Influence of protein and lipid concentration of the test lubricant on the wear of ultra high molecular weight polyethylene

To gain a better understanding of the ultra-high molecular weight polyethylene (UHMWPE) wear mechanism in the physiological environment, the effects of protein and lipid constituents of synovial fluid on the specific wear rate of UHMWPE were examined experimentally. The multidirectional sliding pin-on-plate wear tester was employed to simulate the simplified sliding condition of hip joint prostheses. Bovine serum γ-globulin and synthetic l--DPPC were used as model protein and lipid constituents of synovia, respectively. Results of the wear test indicated that the UHMWPE wear rate primarily depended on the protein concentration of the test lubricant. Lipids acted as a boundary lubricant and reduced polyethylene wear in the low protein lubricants. However, the polyethylene wear rate increased with increasing lipid concentrations if the protein concentration was within the physiological level. Increased interactions between protein and lipid molecules and lipid diffusion to polyethylene surface might be responsible for the increased wear.     

Schwingfestigkeit von Schraube‐Mutter‐Verbindungen

High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence.     

A Bayesian approach to the multivariate Behrens-Fisher problem under the assumption of proportional covariance matrices

Summary Two independent random samples of sizesN ₁ andN ₂ from multivariate normal populationsN _p (θ₁,∑₁) andN _p (θ₂,∑₂) are considered. Under the null hypothesisH ₀: θ₁=θ₂, a single θ is generated from aN _p(μ, Σ) prior distribution, while underH ₁: θ₁≠θ₂ two means are generated from the exchangeable priorN _p(μ,σ). In both cases Σ will be assumed to have a vague prior distribution. For a simple covariance structure, the Bayes factorB and minimum Bayes factor in favour of the null hypotheses is derived. The Bayes risk for each hypothesis is derived and a strategy is discussed for using the Bayes factor and Bayes risks to test the hypothesis.     

弹药包装冲击强度试验方法的改进研究

介绍一种新的弹药包装冲击强度试验方法，应用该试验方法可以防止冲击强度试验时出现与期望值相反的现象。     

Pressure infiltration of boron nitride preforms with molten aluminum

The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment.     

棕刚玉粉中Al2O3含量分析方法的探讨

对耐火材料——棕刚玉粉的质量分析控制，提出了用实用性的检测方法测定其Al2O3含量。通过与国家标准分析方法的对比试验，证实快速实用分析方法测定棕刚玉粉中Al2O3含量是可行的。     

Failure of greenstone, jasper and cataclasite aggregate in bituminous concrete due to studded tyres: Similarities and differences

In wintertime, the use of studded tyres is common in the Nordic countries, steeply in creasing road wear. Apart from reducing surface quality and durability, the airborne dust presents a potential health hazard. To reduce road wear and dust release, there is a tendency to use harder and more wear-resistant aggregate materials.On the roads in and around Trondheim, mid-Norway, three types of aggregate material are common: greenstone, jasper and ‘mylonite’, in fact a cataclasite. Extensive laboratory testing suggests that cataclasite aggregate has better wear resistance than greenstone, but less than jasper [Erichsen E, Schiellerup H, Gautneb, H, Ottesen RT, Broekmans M. Road dust in Trondheim — analysis of the mineral content of airborne dust. (In Norwegian.) Geological Survey of Norway, NGU-report 2004. 037; 2004. p. 73]. However , observations on fluorescence-impregnated plane and thin sections demonstrate that in practice, cataclasite wears faster than greenstone, which may be attributed to its oriented fabric, as opposed to the random fabric in greenstone and jasper. The original article by Rosiwal from 1896 [Rosiwal A. Neue Untersuchungser gebnisse über die Härte von Mineralien und Gesteine. Verhandlungen der kaiserlich-königlichen geologischen Reichsanstalt, vol. 17/18; 1896. p. 475–491] on abrasion hardness and anisotropy provides an elegant explanation for the field observations.     

Case Study of an Aerosol Explosion and a Method to Determine Explosion Temperatures

A failure analysis case study is presented for a two-piece aerosol containing tetrafluoroethane, commonly referred to as Refrigerant 134a. A gentleman was preparing to recharge the air conditioning system of an automobile when the bottom exploded off the aerosol container, propelling the body of the aerosol container like a rocket, which hit the man in the eye and blinded him in that eye. The aerosol was never connected to the air conditioner, therefore backpressure from the air conditioner (AC) compressor was ruled out as a cause for the explosion. The objective of the study was to determine why the aerosol exploded. Several recently developed test methods were used, including two types of heat-to-burst tests and a puncture chamber to measure the pressure-versus-temperature behavior of aerosols. More common test methods were also used, such as water bath pressure tests, hydro pressure burst tests, pneumatic pressure burst tests, hardness measurements, weight measurements, metallography, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an accident scenario recreation. A semi-empirical correlation between the hardness and weights of the container bottoms was used to determine the explosion temperature and/or pressure. This semi-empirical correlation agrees in principle with an analysis of the explosion pressures using finite-element analysis (FEA). The root cause for the explosion was determined to be a lack of strength of the bottom of the two-piece aerosol coupled with heating the aerosol to temperatures significantly above room temperature.     

锅炉炉管爆破原因分析

对在爆裂的水冷壁管正常管段和鼓包处所取的试样分别进行化学分析、金相检验、硬度测定和高温拉伸试验。分析结果表明，在近烧嘴的炉管长期处于超温工作状态，引起该部位材质严重劣化，高温强度不断下降，当该部位的高温强度低于锅炉炉管对材质所要求的技术条件即会发生爆裂。对炉管的继续使用提出了应急的预防措施。     

Schäden durch kerbinduzierte Schwingbrüche

Failures by notch induced fatigue fractures Notches produce local stress concentrations and promote the formation of fatigue cracks. Characteristic types of notches as a result of design, manufacturing and operation are presented and remedial measures are discussed. Examples demonstrate the effect of different kinds of notches on various components.