Editorial Feature

# Perforated Materials - Strength of Perforated Metals

When considering the use of perforated metal, the ability to provide a desired level of strength can be of great importance. Realising that perforated metal is not as strong as non-perforated metal, strength levels can be established by comparing the two forms of metal. This comparison is referred to as the Equivalent Solid Material Concept.

In an effort to provide designers with the information they need to make decisions about perforated metal, solid material equivalent tests were performed. The tests compared the strength of 26 different perforated metal samples to the equivalent solid metal. Because they account for more than half of the perforating industry’s production, the tests were performed on round hole 60° staggered patterns (figure 1) ranging from .020” to ¾”. The samples tested are listed at the bottom of this page.

 Figure 1. Round 60° staggered pattern.

## Strength Test - Methodology and Results

In this test, the equivalent strength of the perforated material is used in place of the strength of the solid material. By evaluating the effect of the perforations on the yield strength of the material, S*, can be obtained as a function of the yield strength of the solid or unperforated material, S. Thus, the designer is able to determine safety margins for the perforated material for any geometry of application and any loading conditions. The S*/S ratios are the same for bending and stretching of the material. Having the S*/S ratio for the particular penetration pattern of interest, it is therefore easy for the designer to determine what thickness of the perforated material will provide strength equal to that of unperforated material.

Perforated material has different strengths depending on the direction of loading. Values of S*/S are given for the width (strongest) and the length (weakest) directions. The values for the length direction have been calculated conservatively. Refer to Figure 1 (above) for the length and width directions corresponding to the directional results given in the following table.

## Strength of Materials Perforated with Round Holes in a Standard Staggered Pattern

Table 1. Strength of materials perforated with round holes in a standard pattern, where strength is defined as yield strength of perforated material/yield strength of unperforated material.

 IPA Number Perf-orations Centres Holes/in2 Open Area Str.∇ Width Direction Str.∇ Length Direction 100 .020” - 625 20% .530 .465 106 1/16” 1/8” - 23% .500 .435 107 5/64” 7/64” - 46% .286 .225 108 5/64” 1/8” - 36% .375 .310 109 3/32” 5/32” - 32% .400 .334 110 3/32” 3/16” - 23% .500 .435 112 1/10” 5/32” - 36% .360 .296 113 1/8” 3/16” - 40% .333 .270 114 1/8” 7/32” - 29% .428 .363 115 1/8” ¼” - 23% .500 .435 116 5/32” 7/32” - 46% .288 .225 117 5/32” ¼” - 36% .375 .310 118 3/16” ¼” - 51% .250 .192 119 3/16” 5/16” - 33% .400 .334 120 ¼” 5/16” - 58% .200 .147 121 ¼” 3/8” - 40% .333 .270 122 ¼” 7/16” - 30% .428 .363 123 ¼” ½” - 23% .500 .435 124 3/8” ½” - 51% .250 .192 125 3/8” 9/16” - 40% .333 .270 126 3/8” 5/8” - 33% .400 .334 127 7/16” 5/8” - 45% .300 .239 128 ½” 11/16” - 47% .273 .214 129 9/16” ¾” - 51% .250 .192 130 5/8” 13/16” - 53% .231 .175 131 ¾” 1” - 51% .250 .192

Notes: Strength = S*/S, where S* = Yield strength of perforated material, S = Yield strength of unperforated material Length Direction = parallel to straight row of closely spaced holes, Width Direction = direction of stagger (see Figure 1 above).

The strength tests were performed by O’Donnell and Associates and have been made available by the Industrial Perforators Association.

Source: Diamond Manufacturing Company.