Analysis of strain-amplitude-dependent internal friction in thin-layer materials

Abstract

Abstract Internal friction in aluminium thin films on a silicon substrate has been measured as a function of strain amplitude by means of a free-decay method of flexural vibration. Procedures for analysing the strain amplitude dependence of internal friction in thin-layer materials are presented, firstly for evaluating the internal friction in the film separately from the measured damping of the composite system, and secondly for converting the internal friction in the film into the plastic strain as a function of effective stress on dislocations. The stress-strain responses thus obtained for the aluminium films show that plastic strain of the order of 1019 increases nonlinearly with increasing stress. The microflow stress at a constant level of plastic strain is inversely proportional to the film thickness, which agrees with the variation in the macroscopic yield strengths.