An improved semi-circular bend specimen for investigating mixed mode brittle fracture M.R. Ayatollahi ⇑ , M.R.M. Aliha, H. Saghafi Fatigue and Fracture Lab., Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran article info Article history: Received 29 December 2009 Received in revised form 20 July 2010 Accepted 11 October 2010 Available online 16 October 2010 Keywords: Mixed mode loading Finite element analysis Brittle fracture Fracture experiments PMMA abstract An edge cracked semi-circular specimen subjected to asymmetric three-point bend loading was suggested for investigating mixed mode fracture in brittle materials. Using finite ele- ment analysis, the crack parameters were obtained for various crack lengths and different locations of loading points. It was shown that by selecting appropriate positions for the loading points, full mode mixities from pure mode I to pure mode II could be achieved. Then, a series of fracture tests were conducted on PMMA using the proposed specimen. Very good agreement was found between the experimental results and those predicted from the generalized maximum tangential stress criterion. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The presence of flaws and cracks are very often inevitable in engineering structures and components. The cracks can be generated during the manufacturing processes or due to cyclic loading or environmental causes, etc. Pure mode I and pure mode II are two modes of deformation that take place for a cracked component subjected to in-plane loading. In practical situations, the cracked structures sometimes experience mixed mode loading, i.e. a combination of mode I and II. Mixed mode brittle fracture is one of the common types of mechanical failure in cracked components made of brittle or quasi- brittle materials. Therefore, it is important to investigate the structural integrity of cracked components under mixed mode loading. Several theoretical and experimental methods have been suggested by researchers for exploring mixed mode brittle frac- ture. While the experimental fracture studies on real components are often expensive and difficult, researchers prefer to con- duct their experiments on laboratory specimens. However, appropriate fracture criteria are also required to correlate the experimental results obtained from the simple laboratory specimens to the fracture event in cracked structures under their complex service loading conditions. In order to validate a fracture criterion, researchers have to conduct a series of exper- iments on appropriate test materials by using suitable test specimens. PMMA (polymethylmethacrylate or Perspex) has been recognized as a favorite model material for conducting brittle fracture experiments. The brittle type of fracture at room tem- perature, the convenience of machining and introducing a sharp crack and the optical transparency (which allows direct observation of fracture path) are among the advantages of PMMA in brittle fracture experiments. In addition to the choice of test material, a valid fracture test requires an appropriate test configuration. For mixed mode fracture experiments, a suitable test configuration should have simple geometry and loading condition, inexpensive 0013-7944/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfracmech.2010.10.001 ⇑ Corresponding author. Tel.: +98 21 77240201; fax: +98 21 77240488. E-mail address: m.ayat@iust.ac.ir (M.R. Ayatollahi). Engineering Fracture Mechanics 78 (2011) 110–123 Contents lists available at ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech