AlllOO RflROOO

( NBS

PUBLICATIONS

NBSIR 80-2043

Examination of Expanded Metal

Grating Material Used for Fencing along

the United States-Mexico Border

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

U S. Department of Commerce

Washington, D C 20234

May 1980

Failure Analysis Report

Prepared for Immigration and Naturalization Service

•QO»^^"wartment of Justice

]_QQ ton. D.C. 20536

U56

80-2043

1980

C.2

NBSIR 80-2043

EXAMINATION OF EXPANDED METAL

GRATING MATERIAL USED FOR FENCING ALONG

THE UNITED STATES-MEXICO BORDER

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

U S Department of Commerce

Washington. D C 20234

NATIONAL BUREAU OF STANDARDS

LIBRARY AUP 1 2 1980

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May 1980

Failure Analysis Report

Prepared for Immigration and Naturalization Service

U S. Department of Justice

Washington, D C. 20536

U S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and lm ovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

SUMMARY

1. INTRODUCTION

1.1 Reference

1.2 Background Information

1.3 Parts Submitted

2. PURPOSE OF THE EXAMINATION

3. RESULTS OF THE EXAMINATION

3.1 Photographic Documentation

3.2 Determination of Weight per Square Foot

3.3 Dimensional Measurements

3.3.1 Nominal Width of Opening

3.3.2 Width of Bridge

3.3.3 Length of Bridge

3.3.4 Width of Strand

3.4 Determination of the Galvanized Coating Thickness

3.4.1 Bend Test Method

3.4.2 Microscopic Test Method

3.5 Chemical Analysis

3.6 Metal lographic Examination

3.7 Hardness Measurements

3.8 Simulated Field Intrusion Test

4. DISCUSSION

5. CONCLUSIONS

6. ACKNOWLEDGEMENT

7. REFERENCES

l
TABLE OF CONTENTS (continued)

FIGURES

1. Galvanized expanded steel fencing sample from San Ysidro, California

as received at NBS.

2. Galvanized expanded steel fencing sample from El Paso, Texas as received at NBS.

3. Galvanized expanded steel fencing sample from San Luis, Arizona as received at NBS.

4a. Galvanized expanded steel fencing samples from Nogales, Arizona as received at NBS.

4b. Galvanized expanded steel fencing sample from Nogales, Arizona as received at NBS on March 11, 1980.

5. Unetched section parallel to the plane of the expanded steel

fencing material from San Ysidro.

6. Unetched section parallel to the plane of the expanded steel

fencing material from El Paso.

7. Unetched section parallel to the plane of the expanded steel

fencing material from San Luis.

8. Unetched section parallel to the plane of the expanded steel

fencing material from Nogales A.

9. Unetched section parallel to the plane of the expanded steel

fencing from one of the small pieces of material from Nogales A.

10. Unetched section through material from San Luis.

11. Unetched section through material from Nogales A.

12. Etched section parallel to the plane of the expanded steel fencing

material from San Ysidro.

13. Etched section parallel to the plane of the expanded steel fencing

material from El Paso.

14. Etched section parallel to the plane of the expanded steel fencing

material from San Luis.

15. Etched section parallel to the plane of the expanded steel fencing

material from Nogales A.

Etched section parallel to the plane of the expanded steel fencing

from one of the small pieces of material from Nogales.

i i

16.
TABLE OF CONTENTS (continued)

17. Etched section through material from San Ysidro

18. Etched section through material from El Paso

.

19. Etched section through material from San Luis.

20. Etched section through material from Nogales A.
SUMMARY

At the request of the Immigration and Naturalization Service,

U. S. Department of Justice, the NBS Fracture and Deformation Division

performed an examination of samples of galvanized steel expanded metal

grating used for fencing along the United States-Mexico border. The

samples were from four locations - San Ysidro, California; El Paso,

Texas; San Luis, Arizona; and Nogales, Arizona.

The properties of the material were compared to the specifications

in Military Standard MIL -M - 1 7 1 94 C . Samples from El Paso, San Luis, and

Nogales failed to meet the weight per square foot requirement of the

standard. All samples met dimensional and thickness of the galvanized

coating requirements. The primary rolling direction of the material

from El Paso, San Luis, and Nogales was not in accordance with specifications, and the material from El Paso exhibited direc tional i ty of the

microstructure.

