Investigation on the effect of cavitation in ultrasonic-assisted AWJ

In order to provide some insight into the complex fluid behavior involved in ultrasonic vibration-assisted abrasive waterjet machining, a three-dimensional     

磨料水射流切割碳纤维复合材料的表面粗糙度试验

采用超高压磨料水射流技术对碳纤维复合材料进行切割试验,借助μscan激光共聚焦显微镜重构样品切口的三维表面,测得样品切口表面粗糙度;研究了扫描分辨率对表面粗糙度测量的影响,以及切割速度、样品厚度对样品切口表面粗糙度的影响规律。试验结果表明：扫描分辨率对表面粗糙度的测量无明显的影响;当切割深度较小（0~0.6 mm）时,即在切口入口处,表面粗糙度随切割深度的增大而减小,当切割深度较大（大于0.6 mm）时,表面粗糙度随切割深度的增大而增大;当样品厚度一定时,随着切割速度的增大,切口最大表面粗糙度在整体趋势上是增大的,而样品厚度的大小对表面粗糙度的影响并无明显的规律。     

圆锥量规锥度的高精度光学干涉法测量

针对超精密数控机床对圆锥量规锥度高精度测量的需求,研究了一种将“大数”和“小数”相结合,准确测量圆锥量规锥度的方法.介绍了锥度测量系统的基本原理及组成,给出了实验测量结果,分析了测量系统的不确定度.该测量方法利用最大分度间隔误差为0.10〞的多齿分度台构成高准确度分度系统保证测量“大数”部分的准确性,采用激光偏振干涉装...     

不同金属材料在磨料水射流加工时的可加工性的试验研究

通过对磨料水射流切割金属材料过程的能量转移过程的分析,并且将粉碎原理中的比表面能的理论引入切割深度的分析。得出了不同金属材料被切割时由于比表面能的不同,在相同的切割参数的情况下达到相同切割深度时候的切割速度不同。并且通过试验加以验证,同时得出316不锈钢和6061铝合金板材切割时的可加工性特征系数。该系数可以很好的用于磨料水射流切割时候的参数设定。     

Investigation on holding force and failure load of locking taper LOTA implant

The holding force of connection between a pressure fit abutment and a fixture was tested at different contact lengths of the pressure fit for a newly invented LOTA implant. This study proposes formulas on the critical load that the implant can bear by applying theories of stress and fatigue to the fixture model. The holding force was 12.2 % less when the pressure fit length was 2 mm than when it was 3 mm. The failure loads obtained from the proposed formulas were similar to those obtained from the experiments.

     

小波分析在水切割表面拓扑结构特征提取中的应用

为了详细地研究水切割--AWJ (abrasive water jet)表面的主要特征,研究了由传统接触式测量仪和光学测量仪获得的信号.通过对信号的小波分解和重构,提取了形态误差、波纹度以及粗糙度值等表面特征.另外,还详细地论述了小波基函数的选择以及小波分解层次确定等基本的应用问题.实验结果表明小波能够有效地应用于AWJ表面拓扑结构特征的分析和描述.     

Investigation of the microstructure and mesotexture formed during thermomechanical controlled rolling in microalloyed steels

Thermomechanical controlled rolling (TMCR) has been widely used as an effective method to improve the properties of steels. In the present paper, two commercial TMCR microalloyed steels were investigated. The grain size distributions and grain boundary misorientation angles were measured using electron backscattered diffraction patterns obtained using orientation imaging microscopy (OIM). The equivalent grain diameters were also measured using optical microscopy. Mixed coarse‐ and fine‐grained regions were observed and the microhardness values were measured for both areas. Grain boundary misorientation angle distributions showed that the magnitude of mesotexture developed in the steel is dependent upon the rolling passes, the reduction ratio and the rolling temperatures including the finish rolling temperature. The surface layer, up to 2 mm depth, in Com‐A steel had about 55% of grain boundaries with a misorientation angle below 12°, much higher than in the central area (～30%), whereas Com‐B steel showed similar distributions from the rolling surface to the centre. Misorientation results obtained from laboratory rolled steel plates with various TMCR procedures are also discussed as are OIM results from Charpy impact brittle fracture surfaces examining the effect of misorientation on crack propagation.     

Investigation of mass transfer during tribological interaction of alloyed steels

Variations in the chemical composition of the surface layers of two alloyed steels are studied in a tribojoint operating according to the ??shaft-on-bush?? geometry (bushing test) where the shaft is copper electroplated. Complex interactions are observed during testing in the presence of a molten tin and lead-containing metal lubricant that separates the rubbing surfaces; wear, oxidation, adhesion, and diffusion phenomena are observed in all components of the joint, including the metal lubricant. Comparative studies are performed to study the changes in the surface layer composition of all elements of a ball bearing with a cage fractured due to misuse.     

