Weld Strength Verification and Proposed Weld Testing 

and Inspection Criteria for the 

MK83 and MK84 Conical Bomb Fins 

by Marc S. Pepi and Victor K. Champagne 

ARL-TR-2862 October 2002

performed for 

The Naval Air Warfare Center 

Pt. Mugu, CA 93042

Approved for public release; distribution is unlimited.
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator.
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2862 October 2002

Weld Strength Verification and Proposed Weld Testing and 

Inspection Criteria for the MK83 and MK84 

Conical Bomb Fins 

Marc S. Pepi and Victor K. Champagne 

Weapons and Materials Research Directorate, ARL 

performed for 

The Naval Air Warfare Center 

Pt. Mugu, CA 93042

Approved for public release; distribution is unlimited.
Abstract 

The U.S. Army Research Laboratory (ARL) performed weld strength verification testing on 

manufactured specimens to characterize four different types of welds found on both the MK83 

and MK84 conical bomb fins. Based on the results obtained by testing, as well as existing 

requirements, ARL established test and inspection criteria that may be employed at the discretion 

of the Naval Air Warfare Center for future First Article Inspections and/or during production as 

a tool for evaluating the quality and integrity of the weldments.

ii
Acknowledgments 

The authors wish to thank Robert Fusick of Aerotek Welding, North Granby, CT, for his input in 

determining the welding parameters and for the fabrication of the welding specimens. 

iii
INTENTIONALLY LEFT BLANK.

iv
Contents 

Acknowledgments iii

List of Figures vii

List of Tables ix

1. Background 1

2. Drawing/Specification Review 1

3. Current Visual/Nondestructive/Mechanical Property and Metallographic 

Requirements 2

4. Test Specimen Fabrication 4

4.1 Plug Weld Specimens......................................................................................................6 

4.2 Spot Weld Specimens......................................................................................................6 

4.3 Seam Weld Specimens....................................................................................................9 

4.4 Fillet Weld Specimens.....................................................................................................9

5. Visual Examination 9

6. Metallographic Examination 12

7. Mechanical Testing 16

7.1 Plug Weld Tensile Shear Testing ..................................................................................16 

7.2 Spot Weld Tensile Shear Testing ..................................................................................18 

7.3 Seam Weld Tensile Shear Testing.................................................................................19

7.4 Fillet Weld Tension Testing..........................................................................................19 

8. Further Mechanical Testing 23

8.1 Additional Plug Weld Tensile Shear Testing................................................................25 

8.2 Plug Weld Peel Testing .................................................................................................25 

8.3 Additional Spot Weld Tensile Shear Testing................................................................29 

v
8.4 Spot Weld Peel Testing .................................................................................................30 

9. Discussion 33

9.1 Quality of Welds ...........................................................................................................33 

9.2 Inspection of Welds.......................................................................................................35 

9.3 Mechanical Testing of Welds........................................................................................36 

9.4 Strength of Base Metal..................................................................................................36 

10. Recommended Testing and Inspection Criteria 36

10.1 Visual Inspection...........................................................................................................37 

10.2 Metallographic Inspection.............................................................................................37

10.3 Establishment of Minimum Mechanical Property Criteria ...........................................38 

10.3.1 Plug Weld ..........................................................................................................38 

10.3.2 Spot Weld ..........................................................................................................38 

10.3.3 Seam Weld.........................................................................................................38

10.3.4 Fillet Weld.........................................................................................................38 

11. References 40

Appendix A. Parameters Utilized by Aerotek for Plug Weld Fabrication 42

Appendix B. Parameters Utilized by Aerotek for Spot Weld Fabrication 44

Appendix C. Parameters Utilized by Aerotek for Seam Weld Fabrication 46

Appendix D. Parameters Utilized by Aerotek for Fillet Weld Fabrication 48

Appendix E. Chemical Analysis of the Weld Wire Used by Aerotek Welding 50

Appendix F. Parameters Utilized by Aerotek for Improved Plug Weld Fabrication 52

Appendix G. Parameters Utilized by Aerotek for Improved Spot Weld Fabrication 54

Appendix H. Proposed Method of Sectioning and Testing Welds for the MK83 

and MK84 Conical Bomb Fins 56

Report Documentation Page 61 

vi
List of Figures 

Figure 1. Representative plug weld specimen in the as-received condition; reduced 25%............4 

Figure 2. Representative spot weld specimen in the as-received condition; reduced 25%. ...........5 

Figure 3. Representative seam weld specimen in the as-received condition; reduced 25%...........5 

Figure 4. Representative fillet weld specimen in the as-received condition; reduced 25%. .........6 

Figure 5. Schematic illustrating dimensions of plug weld assembly..............................................7 

Figure 6. Photograph showing plug weld assembly at Aerotek Welding.......................................7 

Figure 7. Photograph showing another view of the plug weld assembly at Aerotek Welding......8 

Figure 8. Schematic illustrating dimensions of spot weld assembly. .............................................8 

Figure 9. Schematic illustrating dimensions of fillet weld assembly. ..........................................10 

Figure 10. Method utilized by Aerotek to perform fillet weld. ....................................................10 

Figure 11. Photograph showing fillet weld assembly, as welded, at Aerotek. .............................11 

Figure 12. Photograph showing as-welded fillet weld assembly, from a different angle, at 

Aerotek.....................................................................................................................................11 

Figure 13. Schematic illustrating metallographic sectioning for the plug, spot, and seam 

weld specimens. .......................................................................................................................13 

Figure 14. Schematic illustrating metallographic sectioning for the fillet weld specimen. .........13 

Figure 15. Cross section of a plug weld specimen etched with 1% nital etchant (note the 

unfilled hole); magnified 10H. .................................................................................................14 

Figure 16. Cross section of a spot weld specimen etched with 1% nital etchant (note the 

interface of the two steel sheets present within the weld region); magnified 10H. .................14 

Figure 17. Cross section of a seam weld specimen etched with 1% nital etchant; magnified 

10H. ..........................................................................................................................................15 

Figure 18. Cross section of a fillet weld specimen etched with 1% nital etchant; magnified 

10H. ..........................................................................................................................................15 

Figure 19. Schematic illustrating pull test direction for each type of weld specimen..................20 

Figure 20. Typical “male” and “female” plug weld nugget failure; magnified 1H. .....................21 

Figure 21. Plug weld failure in which a nugget tore steel around the weld region; reduced 

50%. .........................................................................................................................................21 

Figure 22. A macrograph showing a representative sheared plug weld; magnified 1H................22 

Figure 23. A typical spot weld shear failure; magnified 1H. ........................................................22 

Figure 24. A typical seam weld failure; reduced 50%..................................................................23 

Figure 25. A typical fillet weld failure; reduced 50%. .................................................................23 

Figure 26. A typical peel test specimen; reduced 50%.................................................................24

vii
Figure 27. Macrograph of a typical improved plug weld tensile shear specimen; 

magnified 9H, etchant: 1% nital..............................................................................................25

Figure 28. Macrograph of a plug weld peel specimen welded using improved conditions 

by Aerotek; magnified 9H, etchant: 1% nital..........................................................................26 

Figure 29. Macrograph of a typical improved spot weld tensile shear specimen; 

magnified 9H, etchant: 1% nital..............................................................................................26 

Figure 30. Macrograph of a spot weld peel specimen welded using improved conditions 

by Aerotek; magnified 9H, etchant: 1% nital..........................................................................27 

Figure 31. Typical failure of an improved plug weld tensile shear specimen. Failure 

occurred in the parent material; magnified 1H.........................................................................28 

Figure 32. Typical failure of a plug weld peel specimen welded under improved 

conditions. Failure occurred by metal tearing initiated within the heat-affected zone; 

magnified 1H. ...........................................................................................................................29 

Figure 33. “Parent metal” failure of an improved spot weld tensile shear specimen; 

magnified 1H. ...........................................................................................................................31 

Figure 34. “Metal tearing” failure of an improved spot weld tensile shear specimen; 

magnified 1H. ...........................................................................................................................31 

Figure 35. “Nugget formation” failure of an improved spot weld tensile shear specimen; 

magnified 1H. ...........................................................................................................................32 

Figure 36. “Weld shear” failure of an improved spot weld tensile shear specimen; 

magnified 1H. ...........................................................................................................................32 

Figure 37. Typical failure of a spot weld peel specimen welded under improved 

conditions. Failure occurred by metal tearing initiated within the heat-affected zone; 

magnified 1H. ...........................................................................................................................35 

Figure H-1. Plug weld assembly...................................................................................................56 

Figure H-2. Method of sectioning for spot weld specimens.........................................................57 

Figure H-3. Method of sectioning for seam weld specimens. ......................................................58 

Figure H-4. Seam weld fixture dimensions (material shall be AISI 4XXX steel, 

HRC 35–40).............................................................................................................................59 

Figure H-5. Shear test assembly for seam weld specimens..........................................................59 

