Nonlinear Ultrasonic Methods for Nondestructive Damage Assessment in Structural Materials
Professor Jianmin Qu, Tufts University
Ultrasonic nondestructive evaluation (NDE) techniques have been used extensively for assessing various engineering structures and components. Most existing ultrasonic NDE techniques utilize the linear behavior of ultrasound. These linear NDE techniques are effective in detecting discontinuities in the materials such as cracks, voids, interfaces, inclusions, etc. However, they are less effective in assessing the state of damage before visible cracks are formed. On the other hand, our recent work has demonstrated that nonlinear ultrasonic NDE techniques offer the potential to characterize and quantify early stages of damage in structural materials.
In this talk, I will first introduce recent models that relate the measured nonlinear ultrasonic signals to pertinent microstructural parameters that characterize the state of damage in structural materials. This will be followed by discussions of several ultrasonic measurement techniques including the generation of second harmonic and nonlinear wave mixing. The talk will conclude with several case studies involving fatigue damage in high-strength superalloys, radiation damage in stainless steels, plastic deformation in aluminum alloys, ASR-induced damage in concrete, etc. These studies clearly demonstrated that nonlinear ultrasonic measurements provide quantitative inputs to determine the material state and measure damage in structural materials.