Investigation of the influence of specimen geometry on quench behaviour of steels by X-ray determination of surface residual stresses

Considerable residual stresses may form during quenching due to the differential cooling and the increase in volume accompanying the phase transformations. The design of a part may be entirely responsible for the formation of residual stresses at a critical level and even cracking during quenching. Furthermore, a certain design may be perfectly safe for one type of steel, or one type cooling conditions, and unsafe for another.In this study, an experimental procedure to investigate the influence of specimen geometry on the evolution residual stresses is proposed. The cylindrical specimens with 30 mm outer diameter were prepared from C60 and 90MnCrV8 steel bars. First, solid cylinders were quenched according to different procedures. Then, the treatment giving the minimum residual stress was applied to the hollow cylinders having various hole diameter and degree of eccentricity. By changing the position of holes in the cross-section of the specimens, a thickness gradient as a function of the eccentricity ratio was obtained. Thus, for a given transformation behaviour and quenching conditions, the effect of shape becomes more discriminating on the eccentrically drilled holes. The tangential residual stresses were determined at the specified points along the circumference of the cylinders by X-ray diffraction and d-sin² Ψ technique. The microstructures of the specimens were determined by metallographic investigation also using hardness values and respective CCT-diagrams. The results were discussed considering the microstructural evaluation of the specimens.     

Investigation of the mechanical behaviour of multi-phase TRIP steels using finite element methods

In recent years, the development of high-strength steels such as multi-phase TRIP (transformation-induced plasticity)-aided steels have shown great promise due to their excellent combination of high strength and ductility, which allows for the use of thinner car frame components and subsequently weight reduction. The TRIP effect, characterized by the phenomenon known as strain-induced martensitic transformation (SIMT), enhances the work hardenability of such steels as the austenite phase transforms to the much harder martensite phase during plastic straining. However, various factors exist which affect the mechanical behaviour of TRIP steels. This study will aim, through the use of finite element models, to investigate the role and influence of each of these factors on the TRIP effect in multi-phase TRIP steels. These factors include the rate at which the martensitic transformation proceeds, the state of stress to which the material is subjected to and the interaction between the surrounding matrix and embedded retained austenite islands in multi-phase TRIP steels. Investigation of these factors will provide further insight on each of their contributions to the TRIP effect in order to exploit the potential benefits offered by these steels.     

在加工中心上用平旋盘加工屏蔽泵方锥体形吐出段流道

详细介绍了在CNC加工中心上用平旋盘加工屏蔽泵方锥体形吐出段流道的方法.叙述了由数学模型建立、刀具选择、数控加工程序编制到实际加工中如何应用的全过程,具有较高的通用性.     

Improvements in grinding steels by cryogenic cooling

The intensive temperatures in high-speed machining and grinding not only limit the tool life but also impair the machined surface by inducing tensile residual stresses, micro-cracks and thermal damage. This problem becomes acute when the components are made of hard and strong materials and used in dynamic loading. In such cases drastic cooling is essential during machining. The authors have employed liquid nitrogen in the form of a jet in the surface grinding of a number of steels and found appreciable improvement, though to varying degrees, in their surface quality without significant change in specific energy requirement.     

Tool wear mechanisms in the machining of steels and stainless steels

In this article, we study the effects of the temperature control on a dehydration tomato slices process when two control strategies are considered: PID controller and optimal linear control when inherent input time delay is considered. The first controller is tuned by D-partitions method and a numerical procedure in order to minimize a quadratic performance index, the second one considers a state predictor to compensate the effects of the input delayed. The energy savings and the intrinsic characteristics in the tomato slices (vitamin C, total phenols, and lycopene levels) are quantified in order to conclude advantages of the two controllers under study.     

Design of profiled taper roller bearings

Numerical solutions are given for the pressure distribution and footprint shape for a tapered roller. The effect of roller misalignment and its axial profile are investigated for a taper roller thrust bearing. A design procedure is described which indicates the value and whereabouts of the maximum pressure that will occur under equilibrium conditions     

混合体锥度对油气混合器性能的影响

根据一种新的油气混合原理,在混合腔体中加入一个锥形体,设计了一种新型油气混合器,并利用FLUENT对三种不同混合体锥度的油气混合器内流场进行了仿真分析。仿真实验结果显示：锥体锥度对油气两相环状流的形成和周向分布均匀性有一定影响;选择合理的锥度有利于提高混合器性能。