Characterization of strain and strain rate histories in high strength steel during asymmetric tube crush

Asymmetric crushing of circular tubes made of mild and High Strength Steel has been investigated under constant velocity loading using hydraulically driven equipment. Tube crush experiments were conducted using velocities within the range of quasi-static to 4 m/s. The characteristics of the testing equipment, primarily its high stiffness and ability to maintain constant velocity during crush, provided a controlled environment for detailed investigation of strain rate effects on structural response. Strain histories in the tubes were measured using electric resistance strain gages. The gages were positioned to coincide with the locations at or near occurrence of plastic folds. By prescribing imperfections in the boundary conditions, we were able to generate a repeatable folding pattern that was necessary for strain gage placement in the areas of interest. The developed information also provides guidelines for the extent of experimental programs required for characterization of strain rate effects in steels. For the crush velocities and experimental techniques considered, current results indicate that strain rate magnitudes of the order of 10 ⁺²/s prevail.