FE-BASED FATIGUE ANALYSIS OF UNNOTCHED COMPOSITE LAMINATE USING STIFFNESS DEGRADATION APPROACH

Abstract

The composites such as carbon fibre reinforced polymer (CFRP)/ glass fibre reinforced polymer (GFRP) composite material are being extensively used in aerospace industries for aircraft primary structural elements. The fatigue evaluation of composites is very complex and challenging. To the authors' knowledge, no computational tools are available to predict the fatigue life of composites. This project aims to carry out an FE-based fatigue analysis to estimate the fatigue life of GFRP composite aircraft structural elements by performing progressive damage growth analysis (PDGA) based on the stiffness degradation rule up to last ply failures (LPF). A glass fibre-reinforced plastic (GFRP) composite laminate, according to the Chinese standard of materials testing GB/T1447 2005 [1], is considered in the analysis. Two stacking sequences [45/90/-45/0]s and [45/0/0/-45]s are considered. First, the static analyses are conducted on GFRP composite laminate for various applied loads using LPF-based PDGA to determine the static strength of the laminate using Tsi-Wu failure criteria. Then, a similar procedure using the Tsi-Wu failure criterion is followed for the fatigue analyses to assess the fatigue strength of the laminate with the above two stacking sequences by using S-N data of the unidirectional composites for longitudinal, transverse and shear directions. FEA predicted fatigue strength results are slightly more than the experimental results. This trend may be because the delamination and debonding occurring in the experiment (which is a real scenario) are not considered in FEA. The error %age in fatigue strength for 103 cycles is of the order of 5% for [45/0/0/-45]s laminates and 7% for [45/90/-45/0]s laminate. This study is essential for evaluating the structural integrity of composite airframe structures.