Key Engineering Materials Vols. 385-387

Abstract: Accelerated thermal cycling (ATC) tests were conducted to investigate an effect of thermal cycle conditions on thermal fatigue life of a chip size package (CSP) lead-free solder joint. A ternary Sn-Ag-Cu alloy was used as a lead-free solder material. For frequency of thermal cycle (1~3 cycles/h) and maximum (388~423 K) and minimum (223~273 K) temperatures investigated, the effects of them on thermal fatigue life of the solder joint were slight. On the contrary, correlation was recognized between temperature amplitude and thermal fatigue life of the solder joint. The thermal fatigue life increased with decreasing temperature amplitude. The relationship obeyed the Coffin-Manson’s type equation.

Abstract: The objective of this study is to develop inelastic displacement ratio for calculating peak inelastic displacement of SDF systems. The inelastic displacement ratio is defined as the ratio of peak displacement of inelastic SDF system to the peak displacement of corresponding elastic SDF system. Statistical studies are carried out to estimate median inelastic displacement ratios and those dispersion of bilinear SDF systems with given yield-strength reduction factors, natural periods, post-yield stiffness ratios and damping ratios ranging from 1 to 20% when subjected to 60 earthquake ground motions recorded on stiff soil sites. This study shows that equal displacement rule overestimates the peak inelastic displacement of the system which has a fundamental period ranging from the intermediate to long period. It is also observed that no significant difference was observed in the value of median inelastic displacement ratio across site classes.

Abstract: Zirconium oxide doped with scandium oxide is one of the most promising materials for electrolytes of solid oxide fuel cells because of its high ionic conductivity. In this study, temperature dependence of mechanical property, especially strength, of 9 mol% scandia doped zirconia polycrystalline samples with 0 to 30 wt% of alumina additions was examined at temperatures from 293 to 1273 K. Ionic conductivity was also measured by AC impedance analysis. From both mechanical and electrical standpoints, the experimental results were discussed in terms of alumina addition.

Abstract: In this paper a micromechanics-based design is proposed for the development of a material with enhanced ductility and flexural strength combined with low production cost. The composite performance is described by 11 micromechanical properties of the system consisting of cement matrix, fibres and fibre-matrix interface. Most of these properties are defined through laboratory tests. A strain-hardening behaviour with multiple microcracks prior to failure is is the goal for the composite with enhanced ductility. The amount and size of the fibres needed for bridging the microcracks as well as the composition of the cement matrix will be determined in order to achieve this behaviour.

Abstract: Semi-elliptical shear-mode fatigue cracks were promoted in the axial direction of round specimens of SAE52100 bearing steel by fully-reversed cyclic torsion tests under a static axial compressive stress. Non-propagating cracks smaller than 1 mm were obtained in two ways; (i) stress amplitude decreasing tests of notched specimens, or (ii) constant stress amplitude tests of smooth specimens. The threshold stress intensity factor ranges, (KIIth and (KIIIth, showed a crack size dependency.

Abstract: In this paper, molecular dynamics method has been employed to model mode I crack propagation in body center cubic (BCC) single iron crystal. To maximize the simulation efficiency the parallel computing was performed. Six cases with different lattice orientations have been simulated to investigate the crack propagation behaviors at atomic level. The strain distributions have been calculated to indicate the density of dislocation. It has been found that the lattice orientation significantly affects the propagation behaviors. The crack in BCC iron propagates more readily along the direction <111> on the plane {1-10}.

Abstract: The defects in crystalline materials significantly affect the fracture behaviors. In this paper molecular dynamics (MD) model using a potential of embedded atom method (EAM) has been developed to investigate the effect of the major crystalline defects, stacking fault and edge dislocation, on the crack propagation in Fe crystal. Six cases with different locations of stacking fault and edge dislocation have been studied. The strain distribution in lattice aggregate was heterogeneous. The dislocations were observed slipping along directions [100] and [-100] on the plane (100). Simulation results showed that the location of the stacking fault and edge dislocation significantly influenced the crack propagation speed.

Abstract: The pore properties of the porous material are important factors influencing the vegetation to grow. The pore properties of an artificial planting material and soil were studied by a mercury intrusion test. Based on the fractal concept of Menger-sponge, the fractal dimensions characterizing pore volume-size distribution of planting material and soil are obtained from the experimental data, and the different of both of the fractal dimensions is compared. The testing results show that the total porosity of planting material varies from 30.27 % to 32.11%, and the total porosity of soil is 24.87%. The law of their pore volume-size distribution in different range of pore-size is identical. The fractal research exhibits that the fractal dimensions have a different value in all the range of pore-size for planting material or soil, and small fractal dimension corresponds to small pore-size. As compared with soil, the fractal dimension of planting material is larger slightly in range of small pore, and is same basically in range of micro and medium pore. These results indicate that the fractal dimension is a useful measure of pore grading, which divides the pore into four groups with micro pore, small pore, medium pore and large pore. And the pore properties of eco-material for erosion control of slope are helpful to the vegetation growth.

Abstract: The goal of this paper is to generate the stability maps for an elastic cracked beam resting on elastic soils and loaded by a constant distribution of sub-tangential forces. The soil behavior is simulated by a two-parameter Pasternak model. Firstly, the extend version of the Hamilton principle is used to formulate the weak form of the governing equation for the undamaged beam problem. Secondly, a finite element procedure, in which the effect of an open surface crack is computed via the Line-spring model, leads to the discrete governing equation for the cracked beam. Finally, the effect of several parameters on divergence or flutter instability, such as the crack depth and location, the non-conservativeness of the applied load as well as the stiffness of the two soil parameters, is highlighted.

Abstract: The conductive behavior of asphalt concrete can be improved with the addition of conductive materials, thus a multifunctional asphalt-based composite can be obtained. The conductive asphalt-based composite modified by graphite was studied extensively. Conductive materials percentages may have influences on performance of asphalt mixture. The performance of an asphalt pavement is significantly affected by its resistance to permanent deformation and its fatigue performance. The paper presents the results of a project aimed at investigating static and dynamic response as cracking and fatigue behaviors of conductive asphalt-based composite using the ITT. In particular ITT were performed in which the graphite percentages, loading mode was varied. As test results indicate that the addition of graphite shows positive influence on the indirect tensile strength, failure stiffness modulus in static loading test, especially in high loading speed. The number of load cycles to fatigue failure presents a bit decrease with graphite percentages in dynamic loading test. After adding discontinuous carbon fibers, conductive asphalt-based composite shows good fatigue property, which can prevent crack propagation. It can be concluded that the combined modification brings reinforcement effect to asphalt concrete and improves its mechanical and fatigue properties.