Preliminary investigation into the cracking of polyurethane

It is known that the classical inverse square root singularity used in Linear Elastic Fracture Mechanics (LEFM) is lost as a crack intersects a stress free surface. As a result, the stress and displacement equations are given as eigenvalue series expansions, with the lowest order eigenvalue dominating the series.

The thickness averaged stress and surface displacement singularity exponents were determined for a commercially available polyurethane. Multiple specimen geometries were used to “benchmark” the optical methods. Tests have been run to determine the surface effect on a straight front crack. Results of these tests were compared with analytical results and related to LEFM concepts.