Critical mechanical properties and FEA simulation for crashworthiness assessment of a coarse-grained cast AM50 alloy

A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques.For cast Mg alloys,the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension.The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant.The load vs.deflection of Charpy specimens were measured for modelling,and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression.The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality;though for the flat-grooved plane strain specimen,the equivalent fracture strain remains constant over the range of stress triaxiality investigated.Because the two different specimen geometries give rise to different Lode angle values,the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys.Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model,and were found to provide a reasonable description of the load-displacement curves measured in the tests.For the flat-grooved plane strain specimens,the computations under-predicted the force-displacement response measured.

商用和工业用发动机发展趋势

降低排放和改善能耗是决定道路用和非道路用发动机未来发展方向的重要因素。通过采用天然气替代柴油以实现燃料灵活性。为了满足未来的需求,发动机将变得更加复杂。此外,基型机上将采用更先进的附属系统,用来进行回收废热、气态燃料供给、排气后处理及其控制。增加发动机的复杂性将会增大整个动力系统的尺寸、质量及成本。未来发动机发展的另一个关键因素是优化基型机,满足未来的排放法规(包括CO2)要求,通过优化基型机弥补附件增加带来的尺寸、质量和成本的增加。发动机缩缸强化、新材料、减小摩擦、先进增压和燃油喷射系统技术等方面已在轻型车辆领域显示出潜力并已处于具体实施阶段。介绍未来商用和工业用发动机基型机的改进方案及潜力,描述这些技术如何改善商用和工业用基型发动机,以满足未来排放法规及燃油效率要求。

Measurement of^(25)Al+p Resonant Scattering

Type I X-ray bursts are the most frequently observed thermonuclear explosions in nature[1].They take place on the surface of accreting neutron star in low-mass X-ray binary systems.

解释渗透率不均衡下降的井壁效应／凝胶滴模型

许多聚合物和凝胶都可以使水的渗透率降得比油或气的渗透率还要低，但造成渗透率不均衡下降的机理尚不清楚，本文提出了一种综合了“井壁效应”和“凝胶滴”模型的解释，渗透率不均衡下降的诸多方面都可以利用井壁效应模型来解释使用的凝胶是否与润湿相相匹配；也可以通过凝胶滴模型解释出所用的凝胶是否或与非润湿相相匹配，综合模型预测到渗透率不均衡下降的程度会随着非润湿相饱和度的增加而增加，新的实验结果证实了这一预测。