Development of a mathematical model for propagation of ultrasonic waves in thick-walled cylinders in the presence of a thermal gradient - Case of axial scanning.

Investigation of variations in ultrasonic wave velocity and travel path in the presence of thermal gradient is essential for accurate ultrasonic testing of engineering components which are subjected to high temperatures. In this paper, a mathematical model is developed for calculation of the wave velocity and travel path in thick-walled hollow cylinders that are subjected to thermal gradients during axial scanning. The cylinder is assumed to be homogeneous, isotropic, and made from Structural steel. The independent variables are incidence angle, cylinder outer radius, and temperature of the cylinder's inner surface. The results obtained from the theoretical model indicate that the wave velocity and travel path are highly sensitive to inner-surface temperature of the cylinder. Moreover, at incidence angles much lower than critical angles (especially at low temperatures), the wave velocity is almost independent of the incidence angle and the travel path is very close to a straight line. However, as the incidence angle approaches one of the critical angles, the wave travel path considerably deviates from a straight line. An experimental setup was designed and built in-house for measuring the longitudinal wave velocity in a steel hollow cylinder in the presence of a thermal gradient. The preliminary experimental results were found to be in good agreement with theoretical results.

A review of ultrasonic testing applications in additive manufacturing: Defect evaluation, material characterization, and process control.

Ultrasonic testing (UT) techniques are highly capable of detecting defects in engineering components. The present manuscript intends to review the ultrasonic testing techniques applied to additive manufacturing products; either in-situ or offline. While the in-situ applications of ultrasonic testing to additive manufacturing are more favorable, literature holds a few research works on this topic. On the other hand, most of the works reported on ultrasonic testing of additive manufacturing products deal with offline applications. In many of these works, samples with artificial defects are prepared and tested through ultrasonic testing techniques including laser ultrasonics, phased arrays, guided waves and immersion ultrasonic testing. These UT methods and their applications in damage detection of additive manufacturing products are discussed in detail. Moreover, the codes and standards which are currently being developed for ultrasonic testing of additive manufacturing products are introduced. The choice of UT methods in detecting defects and material characterization in additive manufacturing is found to be highly dependent on the manufacturing process and capabilities of UT techniques.

Nondestructive evaluation of explosively welded clad rods by resonance acoustic spectroscopy.

A resonance acoustic spectroscopy technique is assessed for nondestructive evaluation of explosively welded clad rods. Each rod is modeled as a two-layered cylinder with a spring-mass system to represent a thin interfacial layer containing the weld. A range of interfacial profiles is generated in a set of experimental samples by varying the speed of the explosion that drives the copper cladding into the aluminum core. Excellent agreement is achieved between measured and calculated values of the resonant frequencies of the system, through appropriate adjustment of the interfacial mass and spring constants used in the wave scattering calculations. Destructive analysis of the interface in the experimental specimens confirms that key features of the interfacial profile may be inferred from resonance acoustic spectroscopy analysis applied to ultrasonic measurements.