Editorial Feature

The Strength of Perforated Metals

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When contemplating the use of perforated metal, the ability to offer a preferred level of strength can be very significant. If it is known that perforated metal is not as robust as non-perforated metal, strength levels can be defined by comparing the two types of metals. This comparison is called the Equivalent Solid Material Concept.

In an attempt to offer designers with the data they require to make decisions regarding perforated metal, solid material equivalent tests were carried out. The tests equated the strength of 26 different perforated metal samples to the corresponding solid metal.

Since they account for over half of the production of the perforating industry, the tests were carried out on round hole 60° staggered patterns ranging from 0.020″ to ¾″. The samples tested are mentioned at the end.

Strength Test—Methodology and Results

In the strength test, the same strength of the perforated material is used instead of the strength of the solid material. By assessing the effect of the perforations on the yield strength of the material, S* can be acquired as a function of the yield strength of the solid or unperforated material, S. Therefore, the designer can establish safety margins for the perforated material for any loading conditions and any geometry of application.

The S*/S ratios are the same for stretching and bending of the material. Having the S*/S ratio for the specific penetration pattern of interest will allow the designer to easily determine the level of thickness at which the perforated material will have strength equivalent to that of the unperforated material.

A perforated material has diverse strengths based on the loading direction. S*/S values are provided for the length (weakest) and the width (strongest) directions. The values for the length direction have been calculated conventionally. The length and width directions correspond to the directional results provided in Table 1.

Strength of Materials Perforated with Round Holes in a Basic 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 Perforations Centres Holes/in2 Open Area Str.∇ Width Direction Str.∇ Length Direction
100 0.020” - 625 20% 0.530 0.465
106 1/16” 1/8” - 23% 0.500 0.435
107 5/64” 7/64” - 46% 0.286 0.225
108 5/64” 1/8” - 36% 0.375 0.310
109 3/32” 5/32” - 32% 0.400 0.334
110 3/32” 3/16” - 23% 0.500 0.435
112 1/10” 5/32” - 36% 0.360 0.296
113 1/8” 3/16” - 40% 0.333 0.270
114 1/8” 7/32” - 29% 0.428 0.363
115 1/8” ¼” - 23% 0.500 0.435
116 5/32” 7/32” - 46% 0.288 0.225
117 5/32” ¼” - 36% 0.375 0.310
118 3/16” ¼” - 51% 0.250 0.192
119 3/16” 5/16” - 33% 0.400 0.334
120 ¼” 5/16” - 58% 0.200 0.147
121 ¼” 3/8” - 40% 0.333 0.270
122 ¼” 7/16” - 30% 0.428 0.363
123 ¼” ½” - 23% 0.500 0.435
124 3/8” ½” - 51% 0.250 0.192
125 3/8” 9/16” - 40% 0.333 0.270
126 3/8” 5/8” - 33% 0.400 0.334
127 7/16” 5/8” - 45% 0.300 0.239
128 ½” 11/16” - 47% 0.273 0.214
129 9/16” ¾” - 51% 0.250 0.192
130 5/8” 13/16” - 53% 0.231 0.175
131 ¾” 1” - 51% 0.250 0.192

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.

The strength tests were done by O’Donnell and Associates, and have been made accessible by the Industrial Perforators Association.

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