Some experiments on the scratching of silicon:: In situ scratching inside an SEM and scratching under high external hydrostatic pressures

To elucidate the mechanisms of material removal in ultra precision machining of silicon involving deformation and fracture, in situ scratching of silicon with a diamond stylus inside a scanning electron microscope (SEM) using a specially designed tribometer and scratching under zero and high (400 MPa) external hydrostatic pressures using a specially designed high-pressure machining apparatus were conducted. The resulting scratches were examined in an SEM to evaluate the influence of depth of cut and hydrostatic pressure on the nature of scratches produced (smooth versus fractured surfaces) and the possible brittle–ductile transition. Experimental results indicate that hydrostatic pressure plays an important role in minimizing fracture and producing smooth surfaces. Reasonable agreement of the experimental results with the meso-plasticity FEM simulation of indentation was obtained.     

基于质量守恒边界条件的动载滑动轴承性能分析

用不可压缩流体空穴算法描述径向滑动轴承非线性油膜力,并在此基础上分析了动载滑动轴承的性能变化。结果表明,在动载工况下,空穴的位置随着时间的推移而变化;轴颈转速对完整油膜区分布没有影响,对油膜压力大小有影响。     

A study of the lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing (T1516)

The lubricating effectiveness of micropolar fluids in a dynamically loaded journal bearing is studied. On the basis of the theory of micropolar fluids, the modified Reynolds equation for dynamic loads is derived. Results from the numerical analysis indicated that the effects of micropolar fluids on the performance of a dynamically loaded journal bearing depend on the size of material characteristic length and the coupling number. It is shown, compared with Newtonian lubricants, that under a dynamic loading the micropolar lubricants produce an obvious increase in the oil film pressure and oil film thickness, but a decrease in the side leakage flow. It is also shown that the friction coefficient for a dynamically loaded journal bearing with micropolar fluids is in general higher than that of Newtonian fluids, which is not the same as the results for a steadily loaded journal bearing. Furthermore, a parametric study of flow and friction for different mass parameters keeping micropolar parameters fixed is undertaken. It is indicated that, with the increase of the mass parameters, the crank angles corresponding to the maximum flow are changed and the maximum friction coefficients are obviously decreased either for the Newtonian fluids or for the micropolar fluids.     

内燃机曲轴主轴承压力分布的Matlab解法

以内燃机曲轴主轴承为研究对象,考虑雷诺边界条件,优化雷诺方程以求解主轴承压力分布。计算结果表明,这种计算主轴承油膜压力的方法较为合理。     

激光切割头摆动机构的动力学仿真及试验

激光切割裂解槽机床是连杆裂解加工的关键设备之一,用于完成连杆初始裂解槽的切割.本文介绍了该机床的激光头摆动机构,对摆头机构进行了ADAMS动力学仿真.根据仿真结果确定了合理的液压参数(液压压力为2.5 MPa,溢流阀流量系数为0.2),并完成了摆头机构的物理切割试验.试验结果表明,在合适的工艺参数条件下,摆头机构的定位精度达到±0.02 mm,且工作稳定、可靠,连杆裂解槽槽深均为(0.5±0.05) mm.提出了伺服电机驱动激光头摆头方案,对改进的摆头方案进行了ADAMS运动学仿真.仿真结果表明,改进后的摆头机构可在0.4 s内完成摆头动作,且摆动角度调整方便,说明改进后的摆动机构是较理想的激光头摆动方案,可为连杆初始裂解槽激光加工主机结构优化提供可靠的理论依据.     

