Full-field progressive fatigue damage of 3D5D braided composites with yarn-reduction: visualization, classification, and quantification

Abstract

Recently, X-ray computed tomography (Micro-CT) has shown its potential for damage analysis in 3D braided composites. However, the visualization, classification and quantification of progressive damage of 3D braided composites based on Micro-CT are still lacking. The present work aims at the progressive fatigue damage mechanism of 3D5D braided composites with yarn-reduction. A novel “three-step” approach based on Micro-CT was proposed to automatically classify and quantify the fatigue damage initiation and evolution considering the position. Also, the combination techniques of Acoustic Emission (AE) and Digital Image Correlation (DIC) are employed to characterize the post-fatigue residual mechanical properties and failure mechanisms. The results indicated that the initial damage can be simultaneously found at the yarn-reduction point and edge of the specimen after 5.57% of fatigue life. Subsequently, the wedge-shaped damage near the yarn-reduction point are progressively formed. More significantly, the quantitative data of multiple defined cracks propagation is in line with the 3D visual cracks. Furthermore, the post-fatigue residual strength occurred the 38.9% decrease after experiencing the 25.1% fatigue life. It is expected that this study can provide unparalleled quantitative data for the development and validation of fatigue life prediction models of 3D5D braided composite with yarn-reduction.