The material from all four sites was mild steel in accordance with

specifications. The material from El Paso was extremely clean, whereas

the material from the other sites had some sulfide and oxide inclusions.

There was considerable variation in hardness for any given sample,

but there were no significant differences in hardness among the materials

from the four sites.

In a simple mechanical test that attempts to simulate field failure,

the fencing material from El Paso appeared to offer greater resistance

to penetration (failure) than the materials from the other sites.

IV
Examination of Expanded Metal Grating Material

Used for Fencing along the United States-Mexico Border

1.1

Reference

1. INTRODUCTION

Immigration and Naturalization Service, Department of Justice,

425 I Street, NW, Washington, DC 20536. This examination was conducted

at the request of Mr. W. A. Morris, Chief, Facilities and Engineering,

Immigration and Naturalization Service, under order number COW-O-1 371

dated February 12, 1980. The letter of authorization, dated February 19,

1980, was signed by Mr. James A. Kennedy, Associate Commissioner,

Management.

1 .2 Background Information

The information in this section was furnished by Mr. W. A. Morris

of the Immigration and Naturalization Service. New fencing is being

installed along the border between the United States and Mexico. The

fence is ten feet high and consists of four feet of expanded galvanized

steel grating at the bottom overlapped and topped with seven feet of

galvanized chain link material. The expanded metal part of the fence is

installed such that the long dimension of the openings is vertical with

respect to the ground. After installation of some of the fence segments,

intrusion through the expanded metal part was being experienced in some areas, particularly at Nogales, Arizona.

1.3 Parts Submitted

Samples of the expanded metal grating being used for the fencing at

four different sites along the border were submitted to the NBS Fracture

and Deformation Division for examination. The material was specified to

be fabricated in accordance with Military Standard MIL-M-17194C and was reported to be type 1, class 2, grade A galvanized expanded steel.

Samples from San Ysidro, California; El Paso, Texas; San Luis, Arizona,

and Nogales, Arizona, shown as received at NBS in figures 1, 2, 3, and

4a, respectively, were submitted on February 7, 1980. An additional

sample from Nogales, shown as received at NBS in figure 4b, was submitted

on March 11, 1980.

2. PURPOSE OF THE EXAMINATION

The Immigration and Naturalization Service, through Mr. W. A. Morris,

requested that the NBS Fracture and Deformation Division examine the

submitted samples of expanded metal fencing for the following purposes:

1. Photographic documentation of the submitted material.

2. Determination of weight per square foot for samples from each

site in accordance with Standard MIL-M-1 71 94C.

- 1 -
3. Dimensional measurements of samples from each site in

accordance with Standard M I L-M-l 71 94C as follows:

a. Nominal width of mesh opening.

b. Width center to center of bridge.

c. Length center to center of bridge.

d. Width of strand.

4. Determination of the zinc coating thickness on samples from

each site by the bend method and/or the microscopic test

method in accordance with Standard MIL-M-17194C.

5. Chemical analysis of material from each site.

6. Metal lographic examination of material from each site.

7. Hardness measurements of samples from each site.

8. Any test or examination not mentioned above but deemed advisable

as the examination proceeds and agreed to by both NBS and the

Immigration and Naturalization Service.

It was requested that the properties of the material from the four sites

be compared in the report stating the results of the examination.

3. RESULTS OF THE EXAMINATION

Material from all four sites was used in each aspect of the examination.

In the case of the material from Nogales, the large sample shown in

figure 4a and designated Nogales A in this report was used for each

aspect of the examination except for the simulated field intrusion test.

The sample shown in figure 4b, designated Nogales B, was received after

most of the examination had been completed and was used in a limited

number of the tasks specified in section 2.

3.1 Photographic Documentation

Documentary photographs of the expanded steel fencing material as received at NBS appear in figures 1 through 4b. Photographic documentation

of other aspects of the examination appear later in the report.

