Dynamic Response Of The Oblique Impact Of A Rigid Sphere Against A Ductile Solid

A new model of dynamic response to oblique impact is presented, basing on the theoretical study of normal and tangential response of interface to impact loading and the experimental observation on interface relevant to sliding, sticking and ploughing. Available models are discussed which were based on the hypothesis of continuous sliding and constant normal stress and friction coefficient in the impact process. The model treats the average normal stress and the effective friction coefficient as functions of impact process.The normal elastic and elastic-plastic deformation of interface is considered dependent on strain, strain rate and temperature and Johnson-Cook constitutive model is adopted, introducing average strain, strain rate and maximum rise in temperature.The driving component of Split Hopkinson Pressure Bar (SHPB) is used, and some attachments are designed. Experimental investigation of the appearance of crates on target caused by free impact is performed and compared with that by restricted impact. The influence of free or restricted state of rigid spheres in the impact process on sticking and sliding phenomena is indicated, which is relevant to the different friction mechanism.An effective friction coefficient relevant to impact wear is defined as the ratio of the effective friction force in the tangential direction to the load in normal direction, at each instant. The effective friction force is expressed as a combination of shearing term and ploughing term. The shearing term is dependent on the state of shearing the metallic junction by sliding or rolling and the ploughing term on the state of dragging the material from the front of the particle. The effective friction coefficient is applied to the study of the oblique impact of a rigid sphere against a ductile solid.Having a disregard for the shearing term, we have indicated that for Hutchings' experiments, a merely ploughing causes the effective friction coefficient to be a function of the impact process and the initial impact angle and on an average greater than 0.05 and smaller than 0.1, which was used in all of the calculations by Hutchings and Sundararajan for consistency with both experiments and calculations respectively. In certain cases, it is suggested that the effective friction coefficient for the oblique impact of a free sphere against a ductile solid relevant to impact wear is determined, primarily, by ploughing.