Fatigue Damage Monitoring and Stiffness Assessment in Plain Weave Composites by Means of Acoustic Emission and Digital Image Correlation

Abstract

The main objective of this study is to assess the influence of manufacturing flaws on the fatigue life of plain weave composites. The paper proposes combined and complementary approaches for delamination onset monitoring and quantification of the loss of mechanical properties during fatigue loading. Standards test coupons with an artificial delamination, created by inserting an artificial Teflon tape which is implanted in the mid-plan of the layup, were assessed in real time by using Acoustic Emission (AE) and Digital Image Correlation (DIC) under tension-tension cyclic loading. During mechanical cycling, the damage and delamination onset was supervised by detecting elastic waves emitted by cracks while the loss of stiffness of the material is quantified by DIC techniques. The fatigue life curves have been generated by exploiting AE data associated with delamination initiation and predictive fatigue model, based on log-linear straight-line assumption, was derived. Furthermore, the results of mechanical properties monitoring by DIC technique, were used to quantify the stiffness degradation of the plain weave coupons. The mechanical properties degradation has been correlated to matrix crack's development and to delamination extension during fatigue loading