Figure H-6. Method of sectioning for fillet weld specimens........................................................60 

Figure H-7. Fillet weld fixture dimensions (material shall be AISI 4XXX steel, 

HRC 35–40).............................................................................................................................61 

Figure H-8. Pull test assembly for fillet specimen........................................................................61 

viii
List of Tables 

Table 1. Weld drawings and specifications. ...................................................................................1

Table 2. Required visual inspection criteria for each weld. ...........................................................2 

Table 3. Required NDI methods for each weld. .............................................................................2 

Table 4. Current weld mechanical property requirements – MK83 bomb fin................................3 

Table 5. Current weld mechanical property requirements – MK84 bomb fin................................3 

Table 6. Required metallographic examination criteria for each weld (both fins).........................3 

Table 7. Results of plug weld tensile shear testing – first trial.....................................................17 

Table 8. Results of spot weld tensile shear testing – first trial. ....................................................18 

Table 9. Results of seam weld tensile shear testing......................................................................19 

Table 10. Results of fillet weld tensile testing..............................................................................20 

Table 11. Results of plug weld tensile shear testing – improved method. ...................................27 

Table 12. Results of plug weld peel testing..................................................................................28 

Table 13. Results of spot weld tensile shear testing – improved method.....................................30 

Table 14. Results of spot weld peel testing. .................................................................................33 

Table 15. Summary of recommended test and inspection criteria................................................39 

ix
INTENTIONALLY LEFT BLANK.

x
1. Background 

The U.S. Army Research Laboratory’s (ARL’s), Weapons and Materials Research Directorate 

(WMRD) was requested to establish test and inspection criteria for selected welds of the MK83 

and MK84 conical bomb fins by the Naval Air Warfare Center (NAWC), Pt. Mugu, CA. This 

was necessitated when a manufacturer of these bomb fins expressed concern during a First 

Article Inspection (FAI) that the spot weld mechanical property listed on the governing 

engineering drawing was slightly excessive. The contractor felt that even perfect welds may not 

be able to meet this requirement due to dimensional tolerancing allowances and property 

variation within the steel sheet. The bomb fins are currently fabricated according to 

specifications outlined within the Naval Air Systems Command (NAVAIRSYSCOM) drawings 

1380505 and 1380529 [1], respectively. Their purpose is to stabilize gravity bombs after 

deployment in order to provide accurate targeting. To establish the mechanical property 

requirements for these welds, test specimens representing the different types of welds used to 

fabricate the bomb fins were produced by Aerotek Welding Co., Inc., North Granby, CT. This 

investigation focused on the plug, spot, and seam (resistance) and the fillet (fusion) welds. With 

respect to the bomb fins under investigation, the plug weld joins the skin segment to the conical 

fin spar assembly, the spot weld fastens the spars together to form the spar assembly, and the 

seam weld joins the steel sheet of the conical fin skin. The fillet weld fastens the conical fin skin 

to the ring adapter. Mechanical testing and metallographic examination were performed by ARL 

to evaluate the integrity of each type of weld. Strength requirements as well as inspection 

criteria were established for each of these welds and are presented to the NAWC for possible 

inclusion in the appropriate automated data lists (ADLs) or drawing packages to be used at their 

discretion during FAIs and/or production. 

2. Drawing/Specification Review

Table 1 summarizes the applicable NAVAIRSYSCOM drawings [1] and subtier specifications 

for each of the welds and bomb fins under investigation. 

Table 1. Weld drawings and specifications. 

Weld 

NAVAIRSYSCOM 

Drawing 

(MK83 conical fin) 

NAVAIRSYSCOM 

Drawing 

(MK84 conical fin) Applicable Welding Specification

Plug 1380509, Rev. P 1380534, Rev. U MIL-W-8611,a (S/S by MIL-STD-2219,b Class B)

Spot 1350494, Rev. K 1380537, Rev. K MIL-W-12332c

Seam 1380507, Rev. M 1380533, Rev. R MIL-W-12332, alt.: MIL-STD-2219, Class B

Fillet 1380506, Rev. M 1380531, Rev. U MIL-W-8611, (S/S by MIL-STD-2219, Class A) 

a See reference [2].

b See reference [3].

c See reference [4].

1
3. Current Visual/Nondestructive/Mechanical Property and Metallographic 

Requirements 

The applicable engineering drawings and specifications were reviewed in order to determine the 

current bomb fin weld requirements for visual examination, nondestructive inspection (NDI), 

mechanical properties, and metallographic examination. Table 2 lists the current requirements 

for visual examination, while Table 3 lists those for NDI. Tables 4–6 list the current 

requirements for mechanical properties and metallographic examination, respectively. 

Table 2. Required visual inspection criteria for each weld. 

Weld Specification Required Visual Inspection 

Plug MIL-STD-2219, Class B 5.4.4.1: “...Arc strikes, arc burns from loose electrical connections and 

gouge marks on the base metal of the finished weldment are unacceptable 

for Class A and B welds.” Surface requirements for porosity, undercut, 

and underfill and/or concavity are outlined in Table 5-4 of MIL-STD2219. 

Spot MIL-W-12332 7.3.1: “The outer surface of all welds shall be smooth and free or cracks, 

tip pickup, pits, metal expulsion, and other defects which indicate that the 

welds were made with contaminated electrodes or with improperly

prepared surfaces.” 

Seam MIL-W-12332, alt.: 

MIL-STD-2219, Class B

7.3.1: “The outer surface of all welds shall be smooth and free or cracks, 

tip pickup, pits, metal expulsion, and other defects which indicate that the 

welds were made with contaminated electrodes or with improperly

prepared surfaces.” 

Fillet MIL-STD-2219, Class A 5.4.4.1: “...Arc strikes, arc burns from loose electrical connections and 

gouge marks on the base metal of the finished weldment are unacceptable 

for Class A and B welds.” Surface requirements for porosity, undercut, 

and underfill and/or concavity are outlined in Table 5-4 of MIL-STD2219. 

Table 3. Required NDI methods for each weld. 

Weld Required Nondestructive Inspection 

Plug Magnetic Particle Inspection (MPI) (ASTM E1444a or liquid penetrant ASTM E1417b) 

Spot None

Seam None

Fillet MPI (ASTM E1444 or liquid penetrant ASTM E1417) and radiography (ASTM E1742c) a

 See reference [5]. b

 See reference [6]. c

 See reference [7].

2
Table 4. Current weld mechanical property requirements – MK83 bomb fin. 

Weld Governing Drawing Subtier Specification Mechanical Property Requirement 

Plug 1380509, Rev. P MIL-STD-2219, Class B None listed (drawing or specification) 

Spot 1350494, Rev. K MIL-W-12332 3200 lb/inch (drawing), MIL-W-12332: Peel test

(failure outside weld area is acceptable, with a 

minimum required button diameter of 0.29 inch, 

measured in two perpendicular directions). 

Seam 1380507, Rev. M MIL-W-12332, alt.: 

MIL-STD-2219, Class B

2600 lb/inch (drawing) 

Fillet 1380506, Rev. M MIL-STD-2219, Class A None listed (drawing or specification) 

Table 5. Current weld mechanical property requirements – MK84 bomb fin. 

Weld Governing Drawing Subtier Specification Mechanical Property Requirement 

Plug 1380534, Rev. T MIL-STD-2219, Class B None listed (drawing or specification) 

Spot 1380537, Rev. J MIL-W-12332 MIL-W-12332: Peel test (failure outside weld

area is acceptable, with a minimum required 

button diameter of 0.29 inch, measured in two 

perpendicular directions). 

Seam 1380533, Rev. P MIL-W-12332, alt.:

MIL-STD-2219, Class B

2600 lb/inch (drawing) 

Fillet 1380531, Rev. T MIL-STD-2219, Class A None listed (drawing or specification) 

Table 6. Required metallographic examination criteria for each weld (both fins). 

Weld Specification Required Metallographic Examination 

Plug MIL-STD-2219, Class B None 

Spot MIL-W-12332 7.3.3.3.1: “The weldment or simulated specimen shall be crosssectioned and etched. The nugget penetration shall be 30 percent to 

80 percent of the sheet thicknesses involved...” 

Seam MIL-W-12332, alt.:

MIL-STD-2219, Class B

7.3.3.3.1: “The weldment or simulated specimen shall be crosssectioned and etched. The nugget penetration shall be 30 percent to

80 percent of the sheet thicknesses involved. The width of the seam

weld shall conform to Table III.” (0.22-inch for 0.078-inch-thick steel)

Fillet MIL-STD-2219, Class A None 

3
4. Test Specimen Fabrication 

Aerotek fabricated test specimens according to the requirements of the governing engineering 

drawings and applicable specifications. One may argue that these welds were generated under 

“laboratory” and almost optimal conditions, with none of the constraints imposed by not only the 

conical geometry of the part but by a production setting. However, it was felt that if proper 

workmanship and quality controls were adhered to, the specimens produced in this study could 

also be achieved on actual bomb fins during production. The parameters utilized by Aerotek are 

listed in Appendix A (plug welds), Appendix B (spot welds), Appendix C (seam welds), and 

Appendix D (fillet welds). As highlighted in Appendices A and D, the plug and fillet welds 

were produced in accordance with MIL-W-8611. This specification was later superceded by 

MIL-STD-2219. The spot and seam welds were produced in accordance with MIL-W-12332. 

