Evaluation of damage evolution in ceramic-matrix composites using thermoelastic stress analysis

Thermoelastic stress analysis (TSA) has been used to monitor damage evoluti on in several composite systems. The method is used to measure full-field h ydrostatic stress maps across the entire visible surface of a sample, to qu antify the stress redistribution that is caused by damage and to image the existing damage state in composites. Stress maps and damage images are cons tructed by measuring the thermoelastic and dissipational thermal signatures during cyclic loading. To explore the general utility of the method, test samples of several ceramic-matrix and cement-matrix composites have been fa bricated and tested according to a prescribed damage schedule. The model ma terials have been chosen to illustrate the effect of each of three damage m echanisms: a single crack that is bridged by fibers, multiple matrix cracki ng, and shear bands. It is shown that the TSA method can be used to quantif y the effect of damage and identify the operative damage mechanism. Each me chanism is identified by a characteristic thermal signature, and each is sh own to be effective at redistributing stress and diffusing stress concentra tions. The proposed experimental method presents a new way to measure the c urrent damage state of a composite material.