Elasto-Plastic Clamp Load Analysis of Bolted Joint for Bolt Strain Hardening Material Under Separating Loading

A nonlinear model is established for the clamp load analysis of tightened bolted joints that are subjected to a separating service load that is cyclic in nature. The analysis takes into account the strain hardening of the bolt material to determine its behavior beyond the elastic limit. The bolt tension versus elongation curves during the tightening are established. The clamp load loss is determined due to the permanent set in the fastener after a cyclic separating force has been removed. The fastener material with strain hardening plastic behavior is used for modeling the behavior of the bolted joint system. The effect of some non-dimensional variables on the amount of clamp load loss is investigated. Analytical results are presented for a range of stiffness ratios that simulate both soft and hard joint applications.