hold 

Down Stra ps Bend Pa rts To Sha pe $25,000 $6,250 $31,250 2 $62,500 3 $93,750 4 $125,000

Move Ra w Ma teri a l s Forkl i ft $17,000 $4,250 $21,250 2 $42,500 3 $63,750 4 $85,000

Move Assembly EMH Overhea d Cra ne 3 Ton $30,000 $10,500 $40,500 2 $81,000 3 $121,500 5 $202,500

Move Move parts Ca te l i ve re d Hoi s t $1,200 $400 $1,600 8 $12,800 12 $19,200 24 $38,400

Punch Hol es - 

Front Fa ce Front Fa ce Sheet Turret Press $149,500 $37,375 $186,875 1 $186,875 1 $186,875 2 $373,750

Tacking Assembly Mi g Wel der $48,000 $2,000 $50,000 4 $200,000 8 $400,000 12 $600,000

Robot Weld Assembly Motoma n Robot - 2 per Li ne $165,000 $41,250 $206,250 4 $825,000 6 $1,237,500 12 $2,475,000

Hol d Pa nel Assembly Convex Jig Carts $15,000 $15,000 6 $90,000 10 $150,000 18 $270,000

Hol d Pa nel Assembly Conca ve Ji g Ca rts $15,000 $15,000 6 $90,000 10 $150,000 18 $270,000

Bend Stra ps Straps Ci nci nna ti Pre s s Bra ke $42,000 $10,500 $52,500 1 $52,500 1 $52,500

Bend Stra ps Straps Pres s w/ progres s i ve di es $100,000 $15,000 $115,000 1 $115,000

Cl e a n Ra w Pa rts All Degrees Ba th $45,000 $11,250 $56,250 2 $112,500 2 $112,500 2 $112,500

Finishing Line Compl e te l i ne Finishing Line $700,000 $175,000 $875,000 1 $875,000 1 $875,000 1 $875,000

Air Pl a nt Compressed Air source $25,000 $6,250 $31,250 1 $31,250 1 $31,250 2 $62,500

Misc Pl a nt Mi cs Ha nd Trucks , Ra cks a nd Tool s $50,000 $5,000 $55,000 1 $55,000 2 $110,000 3 $165,000

Totals $2,779,750 $3,666,650 $5,832,475

 

 
64

Assuming the fabrication of 10,000 panels per year, the cost of the four different levels of 

protection are as shown in Table 19. All coverage strategies, except the 33 percent coverage, 

require approximately the same amount of mounting hardware. Because the 33 percent coverage 

requires no mounting hardware in the center section of the tank car, the mounting hardware 

requirement would be less. 

Table 19. Options for Tank Car Coverage

Option All Sides 

Covered

All Sides 

Except 

Manway Area

Only Bottom 

Half

Only Above 

Truck 

Assemblies

Percent Coverage 100% 86% 50% 33%

Number of Panels 24 20 12 8

Number of Mounting Straps Wide Outer 5 5 5 1

Narrow Outer 2 2 2 4

Wide Inner 5 5 5 1

Narrow Inner 2 2 2 4

Materials Panels $13,395 $11,162 $6,697 $4,465

Straps $1,274 $1,274 $1,274 $697

Manufacturing Labor @ $20/hour Panels $3,106 $2,588 $1,553 $1,035

Straps $537 $537 $537 $383

Burden 120% of Labor $4,371 $3,750 $2,508 $1,702

Margin 5% $1,134 $966 $628 $414

Estimate: Cost of Panel and Mounting Hardware per Car $23,817 $20,277 $13,197 $8,697

NOTE: Based on 100% coverage figures, a single panel would cost approximately $885 and a mounting strap $184.

Future Considerations

These cost estimates for manufacturing the protective panels assumed similar production 

methods as those used to fabricate a single sample panel that was tested at the Transportation 

Technology Center on May 18, 2011. For example, plug welds were used every 6 inches to 

attach the front face sheet and rear strips to the tubular core. This joining process is timeintensive even with two relatively high speed welding robots working in tandem. The 7.5-foot 

by 6.25-foot panel would require 720 plug welds, 360 on each side, which require a total of 48 

minutes to complete. It is recommended that further study be performed to investigate lowering 

the cost of these protective panels by reducing the welding time. One potential cost saving

strategy would be to decrease the number of welds by increasing the spacing between them. 

Another possibility is to use edge welds at the interface between the pipe and strips which could 

potentially reduce welding time. Both efficiency improvements warrant study before evaluating 

the cost effectiveness of this protective paneling system. 

In addition, the attachment methods proposed in this study are conceptual and were included to 

establish estimated costs for attachment. These attachment methods would need to be built and 

tested along with other possible methods of attachment prior to finalizing the tank car protection 

concept.
65

Appendix B. Protective Panel Attachments to Tank Car

At the beginning of this task, the project team suggested investigating tank car panel attachment 

methods. Stud welding technique was identified as a potential method. Accordingly, the CMI 

team worked with a stud welding tool manufacturer to further investigate the process. To attach 

the sandwich panels to the tank car body, studs would be welded to the outer body of the tank car 

so that the panels could then be bolted to the studs. Although this method was eventually not 

selected for attaching the impact panel to the chlorine tank, the results are presented below.