The chemical analysis of the weld wire is listed in Appendix E. All welding was performed on 

0.075 ± 0.007-inch-thick AISI 1010 steel sheet and bar stock (hot-rolled drawing quality). A 

representative specimen from each group is shown in the as-received condition in Figures 1–4. 

Figure 1. Representative plug weld specimen in the as-received condition; 

reduced 25%. 

4
Figure 2. Representative spot weld specimen in the as-received condition; 

reduced 25%. 

Figure 3. Representative seam weld specimen in the as-received condition; 

reduced 25%. 

5
Figure 4. Representative fillet weld specimen in the as-received condition; 

reduced 25%. 

4.1 Plug Weld Specimens 

Twenty-four plug weld specimens were fabricated from two 4- × 24-inch AISI 1010 steel sheets, 

in conformance with MIL-W-8611. The two steel sheets overlapped by 1 inch in the center, as 

shown in Figure 5. The steel sheets were prepared using 120-grit silicon carbide paper, and the 

weld region was cleaned with acetone prior to welding. The parts were scribed prior to welding 

to ensure proper overlap. Holes 0.25 inch in diameter were drilled into one of the steel sheets to 

be filled by the plug welds. The two pieces were clamped to bar stock to avoid excessive 

penetration. Each side of the plug weld was clamped during the welding operation. 

The sheets were welded moving the clamps to the area being welded, letting the piece cool in the 

clamped state. Figures 6 and 7 illustrate the two-piece steel assembly as welded prior to 

specimen sectioning at the Aerotek plant. The plug welds were distanced 1/2 inch from the edge 

of the steel sheets and spaced 1 inch from each other. The welded sheets were cut without 

burning into 1.000 +0.005/!0.000-inch wide tensile shear specimens, with the plug weld 

centered in each strip. This strict tolerance constraint ensured uniformity during testing. The 

strips were labeled 1 to 24 in order of construction to determine the presence of any time effects. 

The electrodes utilized were in conformance with MIL-E-23765/4 [8], Type 70S-2. 

4.2 Spot Weld Specimens 

Twenty-four spot weld specimens were fabricated from two 4- H 24-inch steel sheets, in 

conformance with MIL-W-12332. The spot welds had a 0.300-inch diameter. The two steel 

sheets overlapped by 1 inch in the center, as shown in Figure 8. The steel sheets were prepared 

using 120-grit silicon carbide paper, and the weld region was cleaned with acetone prior 

6
Figure 5. Schematic illustrating dimensions of plug weld assembly. 

Figure 6. Photograph showing plug weld assembly at Aerotek Welding. 

to welding to ensure proper overlap. The two pieces were clamped to bar stock to avoid 

excessive penetration. Each side of the spot weld was clamped during the welding operation. 

Similar to plug weld fabrication, the sheets were welded moving the clamps to the area being 

welded letting the piece cool in the clamped state. The spot welds were distanced 1/2 inch from

the edge of the steel sheets and spaced 1 inch from each other. 

7
Figure 7. Photograph showing another view of the 

plug weld assembly at Aerotek Welding. 

Weld in center 

of overlap 

0.075” +/- 0.007”

Flush overlap 

for 1 inch 0.075” +/- 0.007”

4”

4”

24”

1”

Figure 8. Schematic illustrating dimensions of spot weld assembly. 

8
The welded sheets were cut without burning into 1.000 +0.005/!0.000 inch wide specimens, 

with the spot weld centered in each strip. The strips were labeled 1 to 24 in order of 

construction. 

4.3 Seam Weld Specimens 

Twenty-four seam weld tensile shear test specimens were fabricated from two 4- H 2-inch steel 

sheets, in conformance with MIL-W-12332. The two steel sheets overlapped by 1 inch in the 

center, as shown in Figure 8. The seam weld was centered in this overlap region. The steel 

sheets were sanded utilizing 120-grit silicon carbide paper, and the weld region was cleaned with 

acetone prior to welding. The parts were scribed prior to welding to ensure proper overlap. The 

parts were tack welded prior to being seam welded, at 6-inch intervals. The welded sheets were 

cut without burning into 1.000 +0.005/!0.000-inch wide specimens. The strips were labeled 1 to 

24 in order of construction. The electrodes conformed to MIL-E-18193 [9], type and class 

optional. 

4.4 Fillet Weld Specimens 

Finally, 24 fillet weld tensile shear test specimens were fabricated from a two-piece AISI 1010 

steel assembly, in conformance with MIL-W-8611, as shown in Figure 9. The steel pieces were 

sanded utilizing 120-grit silicon carbide paper, and the weld region was cleaned with acetone 

prior to welding. The parts were fit together and held down with a clamp bar (as illustrated in 

Figure 10). The parts were then tack welded at 4-inch intervals. The weld was subsequently 

performed, and the parts were left to cool in the clamped state. The fillet weld attached a 6- H

24-inch steel sheet to a 1/2-inch bar, simulating the fillet weld on the MK83 and MK84 conical 

bomb fins. Figures 11 and 12 illustrate the two-piece steel assembly as welded and prior to 

specimen cutting at the Aerotek plant. The welded sheets were cut without burning into 

1.000 +0.005/!0.000-inch wide specimens. The strips were labeled 1 to 24 in order of 

construction. The electrodes utilized were in conformance with MIL-E-23765/4 [8], Type 70S2. The specified maximum allowable height of the weld was 0.06 inch, and grinding was 

permissible to meet this requirement. 

5. Visual Examination 

The outer surface of all the weld specimens was smooth and free of cracks, tip pickup, pits, 

metal expulsion, and any other defects that would have indicated that the welds were made with 

contaminated electrodes, improperly prepared surfaces, or with poor workmanship. NDI was not 

performed on these specimens. 

9
10

1” 

45o

7/16”

0.075” +/- 0.007”

1.13” 

1⁄2”

1”

24”

4”

weld region

Figure 9. Schematic illustrating dimensions of fillet weld assembly. 

Figure 10. Method utilized by Aerotek to perform fillet weld. 
Figure 11. Photograph showing fillet weld assembly, as welded, at Aerotek.

Figure 12. Photograph showing as-welded fillet weld assembly, from a different

angle, at Aerotek. 

11
6. Metallographic Examination 

A specimen from each of the four types of welds was sectioned and prepared metallographically 

in accordance with ASTM E3 [10]. This was performed in order to inspect for the following 

characteristics: 

• Overall quality, 

• Location and depth of penetration, 

• Structure of the weld metal and heat-affected zone, 

• Extent of the heat-affected zone, 

• Size of beads, 

• Undercutting and overlapping, 

• Cracks, and 

• Porosity and inclusions. 

The metallographic specimens were chosen to represent the beginning of a production run (spot 

weld specimen no. 1), the middle of production (plug weld specimen no. 11 and fillet specimen 

no. 15) and the end of a production run (seam weld specimen no. 24). This was performed in 

order to note any quality changes with elapsed time. The specimens were sectioned through the 

weld and mounted, as shown in Figures 13 and 14. Once mounted, the specimens were polished 

then etched with 1% nital etchant. Figures 16 through 19 show the etched cross section of the 

plug, spot, seam, and fillet welds, respectively. 

The plug weld has no metallographic requirements as outlined in MIL-STD-2219. Figure 15 

shows that the Aerotek plug weld specimen had a penetration of ~30%–40%. It should be noted 

the plug weld does not have to fill the hole completely, which was the case with the Aerotek 

weld (Figure 15). MIL-W-12332 lists the metallographic criteria that the spot and seam welds 

should conform to. The spot weld should demonstrate 30%–80% penetration into the thinner of 

the two sheets (each sheet was the same thickness). In general, penetration less than 30% leads 

to a weld that is referred to as “cold,” in that not enough heat was generated in the weld zone 

[11]. This same reference states that penetration above 80% usually results in expulsion, 

excessive indentation, and rapid electrode wear. Figure 16 shows that the Aerotek weld 

conformed to this penetration criterion. Upon closer examination, however, the micrograph 

showed the interface between the two pieces of steel sheet that were spot welded. This indicated 

that the spot welds would most likely break in shear and fail to pull a nugget out of the parent 

material (indicative of a poor spot weld). 

12
 

prepared face 

Figure 13. Schematic illustrating metallographic sectioning for the plug, spot, and seam weld

specimens. 

Figure 14. Schematic illustrating metallographic sectioning for the fillet weld specimen.

