The use of perforated material is limited by the lack of reliable strength and stiffness properties for use in design. The following information covers the strength of materials perforated with round holes in standard staggered 60° pattern as shown in Figure (1).
Standard 60° Staggered
Pattern Showing Length
and Width Orientations
Round holes arranged in a standard 60° triangular pattern ranging from .020" to 3/4" account for more than half of the perforating industries production. They produce the strongest pattern and are the most versatile in their application. The standard 60° staggered formation is the most popular hole arrangement because of its inherent strength and the wide range of open areas it provides. In perforating this pattern, the direction of the stagger is the short dimension or width of the sheet as illustrated. The straight row of closely spaced holes is parallel to the long dimension or length of the sheet. This is the so-called "closed pattern." Under special order, the holes may be punched in the "open pattern." The directional properties are then reversed from those described herein. Refer to Figure (1) for the length and width directions corresponding to the directional results given in the Tables.
The concept of equivalent solid material is widely used for design analyses of perforated materials. As applied herein, 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.
Notes: 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