A Dynamic Photoelastic Study of Crack Propagation in a Ring Specimen

Abstract

Crack propagation in a thick-walled ring specimen subjected to a mechanically simulated thermal stress was investigated by employing dynamic photoelasticity. Ring models fabricated from Homalite 100 were loaded with a specially designed mechanical deformeter which separated and rotated a slit cut into the ring to produce a combination of tension and bending that simulated a steady-state thermal stress. Short starter cracks were machined into a series of ring models and the deformeter adjusted to give KQ/K1m ranging from 1.2 to 3.0. The crack was initiated and high-speed photographs of the isochromatic fringe loops at the tip of the running crack were recorded. The data were analyzed to obtain the instantaneous stress-intensity factor K, the normalized crack position a/w, and the crack velocity ˙a. The relation between K and ˙a was established for Homalite 100 using the ring specimen. It was noted that this K-˙a relation compared well with those determined previously using single edge notch, rectangular double cantilever beam, contoured double cantilever beam, and modified compact tension specimens. A comparison of K, as a function of position a/w, was made between static and dynamic crack growth. A marked difference was noted. For static crack growth, K increases with a/w until a/w = 0.2 and then decreases with further crack extension. For dynamic crack growth, K decreased monotonically with increasing a/w.