Wear tests in a hip joint simulator of different CoCrMo counterfaces on UHMWPE

The objective in this work was to study the effect of different material counterfaces on the Ultra High Molecular Weight Polyethylene (UHMWPE) wear behavior. The materials used as counterfaces were based on CoCrMo: forged with hand polished and mass finished, CoCrMo coating applied on the forged CoCrMo alloy obtained by Physical Vapour Deposition (PVD). A hip joint simulator was designed and built for these studies. The worn surfaces were observed by optical and scanning electron microscopy. The results showed that the hand polished CoCrMo alloy caused the higher UHMWPE wear of the acetabular cups. The CoCrMo coating caused the least UHMWPE wear, while the mass finished CoCrMo alloy caused an intermediate UHMWPE wear. It is shown that the wear rates obtained in this work are closer to clinical studies than to similar hip joints simulator studies.     

The effect of circular bridge piers with different inclination angles toward downstream on scour

A fundamental principle in the safe design of bridge piers is to estimate maximum scour depth. As such, many researchers devoted their efforts to study the phenomenon of scour around bridge piers and to present relationships to estimate maximum scour depth. In the current research, scour around circular bridge piers with two different diameters and different inclination angles toward downstream has been investigated experimentally under clear water and different discharges. The obtained results revealed that increase in the inclination angle leads to a significant decrease in the scour depth, dimensions of sediment ridge and scour hole. Moreover, by comparing the data obtained from vertical bridge pier and well-known relationships, a relationship having the most agreement with the results was selected and modified to estimate equilibrium scour depth around inclined piers.     

Tribological behavior of ultra-high molecular weight polyethylene in a hip joint simulator

In this paper effects of various injection molding parameters on tribological properties of ultra-high molecular weight polyethylene (UHMWPE) were investigated. The tribological properties like coefficient of friction and wear rate were obtained from the experimental results of hip simulator which was designed and fabricated in the laboratory. Bovine serum was used as a lubricant in this study. In addition, the hardness of the specimen was also investigated as well. The injection molding parameters that varied for this study are melt temperature, injection velocity and compaction time. The results show that contact loads and melt temperature were mostly influenced the tribological behavior of UHMWPE. A wear mechanism map was developed to study the dominant wear mechanism that influences the wear behavior of UHMWPE. SEM was employed to study the worn out morphologies of UHMWPE. The dominant wear mechanisms that are dominated through our study are ironing, scratching, ploughing, plastic deformation, and fatigue wear.     

不同元件故障状态下滚动轴承的动态特性研究

为探究局部故障状态下滚动轴承内部动态特性的差异性和相似性,以NU306圆柱滚子轴承为研究对象,利用有限元仿真软件ANSYS/LS-DYNA构建正常以及外圈、内圈和滚动体分别故障时的有限元模型,得到不同故障状态下滚动体的应力特性、振动特性及运动特性。结果表明,当滚动轴承的不同元件发生故障时,故障前端应力均会滞后,后端应力均会提前,其中外圈故障时应力的变化最大;外圈故障时滚动体在经过故障区域期间的振动加速度先减小后增大,内圈和滚动体故障时振动加速度先增大后减小;外圈和滚动体故障时滚动体的公转转速均比理论公转转速小,内圈故障时滚动体的公转转速比理论公转转速大。所构建的有限元模型可用于探究不同元件故障时滚动轴承内部的故障机理,可为进一步研究滚动轴承的承载能力和使用寿命提供有力的分析方法。     

冲击压缩下氧化铝陶瓷中的延迟破坏实验研究

利用轻气炮对不同厚度的氧化铝陶瓷试件进行了平板冲击实验,并借助激光速度干涉仪(VISAR)测试了试件的自由面速度历程。实验结果显示,自由面速度曲线上存在表征破坏波出现的二次压缩信号。根据实验结果计算获得了破坏波穿过试件的运动进程,并确定了试件中破坏波的运动轨迹近似为一条直线,得出在冲击压力为7.16GPa时试件内破坏波波速约为5.051km/s,破坏延迟时间约为0.105μs。最后简单分析了该现象产生的物理机制。     

Effects of a butterfly scale microstructure on the iridescent color observed at different angles

Multilayer thin-film structures in butterfly wing scales produce a colorful iridescence from reflected sunlight. Because of optical phenomena, changes in the angle of incidence of light and the viewing angle of an observer result in shifts in the color of butterfly wings. Colors ranging from green to purple, which are due to nonplanar specular reflection, can be observed on Papilio blumei iridescent scales. This refers to a phenomenon in which the curved surface patterns in the thin-film structure cause the specular component of the reflected light to be directed at various angles while affecting the spectral reflectivity at the same time by changing the optical path length through the structure. We determined the spectral reflectivities of P. blumei iridescent scales numerically by using models of a butterfly scale microstructure and experimentally by using a microscale-reflectance spectrometer. The numerical models accurately predict the shifts in spectral reflectivity observed experimentally.     