3.2 Determination of Weight per Square Foot

The pieces of submitted material from San Ysidro, El Paso and

San Luis as shown in figures 1, 2, and 3, respectively, and the large

piece of material from Nogales (figure 4a) and the second large piece of

material from Nogales (shown in figure 4b) were used in the as-receivedat-NBS condition for the weight per square foot determinations. The two

samples from Nogales were treated separately since it was not known

whether they were from the same sheet. The area from each piece was determined by measuring the dimensions with a scale and the weight was

- 2 -
determined to at least the nearest 1/3 ounce. The results of the weight

per square foot determinations are as follows:

Site

Area of ~ Sample (ft ) Weight of

Sample (lbs)

Pounds

per ff2

San Ysidro 1 .00 3.08 3.08

El Paso 1.13 3.38 2.99

San Luis 1.11 3.14 2.83

Nogales A 0.75 2.19 2.92

Nogales B 4.49 13.46 3.00

The applicable standard, MIL -M - 1 7 1 94 C , specifies a weight per square

foot value of 3 pounds + 5 percent based on the weight of any sheet or bundle of uncoated expanded material. The samples for which the weight

determinations were made were much smaller than a sheet and the samples

were coated. In order to determine the approximate percentage of the

weight attributable to the galvanized coating, one of the small pieces

of the expanded metal from Nogales A (shown in figure 4a) was weighed as received, the coating was stripped off by both mechanical and chemical

means, and the piece was reweighed. The piece weighed about 5 1/2% less

with the coating removed than it did with the coating in place.

Based on the thickness values for the galvanized coating of the

material from the various locations as determined by the microscopic

test method (see Section 3.4.2) and the percentage of the total weight

attributable to the coating for the small Nogales sample, and assuming

that the average coating thickness is representative for a given submitted

sample, the weight per square foot values given above for the material

from San Ysidro, El Paso, San Luis, Nogales A, and Nogales B would be

reduced by approximately 4%, 8%, 4%, 5 1/2%, and 6 1/2%, respectively.

The weight per square foot values adjusted for the galvanized coating

are as follows:

Site Pounds per Square Foot

San Ysidro 2.96

El Paso 2.75

San Luis 2.72

Nogales A 2.77

Nogales B 2.80

Based on these values, only the sample from San Ysidro clearly

meets the weight per square foot requirement of Standard MIL-M-17194C.

The sample from San Luis does not meet the weight per square foot

requirements even with the weight of the coating included.
The value for sample Nogales B fails to meet the required minimum

thickness by less than two percent. The error of measurement may be

greater than two percent; therefore, it cannot be said with certainty

that this sample actually does not meet the weight per square foot

requirement of Standard MIL-M-1 71 94C.

The values for the material from El Paso and Nogales A fail to meet

the minimum requirement by about 3 1/2% and 3%, respectively. It seems unlikely that the errors in measurement would be great enough to permit

the samples from El Paso and Nogales A to meet the standard.

3.3 Dimensional Measurements

Four different dimensions were checked against Standard MIL-4_17194C

for material from each of the four sites. Ten randomly chosen locations

were used for each dimension for each sample.

3.3.1 Nominal Width of Opening

Standard MIL-M-1 71 94C specifies the nominal width of the

opening to be 15/16 inch. The results of the width of opening measurements in inches to the nearest 0.01 inch are as follows:

San Ysidro El Paso San Luis Nogales A

Average 1.00 1.05 1.05 1.04

Range 0.99-1.00 1.05-1.06 1.04-1.07 1.04-1.05

All measurements are greater than 15/16 inch, but no measurement deviates

significantly from the nominal value.

3.3.2 Width of Bridge

Standard MIL-M-1 71 94C specifies the width of the bridge,

center to center, to be 1.33 inches + 10%. The results of the width of

bridge measurements in inches to the nearest 0.01 inch are as follows:

San Ysidro El Paso San Luis Nogales A

Average 1.20 1.25 1.26 1.24

Range 1.19-1.22 1 .23-1.26 1.25-1 .27 1.23-1.25

All average values fall within the specified limits. Except for four

measurements for the material from San Ysidro, all of the individual

measurements also fall within the specified limits. The four measurements

that do fall outside the limits miss by only 0.01 inch. With measurements

being made to the nearest 0.01 inch, this is not considered significant.

- 4 -
3.3.3

Length of Bridge

Standard MIL-M-171 94C specifies the length of the

bridge, center to center, to be 5.33 inches + 10%. The results of the

length of bridge measurements in inches to the nearest 0.01 inch are as follows:

San Ysidro El Paso San Luis Nogales A

Average 5.35 5.33 5.34 5.34

Range 5.32-5.39 5.32-5.37 5.31-5.36 5.31-5.36

All the average values as well as all of the individual values fall

within the limits of the specification.

