CE模型下指数分布步加试验的贝叶斯估计

本文利用Gibbs抽样法得到了CE模型下指数分布场合步进应力加速寿命试验的多层Bayes参数估计,最后通过模拟比较表明多层Bayes估计比最大似然估计更加有效而实用。     

Modelling and forecasting mortality in Spain

Experience shows that static life tables overestimate death probabilities. As a consequence of this overestimation the premiums for annuities, pensions and life insurance are not what they actually should be, with negative effects for insurance companies or policy-holders. The reason for this overestimation is that static life tables, through being computed for a specific period of time, cannot take into account the decreasing mortality trend over time. Dynamic life tables overcome this problem by incorporating the influence of the calendar when graduating mortality. Recent papers on the topic look for the development of new methods to deal with this dynamism.     

A new family of low wear,low coefficient of friction polymer blend based on polytetrafluoroethylene and an aromatic thermosetting polyester

To improve the wear resistance of polytetrafluoroethylene (PTFE), a crosslinked aromatic thermosetting polyester (ATSP) has been blended directly with PTFE. Cured ATSP powder which was directly synthesized as a cured powder form was used for this application. Because of the similar processing temperature range of cured ATSP and PTFE, composites within the entire composition range were successfully prepared by blending these two powders using a hot press. Tribological pin‐on‐disk tests (composite pins sliding against gray cast iron disks) showed improvement on friction coefficient of all composites and much less wear than pure PTFE. The composites survived at contact pressures of 7 MPa, which is higher than either pure PTFE or pure ATSP could sustain. With an increase in the amount of ATSP in the composites, storage modulus, and glass transition temperature were higher, and the wear resistance was enhanced. SEM images helped provide explanations for the unusually low mean wear rates that were observed for these composite samples. Copyright © 2008 John Wiley & Sons, Ltd.     

Notch fatigue of Cu_(50)Zr_(50) metallic glasses under cyclic loading: molecular dynamics simulations

Molecular dynamics simulation is performed to simulate the tension–compression fatigue of notched metallic glasses(MGs), and the notch effect of MGs is explored. The notches will accelerate the accumulation of shear transition zones, leading to faster shear banding around the notches' root causing it to undergo severe plastic deformation. Furthermore, a qualitative investigation of the notched MGs demonstrates that fatigue life gradually becomes shorter with the increase in sharpness until it reaches a critical scale. The fatigue performance of blunt notches is stronger than that of sharp notches. Making the notches blunter can improve the fatigue life of MGs.     

Environmentally benign green composites based on epoxy resin/bacterial cellulose reinforced glass fiber: Fabrication and mechanical characteristics

Bio-based bacterial cellulose (BC) epoxy composites were manufactured and their mechanical properties were examined. The BC was initially fabricated from Vietnamese nata de coco by means of alkaline pretreatment followed by solvent exchange. The obtained fibers were dispersed in epoxy resin (EP) by both mechanical stirring and ultrasonic techniques. The resulting blend was used as the matrix for glass-fiber (GF) composite fabrication using a prepreg method followed by multiple hot-press-curing steps. The morphology, mechanical characteristics and mode-I interlaminar fracture toughness of the fabricated composites were investigated. With a 0.3-wt% BC content, the mode-I interlaminar fracture toughness for both crack initiation and crack propagation were improved by 128.8% and 1110%, respectively. The fatigue life was dramatically extended by a factor of 12, relative to the unmodified composite. Scanning electron microscopy images revealed that the BC plays a vital role in increasing the interlaminar fracture toughness of a GF/EP composite via the mechanisms of crack reflection, debonding and fiber-bridging.     

Determination of reliable fatigue life predictors for magnetorheological elastomers under dynamic equi-biaxial loading

Fatigue life prediction is of great significance in ensuring magnetorheological elastomer (MRE) based rubber components exhibit reliability and do not compromise safety under complex loading, and this necessitates the development of plausible fatigue life predictors for MREs. In this research, silicone rubber based MREs were fabricated by incorporating soft carbonyl iron magnetic particles. Equi-biaxial fatigue behaviour of the fabricated MREs was investigated by using the bubble inflation method. The relationship between fatigue life and maximum engineering stress, maximum strain and strain energy density were studied. The results showed that maximum engineering stress and stored energy density can be used as reliable fatigue life predictors for SR based MREs when they are subjected to dynamic equi-biaxial loading. General equations based on maximum engineering stress and strain energy density were developed for fatigue life prediction of MREs.     

Creep life evaluation of aluminum conductor composite core utilized in high voltage electric transmission

The creep life of aluminum conductor composite core (ACCC) utilized in high voltage electric transmission was investigated using an experimental method based on the equivalence relationship. First, the time-temperature-stress equivalence relationship was developed using the time-temperature and the time-stress equivalence relationships. Then, tensile creep experiments were conducted under different temperatures and different stress levels to obtain the strain-time curves of the ACCC. Finally, the creep strain master curve was obtained using the experimental data based on the time-temperature-stress equivalence relationship, allowing prediction of ACCC creep life. The results will play an important role in evaluation of the long-term characteristics of the ACCC for engineering applications.     

微动摩擦学的发展现状与趋势

对微对摩擦学的发展过程和现状，包括微动磨损、微动腐蚀和微动疲劳作了相当系统耐简要的综合介绍与评论，重点归纳分析了近１０年来劝摩擦学的发展概况，并且分别就法国和国内有关研究工作作了集中评介。指出微动摩擦力学研究在发达国家的进展尤快，说明高科技的发展对这个学科领域研究要求的迫切性，应该引起我国摩擦学界和工程界科技工作者更多的关注，同时认为基础研究、工业应用研究和失效分析，都是微动摩擦学研究今后工作的重     

含纳米粒子溶液对单晶硅表面的冲蚀磨损损伤实验研究

利用高分辨透射电子显微镜和原子力显微镜观察了含纳米颗粒溶液冲蚀硅片表面损伤行为,考察了纳米颗粒碰撞单晶硅片所导致的微观物理损伤.结果表明:冲蚀30 s后,在高分辨透射电子显微镜下可见硅片表面呈现方向性损伤,并可观察到大量非均匀的晶格缺陷;当冲蚀10 min时,硅片表面出现微观划痕和凹坑,在划痕一端可见原子堆积,亚表面可观察到镶嵌晶粒的非晶损伤层;继续延长冲蚀时间将加剧其表面损伤.     

羟基硅酸盐润滑油添加剂对45#钢/球墨铸铁摩擦副摩擦磨损性能的影响

采用MM-200型摩塔磨损试验机考察了45^#钢／球墨铸铁摩擦副在650SN基础油和含羟基硅酸盐矿物复合微粉的650SN基础油(KF-1)润滑下的摩擦磨损性能，结果表明：在650SN基础油润滑下的摩擦系数和磨损率随试验时间增加变化较小；而在KF-1润滑下，试验初期的摩擦系数和磨损率比基础油润滑下的稍大，随着试验时间的延长，相应的摩擦系数和磨损率同基础油润滑下的相比明显降低．磨损表面显微硬度测试结果表明，在KF-1润滑下45^#钢磨损表面形成了多孔摩擦改性层，硬度明显提高，因而摩擦磨损性能显著改善．