Fatigue crack growth of PMMA in organic agents

Abstract

Crack growth tests under cyclic loading were executed at 295 K in various organic agents using compact tension and pure bending specimens of polymethylmethacrylate (PMMA). The cyclic frequencies f for the two kinds of test were 0.4 to 1 and 33 Hz, respectively. Two interesting features are pointed out: (i) transitional behaviour is observed on a crack growth rate against stress intensity factor range ΔK diagram, and (ii) the fatigue fracture surfaces tested in highly viscous agents are covered with a new type of striation named “wavy striation”, as reported previously. The crack growth rate at the transition was analysed based on fluid flow through the pores within the craze forming at the crack tip. The wavy striation was also investigated by use of the theory of meniscus instability. It is found that both the phenomena may be well described by a parameter P = T(ΔK)2/ηf where T and η are the surface tension and viscosity of the organic agents, respectively.