3.3.4

Width of Strand

Standard M IL-M-1 71 94C specifies the width of the strand

to be within 0.259-0.269 inch. The results of the width of strand

measurements in inches to the nearest 0.001 inch are as follows:

San Ysidro El Paso San Luis Nogales A

Average 0.275 0.285 0.273 0.273

Range 0.273-0.279 0.283-0.288 0.269-0.275 0.271-0.277

These measurements were made on the coated material, whereas the standard

specifies values for uncoated material. In order to determine the

approximate width of the strand without the coating, twice the coating

thickness (based on the coating thickness measurements in section 3.4.2) was subtracted from the width of strand measurements resulting in the

following adjusted width of strand measurements:

San Ysidro El Paso San Luis Nogales A

0.268 0.271 0.266 0.263

The adjusted values from San Ysidro, San Luis and Nogales A all fall

within the limits of the specification. The adjusted average value from

El Paso fails to meet the specification by .002 inch. Therefore, the

width of strand value of the material from El Paso is marginal.

3.4

Determination of the Galvanized Coating Thickness

The thickness of the galvanized coating was determined by two

methods in accordance with Standard MIL-M-171 94C, the bend test method

and the microscopic test method.

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3.4.1 Bend Test Method

The thickness of the galvanized coating was measured by

the bend test method on two specimens each from material from San Ysidro,

El Paso, San Luis, Nogales A, and Nogales B. Five measurements were made on each of the two coating chips from each specimen. The results

of these measurements to the nearest 0.0005 inch are as follows:

San Ysidro El Paso San Luis Nogales A Nogales B

Average 0.0030 0.0067 0.0028 0.0030 0.0037

Range 0.0025-0.0030 0.0060-0.0080 0.0025-0.0030 0.0025-0.0035 0.0030-0.0045

The minimum coating thickness for grade A material is specified to be

0.0025 inch. All of the measurements meet specifications.

3.4.2 Microscopic Test Method

As a further check on the thickness of the galvanized

coatings, the coating thickness was measured on metallographically

prepared cross sections through two strands of material from different

locations from the material from San Ysidro, El Paso, San Luis, Nogales A,

and Nogales B. A measuring microscope was used for the measurements.

The coating thickness was determined on each of the four sides of each

sample. Measurements were made to the neares 0.0005 inch. The minimum

and maximum values are given below for each of the four sides of each cross section. In addition, the average thickness value for each sample

is given.

San Ysidro El Paso San Luis Nogales A Nogales B Strand 1 Min, Max. Min. Max. Min. Max. Min. Max

Min. Max

Side 1 .0035 .0045 .0060 .0100 .0020 .0030 .0020 .0080 .0025 .0060

Side 2 .0030 .0035 .0070 .0090 .0020 .0030 .0040 .0070 .0030 .0060

Side 3 .0040 .0060 .0045 .0060 .0020 .0050 .0030 .0060 .0025 .0120

Side 4 .0030 .0050 .0070 .0110 .0035 .0055 .0035 .0060 .0045 .0075

Average 0.0040 0.0075 0.0035 0.0050 0.0055

Strand 2 Min. Max. Min. Max. Min. Max

Min. Max

Min

Max

Side 1 .0025 .0045 .0065 .0080 .0020 .0035 .0035 .0060 .0030 .0100

Side 2 .0030 .0045 .0055 .0060 .0030 .0040 .0035 .0060 .0030 .0065

Side 3 .0020 .0030 .0065 .0080 .0015 .0040 .0030 .0075 .0050 .0070

Side 4 .0025 .0035 .0045 .0065 .0030 .0050 .0020 .0045 .0040 .0070

Average 0.0032 0.0064 0.0032 0.0045 0.0057

Average,

Both

Strands

0.0036 0.0070 0.0034 0.0048 0.0056

- 6 -
Although several of the minimum values for the material from San Luis,

two of the minimum values for the Nogales A material and one of the

minimum values for the San Ysidro material were below the specified

minimum, the average values for all of the material were well above the

specified minimum. Therefore, based on these measurements, the coating

thickness for material from all four sites meets specifications.

