Numerical and Experimental Analysis of General Mixed Mode I/II/III Fracture of Polymethyl Methacrylate

Abstract

Mixed mode loading often has a significant effect on fracture behaviour in components. Cracks is in many cases the reason for failure or fracture of a component. All of the mechanisms of cracks and fracture behaviour are still not completely known. This also applies for the three dimensional loading case of mixed mode I/II/III. This thesis will therefore study the existing theory on two dimensional, and three dimensional mixed mode loading. Mixed mode I/II/III brittle fracture behaviour of polymethyl methacrylate, PMMA, will be studied experimentally and theoretically, using pre-cracked CTS specimens. This specimens contains pre-cracks and will be subjected to different mixed mode loading conditions, ranging from pure mode I to pure mode II and pure mode III. During this thesis, a mixed mode I/II/III loading device were designed and used for the experimental procedure. Experiments were conducted on all twenty five combinations of the loading device. The presented mixed mode loading device allowed mixed mode I/II/III loading combinations in steps of 22:5, for in and out of plane rotations. After the conducted experiments, fracture loads were obtained. In-plane crack initiation angles and out of plane crack initiation angles were measured for all of the fractured specimens. These experimentally obtained results were then compared with predictions of various fracture criteria. Maximum tangential stress criterion, MTS, generalized maximum tangential stress criterion, GMTS, and the criterion by Richard were used for numerical predictions in this thesis. Numerical analysis were conducted by obtaining results from three-dimensional finite element simulations in Abaqus, and applying them in different fracture criteria. The criteria showed a good relation with experimentally obtained angles.