Department of Mechanics: Seminar: Abstract Qu

Nonlinear Ultrasonic Methods for Nondestructive Damage Assessment in Structural Materials

Ultrasonic nondestructive evaluation (NDE) techniques have been used extensively for inspecting and monitoring various engineering structures and components. The vast majority of these ultrasonic NDE techniques utilize only the linear behavior of the ultrasound. These linear NDE techniques are effective in detecting discontinuities in the materials such as cracks, voids, interfaces, inclusions, etc. However, they are incapable of 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 metallic materials subjected to fatigue loading, and in cementitious materials under alkali-silica reaction (ASR) conditions. In this talk, we will first present the general principles based on which various nonlinear ultrasonic NDE techniques can be developed. We will then describe examples of using nonlinear NDE method for assessing fatigue damage in metals (aluminum, steel, nickel-base superalloys, etc.), and ASR-induced damage in concrete. Our results clearly show that nonlinear ultrasonic measurements can provide quantitative inputs to determine the material state and measure damage in structural materials.

Jianmin Qu, Walter P. Murphy Professor in the McCormick School of Engineering and Applied Science at Northwestern University, received his Ph.D. in Theoretical and Applied Mechanics from Northwestern University. Before joining the faculty at his alma mater in 2009, Professor Qu was on the faculty of the School of Mechanical Engineering at the Georgia Institute of Technology from 1989 to 2009. Professor Qu’s research focuses on several areas of theoretical and applied mechanics including micromechanics of composites, interfacial fracture and adhesion, fatigue and creep damage in solder alloys, thermomechanical reliability of microelectronic packaging, defects and transport in ionic solids with applications to fuel cells and batteries, and ultrasonic nondestructive evaluation of advanced engineering materials. He has authored/co-authored two books, 10 book chapters and over 150 refereed journal papers in these areas.