Investigating bolt clamping force effect on the mixed mode fracture strength and stress intensity factor for an edge crack in PMMA specimens

Experimental and numerical investigations have been conducted to evaluate the effect which the clamping force, resulting from torque tightening a nut and bolt, has on the mixed mode (I and II) fracture strength and effective stress intensity geometry/loading factor of a plate having an edge crack. The experimental tests were carried out on three batches of simple edge crack and bolt torque tightened edge crack specimens made from poly methyl-methacrylate (PMMA) rectangular plate. The specimens’ fracture strengths were obtained using a tensile testing machine in different loading angles using a modified Arcan fixture. In numerical part, finite element simulations were used to model the three test specimens variants used and thereby establish their stress intensity geometry/loading factors. The results show that the bolt tightening torque, and hence the plate clamping force, has a significant effect on reducing the equivalent mixed mode stress intensity factor of all loading angles and the equivalent factor, and thus the joint fracture strength compared to bolt-less simple edge crack specimens.