A Study on the Multi-axial Fatigue Failure Behavior of Notched Composite Laminates

TL;DR

This study investigates the multi-axial fatigue failure behavior of notched composite laminates, analyzing damage mechanisms, stiffness degradation, and effects of load ratios to inform future fatigue modeling efforts.

Contribution

It provides comprehensive experimental data on the fatigue behavior of notched composite laminates under multi-axial loading, highlighting damage progression differences from static loading.

Findings

Damage mechanisms vary with multi-axiality ratio and notch configuration.

Fatigue damage progression differs significantly from quasi-static loading.

Data supports development of more accurate fatigue models for composite structures.

Abstract

Composite structures must endure a great variety of multi-axial stress states during their lifespan while guaranteeing their structural integrity and functional performance. Understanding the fatigue behavior of these materials, especially in the presence of notches that are ubiquitous in structural design, lies at the hearth of this study which presents a comprehensive investigation of the fracturing behavior of notched quasi-isotropic [+45/90/$-$45/0]$_{s}$ and cross-ply [0/90]$_{2s}$ laminates under multi-axial quasi-static and fatigue loading. The investigation of the S-N curves and stiffness degradation, and the analysis of the damage mechanisms via micro-computed tomography clarified the effects of the multi-axiality ratio and the notch configuration. Furthermore, it allowed to conclude that damage progression under fatigue loading can be substantially different compared to the quasi-static case. Future efforts in the formulation of efficient fatigue models will need to account for the transition in damaging behavior in the context of the type of applied load, the evolution of the local multi-axiality ratio, the structure size and geometry, and stacking sequence. By providing important data for model calibration and validation, this study represents a first step towards this important goal.