13
Unfilled Unfilled 

hole 

Figure 15. Cross section of a plug weld specimen etched with 1% nital etchant

(note the unfilled hole); magnified 10H. 

Interface Interfac

of steel 

sheets 

e of steel

sheets

Figure 16. Cross section of a spot weld specimen etched with 1% nital etchant 

(note the interface of the two steel sheets present within the weld 

region); magnified 10H. 

14
The seam weld is also required to have a penetration of 30%–80%. Figure 17 shows this 

criterion was satisfied by the Aerotek specimen. Finally, the two parts joined by the fillet weld 

must be on the same plane. The Aerotek specimen satisfied this criterion, as shown in Figure 18. 

Figure 17. Cross section of a seam weld specimen etched with 1% nital 

etchant; magnified 10H. 

Figure 18. Cross section of a fillet weld specimen etched with 1% nital 

etchant; magnified 10H. 

15
7. Mechanical Testing 

It was reported that the bomb fin manufacturer believed that the 3200-lb requirement for the spot 

weld was rather excessive. The testing summarized herein was conducted in order to establish 

minimum weld strength requirements of each weld. 

The test results for the remaining 23 specimens of each type of weld are listed in Tables 7–10

(the specimens from which the metallographic sample was sectioned could not be tested). A 

50,000-lb capacity Instron universal electromechanical tensile testing machine was utilized for 

all testing. Hydraulic grips were used to secure the test specimens, with a gripping force of 750 

psi for the plug, spot, and seam weld specimens and 600 psi for the fillet specimens. Testing was 

conducted at 70 °F and 50% relative humidity. The test parameters included 0.5-inch/minute 

pull rate, a 1-inch/minute chart speed, and a full-scale load range of 5000 lb. The specimens 

were subjected to a straight pull test, as shown in Figure 19. This tested the plug, spot, and seam

welds in tensile shear and the fillet welds in tension. The mechanism of the tension-shear failure 

is described as follows [12]. The misalignment of the overlapping strips allows a couple to form, 

which causes bending near the weld; this bending increases progressively with the tensile load 

on the specimen, and the plane of the weld becomes inclined at an increasing angle to the line of 

the pull. This introduces a tearing action concentrated at two points on the circumference at 

opposite diameters of the weld. Thus, as the load increases, the test changes from pure shear to a 

complex system of shearing and tearing when failure occurs. 

The objective was to fabricate these specimens in order to ensure the welding process was 

adequate through mechanical testing, followed by the fabrication of plug weld peel and spot 

weld peel specimens, based on lessons learned. 

7.1 Plug Weld Tensile Shear Testing 

Table 7 lists the test data acquired for the plug weld specimens. The specimen width, thickness, 

and plug weld diameter are listed as well as the maximum pull load. The specimens averaged a 

maximum load or 2315 lb, with a standard deviation of 165 lb. Most plug welds that were 

subjected to this testing formed a nugget upon failure. In a few cases, however, the nugget 

ripped the steel around the weld, thereby making the nugget immeasurable. Figure 20 shows a 

typical “male” and “female” nugget failure, while Figure 21 shows a specimen in which the 

nugget ripped the steel. A tensile shear test in which the plug weld forms a nugget upon failure 

is desirable, as it verifies an adequate penetration of the plug weld. It is also desirable if the steel 

around the nugget rips, as this also verifies adequate weld penetration. This is substantiated by 

the governing specification of MIL-W-12332 which states that, “failures at or outside the 

periphery of the weld area shall be considered evidence that the welds are satisfactory.” 

16
Table 7. Results of plug weld tensile shear testing – first trial. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of Weld 

(in) 

Max. Load 

(lb) 

Break 

Comments 

Nugget Diameter 

(Measured on Hole) 

(in) 

1 1.0020 0.073 0.25 Metallographic Examination

2 1.0000 0.073 0.25 2250 N, B 3/16 H 5/32 

3 1.0020 0.073 0.25 2325 N, B 7/32 H 5/32 

4 1.0000 0.073 0.25 2500 N, B NA

5 1.0030 0.073 0.25 2350 N, B 7/32 H 3/16 

6 1.0020 0.073 0.25 2480 N, B 1/8 H 3/32 

7 1.0025 0.073 0.25 1870 N, B 3/16 H 5/32 

8 1.0015 0.073 0.25 2180 NN, WS, B NA 

9 1.0000 0.073 0.25 2380 N, B 7/32 H 5/32 

10 1.0015 0.073 0.25 2525 N, B NA

11 1.0005 0.073 0.25 2165 N, B 1/16

12 1.0010 0.073 0.25 2200 N, B 3/32

13 1.0020 0.073 0.25 2250 N, B 3/16 H 5/32 

14 1.0020 0.073 0.25 2375 N, B 5/32 H 1/8 

15 1.0010 0.073 0.25 2175 NN, WS, B NA 

16 1.0015 0.073 0.25 2250 N, B 5/32 H 1/8 

17 1.0030 0.073 0.25 2260 N, B 1/8 H 3/32 

18 1.0010 0.073 0.25 2275 N, B 7/32 H 3/16 

19 1.0020 0.073 0.25 2250 N, B 3/16 H 5/32 

20 1.0020 0.073 0.25 2740 N, B NA

21 1.0020 0.073 0.25 2345 N, B 3/16 H 5/32 

22 1.0010 0.073 0.25 2390 N, B 7/32 H 5/32 

23 1.0015 0.073 0.25 2400 N, B 7/32 H 3/16 

24 1.0025 0.073 0.25 2315 N, B 5/32 H 1/8 

Average — — — 2315 — —

Std. Dev. — — — 165 — — 

Notes: N = Nugget of weld was pulled out of specimen as a result of testing. 

B = Burn marks were noted under the overlap interface, encircling the weld with an approximate 1/4-inch diameter. 

NN = No nugget was formed as a result of testing. 

WS = The weld sheared as a result of testing. 

NA = Not applicable (nugget was immeasurable). 

Two plug weld failures occurred such that no nugget was formed, however, and the weld had 

simply sheared in half. An example of this type of failure is shown in Figure 22. It is 

undesirable for a plug weld to fail in shear, as it shows a lack of weld penetration and indicates a 

poor-quality plug weld. There was no apparent correlation between the order in which the 

specimens were produced vs. the different types of failures noted. 

Discoloration most likely caused by burning was noted under the 1-inch overlap interface of 

each specimen, as noted in Figure 22. The burn mark encircled the weld and emanated from the 

weld with a radius of ~1/4 inch. An increased current could have caused the burning during the 

welding process. There was also the presence of an oily film under the interface, which was the 

light oil placed on the specimens before shipment to ARL to inhibit corrosion. 

17
Table 8. Results of spot weld tensile shear testing – first trial. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of Weld 

(in) 

Max. Load 

(lb) 

Break 

Comments 

Nugget 

Diameter 

1 1.0040 0.073 0.30 2150 NN, WS NA

2 1.0030 0.073 0.30 2120 NN, WS NA

3 1.0040 0.073 0.30 2060 NN, WS NA

4 1.0020 0.073 0.30 2075 NN, WS NA

5 1.0010 0.073 0.30 2060 NN, WS NA

6 1.0000 0.073 0.30 1925 NN, WS NA

7 1.0010 0.073 0.30 2075 NN, WS NA

8 1.0040 0.073 0.30 2150 NN, WS NA

9 1.0030 0.073 0.30 1995 NN, WS NA

10 1.0010 0.073 0.30 2110 NN, WS NA

11 1.0010 0.073 0.30 Metallographic Examination

12 1.0010 0.073 0.30 2100 NN, WS NA

13 1.0030 0.073 0.30 2080 NN, WS NA

14 1.0010 0.073 0.30 2125 NN, WS NA

15 1.0010 0.073 0.30 2070 NN, WS NA

16 1.0030 0.073 0.30 2120 NN, WS NA

17 1.0020 0.073 0.30 2180 NN, WS NA

18 1.0010 0.073 0.30 2085 NN, WS NA

19 1.0020 0.073 0.30 2200 NN, WS NA

20 1.0020 0.073 0.30 2160 NN, WS NA

21 1.0010 0.073 0.30 1930 NN, WS NA

22 1.0020 0.073 0.30 2125 NN, WS NA

23 1.0030 0.073 0.30 1950 NN, WS NA

24 1.0020 0.073 0.30 2045 NN, WS NA

Average — — — 2080 — —

Std. Dev. — — — 75 — —

Notes: NN = No nugget was formed as a result of testing. 

WS = The weld sheared as a result of testing. 

NA = Not applicable. 

