The fabrication and mechanical properties of SiC/SiC composites prepared by SLS combined with PIP

Traditionally, SiC components with complex shapes are very difficult or even impossible to fabricate. This paper aims to develop a new manufacturing process, combining selective laser sintering (SLS), cold isostatic pressing (CIP) and polymer infiltration pyrolysis (PIP), to manufacture complex silicon carbide parts and improve the mechanical properties of silicon carbide ceramic parts. The density and porosity of SiC/SiC composites were measured. Furthermore, the mechanical properties of the specimens with cold isostatic pressing and the specimens without cold isostatic pressing were compared. The bending strength of the specimens with cold isostatic pressing was 201?MPa, and the elastic modulus was 1.27?GPa. And, the bending strength of the specimens without cold isostatic pressing was 142?MPa, and the elastic modulus was 0.88?GPa. Increasing the density of SiC/SiC can enhance the mechanical properties of SiC/SiC composites.     

Rushton桨气液搅拌槽内气泡流对搅拌轴弯矩的影响（英文）

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine, as one of the results of fluid and structure interactions in stirred vessels, was measured using a moment sensor equipped with digital telemetry. An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment, which indicates the elasticity nature of shaft material against bending deformation, fol-lows the Weibull distribution. The trends of amplitude mean, standard deviation and peak deviation character-istics manifest an“S”shape versus gas flow. The“S”trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas–liquid stirred vessels, resulted from the competition among the non-uniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades, and the gas direct impact on the impel er when gas is introduced. A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident. The low-frequency contribution to bend-ing moment fluctuation peaks in the complete dispersion regime.     

Bending collapse of thin-walled circular tubes and computational application

This paper focuses on describing the bending collapse behavior of thin-walled circular tubes. In this paper, global energy equilibrium theory is applied to derive the relationship between the applied moment and the bending angle of circular tubes. A general bending collapse mode of circular tubes is referenced for the derivation, and it is assumed that during bending crush, all impact energy is absorbed and distributed along the hinge lines. After obtaining the relationship, it is compared to a published theory of tubular structure's bending resistance, which was obtained from analytical and experimental studies. The derived bending resistance is then applied to generate simplified circular tube models, which have different cross-sections and are made of different materials. Crashworthiness analyses are performed on these simplified models as well as detailed tube models, and the crash results are compared to verify the efficiency of the generated simplified model and the accuracy of the derived tube's bending resistance. All the problems involved in this paper are solved by means of LS-DYNA.     

A continuous vibration analysis model for cables with sag and bending stiffness

The paper reports an investigation on a continuous model for dynamics of large-diameter sagged cables, taking bending stiffness and sag extensibility into account. Following the classical guidelines of cable dynamics, and by making some simplifications, a continuous model is found in this work; frequency and mode shape equations have been obtained in non-dimensional form. Comparison with Finite Element (FE) and Finite Difference (FD) models has been made to validate the proposed method. Moreover, it allows us to represent local effects at the end zones of cable correctly, if clamped boundary conditions are assumed. To obtain comparable results, the FE model would require a large subdivision, with consequently, a large number of elements. The proposed eigenfunctions allow us to solve the dynamic problem without a large computational effort compared to FE or FD approaches. Finally, in order to show the usefulness of the developed continuous model, an application on the main cables of the designed Messina Strait Bridge has been made.     

磷脱氧铜无缝管断裂原因分析

用ＳＥＭ等方法对电冰箱压缩机用磷脱氧无缝铜管异常断裂进行了分析。结果表明，夹杂物局部偏聚是铜管断裂的内在原因，焊接时产生的热应力及弯曲变形是铜管断裂的外部诱发因素。有效的改进措施是严格控制杂质含量、将高温焊接工艺改为低温焊接工艺。     

Health-monitoring technologies for alumina-fiber-reinforced plastics

Transmitted light could detect matrix cracks that occurred in the early stages of fracture of alumina-fiber-reinforced plastics (alumina-FRPs); these cracks could not be detected by acoustic emission (AE). An optical-fiber Bragg grating (FBG) sensor could detect the matrix cracks but it must be embedded in the FRPs. To determine which wavelength is sensitive to the defects in the FRP, the spectra of the transmitted and reflected light were measured. The intensity of the transmitted light, especially in the visible region (wavelength: 400–800 nm), decreased as the bending stiffness of the test piece decreased. It is thus concluded that to monitor the decrease in bending stiffness of FRPs, a simple sensor using a visible ray is good enough. And this transmitted-light NDE technique can work in the strong electromagentic field associated with a superconductor. It will therefore be useful for detecting defects in the FRP of the load-support system in service.     

A linear theory for bending stress-strain analysis of a beam with an edge crack

In this paper, a new linear theory for bending stress-strain analysis of a cracked beam has been developed. A displacement field has been suggested for the beam strain and stress calculations. The bending differential equation for the beam has been written using equilibrium equations. The required constant for this model is also obtained from fracture mechanics. The bending equation has been solved for a simply supported beam with rectangular cross-section and the results are compared with finite element and empirical results. There is an excellent agreement between theoretical results and those obtained by numerical and empirical methods. The model developed in this research is a simple and precise approximation of the behavior of the cracked beams in bending.     

薄壁小半径弯管与中压内胀成形工艺

针对薄壁小半径弯曲管生产过程中易出现的交薄、断裂、起皱等难点,吸收了当前国外先进技术--管材内高压成形的优点,在充分考虑国内高压成形技术不足的基础上,改用中压成形弯管的新工艺,很大程度上提升了薄壁小半径弯曲管生产的外观质量.这一工艺特别适用于厨房、卫浴等领域中水龙头的前期工序生产,具有较大的实用意义.     

Sheeting interaction failure, from yield-line to two-strip model

This paper presents 20 years of research on failure of sheeting subjected to combined concentrated load and bending moment, performed at Technische Universiteit Eindhoven. The aim of this research is to develop accurate, insight providing design rules using simple mechanical models, based on observed failure modes. The paper summarizes the performed experiments, finite-element simulations, and analytical models. It is concluded that mechanical models may be feasible only for sheeting without stiffeners in web and flanges. For sheeting with stiffeners, the models become so complex that it is not likely that they will lead to simple design rules.