• Zhu, Man
• Gorbatikh, Larissa
• Fonteyn, Sander
• Pyl, Lincy
• Carella-Payan, Delphine
• Lomov, Stepan
• Van Hemelrijck, Danny

Abstract

A digital image correlation (DIC) based method to characterize the Mode I fatigue delamination onset andpropagation in composite laminates is proposed. The characterization is performed using the double cantileverbeam test (DCB) under fatigue loading. The DIC is used to analyse the displacementfield on the edge of a DCBspecimen, from which the crack tip position is determined as a place where opening displacement converges tozero. The method was successfully applied to both the crack onset detection (fatigue onset life) and propaga-tion monitoring under fatigue cycling. The DIC‐based method, which relies on the actual crack tip position,gives conservative values for the fatigue onset life in comparison with the compliance based method recom-mended in the ASTM standard. The DIC assisted method reduces operator and structure dependent errorsand shows promise for real‐time delamination detection under fatigue loadings.1. IntroductionDelamination is one of the primary failure modes in laminatedcomposites. Characterization of material’s resistance to delaminationunder quasi‐static and fatigue loads is essential to develop no‐defect‐growth design and damage tolerance guidelines for composite struc-tures. The double cantilever beam (DCB) test is widely adopted tomeasure Mode I inter‐laminar toughness[1,2]and Mode I fatiguebehaviour[3–8], and standard methods are established in ASTMD5528[9]for quasi‐static and ASTM D6115[10]for fatigue loading.For characterization of the fatigue behaviour two types of the fati-gue tests are normally conducted: fatigue delamination onset andpropagation. In the former case, the growth onset of an existinginter‐laminar crack is characterized by a G‐N curve, which is analo-gous to the S‐N curve, but replacing the stress,S, with the suppliedstrain energy release rate (SERR),G.Nis the number of loading cyclesrequired for the delamination to onset. The characterization methodfor Mode I is described in ASTM D6115[10]. In this standard, threedifferent ways are introduced to determine the delamination onset.They are:(1)visual observation of the crack onset;(2)detection of1% increase in system’s compliance;(3)detection of 5% increase insystem’s compliance. Because of the difficulties in visual mon

Topics

• impedance spectroscopy
• crack
• fatigue
• composite