不同风倾角下典型等边角钢静风力风洞试验研究

角钢作为格构式结构的基本组成部分,其风力系数的精度将直接影响结构整体风力系数取值的准确性。通过刚性模型高频动态天平测力风洞试验,测量了随倾角和风向角变化的典型三维等边角钢的静风力。研究表明：倾斜安装角钢的阻力系数、升力系数与垂直安装相比,随风向变化趋势类似,但在某些风向角下数值明显降低;不同风倾角(β=30°～50°)时风力系数(C_D,C_L,C_M)随风向变化能够较好地吻合,即风倾角的变化对风力系数值影响不明显。角钢垂直安装时,静力折算高度随风向在(0.4～0.6)倍总高附近变化,角钢对于来流前倾安装后,静力折算高度随风向的波动增大明显;此外,根据试验结果分别给出了角钢垂直安装和倾斜安装情况下角度风荷载系数、升力系数的建议公式,并对相关参数进行了拟合。     

The effects of spot treatments on performance in a driving simulator under sober and alcohol-dosed conditions

Accident studies have identified nighttime conditions on rural roads as particular problems for alcohol-impaired drivers. Uneventful driving is hypothesized to result in progressive degradation of tracking performance and a reduced ability to handle the demands of hazardous locations, such as curves. To address these problems, four spot treatments (i.e. herringbone road marking, flashing beacon, chevron, and post delineator) were evaluated in a driving simulator. Twelve subjects drove a simulator under two conditions of task demand (with and without obstacles) and three levels of blood alcohol concentration (BAC): .00%, .07%, and .12%. The purpose of the study was to determine whether providing enhanced visual information about hazardous areas would improve the performance of subjects when sober or alcohol-dosed. Driver performance measures included speed, lateral position, and lateral acceleration on the approach and negotiation of horizontal curves of varying length and curvature. The results indicate that spot treatment effects were primarily curve-specific rather than uniform across curves. The effectiveness of spot treatments as alcohol countermeasures is discussed.     

CHA/UHMWPE复合关节材料的生物摩擦学研究

采用热压成型工艺制备了超高分子量聚乙烯 (U HMWPE) /珊瑚羟基磷灰石 (CHA) 复合关节材料 , 利用人工髋关节模拟磨损试验系统 , 研究了该类复合材料与 CoCrMo 合金组合关节在小牛关节液润滑条件下的摩擦磨损性能。实验结果表明 , 添加 CHA 能有效提高 U HMWPE关节材料的表面硬度 , 降低其磨损率。当CHA添加量为 20 wt %时 , 可获得表面硬度与抗磨损性能的良好匹配。小牛关节液润滑条件下 , U HMWPE及其复合材料的磨损机理主要表现为研磨磨损和疲劳磨损 , 磨损颗粒尺寸随 CHA粉体添加量的增加而增大。      

Simple isolation method for the bulk isolation of wear particles from metal on metal bearing surfaces generated in a hip simulator test

Isolation and characterization of metal-on-metal (MoM) wear particles from simulator lubricants is essential to understand wear behaviour, ion release and associated corrosive activity related to the wear particles. Substantial challenges remain to establish a simple, precise and repeatable protocol for the isolation and analysis of wear particles due to their extremely small size, their tendency to agglomerate and degrade. In this paper, we describe a simple and efficient method for the bulk isolation and characterisation of wear particles from MoM bearings. Freeze drying was used to remove the large volume of water from the serum lubricant, enzymes used to digest the proteins and ultracentrifugation to finally isolate and purify the particles. The present study involved a total of eight steps for the isolation process and a wear particle extraction efficiency of 45% was achieved.     

Brittle fracture of a ceramic in bending under conditions of impulse heating

Strength of Materials -     

Effect of a graded interlayer on the stress intensity factor of cracks in a joint under thermal loading

In a bimaterial joint with and without a graded interlayer, the stress intensity factor of cracks perpendicular to the interface was calculated for a thermal loading by a homogeneous change in the temperature. In joints without an interlayer, the stress intensity factor increases to infinity as the crack approaches the interface for the case of the Young’s moduli E₁/E₂>1 (crack in material 1). Introducing a graded interlayer with a continuous transition in the material properties between the two joined materials leads to a continuous change in the stress intensity factor if the crack propagates from material 1 into material 2. Results are presented for different transition functions of the material properties and for different thickness ratios of the layers. The possible beneficial effect of a graded interlayer is discussed.     

Photoluminescence as a tool for investigations of the junction region in Cu(In,Ga)Se2-based solar cells

We use different modes of photoluminescence (PL) technique to investigate recombination processes within the junction region of Cu(In,Ga)Se₂-based solar cells. Components of the PL spectra associated with recombination within the junction region and in the bulk are distinguished. We provide arguments for the interpretation of the double diode effect in the p+ layer model basing on a close correlation between fill factor, PL intensity, and changes of space charge distribution induced by blue and red illumination.     

