Effect of the difference of materials of the fastening and abutting members of shearing joint on the distribution of contact pressure

The solution obtained for the distribution of a long contact load with the bolt pressure on the wall of a hole in abutting members of a shearing joint is corrected and extended to the more general case where all members of a joint are made from materials differing in their mechanical characteristics. It is shown that the difference in the elastic modulus of materials of the fastening and abutting members affects the distribution of contact pressure significantly less than the ratio of their diameter and thickness.     

Effects of surface geometry and non-newtonian viscosity on the flow field in arterial stenoses

Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been believed to affect the development and progression of arterial stenosis, but previous studies lack of realistic physiological considerations such as irregular surface geometry, non-Newtonian viscosity characteristics and flow pulsatility. The effects of surface irregularities and non-Newtonian viscosity on flow fields were explored in this study using the arterial stenosis models with 48% arterial occlusions under physiological flow condition. Computational flow dynamics based on the finite volume method was employed for Newtonian and non-Newtonian fluid. The wall shear stresses (WSS) in the irregular surface model were higher compared to those in the smooth surface models. Also, non-Newtonian viscosity characteristics increase the peak WSS significantly. The dimensionless pressure drop and the time averaged WSS in pulsatile flow were higher than those in steady flow. But pulsatility effects on pressure and WSS were less significant compared to non-Newtonian viscosity effects. Therefore, irregular surface geometry and non-Newtonian viscosity characteristics should be considered in predicting pressure drop and WSS in stenotic arteries.     

Reliability of an overground oil and gas pipeline with initial bending

For a beam sector of an oil and gas pipeline with initial axial bending, a mathematical model is developed that simulates the probability of nondestruction when the pressure, diameter, wall thickness, load, span length, maximum deflection, elastic modulus, and Poisson ratio are normally distributed. The parameters that decrease the number of emergency failures are established.     

螺栓法兰接头用碟形弹簧压缩回弹性能研究

为研究螺栓法兰接头用碟形弹簧压缩回弹性能,建立碟形弹簧力学性能分析的弹塑性有限元模型,并通过试验验证其可靠性。应用ABAQUS软件对碟形弹簧压缩回弹过程进行分析,讨论碟簧外内径比、倾角和厚度对碟簧压缩回弹性能的影响。结果表明:碟簧的压平载荷随厚度、倾角的增加呈上升趋势,随外内径比的增加呈下降趋势;回弹率随厚度、倾角、外内径比的增加均呈下降趋势。基于正交试验分析方法,结合量纲分析,建立螺栓法兰接头用碟形弹簧压平载荷和回弹曲线的预测模型,并验证其可靠性。     

Influence of different bell-shaped stenoses on the progression of the disease,atherosclerosis

In the present paper, the effect of symmetrical and asymmetrical bell-shaped stenoses on wall pressure drop, streamline contour, and rise in wall shear stress for the progression of the disease, atherosclerosis has been investigated numerically. The governing equations have been solved by finite volume method. Both steady and pulsatile flow at inlet is considered in our study. It is revealed from the study that the impact of wall pressure and peak wall shear stress on progression of disease are always high for asymmetrical shaped stenosis for both steady and pulsatile flow. The impact of asymmetrical shape on plaque deposition zone is less, if the aggravation changes the shape of stenosis due to change in stricture length only keeping percentage of restriction same. Whereas, the impact of asymmetrical shape on plaque deposition zone will be high, if shape of stenosis changes by increasing both stricture length and percentage of restriction for both steady and pulsatile flow. Impact of pulsatile nature of flow on the aggravation of disease is higher at some timesteps in comparison to steady flow.     

An experimental investigation on the machining characteristics of microscale end milling

This paper discusses an experimental approach to assess the machining characteristics in microscale end milling operation through a systematic experimentation procedure. Microchannels were machined on brass plates using a carbide end mill of 1?mm diameter to analyze the effect of chip load (feed per tooth) and cutting speed on the surface roughness, specific cutting pressure, and cutting forces during microend milling operation. The tangential and radial components of forces were analyzed with the help of a three-dimensional model using the force signals acquired through KISTLER dynamometer. Feed per tooth and the interaction of cutting speed and chip load were identified as the critical parameters affecting the surface roughness of microchannel. Applying the concept of elastic recovery on the side wall surface of microchannels, the minimum chip thickness during the above micromilling operation was evaluated as 0.97???m, and the result was validated by the drastic increase in specific cutting pressure and erratic behavior of cutting forces below a chip load of 1???m.     

