Analysis of a new specimen for mixed mode fracture tests on brittle materials M.R. Ayatollahi * , M.R.M. Aliha Fatigue and Fracture Lab., Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran article info Article history: Received 12 October 2008 Received in revised form 11 February 2009 Accepted 16 February 2009 Available online 25 February 2009 Keywords: Mixed mode loading Test specimen Brittle fracture Finite element analysis abstract Numerical and experimental studies were performed on a new fracture test configuration called the diagonally loaded square plate (DLSP) specimen. The mode I and mode II stress intensity factors were computed for different crack lengths and crack orientation angles using finite element analysis. The numerical results show that the DLSP specimen is able to provide pure mode I, pure mode II and any mixed mode loading conditions in between. Fracture experiments were also conducted on Plexiglas using the DLSP specimen. It is shown that the results obtained from the fracture tests are consistent very well with mixed mode fracture theories. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Brittle fracture is one of the common types of mechanical failure in the cracked engineering components and structures. It may occur under pure mode I, pure mode II or mixed mode I and II loading. Mixed mode fracture is usually studied either theoretically using different failure criteria (e.g. [1–4]) or experimentally using appropriate test methods. While experimen- tal fracture studies on real components are often very expensive and difficult, researchers prefer to conduct their experi- ments on laboratory specimens. However, these specimens should be carefully designed since they must be able to provide the same states of stresses and strains around the crack tip as those of the real cracked engineering components under service conditions. Various test specimens have been used by researchers for mixed mode I/II fracture experiments. The rectangular plate containing an inclined center crack and subjected to a uniform far field tension [5–7], the centrally cracked Brazilian disk specimen [8–11], the asymmetric three or four-point bend specimen [12–16], the angled edge crack specimen [17], the compact tension-shear specimen [18–20] and the cracked semi-circular bend specimen [21–23] are some of the specimens used frequently for mixed mode fracture tests on different engineering materials like metals, polymers, ceramics and rocks. A suitable test specimen should have simple configuration, inexpensive preparation procedure, convenience of testing set up and also the ability of introducing complete mode mixities ranging from pure mode I to pure mode II. However, some of the mentioned specimens have their own shortcomings which can affect the fracture test results. For example, some of these test samples can provide only limited combinations of mode I and mode II or require complicated fixtures for testing. In this paper a new test configuration is suggested for mixed mode I/II fracture experiments. First the specimen is described and then its capabilities and advantages are investigated by means of finite element analysis and also through some mixed mode fracture experiments conducted on a brittle polymer. 0013-7944/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfracmech.2009.02.016 * Corresponding author. Tel.: +98 21 7724 0201; fax: +98 21 7724 0488. E-mail addresses: m.ayat@iust.ac.ir (M.R. Ayatollahi), mrm_aliha@iust.ac.ir (M.R.M. Aliha). Engineering Fracture Mechanics 76 (2009) 1563–1573 Contents lists available at ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech