Determination of acoustoelastic/acoustoplastic constants to measure stress in elastic/plastic limits by using LCR wave

Abstract

This experimental study aims to investigate the ability of the ultrasonic method (UM) by using critically refracted longitudinal (LCR) wave for measuring stress in both elastic and plastic limits. In so doing, nine tensile test specimens are used. In order to send and receive the LCR wave into the specimens, the investigation led to design two different types of ultrasonic fixtures (constant fixture and variable fixture). The constant fixture, used to evaluate and compare the results of variable fixture. Three initial distances (0, 30, 50 mm) employed for variable fixture to detect the accurate results and compare with the constant fixture. To determine acoustoelastic and acoustoplastic constants different amounts of stress are applied to the specimens using uniaxial tensile testing machine. Measurement of longitudinal applied stress by UM is done by using 2 MHz probes based on Acoustoelasticity. The results of the study indicated that there is a significant relation between stress and time of flight wave in both elastic and plastic limits. For the first time, this study shows that entering the plastic limit takes tremendous sensitivity. By using variable fixture (without initial distance) enable the process to evaluate stress in the plastic limit accurately. The outcome of the study provides three acoustoplastic and three acoustoelastic constants. All of these constants, by increasing the initial distance between two parts of the variable fixture will reduce. In other words, the comparison between different initial distance tests indicates that increasing initial distance caused to less accuracy of measuring stress.