Destructive disassembly of bolts and screws by impact fracture

Disassembly, the process of removing components from a product at the end of its useful life, is complex due to a variety of fastener shapes and variability in their damage during use. Mechanical impact has been suggested as a cost-effective method for destructive disassembly of joining elements. This research analyzes the process of impact disassembly by studying the characteristics of elastic waves caused by the impact. Elastic waves are modeled in a one-dimensional bar, which transfers the impact energy to a protruded bolt head mounted in an infinite elastic medium or structure. Stress wave equations are presented for each period when they bounce back and forth between the two ends of the bar. It is determined that the maximum stress occurs when the wave front reflects in the second or later period. This higher stress can be applied to shear off the bolt head with the same amount of energy invested as in a single wave impact. The results can be used to design effective destructive disassembly procedures and new demanufacturing tools, resulting in an increase of disassembly efficiency and a reduction of recycling cost.