7.2 Spot Weld Tensile Shear Testing 

The test data for the spot welds including the specimen width, thickness, spot weld diameter, and 

maximum tensile shear load are listed in Table 8. The specimens averaged a maximum load of 

2080 lb with a standard deviation of 75 lb. Each spot weld specimen failed such that the weld 

sheared and no nugget was formed. This was indicative of a poor spot weld in which complete 

melting did not occur (this was verified by the interface line noted during metallographic 

examination). A typical spot weld specimen failure is shown in Figure 23. Similar to the plug 

weld specimens, oil was also present under the 1-inch overlap of these specimens. The burning 

previously noted around the plug welds was not noted with these spot welds. 

18
Table 9. Results of seam weld tensile shear testing.

ID Width

(in) 

Thickness 

(in) 

Maximum 

Load 

(lb) 

Break 

Comments 

1 1.0020 0.073 3250 NN, WS

2 1.0015 0.073 3240 NN, WS

3 1.0010 0.073 3250 NN, WS

4 1.0030 0.073 3275 NN, WS

5 1.0010 0.073 3280 NN, WS

6 1.0000 0.073 3245 NN, WS

7 1.0015 0.073 3260 NN, WS

8 1.0000 0.073 3250 NN, WS

9 1.0015 0.073 3290 NN, WS

10 1.0025 0.073 3300 NN, WS

11 1.0010 0.073 3275 NN, WS

12 1.0010 0.073 3280 NN, WS

13 1.0010 0.073 3280 NN, WS

14 1.0010 0.073 3240 NN, WS

15 1.0020 0.073 3280 NN, WS

16 1.0015 0.073 3270 NN, WS

17 1.0020 0.073 3270 NN, WS

18 1.0025 0.073 3290 NN, WS

19 1.0020 0.073 3290 NN, WS

20 1.0030 0.073 3310 NN, WS

21 1.0020 0.073 3295 NN, WS

22 1.0020 0.073 3290 NN, WS

23 1.0020 0.073 3280 NN, WS

24 1.0010 0.073 Metallographic Examination

Average — — 3270 —

Std. Dev. — — 20 — 

Notes: NN = No nugget was formed as a result of testing. 

WS = The weld sheared as a result of testing. 

7.3 Seam Weld Tensile Shear Testing 

The test data for the seam welds including the specimen width, thickness, and maximum tensile 

shear load are listed in Table 9. These specimens averaged a maximum load of 3270 lb, with a 

standard deviation of 20 lb. Each seam weld specimen failed in the parent material, far from the 

weld region (i.e., not in the heat-affected zone). This was indicative of a high-quality seam

weld. A typical seam weld specimen failure is shown in Figure 24. 

7.4 Fillet Weld Tension Testing 

The test data for the fillet weld specimens are listed in Table 10. This table lists the specimen 

width, thickness, and maximum tensile load. The specimens averaged a maximum load of 

3270 lb, with a standard deviation of 20 lb. Similar to the seam weld specimens, each fillet weld 

specimen failed in the parent sheet material, far from the weld region (i.e., not in the heataffected zone). A typical fillet weld specimen failure is shown in Figure 25. 

19
Table 10. Results of fillet weld tensile testing.

ID Width

(in) 

Thickness 

(in) 

Maximum Load 

(lb) 

Break Comments 

1 1.0010 0.073 3295 PM

2 1.0000 0.073 3270 PM

3 1.0010 0.073 3290 PM

4 1.0010 0.073 3280 PM

5 1.0000 0.073 3265 PM

6 1.0000 0.073 3280 PM

7 1.0020 0.073 3275 PM

8 1.0020 0.073 3300 PM

9 1.0020 0.073 3300 PM

10 1.0010 0.073 3300 PM

11 1.0030 0.073 3300 PM

12 1.0025 0.073 3295 PM

13 1.0015 0.073 3280 PM

14 1.0010 0.073 3280 PM

15 1.0010 0.073 Metallographic Examination

16 1.0020 0.073 3280 PM

17 1.0020 0.073 3295 PM

18 1.0015 0.073 3300 PM

19 1.0015 0.073 3300 PM

20 1.0010 0.073 3270 PM

21 1.0000 0.073 3250 PM

22 1.0015 0.073 3290 PM

23 1.0030 0.073 3285 PM

24 1.0020 0.073 3290 PM

Average — — 3290 —

Std. Dev. — — 15 — 

Note: PM = The failure occurred within the parent material, far from the weld (not in the 

heat-affected zone). 

Plug weld Spot weld Seam weld Fillet weld

Figure 19. Schematic illustrating pull test direction for each type of weld specimen. 

20
“Male” “Female” 

Figure 20. Typical “male” and “female” plug weld nugget failure;

magnified 1H. 

Figure 21. Plug weld failure in which a nugget tore steel around the weld region; reduced 50%. 

21
 

Sheared plug weld Burning

Figure 22. A macrograph showing a representative sheared plug weld; magnified 1H. 

Sheared spot weld

Figure 23. A typical spot weld shear failure; magnified 1H. 

22
Seam weld 

Figure 24. A typical seam weld failure; reduced 50%. 

Fillet weld

Figure 25. A typical fillet weld failure; reduced 50%. 

8. Further Mechanical Testing 

Aerotek fabricated the following additional specimens: 24 plug weld tensile shear, 24 plug weld 

peel, 24 spot weld tensile shear, and 24 spot weld peel. These specimens were fabricated 

23
incorporating a higher amperage to increase the weld penetration (from a previous amperage 

range between 93 and 100 A to a range of 97–115 A). The peel specimens were fabricated since 

it was required for the spot welds [4] and was a simple and low-cost method of evaluating the 

penetration of the spot and plug welds. 

The physical dimensions of these additional specimens remained similar to the previous 

specimens discussed earlier. Aerotek also altered the process in which the plug weld specimens 

were welded. Unlike the previous trial run, in which the backside was accessed, Aerotek was 

limited to only frontal access of the weld. This simulated actual bomb fin production restrictions 

encountered by the bomb fin manufacturer. No restrictions were imposed on the spot weld, as 

contractors have access to both sides of the spar during welding. In addition, Aerotek treated 

these specimens as a production run, similar to the method most likely incorporated by the bomb 

fin manufacturer. The parameters utilized by Aerotek for all improved plug weld specimens are 

listed in Appendix F. The improved spot weld parameters are listed in Appendix G. A typical 

peel specimen is shown in Figure 26. 

Figure 26. A typical peel test specimen; reduced 50%. 

The last specimen (no. 26) from each production run was sectioned, mounted, and 

metallographically prepared such that the weld region could be examined. The plug weld 

penetration had improved and showed at least 50% penetration (as opposed to ~30% penetration 

previously). This indicated the increased amperage utilized by Aerotek led to increased 

penetration, which subsequently led to a stronger weld. The seam weld did not display the 

24
interface previously noted. A macrograph of the weld region of the plug tensile shear, plug peel, 

spot tensile, and spot peel specimens are shown in Figures 27–30. 

Figure 27. Macrograph of a typical improved plug weld tensile shear specimen;

magnified 9H, etchant: 1% nital. 

8.1 Additional Plug Weld Tensile Shear Testing 

Table 11 lists the test data acquired from the additional tensile shear testing of the plug weld 

specimens. The specimens averaged a maximum pull load of 2999 lb, with a standard deviation 

of 76 lb. This was a marked improvement over the previous plug weld shear test results 

(compared to the average of 2315 lb achieved by the previous specimens). The parent material 

failed far from the weld region in each instance. An example of this typical failure is shown in 

Figure 31. 

8.2 Plug Weld Peel Testing 

Table 12 contains the test data acquired from plug weld peel testing. The specimens averaged a 

maximum peel load of 821 lb, with a standard deviation of 69 lb. The samples failed such that 

the metal tore around the weld region (heat-affected zone), creating an immeasurable nugget. 

This type of failure was acceptable and is shown in Figure 32. 

25
Figure 28. Macrograph of a plug weld peel specimen welded using improved 

conditions by Aerotek; magnified 9H, etchant: 1% nital. 

Figure 29. Macrograph of a typical improved spot weld tensile shear specimen; 

magnified 9H, etchant: 1% nital. 

26
Figure 30. Macrograph of a spot weld peel specimen welded using 

improved conditions by Aerotek; magnified 9H, etchant: 

1% nital. 

