Impact Tests on Frames and Elastic‐Plastic Solutions

Abstract

Experimental and analytical work is described in further investigation of a simplified method for estimating final and peak deflection amplitudes of a pulse loaded structure. The method includes effects of elastic response interacting with plastic deformation, but gains simplicity by treating them in artificially separated stages: An initial elastic response stage is followed by a wholly plastic (i.e., rigid‐plastic) stage, which in turn is followed by elastic vibrations. Experiments were performed in which portal frames of aluminum alloy and mild steel were impacted at the midpoint of one column by masses projected at various speeds. The contact force pulse was recorded and used as input data for analyses. In addition to the simplified elastic‐plastic (SEP) method, numerical analyses were carried out by a finite element code (furnishing nominally “exact” solutions) and by an approach assuming rigid‐plastic behavior for the entire response. It is found that with the relatively long pulses produced in the present impact experiments, elastic‐plastic interactions may be critically important. Consideration of strain rate sensitive plastic flow in the steel frames requires special treatment. Reasonably good agreement with results of tests and finite element calculations was given by the SEP method, whereas a rigid‐plastic solution grossly underestimated final deflections in certain cases.