Characterization of Cohesive Zone Laws Using Digital Image Correlation

摘要

Delamination is a major failure mode in composite structures. This workaddresses lack of understanding of delamination cohesive laws which is a fundamentalchallenge of strength and fatigue progressive damage and failure analysis (PDFA) ofcomposite structures. Typically such laws are based on mathematical assumptionswhich are fit to simplify convergence of the analysis tools and are not based onphysics or measurement. The simplifying assumptions may cause wrong cohesivematerial properties as they fit to a specified simulation task. This work presents theresults of a feasibility study focused on developing experimental methods and analysistechniques for capturing material cohesive properties and increasing confidence inmaterial input data for PDFA. A direct approach is proposed to measure cohesive lawsin static Double Cantilever Beam (DCB) and Thick Adherend (TA) shear specimensthat have been pre-cracked under fatigue load. High resolution Digital ImageCorrelation techniques are used to measure crack tip separation in these specimens,supported by X-ray Computed Tomography (CT) reconstructions to locate the crackfront. Additionally, by J-integral and VCCT calculations, the precise shapes of thecohesive damage laws in mode I and mode II are characterized. These cohesive lawswere verified by direct comparison of load-displacement curves between numericalFinite Element models and experimental data of the DCB and TA test. The specimencompliance is accurately reproduced, and maximum strength prediction is within 4%.It is noteworthy that accurate crack location has been essential for consistent results.