海水润滑赛龙轴承热弹流润滑理论分析

利用Reynolds方程,对海水润滑条件下赛龙轴承在考虑热效应时的弹流润滑问题进行数值模拟,讨论载荷、转速和轴承轴径大小对海水润滑膜压力及膜厚的影响。结果表明:热效应对于水膜压力影响很小,而考虑热效应时的膜厚会有所减小;随载荷的增大,压力峰值有所增大,膜厚随载荷的增大有明显的减小;随转速的增大压力峰值减小,而膜厚随转速的增大而有明显的增大;轴径的大小对于水膜压力和膜厚的大小影响不明显。     

内压圆筒厚度计算公式分析讨论

GB 150—2011中采用的是弹性失效准则,规定对设计压力p≤0.4[σ]t的内压圆筒厚度按中径公式进行设计。JB 4732—1995中规定对设计压力p≤0.4[σ]t的内压圆筒厚度按中径公式进行设计,设计压力p>0.4[σ]t时按Tresca全屈服压力进行设计。比较研究表明:基于弹性失效准则时,中径公式算出的厚度最薄;基于塑性失效准则时,中径公式算出的厚度最厚;当径比较小时,按Tresca全屈服压力和中径公式算出的内压圆筒厚度相差很小,在工程设计中,可以统一采用Tresca全屈服压力计算内压圆筒壁厚。     

Strength reliability computation for a beam section of a main gas pipeline

Within the framework of the theory of random values, a formula for the index of the static model of the strength reliability of a beam section of a pipeline is obtained (the probability of indestruction) in the case where the physical and mechanical characteristics of pipes, the load in the bearing structures, the internal gas pressure, the pipe wall temperature difference, the pipe diameter, and the pipe wall thickness are normally distributed. Optimal characteristics of pipeline reliability are obtained at the design stage such that the failure-free operation of the gas pipeline section on equidistant bearing structures is ensured for the service life limit.     

Injection-moulded models of major and minor arteries: the variability of model wall thickness owing to casting technique

Cardiovascular disease of major and minor arteries is a common cause of death in Western society. The wall mechanics and haemodynamics within the arteries are considered to be important factors in the disease formation process. This paper is concerned with the development of an efficient computer-integrated technique to manufacture idealized and realistic models of diseased major and minor arteries from radiological images and to address the issue of model wall thickness variability. Variations in wall thickness from the original computer models to the final castings are quantified using a CCD camera. The results found that wall thickness variation from the major and minor idealized artery models to design specification were insignificant, up to a maximum of 16 per cent. In realistic models, however, differences were up to 23 per cent in the major arterial models and 58 per cent in the minor arterial models, but the wall thickness variability remained within the limits of previously reported wall thickness results. It is concluded that the described injection moulding procedure yields idealized and realistic castings suitable for use in experimental investigations, with idealized models giving better agreement with design. Wall thickness is variable and should be assessed after the models are manufactured.     

内燃机主轴承EHD模拟计算研究

在充分考虑轴承座、瓦背、减摩合金层的弹性变形及轴颈、轴瓦表面粗糙度因素的影响基础上,对某4100QB柴油机主轴承进行了综合的EHD模拟计算研究。采用有限差分法与有限元法相结合对轴承的油膜压力、油膜厚度、弹性变形、表面粗糙度进行了耦合分析,并将EHD耦合算法结果与刚性分析结果及仅考虑轴瓦弹性变形的分析结果进行了比较分析。结果表明,综合考虑轴承座、瓦背、减摩合金层弹性变形及轴颈、轴瓦表面粗糙度因素影响的弹流润滑研究更符合实际工况,其油膜厚度增大,油膜压力减小,油膜承载区扩大,且在轴承载荷峰值处表现最为明显。     

Separation of the reservoir and wave pressure and velocity from measurements at an arbitrary location in arteries

Previous studies based on measurements made in the ascending aorta have demonstrated that it can be useful to separate the arterial pressure P into a reservoir pressure P* generated by the windkessel effect and a wave pressure p generated by the arterial waves: P = P*+p. The separation in these studies was relatively straightforward since the flow into the arterial system was measured. In this study the idea is extended to measurements of pressure and velocity at sites distal to the aortic root where flow into the arterial system is not known. P* is calculated from P at an arbitrary location in a large artery by fitting the pressure fall-off in diastole to an exponential function and assuming that p is proportional to the flow into the arterial system. A local reservoir velocity U* that is proportional to P* is also defined. The separation algorithm is applied to in vivo human and canine data and to numerical data generated using a one-dimensional model of pulse wave propagation in the larger conduit arteries. The results show that the proposed algorithm is reasonably robust, allowing for the separation of the measured pressure and velocity into reservoir and wave pressures and velocities. Application to data measured simultaneously in the aorta of the dog shows that the reservoir pressure is fairly uniform along the aorta, a test of self-consistency of the assumptions leading to the algorithm. Application to data generated with a validated numerical model indicates that the parameters derived by fitting the pressure data are close to the known values which were used to generate the numerical data. Finally, application to data measured in the human thoracic aorta indicates the potential usefulness of the separation.     

