Unfolding the early fatigue damage process for CFRP cross-ply laminates

Xi Li,Julian Kupski,Sofia Teixeira De Freitas,Rinze Benedictus,Dimitrios Zarouchas

doi:10.1016/j.ijfatigue.2020.105820

Xi Li, Julian Kupski + Show 3 more

Open Access

https://doi.org/10.1016/j.ijfatigue.2020.105820

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Abstract

This study investigates the early fatigue damage of cross-ply carbon/epoxy laminates. The aim is to unfold the damage accumulation process, understand the interaction between different damage mechanisms, and quantify their contribution to stiffness degradation. Tension-tension fatigue tests were performed, while edge observation and DIC technique monitored the damage evolution. It was found that different accumulation process and interactive levels between transverse matrix cracks and delamination exist for specimens with similar stiffness degradation. A linear increase of stiffness degradation was observed with the increase of matrix crack density, while the growing trend of stiffness degradation converged with the increase of delamination.

Highlights

During in-service life, composite laminates are subjected to a variety of loads over time that induce fatigue damage and as a consequence degrade the mechanical properties of the structure
It was found that different accumulation process and interactive levels between transverse matrix cracks and delamination exist for specimens with similar stiffness degradation
A linear increase of stiffness degradation was observed with the increase of matrix crack density, while the growing trend of stiffness degradation converged with the increase of delamination

Summary

Introduction

During in-service life, composite laminates are subjected to a variety of loads over time that induce fatigue damage and as a consequence degrade the mechanical properties of the structure. The fatigue damage levels and corresponding loading capacities are generally represented by degradation of stiffness [1,2,3] and variation of self-generated temperature [4,5,6] from the macroscopic perspective. Considering that the stiffness degrades significantly in early fatigue life, it would be of great interest to firstly put emphasis on early fatigue damage, uncovering which damage mechanisms accumulate, how they interact and affect the stiffness degradation. This may help gain a better insight of the significant scatter phenomenon about failure life for composites and further pave the way to probabilistic predictions of fatigue life with physics of damage involved

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