Analysis of Enhanced Resistance to Slow Crack Growth in PE Materials [PE]

The effect of blunting at crack-like notches on the apparent subcritical toughness measured in terms of slow crack growth is discussed with regard to mechanics and materials aspects. Notch tip blunting is shown to rationalize the apparent enhanced subcritical toughness trends, leading to so-called super tough materials. The development of the blunting is argued to depend on the material's compliance and the critical stress for crazing, expressed in terms of the triaxial notch tip stress field. Inherent toughness is compared to apparent toughness by a simple test that generates SCG under high triaxiality. Under the high triaxiality developed in this fashion, there is little evidence of the enhanced cracking resistance expected of super tough materials. It is concluded that the benefits of differences in apparent subcritical toughness in the various polyethylene gas pipe materials are difficult to assess quantitatively using presently available methods. KEY WORDS Slow crack growth, apparent toughness, blunting, compliance, and notch stress fields.