Xuan Fuzhen

Evaluation of material damage using nonlinearultrasonic wave

Generally speaking, damages and defects are inevitable with the operating life consuming of engineer structures. Engineer structures would fail or have to retire ultimately when their load bearing capacity is inadequate to accommodate the working load. It has been revealed that, to ensure the safety and reliability of components, it is essential to accurately evaluate the damages and defects during the service process. Frankly speaking, the traditional linear ultrasonic testing technology is not sensitive to micro-defects being large than 0.2 mm, which usually occur perior to 70%–80% of the material life. By contrast, the nonlinear ultrasonic testing based on the technology of ultrasonic harmonic method provides a possible way for the early evaluation of damages and defects. With the outstanding detective effectiveness and efficiency and high sentivitiy to micro-nano defects, such as dislocations, micro cracks, the nonlinear ultrasonic wave technology has attracted much attention in recent years. In this work, the evaluation of material damages using the nonlinear ultrasonic wave technology was reviewed systematically. Firstly, the basic principle of nonlinear ultrasonic wave technology in the detection of material damages was introduced. One-dimensional longitudinal wave was used as an example to describe how nonlinear ultrasonic wave was generated in damaged solids. Secondly, the interation between the propagating nonlinear ultrasonic wave and microstructures was marked. Three kinds of nonlinear utrasonic wave models were introduced, namely dislocation string models, dislocation dipole models and plastic-dependent models. The advantage and disadvantages of the existing models were discussed comparatively. After that, experimental studies on this topic are presented according to different types of material damage, such as tensile (or compressive) plastic damage, fatigue damage, thermal damage, creep damage, adhesive damage and other damages. Experimental results show that the nonlinear ultrasonic wave technique can characterize the degrees of above damages reasonably accurately. Furthermore, the responses of acoustic nonlinearity depended on the type of damages, materials and loading conditions. Finally, further studies on the evaluation of material damages using nonlinear ultrasonic wave technology were proposed, including the interaciton of nonlinear ultrasonic wave with the discontinuous medium, creation of more robust detective methods and signal processing methods, etc.