Displacement fields around a crack tip in polymers

Moiré interferometry was utilized to experimentally determine displacement fields around a crack tip in single-edge-cracked tensile PMMA and PA6/PPE/SBS alloy specimens. Vertical displacement v was expressed as functions of distance r and angle θ from the 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 experiments in the vicinity of a crack tip in the PMMA specimens, but it yielded a discrepancy as r increased. For the alloy specimens, however, the solution gave much smaller values than the experiments. The principle of superposition was employed to determine 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 expressions for v* and v were also introduced to analyze the effects of r, θ and load P applied to the specimen. v* was found to be an important factor in increasing the displacements near the crack tip, and the v expression well represented the experimental results for both the PMMA and alloy specimens.