Evaluation of multiaxial fatigue life prediction criteria for PEEK

• Multiaxial fatigue tests were conducted for PEEK under four loading paths.
• Four criteria were used for fatigue life prediction.
• Single critical plane criterion cannot characterize the multiaxial fatigue of PEEK.
• Predictions based on modified SWT criterion achieve satisfactory results.
• PEEK exhibits mixed cracking behavior and is proved by observation and calculation.

Multiaxial fatigue test were conducted on PEEK under four loading paths and several criteria were used for life prediction. Predictions based on Fatemi–Socie criterion fall out of the factor-of-two line on the conservative side for proportional loading and non-proportional loading. The normal strain-based Smith–Watson–Topper criterion yield good prediction for proportional loading but non-conservative prediction for non-proportional loading. Taking the contribution from shear component into consideration, the Chen–Xu–Huang criterion achieve satisfactory results for both proportional loading and non-proportional loading, but with non-conservative prediction for pure torsion loading. To consider general cracking behavior, the modified SWT criterion is adopted and good agreement between experimental data and prediction values is achieved.