A new constant life diagram model for the longitudinal fatigue of unidirectional composites

Abstract

A new constant life diagram (CLD) model featuring asymmetric bilinear constant-life curves was proposed to better describe the longitudinal fatigue behavior of unidirectional laminae (UD) under a wide range of stress ratios. This model is able to predict S-N curves with satisfactory accuracy not only in tension-tension (T-T) fatigue mode but also in tensioncompression (T-C) and compression-compression (C-C) modes, whereas the conventional Goodman CLD model shows inferior performance especially in T-C and C-C modes. Apart from static tension and compression tests, high- and low-cycle fatigue tests at two stress ratios corresponding to T-T and C-C modes should be performed to determine the parameters in the proposed model. Fatigue test data of several different GFRP UDs at various stress ratios were utilized to validate the proposed model, and the S-N curves predicted by the proposed model agreed well with the experimental results. Compared with the Goodman CLD model, the proposed CLD model demonstrates an enhanced predictive capability without losing its simplicity.