The Shape of Mechanical Hysteresis Loops for Metals Under Harmonic Loading

Abstract

Abstract Previous experimental investigations (direct and indirect) on the shape of hysteresis loops have been carried out at stress amplitudes that exceeded the fatigue limit, that is, under conditions of active fatigue damage. The experimental procedure used in the present research provides higher resolution than the earlier work and permits investigations at stress amplitudes below the fatigue limit. For the objective estimation of the shape of a hysteresis loop several criteria were proposed and the most effective criterion was chosen. Metals with distinctly different levels of damping were tested. The tests were carried out at resonance bending frequencies. As a result of both analytical and experimental investigations it was shown that hysteresis loops for metals with a high level (Cu-Al alloy, maximum decrement 1.4 × 10−1) and a moderate level (EI-961 alloy steel, maximum decrement 8.7 × 10−3) of damping are close to elliptic in shape. The error of the experimental procedure was too great for testing an alloy with a low level of damping (PT-5 titanium alloy, maximum decrement 1.5 × 10−3). The tests on the PT-5 alloy allowed the investigators to ascertain only that the loop's shape in this case is more elliptic than crescent-shaped or parabolic.