In this work, a general expression of the thermo-acoustic (TA) emission from nanocrystalline porous silicon (nc-PS) is derived by using a fully thermally-mechanically coupled multilayer TA model. This expression takes thermal, mechanical, and geometry properties of every layer in a multilayer structure, as well as the thermal contact resistances between layers into consideration and hence agrees well with the experimental results. Therefore, many fundamental problems in thermally induced ultrasonic emission from nanoporous silicon can be studied.

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Defects in the specimen of missile engine shell was detected by thermal wave image technology in this paper. In order to gain intuitionistic and accurate space structure image of the detected object, subtracting background and high-frequency emphasized filtering method were used to enhance the image quality. Then the defect was segmented from the background using particle swarm fuzzy clustering algorithm, while the defect size and depth were identified quantitatively. On this basis, 3D reconstruction of the defect by thermal wave image was recognized by Volume Rendering method. The results show that the precision of the defect quantitative identification is higher, and 3D reconstruction result is well, which help us to observe the location and size of defects intuitionisticly.

In this paper, the ultrasonic infrared thermography (UIT) technique was applied to detect the composites damage. The frictional heating and thermal conductivity at the location of crack of the composites under ultrasonic excitation was simulated by finite element method (FEM). The excitation parameters including time, amplitude and frequency were studied. The composite involving delamination was detected by the ultrasonic generator. The results show that the UIT can identify the contacting interface-type damages at the surface or subsurface of composites rapidly, for example, delamination, fatigue crack et al.The excitation time, amplitude and frequency are impotent detection parameters. It can be seen accurately and intuitively of location of the damage, and there is no uniform heating problems from the experiment. Suitable coupling material can improve testing quality and eliminate “standing wave” effectively.