The importance of penetration and perforation in to targets in both military and civilian applications has made it the subject of many investigations. But the bulk of these investigations was experimental rather than analytical or numerical because of complexity of the governing equations. Hence most of the existing models are either mathematically rigorous or so simplified that they ... https://www.roneverhart.com/Echo-Fix-EF-P2-Spring-Reverb-Pedal-p32083/