16MnR钢和15MnVR钢在碳酸盐环境中的应力腐蚀研究

采用楔形张开加载（WOL）恒位移预裂纹试样研究了16MnR钢和15MnVR钢在碳酸盐环境中的抗应力腐蚀性能。试验选择常温、90℃和150℃分别在两种碳酸盐浓度下加载不同应力强度因子K1,经一定时间的应力腐蚀试验,测得各试样的扩展速率处于10^-7～10^-8mm／s之间,结果表明两种材料在所选碳酸盐浓度下裂纹基本没有扩展,其应力强度因子临界值KISCC分别不小于126和116MPa√m。同时采用扫描电镜和能谱技术对断口和试样表面膜进行了相应的观察和理论分析。总体而言,这两种材料在单一的碳酸盐溶液中应力腐蚀敏感性较低。     

2mm厚1000 MPa级双相钢板电阻点焊工艺参数的优化

对2 mm厚国产汽车用1000MPa级双相钢板进行了不同工艺条件的电阻点焊,对各点焊接头显微组织、力学性能以及断口形貌等进行了分析,在此基础上优化了工艺参数。结果表明:在试验条件下,最佳点焊工艺参数为焊接电流12 kA,焊接时间12周波(0.24s),焊接压力3.5 kN;此条件下焊接接头的断裂方式以韧性断裂为主。     

Welding polarity effects on weld spatters and bead geometry of hyperbaric dry GMAW

Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding(GMAW) experiments with direct current electrode positive(DCEP) and direct current electrode negative(DCEN) operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows: an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.     

Stiffness and damping characteristics of finite width journal bearings with a non-newtonian film and their application to instability prediction

Starting from the most general fluid flow equation of the power law type expressing rate of shear in terms of powers of shear stress for non-Newtonian lubricants a modified form of Reynolds'equation is derived for dynamically loaded finite width journal bearings. The finite difference technique with successive over relaxation is used incorporating Reynolds' boundary conditions for pressure to obtain the pressure distribution. From the equations of fluid film forces, the values of stiffness and damping coefficients are obtained for a linearised case. The shear thinning effect of non-Newtonian lubricants at higher shear rates is shown to decrease the stiffness and damping values. Finally, the stability limit for such a bearing is obtained for different values of the nonlinear factor.     

Investigations on mechanical and structural aspects of ultrasonic hybrid polymer mixture welding for industrial applications

Two-dimensional C_f/Al composites were fabricated by liquid-solid extrusion following vacuum infiltration technique (LSEVI), and defects were studied and analyzed through optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope(TEM), and the tests of ultimate tensile strength (UTS). Through research, it was found that gas impurities were the main factors to generate hole defects within the 2D-C_f/Al composites, so vacuum level of the test system should be higher than 0.09 MPa. The infiltration of composites would not be sufficient and uniform under the low squeeze pressure of 50 MPa and low squeeze temperature of 590 °C. However, when squeeze pressure was larger than 90 MPa, fiber damage appeared, and macro internal cracks even occurred if it was over 100 MPa. Poor tensile behavior of composites between carbon fibers and matrix might arise because of the inappropriate process parameters. Brittle tensile fracture of composites was observed under the higher preform preheating temperature of 640 °C, and Al₄C₃ was found. Separated fibers and aluminum alloy of tensile fracture might occur under the lower preheating temperature of 580 °C. These defects hindered the improvement of property of C_f/Al composites greatly, and they should be avoided. Through contrast of UTS, internal cracks and poor tensile behavior were the most detrimental factors. Their UTSs were 45 and 117 MPa, respectively, which were less than 120 MPa of matrix. Improved process parameters were used to prepare the 2D-C_f/Al composite, and its defects were seldom found, so UTS of composite was improved 93.3 % than that of matrix.     

Correlation between the characteristics of the thermo-mechanical mixed layer and wear behaviour of Ti–6Al–4V alloy

The sliding friction and wear behaviours of Ti–6Al–4V alloy were investigated under dry sliding wear conditions. The wear tests were carried out on a pin-disc tribometer at sliding speeds from 30 m/s to 70 m/s and at contact pressure ranging from 0.33 MPa to 1.33 MPa. Pins of the Ti–6Al–4V alloy are used in both solution treated and aged conditions. The objective of the study is to understand the influence of thermo-mechanical mixed layers (TMML), which form on the surface of the worn material during the course of the wear test, on the friction and wear behaviour. Detailed characterization of the TMML was carried out using SEM, EDS and micro-hardness testing in order to understand the influence of test velocity and contact pressure on the composition, hardness and thickness of the TMML formed. The influence of the TMML on the friction and wear behaviour was also studied. On the basis of the above characterization, it was demonstrated that the observed friction and wear behaviour of Ti–6Al–4V alloy can be best understood in terms of the formation and fracture rate of the TMML rather than the bulk properties of the material.     

