INDENTATION CRACK-SHAPE EVOLUTION DURING SUBCRITICAL CRACK-GROWTH

Indentation crack-shape evolution during subcritical crack growth was examined in soda-lime glass, Crack-arrest markings were generated on t he fracture surfaces by temporary unloading during subcritical crack g rowth, Crack shapes were determined from these crack-arrest markings b y optical microscopy, The shapes were found to be semielliptical, but the ellipticity changed significantly with crack extension under an ap plied bending stress, Crack-shape evolution was predicted by using the stress intensity factor equation for a semielliptical crack for the a pplied stress distribution and the subcritical crack growth parameters for the material/environment system. Experimental results were found to be in excellent agreement with the predictions, The influence of th e initial crack size and shape, the loading configuration, and the sub critical crack growth exponent n on crack-shape evolution was also inv estigated in the simulations, It was found that, for the particular lo ading configuration and material, there is an equilibrium shape associ ated with the subcritically growing crack. The variation in crack shap e with its extension during subcritical crack growth was found to be a n important factor in lifetime prediction.