New discontinuous fields of stress are derived for materials perforated in a triangular array of circular holes. These stress fields are applicable for loads of arbitrary bi-axiality and orientation with respect to penetration patterns having moderate to high ligament efficiencies. The corresponding effective plastic constants for the equivalent solid material are derived for use in the limit analyses of structures. The method of constructing these stress fields may also be used for irregular penetration patterns and to evaluate the effect of misplaced holes.

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