氮化硅基陶瓷刀具材料力学性能和显微结构的研究

研究了混料介质、超声分散、烧结助剂以及纳米第二相颗粒对自增韧氮化硅陶瓷刀具材料的显微结构和力学性能的影响。结果发现:加入5%Y_2O_3+5%La_2O_3+5%CeO_2烧结助剂的Si_3N_4粉体,以水作为混料介质并对混合浆料进行超声分散处理后,在温度为1700~1800℃下、保温40min、压力30MPa条件下热压烧结,材料的综合力学性能较好,抗弯强度可达1002·1Mpa,断裂韧性达8·2MPa·m1/2,硬度13·56GPa。SEM试验表明材料的显微组织结构均匀,β-Si_3N_4呈现长棒状交错排列;添加纳米TiC7N3第二相颗粒的氮化硅基陶瓷刀具材料后,β-Si_3N_4的长径比明显减小,晶界中嵌入了第二相粒子,材料的抗弯强度有所降低,但硬度和韧性则有所升高。     

超高压管式反应器端部结构应力场的数值模拟

基于大型通用有限元软件ANSYS,对发生疲劳断裂的超高压管式反应器的端部结构进行数值模拟,分析了其在过盈套合、自增强处理以及服役期间开停工循环载荷三种工况下的局部应力场.结果表明:三种工况下,端部结构在过盈套合边缘局部范围内均存在较高的轴向拉应力,且大于环向应力;局部轴向应力随套合过盈量和自增强压力的增加而增大;半径过盈量为0.05 mm时,开停工循环载荷下的局部轴向平均应力最大值可达86.71 MPa,轴向交变应力幅值最大值达到62.2 MPa,裂纹垂直于轴向扩展的推动力较大.模拟分析结果对端部结构失效破坏原因的分析及其设计改进有一定的指导意义.     

The dynamic behaviour of squeeze films in one-dimensional porous journal bearings lubricated by a micropolar fluid

The generalized Reynolds equation governing the pressure distribution for a micropolar lubricant in a dynamically loaded porous journal bearing is derived and applied to one-dimensional squeeze film journal bearings operating under a cyclic load. The analysis indicates how the microstructure in the lubricant, the permeability of the bearing material and the bearing wall thickness influence the operating eccentricity ratio.     

Effects of temperature and pressure on stress corrosion cracking behavior of 310S stainless steel in chloride solution

310S is an austenitic stainless steel for high temperature applications, having strong resistance of oxidation, hydrogen embrittlement and corrosion. Stress corrosion cracking(SCC) is the main corrosion failure mode for 310 S stainless steel. Past researched about SCC of 310 S primarily focus on the corrosion mechanism and influence of temperature and corrosive media, but few studies concern the combined influence of temperature, pressure and chloride. For a better understanding of temperature and pressure's effects on SCC of 310 S stainless steel, prepared samples are investigated via slow strain rate tensile test(SSRT) in different temperature and pressure in NACE A solution. The result shows that the SCC sensibility indexes of 310 S stainless steel increase with the rise of temperature and reach maximum at 10 MPa and 160℃, increasing by 22.3% compared with that at 10 MPa and 80 ℃. Instead, the sensibility decreases with the pressure up. Besides, the fractures begin to transform from the ductile fracture to the brittle fracture with the increase of temperature. 310 S stainless steel has an obvious tendency of stress corrosion at 10 MPa and 160℃ and the fracture surface exists cleavage steps, river patterns and some local secondary cracks, having obvious brittle fracture characteristics. The SCC cracks initiate from inclusions and tiny pits in the matrix and propagate into the matrix along the cross section gradually until rupture. In particular, the oxygen and chloride play an important role on the SCC of 310 S stainless steel in NACE A solution. The chloride damages passivating film, causing pitting corrosion, concentrating in the cracks and accelerated SSC ultimately. The research reveals the combined influence of temperature, pressure and chloride on the SCC of 310 S, which can be a guide to the application of 310 S stainless steel in super-heater tube.     

