Key Engineering Materials Vols. 324-325

Abstract: To find out the effect mechanism of technological parameters on the performance of fiber coupler, the relationship between the technological parameters and the optical performance is investigated by using a six-axes optical fiber coupler machine as experimental setup. It is discovered that the technological parameters such as drawing speed and fused temperature have a great effect on optical performance of fibre coupler. The fused region and taper region of fiber coupler are tested with scanning electron microscope (SEM). It is discovered that there are crystalline grains in the fused region. And the crystalline grains decrease while drawing speed increase. In the taper region, there are micro cracks. And the cracks are more obvious while drawing speed increases. When the fused temperature is above some point (here is 1350
), the micro cracks in the taper region disappear and the optical performance of fiber coupler is the highest at this time.

Abstract: Three kinds of materials, pure aluminum (Al1050), carbon steel (S25C) and eutectoid steel (NHH) with V-notch are used in this study to compare the effect of roller working on the fatigue properties among the test materials. As the result, all of the fatigue strengths are improved after roller working and the optimum deformation values exist for every test materials. Fiberized microstructure at the notch bottom, work hardening and compressive residual stress caused by roller working are considered as the main reasons for the fatigue strength improvement. The highest fatigue strength improvement of Al1050, S25C and NHH was 30%, 118% and 155%, respectively. The optimum fatigue improvement of NHH is the highest and it is much higher than that of Al1050, and the optimum deformation value of Al1050 is much lower than that of the other materials. Moreover, the roller working effect is much remarkable for the materials with better hardenability.

Abstract: Based on the understanding of passive impact of crack induced by fatigue load on ultimate stress and the relation of material strength and elastic modulus, the paper gives expression of residual elastic modulus with the form of cumulative damage and analyzes its digital character. The reliability index is calculated by using advanced first order second moment reliability method and the stochastic finite element method because the structures are stochastic, the significant failure modes are identified by using the advanced branch and bound method, and the reliability of structural system is evaluated by PNET method. A numerical example is indicated that the fatigue reliability index of structural system can fulfils the demand of fatigue reliability in the design life, but the stiffness reliability index of structural system descends with the increase of the service life, and the stiffness reliability index can not fulfils the demand of the design when life over one third of the whole service life, it shows that the cumulative damage influence to structural stiffness reliability analysis can’t be ignored.

Abstract: Because there were many random factors, the failure analysis and reliability analysis of stochastic structural system was very difficult. In this paper, failure procedure and reliability analysis flow chart of stochastic structural system based on stochastic finite element were present. Establishment of the safety margin, reduced member stiffness matrix and opposite sign of the equivalent nodal force was analyzed in the failure process. Stochastic finite element method was adopt to solve the structures’ stochastic, and the reliability of structural system is evaluated by PNET method. According to probabilities of the failure paths redound to probability of failure of the structural system, the most significant failure paths was determined on the basis of the branch-and-bound method. Then, a classical 48-bar space truss problem is made as an example to illustrate the predominance of this algorithm, the calculation shows that the analysis of the failure process is justified; this methodology is efficient and useful for reliability analysis of large stochastic structural system.

Abstract: In this paper, deformation behavior of the MEMS gyroscope package subjected to temperature change is investigated using a high-sensitivity moiré interferometry. Temperature dependent analyses of warpage and extension/contraction of the package are presented. Detailed global and local deformations of the package by temperature change are investigated and its effect on the frequency shift of the MEMS gyroscope is studied.

Abstract: In this paper, mechanical reliability issues of copper through-wafer interconnection are investigated numerically and experimentally. Several factors which could induce via hole cracking failure are investigated such as thermal expansion mismatch, via etch profile, copper diffusion phenomenon, and cleaning process. Improvement methods are also suggested.

Abstract: Manifold Method provides a unified framework for solving problems with both continuous and discontinuous media. In this paper, by introducing a criterion of crack initiation and propagation, the second order manifold method is used to simulate two-hole blasting and Hopkinson spalling of rock. In the study of two-hole blasting, two different initiation conditions are considered. One is simultaneous initiation, the other is 0.1 ms delay initiation. The whole blasting process including crack initiation, crack growth and fragment formation is simulated. In the study of Hopkinson spalling, the propagation and interaction of stress waves and the spalling process caused by a reflected tensile stress wave are reproduced. The simulation results including the thickness of the formed scab and its velocity are in good agreement with theoretical values. Manifold method proves to be an efficient method in the study of dynamic fracture of rock.

Abstract: A crack propagation perpendicular to gradient in a large scale functionally gradient materials, which has (1) a linear variation of Young’s modulus with a constant mass density and Poisson’s ratio, and (2) a exponential variation of Young’s modulus with a constant mass density and Poisson’s ratio, is modelled by finite element methods. Based on the experimental result of large scale functionally gradient materials, the dynamic propagation process of the FGMs is modelled and the dynamic parameters, like the energy release rate and crack tip opening angle, are calculated through a generation phase.

Abstract: Concrete is taken as three-phase composites consisting of aggregate, interface and mortar matrix in the paper. The tensile strength and elastic modulus of each phase material are assumed to obey Weibull distribution. A few random aggregate and random parameter models are generated by Monte-Carlo method. Tensile failure of micro element is described by tension damage model, in which the stress will be reduced linearly after the stress reaches the maximum tensile strength. The results show that more cracks of lower homogenous specimens are observed than those of higher homogenous specimens. The phenomenon of discontinuous cracking is observed in the former, while strain localization and brittle behavior is observed in the latter. The ultimate load obtained in the numerical simulation agrees well with that of the test.

Abstract: A two-dimensional electromechanical analysis is performed on a transversely isotropic piezoelectric material containing a crack based on the impermeable electric boundary condition. By introducing stress function, a general solution is provided in terms of triangle series. It is shown that the stress and electric displacement are all of 1/2 order singularity in front of the crack tip. In addition, the electromechanical fields in the vicinity of the crack when subjected to uniform tensile mechanical load are obtained using boundary collocation method.