3 . 5 Chemical Analysis

Samples of material from each of the four sites (not including

Nogales B) were submitted to a commercial laboratory for chemical analysis

of the basis steel material. The results of these analyses given as weight percent are as follows:

San Ysidro El Pa so San Luis Nogales A

Carbon 0.08 0.06 0.05 0.08

Manganese 0.45 0.24 0.41 0.40

Phosphorus <0.005 0.010 0.013 <0.005

Sulfur 0.008 0.012 0.011 0.010

Si 1 icon <0.01 0.08 0.01 <0.01

Nickel <0.01 <0.01 <0.01 <0.01

Chromium 0.01 0.01 0.02 <0.01

Molybdenum <0.01 <0.01 <0.01 <0.01

Copper 0.03 0.01 <0.01 0.03

The chemical composition of the material from all four sites indicates

that all four samples of the fencing material analyzed were fabricated

from mild steel in accordance with Standard MIL-M-1 71 94C ' . There are no specific chemical composition requirements in the standard. There are

some minimal differences in the composition among the samples from

San Ysidro, San Luis, and Nogales A, but the material from all three

could be classified as either AISI 1006 or 1008 low carbon steels. The

sample from El Paso differs from the others in that it is much lower in

manganese content and somewhat higher in silicon content. The material

from this sample could be classified as an AISI 1005 low carbon steel.

3.6 Metal lographic Examination

For material from all four sites, two types of sections were examined

metal lographically: 1) sections through the strands parallel to the

plane of the fencing and 2) sections through the strands perpendicular

to both the plane of the fencing and the long diagonal of the openings.

Representative fields parallel to the plane of the fencing from San Ysidro,

El Paso, San Luis and Nogales A are shown in figures 5, 6, 7, and 8,

respectively. In these figures, the material is shown in the as-polished

condition and the direction of the long diagonal of the openings in the

fencing is horizontal. These fields are away from the sheared edges of

the strands. They are shown to indicate inclusion content and as an aid

in determining the rolling direction of the material.

1
The inclusion content varies considerably among the materials from

the four sites. There appear to be both sulfide and oxide type inclusions

in the material from San Ysidro, San Luis and Nogales A. The material

from San Ysidro (figure 5) is quite clean with few inclusions. The

placement and configuration of the inclusions present indicate that the

rolling direction of the material is in the direction of the long diagonal

of the openings which is in accordance with Standard MIL-M-17194C. The

material from El Paso (figure 6) is extremely clean with very few inclusions.

In fact, there are so few inclusions that the rolling direction cannot

be determined from an examination of the as-polished material. The

material from San Luis (figure 7) has approximately the same inclusion

concentration as the material from San Ysidro, but some of the inclusions

are much larger. The configuration of the inclusions indicates that the

primary rolling direction is in the direction perpendicular to the long

diagonal of the openings which does not conform to specifications.

The material from Nogales A (figure 8) has a number of rather large

inclusions, but the concentration appears to be no greater than that of

the material from either San Ysidro or San Luis. As in the material

from San Luis, the rolling direction appears to be perpendicular to the

long diagonal of the openings which does not conform to specifications.

A section in the plane of the fencing was taken through one of the

small pieces of material from Nogales A. An as-polished field from this

section is shown in figure 9. The size of the inclusions in this field

is somewhat less than that in figure 8, but it is still evident that the

rolling direction is perpendicular to the long diagonal of the openings

in the fencing.

As-polished fields from sections perpendicular to both the plane of

the fencing and the long diagonal of the openings for material from

San Luis and Nogales A are shown in figures 10 and 11, respectively

There is some evidence in figure 10 that the primary rolling direction

of the material from San Luis is perpendicular to the long diagonal of

the openings which is consistent with the findings shown in figure 7.

Figure 11 strongly reinforces the conclusion that the rolling direction

of the material from Nogales A is perpendicular to the long diagonal of

the openings.

Representative etched fields parallel to the plane of the fencing

from material from each of the four sites are shown in figures 12 through

16. The horizontal direction in the photographs is parallel to the long

diagonal of the openings in the expanded material. The fields shown are away from the sheared edges of the strands.

