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

Abstract

► The fracture strength of bolted specimens is greater than the simple edge crack specimens. ► The fracture strength of the PMMA specimens in mode II is bigger than mode I. ► The geometry factor of both modes I and II decreases when the specimen is bolt clamped. 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.