Table 11. Results of plug weld tensile shear testing – improved method. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of Weld 

(in) 

Maximum Load 

(lb) 

Break Comments 

Nugget Diameter 

(Measured on 

Hole) 

1 1.0015 0.074 0.25 2900 PM NA

2 1.0020 0.074 0.25 2825 PM NA

3 1.0015 0.074 0.25 2900 PM NA

4 1.0040 0.074 0.25 2950 PM NA

5 1.0010 0.074 0.25 3050 PM NA

6 1.0030 0.074 0.25 2990 PM NA

7 1.0020 0.074 0.25 2980 PM NA

8 1.0010 0.074 0.25 3025 PM NA

9 1.0040 0.074 0.25 3100 PM NA

10 0.9930 0.074 0.25 2920 PM NA

11 1.0040 0.074 0.25 3015 PM NA

12 0.9970 0.074 0.25 3030 PM NA

13 1.0010 0.074 0.25 2965 PM NA

14 1.0020 0.074 0.25 3030 PM NA

15 1.0025 0.074 0.25 3100 PM NA

16 1.0020 0.074 0.25 3000 PM NA

17 1.0010 0.074 0.25 3000 PM NA

18 1.0020 0.074 0.25 3075 PM NA

19 1.0025 0.074 0.25 2975 PM NA

20 1.0010 0.074 0.25 3090 PM NA

21 1.0015 0.074 0.25 3140 PM NA

22 1.0020 0.074 0.25 2925 PM NA

23 1.0020 0.074 0.25 3000 PM NA

24 1.0030 0.074 0.25 Metallographic Examination

Average — — — 2999 — —

Std. Dev. — — — 76 — — 

Note: PM = The failure occurred within the parent material, far from the weld (not in the heat-affected zone). 

NA = Not applicable.

27
Figure 31. Typical failure of an improved plug weld tensile shear specimen. 

Failure occurred in the parent material; magnified 1H. 

Table 12. Results of plug weld peel testing. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of 

Weld 

(in) 

Maximum Load 

(lb) 

Break

Comments

Nugget

Diameter 

(Measured on 

Hole) 

1 1.0015 0.073 0.25 680 MT, NI NA

2 1.0030 0.073 0.25 865 MT, NI NA

3 1.0025 0.073 0.25 850 MT, NI NA

4 1.0020 0.073 0.25 760 MT, NI NA

5 1.0010 0.073 0.25 850 MT, NI NA

6 1.0030 0.073 0.25 925 MT, NI NA

7 1.0015 0.073 0.25 725 MT, NI NA

8 1.0020 0.073 0.25 890 MT, NI NA

9 1.0025 0.073 0.25 895 MT, NI NA

10 1.0015 0.073 0.25 835 MT, NI NA

11 1.0020 0.073 0.25 840 MT, NI NA

12 1.0015 0.073 0.25 740 MT, NI NA

13 1.0005 0.073 0.25 875 MT, NI NA

14 1.0010 0.073 0.25 710 MT, NI NA

15 1.0015 0.073 0.25 880 MT, NI NA

16 1.0030 0.073 0.25 720 MT, NI NA

17 1.0025 0.073 0.25 865 MT, NI NA

18 1.0015 0.073 0.25 840 MT, NI NA

19 1.0015 0.073 0.25 760 MT, NI NA

20 0.9900 0.073 0.25 800 MT, NI NA

21 0.9950 0.073 0.25 885 MT, NI NA

22 1.0015 0.073 0.25 850 MT, NI NA

23 1.0010 0.073 0.25 835 MT, NI NA

24 1.0020 0.073 0.25 Metallographic Examination

Average — — — 821 — —

Std. Dev. — — — 69 — — 

Notes: MT = Parent metal tore around the weld.

NI = Nugget was immeasurable.

NA = Not applicable.

28
Figure 32. Typical failure of a plug weld peel specimen welded under improved 

conditions. Failure occurred by metal tearing initiated within the 

heat-affected zone; magnified 1H. 

8.3 Additional Spot Weld Tensile Shear Testing 

The results of the additional spot weld tensile shear tests are listed in Table 13. The specimens 

averaged a maximum pull load of 2897 lb, with a standard deviation of 96 lb. This was also a 

marked improvement over the previous spot weld tensile shear testing results (compared to the 

average of 2080 lb achieved previously). Four different failure modes were noted during testing, 

most likely due to inconsistencies during the welding process. The higher maximum loads 

corresponded to a failure mode which occurred in the parent material far from the heat-affected 

zone. The next highest loads corresponded to failures in which the metal tore around the weld, 

through the heat-affected zone. The formation of a weld nugget corresponded to the next highest 

load. Finally, the lowest loads corresponded to failures in which the weld bead had sheared in 

half, indicating poor penetration. Each of these failure modes is displayed in Figures 33–36. 

The specimens that were produced early in the production run achieved higher maximum loads 

than the specimens produced later in the run. 

29
Table 13. Results of spot weld tensile shear testing – improved method. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of 

Weld 

(in) 

Maximum Load 

(lb) 

Break

Comments 

Nugget 

Diameter 

1 1.0015 0.075 0.30 3025 PM NA

2 1.0030 0.075 0.30 2970 PM NA

3 1.0020 0.075 0.30 3000 PM NA

4 1.0010 0.075 0.30 3000 PM NA

5 1.0025 0.075 0.30 3000 PM NA

6 1.0020 0.075 0.30 3000 PM NA

7 1.0020 0.075 0.30 3000 PM NA

8 1.0010 0.075 0.30 2990 PM NA

9 0.9980 0.075 0.30 2900 PM NA

10 1.0000 0.075 0.30 2800 NN, WS NA

11 1.0000 0.075 0.30 2900 PM NA

12 1.0000 0.075 0.30 2850 PM NA

13 1.0020 0.075 0.30 2900 PM NA

14 1.0040 0.075 0.30 2950 PM NA

15 1.0000 0.075 0.30 2775 NN, WS NA

16 1.0030 0.075 0.30 2740 NN, WS NA

17 1.0030 0.075 0.30 2800 NN, WS NA

18 1.0020 0.075 0.30 2850 NN, WS NA

19 1.0030 0.075 0.30 2920 N 7/32 H 5/32 

20 1.0010 0.075 0.30 2870 NN, WS NA

21 1.0020 0.075 0.30 2875 NN, WS NA

22 1.0000 0.075 0.30 2850 MT NA

23 1.0010 0.075 0.30 2675 NN, WS NA

24 1.0010 0.075 0.30 Metallographic Examination

Average — — — 2897 — —

Std. Dev. — — — 96 — — 

Notes: PM = The failure occurred within the parent material, far from the weld (not in the heat-affected zone). 

NN = No nugget was formed as a result of testing.

WS = The weld sheared as a result of testing. 

N = Nugget of weld was pulled out of specimen as a result of testing.

MT = Parent metal tore around the weld.

NA = Not applicable. 

8.4 Spot Weld Peel Testing 

Table 14 lists the test data acquired from peel testing the spot weld specimens. The specimens 

averaged a maximum peel load of 1010 lb, with a standard deviation of 108 lb. In each instance, 

the samples failed such that the metal tore around the weld region (the heat-affected zone), 

creating an immeasurable nugget, as shown in Figure 37. The torn metal contained the weld and 

thereby exceeded the 0.29-inch minimum nugget diameter required. 

30
Figure 33. “Parent metal” failure of an improved spot weld tensile shear 

specimen; magnified 1H. 

Figure 34. “Metal tearing” failure of an improved spot weld tensile shear 

specimen; magnified 1H. 

31
Figure 35. “Nugget formation” failure of an improved spot weld tensile shear specimen;

magnified 1H. 

Figure 36. “Weld shear” failure of an improved spot weld tensile shear specimen;

magnified 1H. 

32
Table 14. Results of spot weld peel testing. 

ID Width 

(in) 

Thickness 

(in) 

Diameter of 

Weld 

(in) 

Maximum Load 

(lb) 

Break 

Comments 

Nugget 

Diameter 

(Measured 

on Hole) 

1 1.0005 0.075 0.30 1300 MT, NI NA

2 1.0005 0.075 0.30 1025 MT, NI NA

3 1.0040 0.075 0.30 890 MT, NI NA

4 1.0005 0.075 0.30 940 MT, NI NA

5 1.0030 0.075 0.30 1030 MT, NI NA

6 1.0030 0.075 0.30 1040 MT, NI NA

7 1.0015 0.075 0.30 1120 MT, NI NA

8 1.0010 0.075 0.30 960 MT, NI NA

9 1.0030 0.075 0.30 920 MT, NI NA

10 1.0015 0.075 0.30 850 MT, NI NA

11 1.0020 0.075 0.30 910 MT, NI NA

12 1.0030 0.075 0.30 1140 MT, NI NA

13 1.0025 0.075 0.30 780 MT, NI NA

14 1.0010 0.075 0.30 1030 MT, NI NA

15 1.0020 0.075 0.30 990 MT, NI NA

16 1.0020 0.075 0.30 995 MT, NI NA

17 1.0010 0.075 0.30 1040 MT, NI NA

18 1.0000 0.075 0.30 1050 MT, NI NA

19 1.0010 0.075 0.30 1060 MT, NI NA

20 1.0010 0.075 0.30 1140 MT, NI NA

21 0.9950 0.075 0.30 1040 MT, NI NA

22 1.0010 0.075 0.30 980 MT, NI NA

23 1.0010 0.075 0.30 1000 MT, NI NA

24 1.0010 0.075 0.30 Metallographic Examination

Average — — — 1010 — —

Std. Dev. — — — 108 — — 

Notes: MT = Parent metal tore around the weld. 

NI = Nugget was immeasurable. 