There are some differences in the microstructure of the material

from the various sites, and in the case of Nogales A (figures 15 and

16), there may be some differences in the microstructure of different

pieces of material from the same site. In all cases, the microstructure

consists primarily of ferrite with a small amount of pearl ite^. There

appears to be no directionality of the microstructure in the material

from San Ysidro (figure 12), San Luis (figure 14), and Nogales A (figures

15 and 16). There is some evidence of directionality, particularly of

the pearl ite, in the material from El Paso (figure 13). The pearl ite

appears to be somewhat stretched out in the direction perpendicular to

the long diagonal of the openings.
Representative etched fields from sections perpendicular both to

the plane of the fencing and to the long diagonal of the openings are

shown in figures 17, 18, 19, and 20 for material from San Ysidro,

El Paso, San Luis, and Nogales A, respectively. The direction perpendicular

to the long diagonal of the openings is horizontal in these figures.

The grains in the microstructure are essentially equiaxed for the material

from San Ysidro, San Luis, and Nogales, but there is a definite microstructure

directionality exhibited by the material from El Paso (figure 17).

There was some evidence of that directionality in figure 13. That

directionality indicates that the rolling direction is perpendicular to

the long diagonal of the openings which is not in accordance with

specifications.

3.7 Hardness Measurements

Initially, Rockwell B (HRB) hardness measurements were made on the

basis steel in sections perpendicular both to the plane of the fencing

and to the long diagonal of the openings. These measurements were made

about mid-thickness in the bridge areas and strand areas for material

from all four sites. The average HRB results of these measurements are

as follows:

San Ysidro El Paso San Luis Nogales A

Bridge 65 60 57 63

Strand 69 81 77 82

There is considerable variation among the hardness values presented

above. During fabrication, the material is strain hardened by both the

shearing operation and the expanding operation, and the degree of strain

hardening varies, being greatest where the strain has been greatest.

Because of this, the hardness of the finished product can be expected to

vary considerably. Therefore, it is not surprising that there is a good

deal of variation in the hardness results and that the hardness values

for the strand material are consistently higher than those for the

bridge material

.

Rockwell 30T (HR30T) hardness measurements were made on strand

sections parallel to the plane of the fencing material. Measurements

were made near the center of the sections and near a sheared edge (but

not in the galvanized coating). When converted to their approximate HRB

equivalent hardness values, the average results of the measurements are

as follows:

San Ysidro El Paso San Luis Nogales A

Center 68 63 80 81

Edge 81 84 86 86

In every case, the hardness near the edge is greater than that near the

center demonstrating the effect of strain hardening due to the shearing

action.

- 9 -
The preceding discussion indicates that regardless of the initial

hardness of the sheet material before fabrication, it will harden during

fabrication, and any further working after fabrication will tend to

harden it further until the hardness reaches a maximum. As the hardness

increases, the tensile strength also increases, but ductility decreases,

and this decrease may be very significant.

3.8 Simulated Field Intrusion Test

After most of the examination had been completed, it was agreed by

both Mr. Morris of the Immigration and Naturalization Service and NBS

that a sample from each site would be tested to determine how difficult

it would be to break through the material. A simple test was devised to

simulate as nearly as possible the type of failure observed in service

for the expanded metal fence, and to rank, at least qualitatively, the

fencing samples from the various sites according to their breaking

(mechanical) strength. This simulated field test consisted of inserting

a crowbar into an opening in the expanded metal and bending the material

manually until at least one strand fractured completely.

The crowbar was placed in one of the openings of a sample such that

it was across the small diagonal of the opening, i.e., the crowbar was

in a plane perpendicular both to the plane of the fencing and the long

diagonal of the opening. Force was applied manually to the handle of

the crowbar until the strand on one side of the opening was displaced

approximately one strand width relative to the strand on the other side

of the opening. The position of the crowbar was then reversed but kept

in the same plane perpendicular to the plane of the fencing and to the

long diagonal of the opening. Force was applied to the handle of the

crowbar until the relative positions of the strands on either side of

the opening had been reversed, i.e., the strand that had been displaced

by one full strand width initially was now displaced one full strand

width in the opposite direction. The above sequence was considered to

be one cycl e.

One test was performed on material from each site. For Nogales,

the material designated sample B was used.

The results of these tests show that the sample from El Paso required

2 1/2 cycles to fail, whereas the samples from San Ysidro, San Luis, and

Nogales failed after only 1 to 1 1/2 cycles. The interpretation of

these results is highly subjective. However, the results do suggest

that qualitatively, the material from El Paso is probably stronger and

stiffer than the material from the other sites.

