An experimental study on the mixed-mode crack tip deformation fields in polymethyl methacrylate

Stereo vision was used to measure the full three-dimensional deformation field around the crack tip region of a compact tension shear (CTS) specimen made of polymethyl methacrylate (PMMA) subjected to mixed-mode (I/II) loading. The stress intensity factors (SIF), K1 and KII, were then estimated using both measured in-plane and out-of-plane deformation fields. The KI and KII values determined from in-plane displacements are in very good agreement with those determined from out-of-plane displacement. The far-field J integral values computed using the line integral are compared with those evaluated using the measured KI and KII values. The extent of the region near a mixed-mode crack tip where the plane stress solutions can reasonably predict the in-plane and out-of-plane displacements was investigated. Experimental results indicate that the solution of the out-of-plane displacement derived on the basis of the plane stress condition does not provide a good approximation to the experimental data for distances from the crack tip within half the specimen thickness. However, there is good agreement between the in-plane displacement measurements and the computed results, even for r/h < 0.5.