Papers by Keyword: Microcrack

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Authors: Jing Feng Guo, Ren Gen Xu, Li Zhao, Wen Zhu Shao, Lian Jie Qin
Abstract: Initiation and propagation of micro cracks in the Fe-25Cr-35Ni based superalloy were observed and investigated through in situ tensile test in SEM using a single-edge notched specimen. The results show that the micro crack sources may easily occur with one of those, the second phase particles and matrix interface, and the stress concentration region. The micro-cracks which propagated at first for those that are perpendicular to the tensile load would be growing up and connected mutual with the increase of external stress until forming the main crack. While the length of the mail crack enlarged enough in the specimen, it become instable for the main cracks and the fracture occurred rapidly.
Authors: Bing Zhang, Masato Yoshioka
Abstract: A three dimensional finite element model for Vickers indentations on brittle materials is presented in order to analyze the stress distribution. The objective of this paper is to study when and where cracks are most likely to initiate and propagate in the indentation cycle based on the analyzed stresses. Therefore the time-dependent stresses around and below the surface of the contact area during the indentation cycle, especially at the end of loading and at the beginning of unloading phase are investigated in detail. The analytical results are shown to be in good agreement and verified with the experimental results.
Authors: Wei Bo Li, Osamu Umezawa
Abstract: The characterization of subsurface fatigue crack initiate sites of near α and α-β types titanium alloys and their cracking models proposed were reviewed. The crack initiation sites consisted of facets mostly on near basal plane of α grain, although the crystallographic orientation and surface topography of the facets presented a subtle difference. The crack initiation mechanisms were a quasi-cleavage accompanying high normal stress on the plane, a combination of basal slip and normal stress across the basal plane, and a pure slip on facet plane inclined near 45 degree to loading axis.
Authors: Guo Shuang Shui, Yue Sheng Wang, Jian Min Qu
Abstract: In this paper, a new theoretical model is developed to characterize the damage of the adhesive joint. Elastic modulus of adhesive joints is an important parameter to represent damage characteristics. Based on the fact that the thickness of the adhesive layer is very small, it is reasonable to believe that damage will decrease the tension modulus of the adhesive joint while the compression modulus will keep unchanged. Modeling the adhesive joint as an interface with different modulus in tension and compression, and applying integral transform method, we solve the associated nonlinear boundary problem to obtain the nonlinear ultrasonic waves transmitting through the adhesive layer. With this nonlinear ultrasonic wave, variation of elastic modulus and damage variable of the adhesive layer are thereafter characterized nondestructively by a nonlinear coefficient.
Authors: Oleg Bashkov, Roman Romashko, Sergey V. Panin, Tatiana Bashkova
Abstract: The paper presents the results of studies the deformation behavior of aluminium alloy D16 by acoustic emission (AE) method. The purpose of this study was to establish the deformation stages and deformation mechanisms at each stage. Studies were carried out on the samples of aluminum alloy D16 (analog 7075). This paper contains a method for the separation of AE signals. The method of AE sources identification based on the the two-parameter distribution analysis (frequency parameter Kfvs energy of AE signals). The frequency parameter Kf is based on wavelet transform of AE signals. Two-parameter distribution allows one to separate the AE signals emitted by dislocations from the signals of micro cracks. The investigation results allowed the various deformation stages to establish by the different types of AE signals. By the AE analysis shows the dislocation mechanism of hardening the aluminum alloyD16. The paper presents the results that characterize the influences of heat treatment and structural condition of aluminum alloy on the AE parameters.
Authors: Kang Zhao, Qun Yan Jia
Abstract: Based on extremely complex geological characteristics of metal mines, a mining model was built up, and from the micro - meso - macro point of view, relationship between rock AE and failure characteristics of overlying rock mass was studied and AE is divided into four stages. From the view of AE energy and distribution, the generation location, shape and size of caving of overburden rock was predicted. Through studies on the difference of goaf size, the author obtained the displacement variation and failure characteristics of metal mine overburden rock under tectonic stress, self-weight stress and dynamic mining conditions.
Authors: Jian Fu Shao, F. Bourgeois, O. Ozanam
Authors: Yun Zi Cai, Chih Hsiung Shen, Shu Jung Chen
Abstract: A new idea of improving complementary metal-oxide-semiconductor (CMOS) thermopile performance is introduced to reduce the thermal conductance by leading the microcracks into structure of thermopile, which greatly increases the heat flow barrier. A highly sensitive infrared detector requires a low thermal conductance to maximize the temperature change and signal induced by incident IR radiation. Several designs of infrared microsensors are proposed to study influential parameters from microcrack for improving performance of thermopile. To that end, by using some adequate designs of polysilicon architecture, we can greatly reduce the heat flow from the main stream without introducing further electric resistance, which is related with noise. Firstly we develop such a structure of thermopile with low thermal conductance and high performance by using CMOS compatible process which can be easily and exactly fabricated. The suspended structure of infrared sensors is used in this study to provide ideal, thermally isolated, structures for support of the thin film detector. We also simulate the heat flow of the new structures. The results show good match with our original idea.
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