4. DISCUSSION

This examination was initiated because some installed fencing

segments were experiencing intrusion more easily than others. This was especially true of the segment near Nogales, Arizona. A simulated field

intrusion test showed that the fencing material from El Paso appeared to

be more resistant to failure by intrusion than the material from San Ysidro,

San Luis, and Nogales. These tests were highly qualitative and the

interpretation of the results is highly subjective. More extensive and

qualitative testing is required to verify these results. However, if

the material from El Paso is actually significantly better in resisting

- 10
failure, this improvement may be expected to result from the following

differences between the material from El Paso and the material from the

other sites: (1) an extremely low inclusion content, and (2) lower

manganese and higher silicon content. Most of the sulfide inclusions in

steel consist of manganese sulfide, and the low manganese content of the

material from El Paso might help to account for the low inclusion content.

The low inclusion content could contribute to improved mechanical properties,

whereas the directionality exhibited by the material from El Paso, if it

has any effect at all, could have a negative effect on the properties in

the direction transverse to the grain orientation.

Samples from San Luis, El Paso and Nogales A fail to meet the

weight per square foot requirement of Standard MIL-M-1 71 94C, and the

sample from Nogales B is marginal. These deviations from specifications

are not expected to significantly affect the mechanical/structural

performance of the material. The sample from San Ysidro did meet the

weight per square foot requirement. It should be noted that the weight

per square foot determinations were made on samples much smaller than a full sheet.

Samples from all sites meet the dimensional and galvanized coating

thickness requirements of Standard MIL-M-17194C with possible exception

of the marginal width of strand value for the material from El Paso.

The metal 1 ographic specimens from Nogales A exhibited the largest

inclusions of all the samples examined which could have an adverse

effect on mechanical properties. The metal lographic examination also

revealed that the primary rolling direction of the material from El Paso,

San Luis and Nogales A was perpendicular to the long diagonal of the

openings in the fencing which is not in accordance with Standard MIL-M17194C. If there is any effect of directionality on mechanical properties,

these properties would be expected to be greater in the rolling direction

than transverse to it(3,4) #

Although the chemical composition of the material from all four

sites satisfies the applicable standard, the lower manganese and higher

silicon content of the material from El Paso indicates that the steel

making process, most likely the deoxidation procedure or casting practice,

used to produce this steel was significantly different from the steel

making process used to produce the materials from the other sites.

5. CONCLUSIONS

1. The sample from San Ysidro satisfies the weight per square foot

requirement of Standard MIL-M-1 71 94C

.

The samples from San Luis, El Paso and Nogales A fail to meet

the weight per square foot requirement of Standard MIL-M-1 71 94C.

- 11 -

2 .
3. The weight per square foot result for the material from Nogales

B indicates that the material is marginal.

4. Based on the determinations in this examination, the samples from

all four sites satisfy the requirements of Standard MIL-M-1 71 94C

for nominal width of opening, width center to center of bridge,

length center to center of bridge, and width of strand dimensions

with the possible exception of the marginal width of strand value

for the material from El Paso.

5. Materials from all four sites satisfy the requirements of MIL-M17194C for chemical composition, although the composition of the

material from El Paso is different (lower in manganese and higher

in silicon) from the composition of the materials from the other

sites, all of which are similar. All the material would be classified

as mild steel

6. The material from El Paso is extremely clean with almost no inclusions,

whereas the materials from San Ysidro, San Luis and Nogales A all

have both sulfide and oxide inclusions.

7. The microstructure of the material from all four sites consists

primarily of ferrite with small amounts of pearl ite.

8. The material from El Paso exhibits directionality in the microstructure

in the direction perpendicular to the long diagonal of the openings

in the fencing, whereas the material from the other sites exhibits

no directionality and consists of essentially equiaxed grains.

9. The primary rolling direction of the material from El Paso, San Luis

and Nogales A is perpendicular to the long diagonal of the openings

in the fencing which is not in accordance with Standard MIL-M17194C.

10. The rolling direction of the material from San Ysidro is parallel

to the long diagonal of the openings of the fencing which is in

accordance with Standard MIL-M-1 7 1 94C

11. There are no significant differences in hardness among the materials

from the four sites.

