Crack growth under static and cyclic loading in hot-stretched PMMA

Crack growth behaviour under static and cyclic loading was investigated using anisotropic plates of PMMA oriented by hot-stretching. Both tests were performed at room temperature for samples with different degrees of orthotropy. A slight increase in the degree of orthotropy considerably improves the resistance to both static and cyclic crack growth in the case where the crack propagates perpendicularly to the hot-stretched direction. A power law relationship between crack growth rate and stress intensity factor may hold for both types of crack growth in the ranges of orthotropy tested. The experimental data for static crack growth were compared with a viscoelastic criterion based on the crack opening displacement theory for fracture. The criterion discussed here explains comparatively not only the beginning of cracking from a pre-introduced crack, but also the crack growth rate in oriented PMMA.