筒形件冷挤压凹模强度设计及结构优化

基于厚壁圆筒理论,分析了整体式凹模工作载荷特点,讨论了单纯通过增加壁厚来提高模具强度的局限性。为提高承载能力,探讨了多层预应力组合凹模方案。基于第四强度理论,推导了n层组合凹模承受内压的数学表达式。采用Lagrange乘子法对组合凹模参数进行了优化设计,推导了n层组合凹模各层最佳径比分配、凹模极限内压、套缩界面残余压力及最优过盈量等设计变量的计算式。以三层组合凹模为算例,运用理论分析和数值模拟相结合的方法,对上述n层组合凹模的各设计变量计算式进行了验证,结果表明两者的结果吻合较好。     

Analysis of heavy duty tilting-pad journal bearing taking into account pad distortion and possible adoption of rubber pad segments

In this work a comparative study has been made between the thermo-hydrodynamic performance of a three shoe tilting-pad journal bearing with rigid and elastic pads subjected to unbalance load. A case study of a bearing adopting three rubber pad segments has also been studied. The distortion of the elastic pad is introduced into the distribution of the film thickness through an iterative scheme to assess its effect on the load carrying capacity of the bearing. A finite element mesh is used to calculate the distortion of the elastic pad while a finite difference mesh is used to calculate the pressure field in the lubricant film. Results have shown a number of interesting conclusions regarding the adoption of rubber pad segments instead of tilting-pads. There is an increase in minimum oil film thickness when using elastic pad or even rubber pad segments compared with rigid pads. Also the maximum pressure and load carrying capacity are not significantly affected.     

UHMWPE基水润滑尾轴承润滑特性仿真及试验研究

针对UHMWPE基高分子复合材料水润滑轴承的润滑特性开展研究。采用双向流固耦合算法研究弹性模量和泊松比等材料参数以及转速、负载等工况参数对水润滑轴承偏心率、最大水膜压力、轴承最大变形量、最小水膜厚度、摩擦因数等润滑特性的影响。基于改性UHMWPE高分子复合材料轴承的试验,验证了仿真方法的正确性。研究表明:计入弹性变形的流固耦合算法在研究高分子复合材料轴承性能方面具有更高的精度;随轴瓦材料弹性模量和泊松比的增大,轴承承载力逐渐增大、弹性变形量逐渐减小;随负载增大,轴承最大水膜压力和最大变形量基本呈线性增长;随转速增大,轴承最大水膜压力和轴承最大变形量显著减小;对于高分子复合材料轴承,低速、重载工况下不计入弹性变形的算法误差更大。     

点接触弹流动压性能的多网格法分析

点接触问题主要研究在一定载荷作用下,运动球体间的接触力学性能,涉及物体的弹性变形和流体动压的相互作用。本文应用多网格重积分方法,在给定的物体几何结构、载荷、速度、流体性质条件下,对运动球体的弹性变形、流体膜的厚度分布、流体膜的压力分布等参数的性能及其关系做了研究。分析结果反映出这类问题的基本特征和参数之间相互作用的规律。这一分析技术为相关结构和参数的设计及进一步分析提供了一个强有力的手段。     

特种高强度钢等厚冷压成球面工艺

球缺封头传统成形工艺无法满足某水下使用设备球形板形状、厚度、力学性能、重量等设计要求。通过开展特种高强度钢等厚冷压球面工艺研究，掌握了冷压成形中板厚变化规律、形状误差控制、消除冷作硬化及保证力学性能控制和成形压力控制四项主要关键技术，实现了特种高强度钢等厚球面冷压成形，满足了球形板设计要求。     

板翅式换热器斜接管封头极限压力研究

针对板翅式换热器斜接管封头强度设计问题,基于有限元软件ANSYS和CAD软件Solidworks,给出塑性功曲率(Plasticwork curvature,PWC)准则极限载荷计算方法,比较30o斜接管封头的PWC准则极限压力、两倍弹性斜率(Twice elastic slope,TES)准则极限压力和美国机械工程师协会(American Society of Mechanical Engineers,ASME)理想塑性极限载荷准则极限压力的计算结果,并对影响极限压力的接管倾斜角β、筒体径厚比iDδ、接管开孔率idD进行参数关系研究。30o斜接管封头极限压力计算结果比较表明,PWC极限压力以总塑性功及其曲率作为封头结构整体塑性失效判别的全局指标,与TES准则人为选择的变形参数指标和两倍弹性斜率失效线相比较,具有客观性,也能反映材料应变硬化对封头增强的效应;极限压力与尺寸参数关系研究表明,小倾斜角、大开孔率和大径厚比将使得封头极限压力降低。研究结果为板翅式换热器斜接管封头这种复杂结构极限压力的计算和尺寸参数的选择提供参考。     

纳米硬度技术在表面工程力学性能检测中的应用

结合纳米硬度技术测量各类薄膜和块体材料表层的纳米压痕硬度、弹性模量、断裂韧性、膜厚、微结构的弯曲变形，采用纳米划痕硬度技术测量各类薄膜和块体材料的粗糙度、临界附着力、磨擦系数、划痕横剖面。纳米硬度计是检测材料表层微米乃至几十纳米力学性能的先进仪器，可广泛应用于表面工程中的质量检测。