动态条件下Fe-24Mn-0.5C孪晶诱发塑性钢的断裂机制

对Fe-24Mn-0.5C孪晶诱发塑性钢进行了动态冲击拉伸试验,并采用扫描电镜、透射电镜等研究了该钢的断裂机制。结果表明:试验钢的抗拉强度为1 100 MPa,断后伸长率为50%;试验钢表现为典型的韧性断裂特征,断口主要由呈阶梯状的韧窝组成;其断裂机制为变形过程中塞积在晶界和孪晶界处的大量位错促使孔洞及裂纹的产生,继续变形则发生断裂。     

大尺寸轻型碳化硅质镜体的制造与材料性能测试

利用凝胶注模(gel-casting)成型工艺制备了620 mm和700 mm×300 mm的碳化硅(SiC)轻型反射镜素坯,经过脱模、干燥、脱脂和反应烧结等工艺,制备了反应烧结SiC(RB-SiC)镜体。镜体经过加工和测试,结果表明:制备的RB-SiC内部结构均匀致密;力学性能和热学性能优异,抗弯强度、断裂韧性和热膨胀系数分别达到了350 MPa、 4.1 MPa·m^1/2和2.67×10^－6/K;镜体经抛光后的表面粗糙度RMS值可优于3 nm,适合用于制备空间用大尺寸轻型反射镜。     

A Study of Dynamically Loaded Journal Bearings Lubricated with Non-Newtonian Couple Stress Fluids

This paper is to theoretically investigate the behavior of dynamically loaded journal bearings lubricated with non-Newtonian couple stress fluids. To take into account the couple stress effects due to the lubricants blended with various additives, the modified Reynolds equation for dynamic loads governing the film pressure is derived. The film pressure is solved numerically with Reynolds boundary conditions and then various bearing characteristics are calculated. The effects of couple stresses on bearing performance characteristics are analyzed. The results conclude that couple stress fluids lubrication improves the bearing performance under dynamic loads.     

深海原位保压取样装置设计及性能研究

针对深海浮游生物的取样需求,设计了一种高通量的深海压力补偿取样装置,装置包括深海泵总成、自适应压力平衡过滤取样装置、压力补偿装置以及检测控制系统等。仿真分析了硬度90 HA的O形密封圈,在安装压缩率22%、60 MPa的密封环境下的密封压力69.2 MPa,满足密封需求;通过磁力扭矩实验发现,扭矩0.2 N·m时密封舱壁厚7 mm,满足传动及耐压性能的要求;60 MPa高压舱试验中深海泵总成的耐压、密封性能良好;建立了取样装置的压力补偿物理模型。仿真研究表明,公称体积1 L、壁厚25 mm、预充压力25 MPa的囊式蓄能器,在6000 m深海取样的计算中,温度的变化使取样系统有8.75%的压力增加,材料变形引起的压力损失约为0.4%,温度变化对保压效果的影响较大,为确保样品的原位特性,在保压回路中增设溢流阀,并配备样品储运冰箱。     

TRT蜗壳结构特性的有限元数值模拟

采用弹塑性有限元方法,对静力载荷及水压试验条件下的TRT焊接蜗壳的应力和变形进行了数值模拟。结果表明,在静力载荷作用下,机壳整体最大等效应力仅为19.1MPa,主要集中在法兰上施加约束的位置;最大合位移为0.0776mm,出现在下机壳支撑柱处。水压试验过程中,机壳整体的等效应力值大部分在40～85MPa之间,仅局部小范围达到382MPa;壳体的整体合位移最大值为1.511mm,出现在出口挡板处,而机壳本身的变形并不显著。