不同配系自反应喷射成形复相陶瓷坯件的组织与性能

以化学反应摩尔比配制的Ti-B₄C-C（以蔗糖为前驱体）为基础体系, 再分别添加5wt%Al、 5wt%Al＋20wt%Al-Ni、 5wt%Al＋20wt%Cu-Ni组成4种反应体系, 进行自反应喷射成形Ti(C,N)-TiB₂基复相陶瓷坯件试验, 研究比较4种反应体系喷射沉积坯件的组织与性能特点。研究发现, 4种坯件的组织结构均表现为以Ti(C_x, N_y)-TiB₂为主相, 以其它产物为副相的特点, 且微/纳米尺度的TiB₂棒晶弥散分布在Ti(C_x, N_y)基体相内, 其它副相则不规则地散布于整个坯件之中, 此外坯件内部均不同程度地存在孔隙。Ti-B₄C-C-Al体系的喷射沉积坯件硬度最高, 这与其主相所占比重较大并存在Al₂O₃等硬质相有关; Ti-B₄C-C-Al＋Cu-Ni体系的喷射沉积坯件的致密度和弯曲强度最低, 这与喷射过程中碳的氧化损失严重, 碳氮化钛中氮含量与其它副产物相增多有关; Ti-B₄C-C-Al＋Al-Ni体系的喷射沉积坯件的致密度、弯曲强度和断裂韧性最高, 这是由于该坯件内除存在裂纹偏转与裂纹被钉扎外, 还出现了微裂纹增韧机制。      

Influence of different parameters and their coupled effects on the stability of alumina nanofluids by a fractional factorial design approach

Nanofluids have been introduced as new-generation fluids able to improve energy efficiency in heat exchangers. However, stability problems related to both agglomeration and sedimentation of nanoparticles have limited industrial-level scaling. A fractional factorial experimental 2^k?1 design was applied in order to evaluate the effects of nanoparticle concentration, surfactant type and concentration, ultrasonic amplitude as well as ultrasonic time on the stability of alumina (Al₂O₃) nanofluids. Commercial alumina nanoparticles (particle diameter <50 nm) were dispersed in deionized water using ultrasonic probe dispersion equipment. Sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) were used as surfactants. The stability of the nanofluids in static mode was monitored by visual inspection and UV visible spectroscopy. The results of the experimental design showed that the coupled effects between surfactant type and surfactant concentration and between ultrasonication tip amplitude and ultrasonication time had the most pronounced effects on nanofluid stability. The experimental conditions providing the best stability were 0.5 wt% of Al₂O₃, CTAB, critical micelle surfactant concentration, 30% ultrasonic amplitude and 30 min of ultrasonication.     

The effect of different delineator post configurations on driver speed in night-time traffic: A driving simulator study

The aim of the study was to investigate how different delineator post configurations affect driver speed in night-time traffic. In addition, the potential speed effect of introducing a secondary task was investigated. The study was carried out in a car simulator on a road stretch including straight road sections as well as curves with different radii. Fourteen drivers participated in the study and the results show that absence of delineator posts leads to reduced speed. However, provided that there are delineator posts continuously present along the road, the overall driver speed is basically the same, regardless of the spacing between the delineator posts. The results also imply that to reduce driver speed in curves with small radius, using more compact spacing of posts in these curves as compared to in curves with a larger radius, could be a potential strategy. Additionally, the speed reducing effect of a secondary task was only prevailing where the task was initiated.     

Changes in contact angles as a function of time on some pre-oxidized biomaterials

Interfaces between biomaterials, tissue and body fluids such as blood play a key role in determining the nature of the interaction between biomaterials and the living organism. The wettability of these biomaterials in relationship to their microenvironment is an important factor to consider when characterizing surface behaviour. The measure of the contact angle between a fluid and material surface can be used to define wettability for that particular microenvironment.In this study, pure Ti, Ti6AI4V alloy, austenitic and martensitic Ni-Ti alloys, pure Ni, AISI Type 316L stainless steel, Co-Cr alloy, and -alumina were investigated. All metallic materials were mechanically polished and oxidized at 300 °C for 30 min in pure oxygen. Oxide films formed on the surfaces of these materials were examined under the electron microscope and their crystalline structures were identified by the electron diffraction method. The initial contact angle (_o) and its changes (/t) as a function of time in 1% NaCl solution drop were measured.The results of this study indicated that (i) Ti and its alloys were covered with mainly TiO₂ (tetragonal structure), (ii) NiO (cubic structure) was found on pure Ni, (iii) the spinel type oxide (cubic structure) was formed on both 316L stainless steel and Co-Cr alloy, (iv) TiO₂ (except for oxides formed on Ti6AI4V alloy) showed a rapid spreading characteristic in 1% NaCl solution; while (v) a relatively slow spreading behaviour was observed on the cubic structure oxides.