Abstract
Crack growth tests under cyclic loading were performed in various organic agents by use of compact tension and pure bending specimens of PMMA. It was found that the fracture surfaces were covered with new type striations named as “wavy striation” because of their sinusoidal shape. This paper describes the details of the observed results of the striation and infers its initiation mechanism. A formation model for the wavy striation is proposed based on the meniscus instability that, when viscous fluid flows through a narrow gap between crack planes, the fluid head becomes unstable due to a small perturbation. The proposed model indicates that the wave length of the wavy striation increases with an increase in aparameter P=T(ΔK)2/ηf where ΔK is the stress intensity factor range, f is the cyclic frequency and T and η are the surface tension and the viscosity of the agent. This model is in good agreement with the experimental results.
