Application of acoustoelasticity in studying compressive stress state in Polymer bonded explosive

Abstract

The acoustoelastic technique is a nondestructive technique for analyzing the stress state in materials using ultrasonic waves. The velocities of the ultrasonic waves propagating through Polymer bonded explosive (PBX) change depending on the applied stress (compression or tension). In this paper, PBX specimens at close range of densities and ultrasonic wave velocities under similar initial conditions are applied in the compressive loading tests. Ultrasonic longitudinal wave propagation direction is parallel and perpendicular to applied stress direction respectively. Longitudinal wave velocities are accurately and efficiently achieved by real-time Ultrasonic time differences (velocity) measurement unit. In the range of stress evaluated under compression between 0 and 15MPa, these relations between the relative variation of the longitudinal wave velocity and the applied stress vary linearly. The value of acoustoelastic constant (K) can be determined by the compression tests. These founds suggest the potential of applying the acoustoelastic effect to determine the compressive stress condition of PBX in a certain stress range.

An Ultrasonic Longitudinal Through-Transmission Method to Measure the Compressive Internal Stress in Epoxy Composite Specimens of Gas-Insulated Metal-Enclosed Switchgear

“…The K values of the #1, #2, and #3 specimens are listed in Table 1. The average acoustoelastic coefficient of the GIS epoxy composite using the longitudinal waves vertical to the stress is 4.556 × 10 −5 /MPa, which is smaller than the acoustoelastic coefficient of 96 × 10 −5 /MPa for a polymer-bonded explosive with longitudinal waves perpendicular to the stress [18], and slightly larger than the acoustoelastic coefficient of 2.68 × 10 −5 /MPa of low-carbon steel using longitudinal waves parallel to the stress [31].…”

“…The length (a) was the same as the thickness of the 126 kV three-phase-in-one-tank type GIS basin insulators. The cuboid specimen has been used for ultrasonic compressive stress measurements in published reports [18,[23][24][25][26]. If the material of the cuboid specimen is uniform, the internal stress in the specimen will be homogeneous [23].…”

“…In this paper, ultrasonic longitudinal wave technology was used to measure the internal stress in epoxy composites. The acoustoelastic equation for ultrasonic longitudinal waves in the case of uniaxial stress is defined as Equation (1) in the following [18]. Equation (1) is applicable to isotropic materials but not for composites.…”

“…They used the longitudinal pulse-echo method to measure the ultrasonic velocity based on the time interval between first and second reflected waves at the back surface. Based on the longitudinal pulse-echo method, Xu et al [18] observed a linear relationship between the longitudinal wave velocity and the compressive internal stress in polymer-bonded explosives, calculated the acoustoelastic coefficient, and measured the internal stress. In this method, the ultrasonic wave velocity was measured based on the propagation time obtained through a phase correlation algorithm, and the strain was obtained using a scanning acoustic microscope.…”