When considering the use of perforated metal, the ability to provide a desired level of strength and elasticity can be of great importance. Realizing that perforated metal is neither stronger nor stiffer than unperforated metal, strength and elasticity 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 strength and elasticity of perforated metal, solid material equivalent tests were performed. The tests compared the strength and elasticity of 26 different perforated metal samples to the equivalent solid metal. Because they account for more than half of the perforating industry’s production, due to their inherent strength and wide range of open areas, the tests were performed on round hole 60° staggered patterns ranging from .020” to 3/4”.

The direction of the stagger is the short distance or width of the sheet and the straight row runs parallel to the long dimension or length of the sheet as illustrated in Figure 1 below. This is the standard formation for 60º staggered patterns and is often referred to as an Actual Center Pattern. In some cases the hole orientation in relationship to the length and width dimensions may be reversed. This 60º pattern formation is often referred to as Reverse Actual Center.

The strength and elasticity tests were
performed by O’Donnell & Associates and
are courtesy of the Industrial Perforators Association.

Strength
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 (left) for the length and width directions corresponding to the directional results given in the Tables.

THIS MATERIAL WAS DEVELOPED FOR THE IPA BY O’DONNELL & ASSOCIATES, INC.

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