Study Welding Study

TC128-B is the standard steel used in the construction of the tank car bodies; therefore, stud 

welding to the TC128-B steel was investigated. For this study, 7⁄8-inch diameter studs were 

welded to 0.453-inch thick normalized TC128-B plate. The stud welding technique used was the 

capacitance discharge method performed at Nelson Stud Welding’s test lab. Two of the samples 

were tensile tested to failure. Both samples failed in the stud, at 29,000 pounds and 30,400 

pounds of tension, and showed no distortion in the weld area. In addition, weld adhesion was 

tested by bending a welded stud 90 degrees. No failure occurred in the weld area, but there was 

evidence of failure initiating in the stud itself between some of the threads, as shown in Figure 

57.

 

Figure 57. Stud Weld after Tensile Test (left) and Bend Test (right)

In view of this positive preliminary test result, it appeared that stud welding to a TC128-B

pressure vessel could be achieved without requiring post heat treatment. In order to verify this, 

the stud welds were sectioned axially through the center of the studs, polished, and etched in 2

percent nital; the cross-sections were then examined metallographically. TC128-B has a 

microstructure of banded ferritic steel—with a ferrite grain size of 10 μm or less—and a pearlite 

phase dispersed into it. In the rolled condition, the pearlite stringers are elongated in the rolling 

direction. The stud bolt blank is a forged low carbon steel material. Its microstructure is a 

mixture of banded ferrite and pearlite with a ferrite grain size of about 30 μm. 
66

A composite micrograph of the cross section of the stud welds is shown in Figure 58, illustrating 

the TC128-B base metal on the top and the stud bolt cross-section on the bottom. There were 

HAZs in both the steels; in addition, between the HAZs, where the stud was plunged into the 

base metal, there was a “mushy” zone. The mushy zone was overetched making it difficult to 

identify the phases present; however, it appeared to contain lower transformation products. In 

the HAZ in the TC128-B steel, the stringer pearlite phase had transformed to martensite, which 

is a hard, plate-like structure (Figure 25). This phase is brittle with internal stresses that can lead 

to weld cracking. 

Figure 58. Cross Section of Weld Figure 59. HAZ in TC128-B Steel

The HAZ in the stud area is shown in Figure 60. Since the carbon content in this steel is higher 

than that of TC128-B, the dissolved carbon was transformed into bainite and spherodized 

pearlite. The transformed product in the microstructure will contribute residual stresses leading 

to structural weakness and cracking; therefore, a post stress relieving treatment is necessary. The 

base metal microstructure of the stud bolt, typical of high carbon ferritic and pearlitic steel, is 

shown in Figure 61. The stress relieving treatment will normalize the residual stresses and 

modify the microstructures of both martensite in the TC128-B steel and bainite in the plain 

carbon steel in order to provide more ductility and better toughness.

Figure 60. HAZ in Stud Bolt Region Figure 61. Microstructure of Stud Bolt

Stud

TC128-B Base
67

The hardness of the stud and the TC128-B base plates were 170 and 200 HV (at 200-gram 

indenter load), respectively, consistent with their pearlite (carbon) contents. The “mushy” zone 

had a peak hardness of 495 HV, and the HAZs transitioned from base metal hardness to 300 HV 

for the stud and 380 HV for the TC128-B plate. The higher hardness is attributable to the lower 

transformation products.

In order to relieve the stress and improve the ductility, the weld requires post heat treatment. A 

temper heat treatment at 1150 °F for 1⁄2 to 1 hour is recommended. Based on this study, it is 

recommended that the studs be attached to the tank car before the tank car is stress relieved.

Alternate Attachment Schemes

Since the protective panels may be retrofitted onto existing tank cars, stress relieving the entire 

tank car is not practical. Other attachment methods will need to be developed. One method 

proposed by CMI is to wrap straps around tank cars that have either studs or brackets to which 

the panels could be attached. For a retrofit, in order to save weight and cost, only the areas of the 

tank car which, based on history, are the most likely to be punctured would be protected. Since 

the bottom half of the tank is the primary region that needs protection [19], it is possible that 

studs could be welded to existing brackets that are used for the braking system. The panels could 

then be attached to those studs. An outer strap may act as a hoop or belt on the exterior of the 

panel to provide additional tension to hold the panel in place.

Future Considerations

Based on the work completed during the 3-year project and, in particular, the results from the 

manufacturing and testing of the full-scale panel, the following recommendations were 

compiled:

• Spot welding should not be utilized to manufacture the panels.

• The two mating fixtures on which the curved panel was fabricated offer a solid 

manufacturing approach for building a panel with a defined radius.

• Further study is recommended to decrease weld time by (1) decreasing density of welds 

and/or (2) using edge welds on strip in place of plug welds.

• To prevent the lateral movement of tubes, a half tube is positioned on each end of the 

panel.
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Abbreviations and Acronyms

AAR Association of American Railroads

AISI American Iron and Steel Institute

ATLSS Advanced Technology for Large Structural Systems

ASTM American Society for Testing and Materials

CMI Cellular Materials International, Inc.

EWI Edison Welding Institute

FRA Federal Railroad Administration

GMAW gas metal arc welding

HAZ heat affected zone

HD high definition

HS high speed

HSLA high strength low alloy

SBIR Small Business Innovation Research

TIH toxic inhalation hazard

TTCI Transportation Technology Center, Inc.

VTRC Virginia Transportation Research Council