12. There is a large variation in hardness (from the upper HRB 50 1 s or low 60' s up to the high HRB 80' s) within any given sample. This

variation reflects the differing amounts of strain hardening

induced into different regions of the finished product by the

shearing and expanding operations.

13. Based on the results of a simulated field intrusion test, the

material from El Paso appears to withstand failure by intrusion

better than the material from the other sites.

6. ACKNOWLEDGEMENT

The assistance of Leonard C. Smith in this examination is gratefully

acknowl edged.

- 12 -
7. REFERENCES

1. Metals Handbook, 8th Edition, Volume 1, American Society for

Metals, 1961

.

2. Metals Handbook, 8th Edition, Volume 7, American Society for

Metals, 1972.

3. Principles of Physical Metallurgy, Morton C. Smith, Harper & Brothers, 1956.

4. Metals Handbook, 9th Edition, Volume 1, American Society for

Metals, 1978.

- 13

Figure 1. Galvanized expanded steel fencing sample from

San Ysidro, California as received at NBS.

X 1/3
II

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Figure 2. Galvanized expanded steel fencing sample from

El Paso, Texas as received at NBS. X 1/3
V[Ir1riii
Figure 3. Galvanized expanded steel fencing sample from

San Luis, Arizona as received at NBS. X 1/3

Figure 4a. Galvanized expanded steel fencing samples from

Nogales, Arizona as received at NBS. The two

small pieces had been fractured from the fencing

before the material was submitted for examination.

X 1/3

Figure

4b.

Galvanized

expanded

steel

fencing

sample

from

Nogales,

Arizona

as

received

at

NBS

on

March

11

,

1980.

X

1/4
1mm
Figure 5. Unetched section parallel to the plane of the expanded steel

fencing material from San Ysidro. The direction of the long

diagonal of the openings in the material is horizontal. There are some sulfide and oxide inclusions. The direction of rolling

is parallel to the long diagonal of the openings.

As polished X 100

Figure 6. Unetched section parallel to the plane of the expanded steel

fencing material from El Paso. The direction of the long

diagonal of the openings in the material is horizontal. There

are extremely few inclusions. The direction of rolling is

unclear.

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of the openings.

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Figure 10. Unetched section through material from San Luis. This section

is perpendicular to both the plane of the fencing and the long

diagonal of the openings in the material. The direction of the

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long diagonal of the openings.

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Figure 11. Unetched section through material from Nogales A. This section

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long diagonal of the openings in the material. The direction

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Figure 13. Etched section parallel to the plane of the expanded steel fencing

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NBS-114A (REV. 9-76)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2043

\v N Vi;

:J. Accession No.

4. TITLE AND SUBTITLE

Examination of Expanded Metal Grating Material Used

for Fencing along the United States-Mexico Border

5. Publication Date MAY 1 980

I V . 7. AUTHOR(S)

T. Robert Shives

8. Performing Organ. Repott No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

COW -0-1 371

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP)

Immigration and Naturalization Service

U. S. Department of Justice

425 I Street, NW

Washington, DC 20536

13. Type of Report & Period Covered Failure Analysis

15. SUPPLEMENTARY NOTES

Contract/Grant No. COW-O-1 371

I | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

1

16. ABSTRACT (A 200-word or less factual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.)

Samples of galvanized expanded steel fencing from four sites along the

United States-Mexico border were characterized. The sites were San Ysidro,

California, El Paso, Texas, San Luis, Arizona and Nogales, Arizona.

Properties were compared to the specifications in Military Standard

MIL-M-1 71 94C. Samples from El Paso, San Luis and Nogales failed to meet

the weight per square foot requirement, and the rolling direction of these

samples was not in accordance with specifications. All samples met

dimensional and coating thickness requirements, and all were fabricated

from mild steel as called for in the specification. The material from

El Paso had extremely few inclusions compared to the materials from the

other sites. In a simple mechanical test that attempts to simulate

field failure, the fencing material from El Paso appeared to offer greater

resistance to intrusion than the materials from the other sites.

.J

II

I

17. KEY WORDS (six to twelve entries; alphabetical order; capitallxe only the first letter of the first key word unless a proper name;

separated by semicolons)

Expanded steel; fencing; galvanized expanded steel; microstructure

directionality; mild steel

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