Experimental analysis of displacement fields around a crack tip in polymers

Moire interferometry was utilized to determine the displacement fields around a crack tip in single-edge-cracked tensile PMMA and PA6/PPE/SBS alloy specimens. Vertical displacement v was expressed as a function of the distance r and the angle θ from a crack tip, and compared with the approximate solution of linear elastic fracture mechanics to study its applicability to polymers. The results showed that the solution agreed with the experimental results for the vicinity of a crack tip in the PMMA specimen. For the alloy specimen, however, the solution gave much smaller values than the experiments. The principle of superposition was employed for determining the values of v*(= v-v′), i.e. the difference between two displacements v and v′ which was related to a uniform strain field without a crack. The expression for v* was also introduced to analyze the effects of r and θ. It was found that v* was an important factor in increasing v values near the crack tip, and the v* expression well represented the effects of r and θ for both the PMMA and alloy specimens.