An assessment of crazing criteria for polyetherimide in three-dimensional stress space

Three point bend tests of notched, polyetherimide (PEI) beams are performed for varying notch radii and beam thicknesses. Finite element stress results including pressure sensitive yielding effects are correlated with experimental load-to-craze observations to determine the three-dimensional stress state at craze initiation. Three crazing criteria; maximum principal stress, hydrostatic stress, and the critical strain criterion of Oxborough and Bowden are examined for consistency. Over the range of geometries studied, the critical strain criterion provides the best fit to the experimental data. This criterion could be used as a brittle failure criterion to help understand and prevent brittle failures.