查看更多>>摘要：Fixed point iteration method for multi-particle unit cell's boundary condition is presented. On the basis of this method, the macroscopic effective material parameters can be obtained from a microscopic point of view. Multi-particle unit cell models containing some important microstructure characteristics of TP-650 titanium matrix composites are established. The real displacement constrained conditions are applied on the multi-particle unit cell using this method, and the mechanical properties and fracture behaviors of the composites under tensile loading are simulated. A good agreement was obtained between the experimental results and the numerical predictions, which verifying the rationality of the FE models based on fixed point iteration method.
查看更多>>摘要：Dynamic failure of brittle materials is a rather complex issue. In this paper, experimental work was carried out for plaster model, to study the crack development features of brittle materials under the action of explosion. It shows that couple medium has great influences on detonation wave type. The water has the cushioning effect on detonation wave, which makes the wave crest truncated and results in low wave amplitude and large wave width. Detonation wave type has apparent influence on failure features of brittle materials, of which larger wave width would keep the wall of exploded hole intact and increase the development length of cracks. The research results would be applied to coal mining to increase the efficiency of gas pumping drainage.
查看更多>>摘要：For developing a unique model in which the rheological performance of fresh concretes from zero-slump to self compacting concrete can be described, it is necessary to define workability in terms of fundamental physical entities. In order to achieve this, the concept of capillary cohesion from science of granular physics has been considered as the first step for investigation. In this paper, focus is on this concept and providing some preliminary achievements of the experimental work. In wet granular material the presence of liquid generates cohesion between particles and affects the mechanical properties of the granular media to a large extent. For the simulation of the behavior of this material by considering pendular state for liquid content, a discrete element method (DEM) is used. The cohesion between a grain-pair is expressed as an explicit function of local geometrical and physical parameters. In this study emphasis is on static and/or quasi-static situations. Since the cohesion dominates over other effects of the liquid, such as viscosity and lubrication, the effect of the size of particles on the cohesion arising from the liquid bridge is investigated explicitly. Based on experimental results, a closed-formula approximation is developed that can be used to calculate the capillary force acting between two glass spheres as a function of the separation distance for a given bridge volume.
查看更多>>摘要：In the present work, the three-dimensional finite element method is used to analyze the propagation criteria for a semi-elliptical crack in a polypropylene pipe under internal pressure. The crack propagation behavior is analyzed by J-integral calculation. The effects of the crack position in the pipe and the loading, as well as the size and configuration of the crack, are examined. The results obtained enable us to deduce that the propagation of a crack depends on several factors.
查看更多>>摘要：The effect of water absorption on tensile strength and fatigue life of the Fiberdux HTA/6376 composite laminated material was experimentally and numerically investigated. For the investigation, a quasi-isotropic and a cross-ply layup were considered. Tensile and fatigue tests were carried out with dry and wet specimens subjected to water absorption up to the water uptake saturation point. Fractographic analyses of fracture surfaces were conducted to detect the type of accumulated damage. To describe the mechanical behavior of the material a FE-based progressive damage model was developed. Material properties used in the model are those of the saturated material evaluated experimentally. Convergent results reveal an appreciable degradation in the ultimate tensile strength and fatigue life of the composite material owing to water absorption.
查看更多>>摘要：Contact damage of curved multi-layered systems, consisting of a brittle zirconia (3Y-TZP)/Alumina (Al_2O_3) coating - prepared by slip casting - on a compliant polymeric substrate from indentation by a hard tungsten carbide sphere is investigated. The essence of this study is to compare the structural performance of layered ceramics, and monolithic ceramic in the brittle coating and compliant substrate of dental crown-like systems. The specimens are loaded at the axis of symmetry. The failure evolution to initiate cracking and final failure patterns in curved multi-layered specimens are compared to those of the single layer specimens of the same thickness and the same study are conducted again with the flat specimens. The onset of fracture is observed in situ using a video camera. It is demonstrated that in all specimens, cone cracking occurs prior to radial cracking, with the latter being defined as the primary mode of catastrophic failure. The multi-layered ZTA (Zirconia Toughened Alumina) specimens prepared by slip casting possessed a distinct final failure pattern in comparison with a single layer specimen. The results of this study provide useful guidelines for building brittle multi-layered coating systems with the functionally graded feature, and complex shapes with geometrical uniformity.
查看更多>>摘要：The polylactic acids (PLA) scaffolds materials have been used to be the scaffolds materials of bone, cartilage gristle, blood vessel, nerve and skin due to its bioactivity, biocompatibility and biodegradable, today, the porous polylactic acid scaffolds had widely applied to tissue engineering. In the paper, the advance in study of microstructure and biocompatibility for this material were summarized. The lack in study of microstructure and compatibility has been pointed out and some viewpoints for further investigations are also made in this paper.
查看更多>>摘要：Anti-fatigue design is a key content in product lifecycle management and there are many factors to affect the fatigue life of parts. For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The mechanics model for assessing the fatigue life of shaft is set up. The assessment method of fatigue life for shaft is set up according to the traditional fatigue life estimation. The effect of wearing parameter to fatigue life is analyzed and the results show that the wear is an important factor to affect the fatigue life.
查看更多>>摘要：The dynamics stress intensity factor of fixed specimen with several notches was analyzed by semi-analytic method. The semi-analytic formula was taken as the interpolation function near notch tip and the degrees of freedom near notch tip were transformed into a small set of generalized coordinates by means of the series expansion formulas of the displacement field. The dynamics stress intensity factor for fixed specimen with two notches or cracks under centralized loading and well-proportioned loading was obtained. The results show that the K_Ⅰ and K_Ⅱ are existed at the same time for fixed specimen with several notches under dynamics loading.
查看更多>>摘要：Two-dimensional (2D) finite element analyses have been carried out to study the crack opening displacement and stress intensity factor of a cracked centre-hole plate. With the different interference levels (2%, 4%, 6% and 8%) and acted by residual stress caused by cold expansion, the crack opening displacement, the stress intensity factor and J-integral around the crack tip is presented. With the different interference levels and acted by different applied loads , the crack opening displacement, the stress intensity and J-integral around the crack tip is also presented. The results of the 2D FEM analysis show, 1) with the different interference levels and acted by residual stress caused by cold expansion, the crack mouth is throughout closed and the middle part is open, but the opening displacement is constant; 2) under some applied loads, with the interference levels up, the stress intensity factor on the crack tip and J-integral, become weak gradually, then they keep constant values; 3) with the interference increases, the stress intensity factor and J-integral decreases. When the interference increases a certain value, the stress intensity factor and J-integral do not decrease and keep constant values.
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