NA = Not applicable. 

9. Discussion 

9.1 Quality of Welds 

This investigation demonstrated that even in a nonproduction setting, the quality of the plug and 

spot welds was not easily assured. Once Aerotek enhanced their welding procedure, these welds 

showed improvement; however, the spot welds could have been optimized further. In any case, 

it was shown that even for these simple welds, care must be taken to create a quality weld. 

Despite this fact, it is believed that the criteria listed in section 10 are adequate in assuring a 

quality weld during production of the bomb fins. It should also be noted that bomb fin 

contractors would most likely extend considerable time and effort in optimizing these welds. 

For this investigation, only two trials were needed to produce specimens with high-quality 

33
welds. 

34
Figure 37. Typical failure of a spot weld peel specimen welded under 

improved conditions. Failure occurred by metal tearing initiated

within the heat-affected zone; magnified 1H. 

9.2 Inspection of Welds 

Visual inspection is a suitable means of verifying the integrity of noncritical welds. However, 

care should be taken when assessing weld quality from solely visual inspection since it cannot be 

used to judge subsurface weld integrity. This is the reason that NDI often accompanies visual 

inspection requirements. Each of the welds discussed herein require visual inspection as part of 

the specification requirements. This method of inspection is used either with or without further 

NDI. Visual inspection is useful in checking for the following [13]: 

• Dimensional accuracy of weldments, 

• Conformity of welds to size and contour requirements, 

• Acceptability of weld appearance with regard to surface roughness, weld spatter, and 

cleanliness, and 

• Presence of surface flaws such as unfilled craters, pockmarks, undercuts, overlaps and 

cracks. 

As stated in reference [13], NDI of weldments has two main functions: 

(1) Quality control – the monitoring of the welder and equipment performance and of the 

quality of the consumables and the base materials used. 

(2) Acceptance or rejection of a weld on the basis of its fitness-for-purpose under the service 

conditions imposed on the structure. 

35
NDI is used primarily to inspect for surface or subsurface discontinuities. Methods generally 

used include liquid penetrant, magnetic particle, radiographic, ultrasonic, eddy current, and 

acoustic emission. The bomb fin governing specifications list NDI as required for both the plug 

(liquid penetrant or magnetic particle) and fillet (liquid penetrant or magnetic particle plus 

radiography) welds. 

9.3 Mechanical Testing of Welds 

The problem of predicting the performance of structures from a “laboratory-type” test is a 

complex one because the size, configuration, environment, and the type of loading normally 

differ [14]. No amount of mechanical testing will provide information regarding the suitability 

of the welded joints for service. However, in this investigation, ARL attempted to have 

specimens created in a production setting to (a) furnish welds whose mechanical properties 

would simulate those obtained by a bomb fin manufacturer and (b) establish a minimum criteria 

for samples made from actual bomb fins by a contractor. 

9.4 Strength of Base Metal 

The strength of resistance welds depends on the strength of the base metal, which in turn, 

depends on the composition, heat treatment, and degree of cold work [12]. As mentioned 

previously, AISI 1010 steel is utilized for the skins of both conical bomb fin designs. The sheets 

are required to be 0.075 ± 0.007-inch-thick (hot-rolled drawing quality). The ultimate tensile 

strength (UTS) of this material is 46,000 psi [15]. This is a typical value and could range, 

conservatively, ±5%. This would lead to a UTS range of 43,700–48,300 for this material. For a 

1-inch section of both the seam and fillet weld, this specimen may have a thickness range from

0.068 to 0.082 inch, based on the dimensional tolerance of the material. The corresponding 

maximum attainable loads for these cross-sectional areas are 2971–3284 lb for the low-end UTS 

and 3583–3961 lb for the high-end UTS. Therefore, based on the dimensional tolerance and the 

mechanical property variability of the steel sheet, the material itself can exhibit a range of pull 

loads from 2971 to 3961 lb for a 1-inch wide specimen. These figures were taken into account 

when deriving the minimum load achievable for these types of weld specimens. 

10. Recommended Testing and Inspection Criteria 

The spot and seam welds examined in this study are classified as noncritical according to the 

governing drawings and specifications. The noncritical classification indicates that NDI (i.e., 

magnetic particle, liquid penetrant, or radiographic inspection) of these welds is not required. 

Although the seam weld lists MIL-STD-2219 as the alternative, MIL-W-12332 is the default 

specification and does not require NDI. The plug weld is governed by MIL-STD-2219, Class B. 

The Class B classification requires penetrant testing or magnetic particle inspection. The fillet 

36
weld is considered critical by the Class A designation of MIL-STD-2219. This specification 

states that Class A welds are critical where a failure of any portion would cause loss of the 

system, loss of major component, loss of control, unintentional release of critical stores, or 

endangering of personnel [3]. These welds are required to be radiographically inspected as well 

as either magnetic particle or penetrant inspected. 

The destructive testing plan proposed by ARL would entail either a First Article sampling and/or 

a sampling of not more than 5% of a production run. The spot, seam, and fillet welds shall be 

sectioned from actual components and be visually inspected, mechanically tested, and 

metallographically inspected (if welds fail to meet the minimum mechanical properties). The 

plug weld specimens shall be fabricated as highlighted in section H.1 of Appendix H. The 

general criteria of the visual and metallographic inspections are described next. 

10.1 Visual Inspection 

In general, the workmanship of the welds shall be of a quality such that the outer surface of all 

welds shall be smooth and free of cracks, tip pickups, pits, metal expulsion, and other defects 

which would indicate the welds were fabricated with contaminated electrodes or with improperly 

prepared surfaces. Where practicable, all welds should meet with the adjacent metal in gradual, 

smooth curves. Fillet weld beads should be smooth and free of slag, excessive undercut, or 

excessive splatter. In no case should the weld metal be burnt (oxidized) or contain holes or pores 

through the material. The requirements listed in Table 2 shall apply. 

10.2 Metallographic Inspection 

Metallographic inspection is already required for the spot and seam welds, as dictated by MILW-12332. For the plug and fillet welds, ARL recommends that metallographic inspection should 

be necessary only as a result of weld specimens not meeting the minimum mechanical properties. 

In this manner, the possible reason for nonconformance may be established. However, 

metallographic inspection must be performed on specimens from the same production run as 

those that failed to meet mechanical properties. In general, the following characteristics should 

be examined when performing a metallographic inspection: weld fusion (including root and 

joint penetration—30%–80% for plug and spot welds), convexity, concavity, size of the bead, 

undercutting, overlapping, cracks, porosity, inclusions, and any other metallic discontinuities. 

Typically, minor defects toward the center of the weld are not of great concern. These generally 

do not play a role in either the performance of the weld or the mode of failure. However, when 

internal defects extend toward the weld edges, these can act as fast fracture paths upon loading. 

These types of defects are indicative of poor welds. 

37
10.3 Establishment of Minimum Mechanical Property Criteria 

Appendix H contains the proposed method of sectioning and testing welds for the MK83 and 

MK 84 conical bomb fins. As mentioned before, unlike the plug weld, the spot, seam, and fillet 

weld specimens can be sectioned directly from the bomb fins. In order to mechanically test the 

plug welds produced by a prospective manufacturer of these bomb fins, specimens would need to 

be generated similarly to those fabricated for this investigation. 

10.3.1 Plug Weld 

Based upon the results of the testing described herein, it is recommended that plug weld 

specimens fabricated by a bomb fin manufacturer having a 0.25-inch diameter shall achieve a 

minimum load of 2800 lb when subjected to a tensile shear test and a 700-lb load as a minimum

when a single plug weld is subjected to a peel test. The general principles of ASTM A370 [16] 

shall be followed when performing these tests. 

10.3.2 Spot Weld 

It is recommended that spot weld specimens sectioned directly from a finished conical bomb fin 

having a 0.300-inch diameter shall achieve a minimum load of 2800 lb when subjected to a 

tensile shear test and a 1000-lb load as a minimum when a single spot weld is subjected to a peel 

test. The general principles of ASTM A370 shall be followed when performing these tests. 

10.3.3 Seam Weld 

The seam weld specimens averaged 3270 lb at a thickness of 0.073 inch. However, as 

mentioned previously, a sheet thickness as low as 0.068 inch could have been employed. At this 

thickness, an average load of approximately 3050 lb could be expected. Accounting for 

mechanical property variability, the maximum attainable load could be further decreased. 

Therefore, it is recommended that seam weld specimens sectioned directly from a finished 

conical bomb fin shall attain a minimum load of 2900 lb/linear inch of weld when tested in 

tension. The general principles of ASTM A370 shall be followed when performing these tests. 

10.3.4 Fillet Weld 

The fillet weld specimens averaged 3290 lb at a 0.073-inch thickness. If a sheet thickness as low 

as 0.068 inch was used, this load could have decreased to approximately 3060 lb. Again, taking 

into account mechanical property variability, it is recommended that fillet weld specimens 

sectioned directly from a finished conical bomb fin shall attain a minimum load of 2900 lb/linear 

inch of weld when tested in tension. The general principles of ASTM A370 shall be followed 

when performing these tests. 

