Grinding characteristics and removal mechanisms of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites

The grinding performance of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites (C_f/SiC) was investigated in this paper. The effects of the fibre orientation and grinding depth on the surface integrity and grinding forces and an understanding of the grinding mechanisms are the primary concerns of this article. This problem is relatively unexplored; therefore, the main value of this research is to improve the processing quality and reduce the production cost. In the C_f/SiC grinding procedure, cracks, fibre wear, interfacial debonding, fibre pull-out and outcrop can be detected on the ground surface. The grinding depth and deflection angle have been shown to have a notable influence on the surface quality in different datum planes. A suitable grinding depth and deflection angle should be carefully chosen to achieve good surface quality in different machined surfaces. Specifically, the surface quality decreases and the grinding forces increase with increasing grinding depth. In addition, greater grinding surface quality is observed at β?=?90°, i.e., γ?=?0°, but poorer machined surfaces are obtained at α?=?0°, i.e., γ?=?90°. The surface topography, roughness and grinding forces of unidirectional C_f/SiC could be forecasted according to the analysis conclusions. This research is expected to offer guidelines for increasing the machining quality of C_f/SiC.     

Experimental study on mechanical drilling of carbon/epoxy composite-Ti6Al4V stacks

This paper concerns the experimental studies on the drilling process of multilayer carbon/epoxy composite-Ti6Al4V stacks and their individual material layers using tungsten carbide drills. The significance of the current work aims to reveal the impact of tool wear on the drilling process for CFRP/Ti6Al4V, CFRP and Ti6Al4V. Four groups of machining tests including drilling individual CFRP, individual Ti6Al4V, multilayer CFRP/Ti6Al4V stacks with and without a cooling treatment were conducted. Drilling forces, cutting temperatures and hole quality attributes were experimentally investigated in terms of the drill wear extents. The mechanism controlling the tool wear effect on the drilling machinability of CFRP/Ti6Al4V was revealed, providing several implications for the industrial manufacturers. The results highlight the significant impact of the titanium chip ejection on the composite surface quality and the necessity of a rigorous tool wear control to guarantee the damage-free drilling of CFRP/Ti6Al4V stacks.     

Critical Condition Expectancy of Flange Beam at the Loss of Flat Form of Stability with Riveted Flanges under the Influence of Random Forces and Initial Flexures

The functioning of multipart flange beam with riveted flanges, which are loaded with random external forces, is examined. Prior to elastic assembling the beam had random initial flexures of the flanges. We obtained relations for determination of probability of flange beam critical condition by the loss of flat form of flexure under the influence of random shear forces, which occur at the welding points between web plate and flanges of the beam. The examples for determination of probability of critical condition of flange beam under the influence of random initial flexures of the flanges are provided. __________ Translated from Problemy Prochnosti, No. 5, pp. 131 – 137, September – October, 2005.     

市场后入者开拓市场的捷径

在市场经济中，企业处于不同的竞争地位，市场后入者在市场竞争中取胜的途径有避实就虚，细分市场，借势发展等等。     

基于强震记录的建筑结构动力特性的初步识别

利用喜来登环球旅馆于1994年北岭地震中获得的强地震反应观测记录,初步识别了该旅馆结构恢复力的时变特性,分析了结构刚度在地震过程中的时变规律,并对该结构的表现做出初步解释。喜来登旅馆结构体系在立面上并不是均匀布置,于四层处发生较大改变,导致结构刚度发生变化。从初步识别结果上看,一至三层的刚度明显高于其他各层,三至九层刚度退化得最快,应该是结构刚度突变所致。该工作可作为进一步研究喜来登旅馆这类建筑结构实际抗震性能的基础。     

空压站厂房圈梁混凝土冬期负温施工

根据工程进度,施工环境与逆作法施工要求,鞍钢1780空压站厂房圈梁混凝土,必须满足低、负温早强要求.阐明工艺原理基础上采取选材、工法、养护等综合技措,获得了较好的技术经济效果.     

Calculation of the second virial coefficient of nonspherical molecules: Revisited

An accurate Hartree–Fock dispersion individually damped (HFD-ID) potential type improved by Boyes for argon has been used as a core potential to calculate both the spherical and nonspherical contributions to the second virial coefficient of simple molecules. The auxiliary functions that occur in the perturbation terms for calculating the nonspherical contributions, have been calculated numerically and are tabulated over a wide range of temperatures from T^*=0.5 to T^*=10, where T^*=kT/ and is the potential well-depth. By fitting the well-depth and the position of the minimum in the core potential, we have calculated the second virial coefficient of N₂, O₂, CO, NO, and CO₂ over the whole temperature range reported in the literature. The calculated results are compared with the large body of experimental data in the literature, and with the pervious calculations by Boushehri et al. (1987). The agreement with both experimental data and theoretical calculations is quite good.     

Quantum mechanics at the core of multi-scale simulations

Quantum mechancial forces at the core of multi-scale simulations, require a one-electron Hamiltonian approach whose solution provide electronic energies, forces, and properties for > 1,000 atoms fast enough that it can drive large scale molecular dynamics. Such a transfer-Hamiltonian is hoped to be as predictive as accurate, ab initio quantum chemistry for such systems. To design the Hamiltonian requires that, we investigate rigorous one-particle theories including density functional theory (DFT) and the recently proposed, correlated orbital potential (COP) approach that has been developed solely from wavefunction considerations. The latter insists upon exact, principal ionization potentials and electron affinities for a system, while DFT insists upon the exact density and the HOMO ionization. These two complementary approaches help identify the essential quantities that an exact one-particle theory of electronic structure requires. The intent, then, is to incorporate these into a simple approximation that can provide the accuracy required but at a speed four orders of magnitude faster than today’s DFT. The theory is presented and its neglect of diatomic differential overlap (NDDO) realization is illustrated for select systems.     

Application of indicial functions in bridge deck aeroelasticity

This contribution deals with some recent studies on numerical and analytical models for the evaluation of aeroelastic response of cross-section models of long span bridges. The time-domain indicial approach, whose validity has been only partially investigated in the past, is selected for the modeling of self-excited forces. Sets of indicial function coefficients are estimated for rectangular cross-sections, and their applicability is proven, through time-domain simulations and comparison with experimental tests. Critical flutter condition and dynamic pre-critical and post-critical behaviors are evaluated.     

SMW工法围护结构变形性状影响因素分析

以特定工程为研究背景，采用考虑基坑开挖时空效应的弹性地基梁计算方法模拟分析了围护结构刚度、支撑位置对SMW工法围护结构侧向变形规律和内力的影响。