Impact And Rebound Of Thin-walled Structures On A Rigid Target

The impact and rebound of a structure in motion is a typical impact problem,in which the deformation mode of the structure,the rebound velocity and the transformation of kinetic energy are studied.The rebound behavior of a structure in the impact problem has not yet attracted much attention,and little achievement was made on this topic.Thin-walled structures like rings are widely used as the basic component in energy absorption devices,thus the dynamic behavior of those structures under impact is worthy of research.This paper focus on the thin-walled structures like rings,elliptical rings,circular arches,and studies the impact and rebound of these structures by finite element method,in which the influence of initial velocities and material properties on rebound behavior and deformation modes are systematically analyzed,thus a series of fundamental problems on this impact problem is raised.Firstly,based on the impact tests of circular rings,the normal impact of rings on the Hopkinson bar are modeled by ABAQUS.And the strains on the bar,the deformation and residual strain of rings,and the rebound velocities and coefficient of restitution of rings are compared.The comparison between tests and FEM calculation shows good agreement,which verifies the applicability of the finite element model in studying the impact and rebound behavior of thin-walled rings.Based on this FEM model,The effects of initial velocity on the rebound velocity and the coefficient of restitution(COR)of the ring are systematically analyzed,and the differences of explicit method and implicit method in calculating peak impact force are investigated,which are further utilized to demonstrate the validity of experimental measurement of impact force with the assumption of one-dimensional elastic wave theory.By the same method,the impact of elliptical rings,circular arches and rings with stiffening bars on a rigid target is studied.And the differences of the rebound behavior of these structures are found.Both structural and kinetic condition have an influence on the rebound behavior.For circular arches,the one with a shape of a half ring has the smallest COR,which is only 0.22.For elliptical rings,when the impact direction is paralleled with the longer axis,the COR is smaller,which gets smaller as the ratio of two axis gets bigger.For rings with stiffening bars,the impact angle and stiffening bars can change COR.Taking all these structures considered,we find that even in an elastic impact,all the CORs are less than 1.0,some as low as 0.2,which reveals the wrong view that people hold on COR,that COR is 1.0 in elastic impact.The research of this paper helps us understand the true concept that COR contains,and the key factor of COR is concluded,thus helps to direct the analysis of impact problems by COR in engineerings.