13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- displacement load versus crack tip position data was used as boundary load conditions to calculate both stress intensity factor “K” and T-stress. Their values are compared with the result obtained by the Digital Image Correlation (Q4-DIC software) [11]. Finally, the performances of the two global approaches are compared. 2. Experimental configuration The experimental setup is shown in Figure 1a and b. A vertical load is applied by means of a metallic wedge at the mouth of the notched sample. The sample is supported along its basis. To minimize friction between wedge and lateral supports, two lines of rollers are used. During testing, the wedge pierces the sample and the crack generated at the tip of the notch propagates in stable way. The crack grows until it reaches the bottom of the sample, splitting it into halves. Figure 1. a) Experimental set-up of the Wedge Splitting loading. b) A telecentric lens is used to minimize artifacts induced by out-of-plane motions. c) Typical load- wedge displacement curve from PMMA fracture test. Due to the compressive stresses in front of the crack tip and due to the small amount of elastic energy stored in the specimen, the crack propagates with a velocity proportional to Vwedge. The elastic energy stored in the testing device is much lower compared to other common test methods because the wedge angle (here choose to 15°) enhances the effect of the vertical force applied by the machine. The material used is Polymethyl methacrylate (PMMA) from Altuglas International (Perspex sheets). This material is brittle with a Young’s modulus E= 2800 MPa and Poisson’s ratio ν=0.33. The specimen is prepared from rectangular plates of length L=140mm, width W=125mm, and thickness H=15mm. A notch is machined i) by cutting out a 25x25x15mm3 parallelepipeds from the middle of one of the WxH edges; ii) by subsequently adding a 8 mm long 800 µm thick groove with a diamond saw; and
RkJQdWJsaXNoZXIy MjM0NDE=