Strength data reported for over 100 tension coupons with central circular holes cut from pultruded glass reinforced plastic (GRP) plate have been used to determine the critical distance and the damage zone critical length according to the point stress and damage zone criteria respectively. It is shown that these quantities are not invariant, as required by the criteria. Indeed, they appear to depend on both geometry and loading direction relative to the principal material axes. It appears, therefore, that neither criterion is suitable for accurate prediction of the open-hole tensile strength of pultruded GRP plate, which is used in infrastructure applications.
The paper shows that the Point Stress and Damage Zone failure criteria (widely used to predict failure of laminated aerospace composites) are not applicable to pultruded GRP structural grade materials. This demonstrates that design procedures are not directly transferable from an advanced sector to a less advanced sector of engineering industry. The paper has been consulted by the US Steel Research