Studies of Damage Evolution in Advanced Polymer Matrix Composites Subjected to Thermomechanical Fatigue Loading

Di Wu
Department of Engineering Mechanics
University of Nebraska - Lincoln
Advisor:  Dr. Yuris Dzenis

Date:  Wednesday, June 14, 2000
Time:  3:30 p.m.
Place:  W106 Nebraska Hall


Advanced polymer matrix composites in aerospace and other high-technology applications are often subjected to temperature changes. Thermally induced stresses in combination with mechanical stresses cause damage accumulation and degradation of properties of composite parts. In spite of the importance of the thermal loading for many applications, little is currently known on the thermomechanical fatigue (TMF) behavior of advanced polymer composites. The objective of this work was a systematic experimental study of damage evolution in a model advanced polymer matrix composite subjected to mechanical, thermal, and combined thermomechanical loading. Thermomechanical testing was performed with the standard testing equipment as well as with a special TMF testing apparatus, recently developed in the group. A new, transient-parametric method of acoustic emission analysis of damage micromechanisms, developed in the group, was used to monitor damage accumulation under thermomechanical loading. Characteristic acoustic emission waveforms were classified based on the transient analysis and the parametric filters for different waveforms were identified in a parametric space. Transferability of the parametric filters between the tests conducted under different environmental conditions was examined and validated. Composite damage modes for the characteristic waveforms were identified. Accumulation histories of different damage micromechanisms were extracted and analyzed for various loading conditions. Models of composite stiffness degradation due to various types of damage were used to predict the modulus based on the classified acoustic emission histories. It was shown that the classified AE histories can be used to predict the stiffness evolution of the laminate subjected to quasi-static and fatigue loading at different temperatures as well as thermomechanical fatigue loading. The results of this research provide better understanding of a complex thermomechanical behavior of advanced polymer composites and can be used in advanced composites design.