38
Table 15 outlines the summary of testing and inspection criteria recommended by ARL. NAWC 

may include these criteria in the appropriate ADLs or drawing packages to be referenced at their 

discretion during FAI and/or production of the MK83 and MK84 conical bomb fins. Welds 

meeting these criteria are assured of being high quality and will contribute to the overall integrity 

of the bomb fins. 

Table 15. Summary of recommended test and inspection criteria. 

Weld 

Visual 

Inspection Nondestructive Inspection

Mechanical 

Test 

Minimum Test 

Load 

(lb) 

Metallographic 

Inspection 

Plug 

(0.25-inch 

diameter) 

Yes MPI (ASTM E1444) or 

liquid penetrant (ASTM 

E1417) 

Tensile shear 

peel 

2800 

700 

a 

a 

Spot 

(0.30-inch 

diameter) 

Yes None Tensile shear

peel 

2800 

1000 

See Table 6 

Seam Yes None Tensile shear 2900/linear inch See Table 6 

Fillet Yes MPI (ASTM E1444) or 

liquid penetrant (ASTM 

E1417) and radiography

(ASTM E1742) 

Tension 2900/linear inch a 

a

Metallographic examination shall be performed only if specimens fail to meet the mechanical properties. 

39
11. References 

1. Naval Air Systems Command (NAVAIRSYSCOM). Drawings 1380505, 1380529, 1380509, 

1380534, 1350494, 1380537, 1380507, 1380533, 1380506, and 1380531. Patuxent River, 

MD. 

2. U.S. Department of Defense. Welding, Metal, Metal Arc and Gas, Steels, and Corrosion and 

Heat Resistant Alloys; Process For. MIL-STD-8611, Washington, DC. 

3. U.S. Department of Defense. Fusion Welding for Aerospace Application. MIL-STD-2219, 

Washington, DC, 30 December 1988. 

4. U.S. Department of Defense. Welding, Resistance, Spot, Seam and Projection; for 

Fabricating Assemblies of Low-Carbon Steel. MIL-W-12332, Amendment 3, Washington, 

DC, 29 August 1994. 

5. American Society for Testing and Materials. “Standard Practice for Magnetic Particle 

Examination.” ASTM E1444, West Conshohocken, PA, 2001. 

6. American Society for Testing and Materials. “Standard Practice for Liquid Penetrant 

Examination.” ASTM E1417, West Conshohocken, PA, 1999. 

7. American Society for Testing and Materials. “Standard Practice for Radiographic 

Examination.” ASTM E1742, West Conshohocken, PA, 2000. 

8. U.S. Department of Defense. Electrodes—Welding, Bare, Solid; and Fluxes, Submerged Arc 

Welding, Carbon and Low Alloy Steels. MIL-E-23765/4, Washington, DC, 15 September 

1989. 

9. U.S. Department of Defense. Electrode, Welding, Carbon Steel and Alloy Steel Bare, 

Coiled. MIL-E-18193, Washington, DC, 23 August 1985. 

10. American Society for Testing and Materials. “Standard Methods of Preparation of 

Metallographic Specimens.” ASTM E3, West Conshohocken, PA, 2001. 

11. Connor, L. P. (ed.). Welding Technology. Vol. 1, 8th edition, American Welding Society, 

p. 371, 1987. 

12. ASM International. Metallurgy of Welding and Joining. Lesson 11, p. 24, 1985. 

13. ASM International. Welding, Brazing and Soldering. Vol. 6, 9th edition, pp. 846–847, 

1984. 

14. Connor, L. P. (ed.). Welding Technology, Vol. 1, 8th edition, American Welding Society, 

p. 386, 1987. 

40
15. Belfour Stulen Inc. Structural Alloys Handbook, 1982 edition. Vol. 2, Mechanical 

Properties Data Center, Columbus, OH, June 1986. 

16. American Society for Testing and Materials. “Standard Test Methods and Definitions for 

Mechanical Testing of Steel Products.” ASTM A370, West Conshohocken, PA, 2002. 

41
Appendix A. Parameters Utilized by Aerotek for Plug Weld Fabrication 

42
INTENTIONALLY LEFT BLANK. 

43
Appendix B. Parameters Utilized by Aerotek for Spot Weld Fabrication 

44
45
Appendix C. Parameters Utilized by Aerotek for Seam Weld Fabrication 

46
47
Appendix D. Parameters Utilized by Aerotek for Fillet Weld Fabrication 

48
INTENTIONALLY LEFT BLANK.

49
Appendix E. Chemical Analysis of the Weld Wire Used by Aerotek Welding 

50
INTENTIONALLY LEFT BLANK.

51
Appendix F. Parameters Utilized by Aerotek for Improved Plug Weld 

Fabrication 

52
INTENTIONALLY LEFT BLANK. 

53
Appendix G. Parameters Utilized by Aerotek for Improved Spot Weld 

Fabrication 

54
55
Appendix H. Proposed Method of Sectioning and Testing Welds for the MK83 

and MK84 Conical Bomb Fins

H.1 Plug Weld Test Specimens 

As previously stated, plug weld test specimens cannot be sectioned directly from the conical 

bomb fins due to their geometry. Therefore, it is necessary for the contractor to fabricate 

specimens in a production run-like manner, similar to the method in which Aerotek employed. 

The plug weld assembly is shown in Figure H-1. This method is described as follows: 

The contractor shall fabricate 24 plug weld specimens upon two (2) 4- H 24-inch AISI 1010 

steel (hot-rolled drawing quality) sheets. The thickness of the sheets shall be 0.075 inch 

± 0.007 inch. The centers of each plug weld shall be spaced at 1-inch intervals. The two 

sheets of steel shall overlap by 1 inch in the center. The diameter of the holes drilled into

one of the sheets (to be filled by the plug weld) shall be 0.25 inch. The welds shall be in

accordance with the requirements of MIL-STD-2219,1 Class B. The electrodes shall be in 

accordance with MIL-E-23765/1,2 Type 70S-2 or 70S-3. The welded sheets shall be 

sectioned without burning into 1.000-inch +0.005-inch/–0.000-inch strips, with the plug 

weld centered in each strip. The strips shall be labeled in order of construction, 1 to 24. The 

following schematic illustrates the specimen dimensions. 

0.25” dia. clearance hole for plug welds

4”

plug welds

4”

1”

24”

Flush overlap for 1 inch

Figure H-1. Plug weld assembly. 

 1 U.S. Department of Defense. Fusion Welding for Aerospace Application. MIL-STD-2219, Washington, DC, 

30 December 1988. 

2

 U.S. Department of Defense. Electrodes—Welding, Bare, Solid; and Fluxes, Submerged Arc Welding, Carbon and Low 

Alloy Steels. MIL-E-23765/4, Washington, DC, 15 September 1989. 

56
H.2 Spot Weld Test Specimens 

Spot weld tensile shear and peel specimens may be sectioned directly from a conical fin spar 

prior to assembly of the conical bomb fin. The method of sectioning is illustrated schematically 

in Figure H-2. One conical fin yields two spot weld peel and one spot weld tensile shear 

specimens. Strips should be sectioned to 1-inch widths. 

Peel test specimen 

Spot weld

Tensile shear test specimen 

Figure H-2. Method of sectioning for spot weld specimens. 

H.3 Seam Weld Test Specimens 

Seam weld shear specimens may be sectioned directly from a completed conical bomb fin, 

provided the specimens are sectioned as close to the ring support as physically possible. This 

minimizes specimen curvature and allows for an axial shear test. Another restriction is that only 

a maximum of three specimens may be sectioned from a single bomb fin because of the 

increased skin curvature as the end of the fin is approached. The method of sectioning and the 

special test fixture needed are illustrated in the schematics of Figures H-3 through H-5. 

57
Figure H-3. Method of sectioning for seam weld specimens. 

58
Figure H-4. Seam weld fixture dimensions (material shall be AISI 4XXX steel, HRC 35–40). 

Figure H-5. Shear test assembly for seam weld specimens. 

H.4 Fillet Weld Test Specimens 

Fillet weld pull test specimens may be sectioned from a completed bomb fin, provided each 

specimen is 1-inch in diameter. This minimizes specimen curvature, which improves the 

gripping ability of the specimens during testing. The method of sectioning and the special 

fixture necessary for testing are illustrated in the schematics of Figures H-6 through H-8. One 

bomb fin yields over 30 fillet weld pull test specimens.

59
1”

6” 

Figure H-6. Method of sectioning for fillet weld specimens. 

60
Figure H-7. Fillet weld fixture dimensions (material shall be AISI 4XXX steel, HRC 35–40). 

Figure H-8. Pull test assembly for fillet specimen.

61
62
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