The Variation of GIc and I'Ic with Crack Growth Rate in Polyethylene

The crack growth rate in HMN 5202 polyethylene has been studied as a function of stress intensity using deeply notched three-point bend specimens. The load-line displacement in response to a static applied load has been measured, with the material compliance as a function of time determined from the specimen compliance prior to the initiation of crack growth. Measured specimen compliance as a function of time after crack growth begins is used to determine crack growth rate as a function of stress intensity.The experimentally determined crack growth rate as a function of stress intensity has been compared to theoretical predictions by Williams and Schapery. This comparison implies that both critical crack tip opening displacement and critical energy release rate increase with increasing crack growth rate. The results also show that the crack growth rate is significantly reduced by plane stress conditions at the surface of the specimen.