Experimental and Numerical Sizing of Delamination Defects in Layered Composite Materials

Abstract

A methodical approach to the estimation of the localization zone and geometric parameters of delamination defects in layered composite materials is discussed. It is based on mathematical processing of the experimental results of deformation measurements obtained with a grid of fiber-optic sensors. The results of methodological developments related to the determination of the optimal topology of the grid of sensors are shown to ensure the detection of defects of a given size with the necessary accuracy and determination of their parameters. Methods for computational analysis and simulation of the strain-stress state in the defect zone based on the algorithm used for modeling the problems of strain-stress analysis in the defect zone using 2D finite elements instead of 3D ones are reported. These procedures allow one to use models of lower dimensionality while retaining all the features of the strain-stress state. The results of methodological developments related to the determination of the defect parameters from the results of strain measurements using the methodology of solving the inverse problem are shown. This methodology is based on solving the problem of minimizing the discrepancy between the vector of deformation response and the vector of initial parameters. The technique is implemented as software consisting of a series of macros for ANSYS and programs for MATLAB. The results of cyclic testing of a sample made of a multilayer composite material with a delamination type of defects are presented. The increment in the defect size upon loading is estimated by the mathematical processing of data recorded by fiber-optic strain sensors glued on one of the sample surfaces based on the solution of the inverse problem. Comparison of the results of calculations of geometric parameters of the defects with the measurement data obtained by the method of ultrasonic flaw detection shows good agreement between them.