Applied Mechanics and Materials Vols. 48-49

Abstract: This paper describes two methods of Fiber Bragg Grating (FBG) embedded in the three-dimensional (3D) braded composite materials and acoustic emission health monitor for 3D braided composite materials condition. The paper mainly analyses the relations of FBG change and the inner straining under the stretching on materials. It is provided that the way of signal collection and processing. The experimental results proved that FBG sensors have exceptional sense characteristic. The braided angle of composites has a little influence on FBG signal. FBG embedded in the 3D braided composite materials has not more effect mechanical property of materials. According to two health monitoring methods and the particularity of 3D braided composites, the health monitoring method based on FBG much more applies to dynamic monitoring on 3D composites special field. This research provides basis for the study and application of advanced intelligent composites.

Abstract: This paper discusses the application and experimental method of acoustic emission for the three-dimensional (3D) braided composite material under flexural testing. It describes the feature of acoustic emission when applied to three-dimensional braided composite material under flexural testing. In order to know the materials damage position precisely, it is very important to collect the signal of acoustic emission source. The results of flexural experiment show that it is precise on the research of acoustic emission source location by the method of wave form analysis .During the collecting signal of acoustic emission , it is compared between parameter analysis and wave form analysis. According to the attenution degree of signal, it is selected signal of acoustic emission source exactly. It is the method to extract the precise acoustic emission signal by the different algorithm of wavelet analysis. We know that humans have been using materials by testing activities support, these tests have developed several centuries. From the traditional rough test to support materials and materials used in all aspects of science and technology, modern, scientific program, at present, there are mutual dependencies between the progress of scientific knowledge and the development of test methods. The 3D braided composite material is a kind of complex structure. Because of the many components and weaving material preparation process characteristic, material mechanics behavior is very complicated. It is characteristics of the 3D braided composite material, that the application on composites is widely more and more. The 3d braided composites have been used widely in aerospace, aviation, transportation, chemical, sports, medical care and other fields, so it is extremely vital significance for research on mechanics performance analysis of 3D braided composite material. Current studies of damage fracture behavior of composite materials are used in homogeneous materials research methods, namely the mechanical test and microscopic observation, but the research cannot distinguish and identify different damage fracture source, due to the combination of mechanical test parameters of the complex fracture micro-mechanism not sensitive. Microscopic observation is in fact observation later, local fracture surface morphology research, so can not observe the interaction of numerous fracture source and micro behavior, and can not study in the character of fracture source of composite materials, therefore the source faults already can not adapt to the traditional methods of composite material damage fracture process. From external or internal force effect material and structure produced deformation or fracture with elastic wave form, the strain energy release phenomenon called acoustic emission or stress wave [1]. Acoustic emission testing method is a kind of material internal defects or potential defects in the dynamic changes in movement, the damage detection method is real-time monitoring and can reflect the characteristics of acoustic emission sources in the load of the dynamic response. The AE information can directly reflect defects and changes [2, 3].

Abstract: A fault diagnosis based on bond graph model is proposed for hydraulic variable pitch system. Because the knowledge representation of bond graph model can provide information of cause and effect between components, a bond graph model of hydraulic variable pitch system is given above rated wind speed. A fault tree, using cause and effect analysis by back propagation, is developed. Qualitative value of parameters is assigned and the fault source is detected by analyzing boundary parameters of fault tree. Comparing with quantitative fault diagnosis based on model, the bond graph fault diagnosis is more flexible and has good completeness.