Passive Thermography for Detection of Damaging Events during Quasi-Static Tensile Testing

Abstract

In order to determine the material properties of anisotropic continuous fiber-reinforced polymers, such as stiffness and strength, quasi-static tensile tests are carried out, in which the test specimen is subjected to a controlled load until failure. In opposite to ductile metals, exact localization of the failure on the test specimen or observation of the initial or final failure in time is not possible because of the brittle failure mechanism. The sample often breaks down into many small fragments. In order to get a deeper understanding of the failure behavior and to optimize the material and the design of the specimen, a characterization of the damage progress under load by passive thermography was implemented. This is a suitable method for the detection of near-surface defects and provides very promising results, especially in combination with sophisticated evaluation methods of active thermography. An important influencing factor is the analysis of the amount of energy released during a micro-damaging event. In this paper, we show an approach to increase the contrast of single damaging events and a possibility to visualize the damaging progress, especially for near-surface defects. The measurements were realized with continuously fiber-reinforced materials.