INTERNAL FRICTION USE IN MONITORING THE DEGRADATION PROCESSES IN A MATERIAL

During the measurement of the fatigue life of material, the specimen undergoes large number of stress cycles. While the observed number of cycles before failure is considered to be the most important result (often the only one), more knowledge can be obtained. Measuring energy consumption of specimen during the cycling, the changes of microstructure of material (especially dislocation structure and crack initialization) can be traced. The evolution of dynamic modulus can be watched on the same equipment. These information becomes very important, especially in the research of gigacycle fatigue strength and fatigue limit below which the continued loading does not lead to structural failure. In this article some remarks on microstructural changes in materials, which can be monitored by nondestructive measurement of internal friction are presented.