Finite Element Analysis Assisted Fatigue Life Estimation Method for Continuous Fiber Reinforced Plastics

Abstract

The ever-growing need in industry to improve efficiency and performance of products by preserving or even reducing the overall cost has led to a continuous development of materials with better strength to weight ratio than their conventional counterparts. The most relevant representatives of a new material generation nowadays are the continuous fiber reinforced plastics (FRPs). Contrary to metals, thermoset matrix based FRPs are proven to be less sensitive to cyclic loading resulting in much shallower lifing curves. Thus, the endurance limit as a simple fatigue limit stress is a reasonable choice to design fatigue tolerant composite structures. However, for a better understanding of the cyclic load bearing capacity numerous theoretical models have been developed to describe the progressive damage mechanism initiating from ply level up to the final delamination failure of the entire laminate. The importance to introduce these approaches into standard composite engineering processes is getting higher as thermoplastic matrix based CFRPs spread across different industries. These materials exhibit more sensitivity to fatigue load including time-dependent effects. The work presented here introduces a new, in-house developed fatigue life evaluation method for composite laminates with arbitrary geometry and ply layup sequence. The method implements the residual strength and stiffness theories combined with mean stress correction and multiaxial failure criterion coupled with FE stress analysis to correctly compute the ply stresses over the cyclic degradation process. The algorithm has been coded in a user subroutine collaborating with ANSYS FE solver. The tool was also validated and calibrated with fatigue tests carried out in fiber direction. The test results are presented and compared with the simulation results evaluated with the newly developed method. [1] [1] L. Takacs, L. Kovacs, and T. Olajos, "Numerical tool with mean-stress correction for fatigue life estimation of composite plates," Engineering Failure Analysis, vol. 111, p. 104456, 2020/04/01/ 2020.