Geometric Propagation Model of the Lateral Rarefaction Wave Under Ideal and Non-ideal Flat Plate Impact

In the flat plate impact experiment, lateral rarefaction waves (LRWs) form when stress waves pass through the side free surface (SFS). These waves alter material response by disrupting one-dimensional strain conditions, thereby affecting spallation behavior and measurement accuracy. This study establishes a geometric propagation model (GPM) based on elastic wave reflection theory to characterize LRW formation and evolution in flat plate impact. Results identify the shape of LRWs whose positions and morphologies are well predicted by the proposed model. Furthermore, systematic investigation of yaw impacts reveals that flyer inclination directly modulates the LRW-affected zone and measurable velocity range. The derived side relaxation angle formula quantifies the relationship between wavefront inclination and impact geometry. It enables indirect measurement of wave velocity, prediction of edge spallation, and determination of optimal measurement boundaries, enhancing experimental design in impact dynamics.