Key Engineering Materials Vols. 452-453

Abstract: Carbon composites have good mechanical properties and preserve the inherent excellent biocompatibility of carbon, which make them great potential as orthopedic implants in human body. The present work reviews the biocompatible behavior and research situation of such materials for medical application. The mechanical properties, interface and surface modification problem of carbon composites are discussed in detail. Finally, the medical prospects and some problems needed to be solved of carbon composites are put forward.

Abstract: In this paper coupling damage behaviors of Liquid Rubber Based Concrete (LRBC) are studied experimentally. Compressive fatigue and impact alternant loading tests were carried out on cylindrical LRBC specimens. The elastic moduli were recorded before and after fatigue and impact tests. The quasi-static compressive stress-strain curves after fatigue and impact tests were obtained. According to the definition of dissipated energy, the cumulating of dissipated energy was used to define damage. The analysis on impact and fatigue damages during the loading processes show that fatigue and impact loading lead to the formation and development of inner damage. During the alternant loading process, impact and fatigue damages are coupled mutually, with the former affects the evolution of fatigue damage evidently.

Abstract: Based on Ježek method of computing the elastic-plastic buckling of the member under the axial compressive load and the bending moment, the analytical expressions of calculating the ultimate load of buckling about the neutral axis with the moment of inertia for a square steel tube column are derived. By degenerated into the analytical expressions of the rectangular column and compared with the values of the finite element analysis (FEA) method, it shows that the analytical method in this paper is valid, which provides a new method of theoretical study for the elastic-plastic buckling of the member.

Abstract: This paper aims to investigate the evolution of aggregate-surface characteristics due to tyre polishing action. Three kinds of aggregates were polished by the Wehner/Schluze polishing machine. The evolution of dynamic friction coefficient, surface height profiles and their power spectral density in polishing process were characterized. Spectrum analysis is conducted to characterization the polishing effects on surface texture. The results reveal that the polishing action of rubber tyre plays an important role in the changes of micro-texture, and the evolution of friction of aggregate is governed by micro-texture changes due to differential removal of mineral components.

Abstract: Based on elasticity theory, the stress field and stress intensity factor of gear crack are discussed. The effect of friction coefficient and crack shape on equivalent stress, displacement at crack tip and stress intensity factor were analyzed by using general finite element software ANSYS, and the formula of stress intensity factor of gear crack was revised. The results showed that the equivalent stress, displacement at crack tip and stress intensity factor increased with the friction coefficient for the same crack. For the same f and different a/c, the front friction surface played a major role when a/B﹤0.05, and the post friction surface played a major role when a/B﹥0.05. The stress intensity factor increase at first, and then decrease with the increase of a/c.

Abstract: According to the Chinese Structure Code and engineering experience, the factors affecting the reliability of structures are properly qualified as input parameters; this paper mainly researches the application of neural networks in the reliability evaluation of structures. Comparisons are made between the traditional methods of reliability evaluation of established structures and the method put forward in this paper. It is found that the method put forward in this paper is practicable, reliable and effective. Meanwhile, the weaknesses of the traditional reliability evaluation of structures, that is, long period of evaluation, huge and tedious calculation and arbitral judgments, are avoided with the introduction of the new method in this paper.

Abstract: Densely arranged underground steel tube system (DAUSTS) is a new kind of structure which can be usually used in constructing spacious underground structures such as metro stations. During the construction, the steel tube is horizontally forced into soil by jacks through a vertical well. The tube may generate local buckling phenomena under the compression force if the parameter of the tube and soil meet the buckling condition. In the paper, the soil perturbation mode and the deformation of the tube before local buckling are both analyzed, considering the possibly concerned buckling failure modes in practical engineering, the confine effect of the soil and interaction between the tubes. A nonlinear buckling analysis on tube-wall of the steel tube located in the most unfavorable place is developed by the arc-length method of the finite element method (FEM), considering the effect of the large deformation. The results of the numerical simulation matches very well to the real application and the key results of the analysis can be used as an estimation principle for the stability of the tube.

Abstract: Micro-cracks which seriously affect the strength of metal materials always exist in metal or alloys during the manufacturing process. In order to investigate the pre-crack effects on deformation and failure mechanisms for pure aluminum at atomic scale, the plastic deformation processes of pure aluminum with face-centered cubic (fcc) crystal structure around the pre-crack tips at atomic scale were examined by means of molecular dynamics (MD) method. The Modified Embedded Atom Method (MEAM) potential was used to describe the interaction among atoms of pure aluminum. The crack propagation and failure processes for fcc structure were observed near the pre-crack tip zone. The calculation results reveal that the pre-crack blunting occurred at first, then the dislocation emitted at the pre-crack boundary and moved along with the specific direction obviously, eventually, cracks propagated along the crystallographic direction family of <110>. By means of VMD software, the graphic pictures of dislocation movement and crack propagation were obtained under different load conditions. The results and methodology given in this study are very significant for understanding more about plastic deformation and destruction at atomic scale for pure Aluminum with fcc structure.

Abstract: Nowadays embedded parts which connect steel members with concrete structures have frequently emerged in civil engineering; however the existing design code for embedded parts cannot satisfy the increasing demand of engineering as it was derived from limited experiments. In the paper, a finite element study on embedded parts with big-diameter reinforcing bars under shear force is conducted. The aim of the study was to fully investigate the mechanical performances of embedded parts under shear force using a three-dimensional finite element analysis with the help of a commercial software ANSYS. Cross-section internal force of anchor bar, embedded part deformation, interaction force between anchor bar and concrete, and friction force were investigated in order to well know the system response. The results show that the shear capacity of embedded part obtained from finite element analysis is conservative.

Abstract: In this paper, the typical seismic damage of earthquake fortification and non-earthquake fortification masonry buildings are analyzed and the causes are illustrated, which are based on a large number of earthquake disaster survey data of Ms8.0 Wenchuan earthquake, Ms6.4 Baotou earthquake and Ms7.8 Tangshan earthquake and so on. According to the damage statistics data of several past earthquakes of China in recent years, the difference of damaging phenomenon and rate of earthquake damage of earthquake fortification and non-earthquake fortification masonry buildings in highly and lowly seismic regions are discussed and analyzed. Finally, based on the analysis conclusions, how to improve the seismic capacity of masonry buildings are discussed combining current seismic design code of China and some reasonable suggestions on the post-disaster reconstruction of masonry buildings have been given.