Using a mixed-mode fatigue delamination criterion

This paper applies a mixed-mode delamination onset criterion to predict edge delamination in quasi-isotropic laminates of IM7/8320 and IM7/5260. The laminates were tested statically and in fatigue at 23 and 175°C. The three stages involved in this process were: (1) determination of the mixed-mode ratio, (2) determination of the mixed-mode delamination onset criterion using the mixed-mode bending apparatus, and (3) comparison with experimental data. To determine the mixed-mode ratio, several finite element analysis (FEA) models were created with different element sizes at the delamination front and with resin layers also modeled. The β = 0 approach was employed to converge the FEA results. Surface fits were made to the mixed-mode data to allow for prediction of the flat laminate experimental data. The influence of the Mode II component in the predictions resulted in the predictions being less conservative than using a Mode I failure criterion, although the predictions were still conservative.