This paper present a wavelet-fractal dimension approach for extracting feature from ultrasonic non-destructive evaluation (NDE) data of a test multilayer adhesive structure specimen. These features are then used to estimate the specimen's bonded quality. When the multilayer adhesive structure undergo ultrasonic NDE, echo from interior layers often overlap severely, causing information from individual layers to be obscured or lost completely. A new idea, using wavelet as the ruler to define fractal dimension, is proposed in this paper, based on self similarity of knowing essence of things from collectivity to part, from macrocosm to microcosm, in fractal theory and wavelet transform. Wavelet-fractal dimension is defined as the sum of high-frequency values of decomposed signals. The fractal characteristics of ultrasonic data are gotten from this dimension. The extracted features displayed are effective to analyze and identify the bonded properties. It is believed that the features extracted via the method outlined in this paper provide considerable promise in the area of the test of multilayered structure.
The nanostructures and nanodevices special fabrication technology including electron beam lithography (EBL), focused ion beam (FIB) technology, microcontact printing (μCP) and nanoimprinting were introduced in this paper. The examples of Y-shape waveguide coupler and high precision nanopattern of China Seal were designed and fabricated based the EBL and FIB technology respectively. Their structures can be characterized by scanning electron microscopy (SEM), scanning tunnel microscopy (STM) and atom force microscopy (AFM) etc. The C60 molecular on a Si (111)-(7×7) surface in variable temperature is deposited and detected by STM. The fabricated pattern and structures results indicated that the novel fabrication and characterization technology is very important and effective tools in nanoscale science field.
Micro-defects inside metal matrix composite structure seriously influence the mechanic properties of materials and can undermine machine operations. In order to detect the micro-defects, we can make use of one of the nonlinear acoustic features, i.e., harmonics, which usually appear together with ultrasound when propagating through a damaged material. Based on the relationship between the harmonics, a method of using nonlinear acoustic harmonic amplitude ratio to distinguish micro-defects in metal matrix composite structure is discussed. The test results show that acoustic features, such as second harmonic excitation efficiency were very obvious for the damaged group samples. The method presented is effective in detecting the micro-defects, which means that nonlinear acoustic waves may provide us a good solution for quantitative evaluation of the early damages in metal matrix composite structure.
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