基于近场动力学理论的混凝土轴拉破坏过程模拟

近场动力学PD(Peridynamics)是一种新兴的基于非局部模型描述材料特性的数值计算方法.该方法假定位于连续体内的粒子通过有限的距离与其他粒子相互作用,通过积分计算在一定近场范围(Horizon)内具有一定影响域的材料点之间的相互作用力,而不论位移场的连续与否,避免了传统的局部微分方程求解在面临不连续问题时的奇异性和现有多尺度算法的复杂性.本文概述了PD方法的基本思想、建模方法和计算体系,给出了用近场动力学方法模拟混凝土在轴向拉伸荷载作用下的计算格式.算例结果表明,PD方法可以很好地刻画和模拟混凝土在轴拉情形下的损伤累积与渐进破坏过程.最后讨论了PD方法在理论、计算和应用等方面有待进一步研究的问题.     

Discrete element modeling of acoustic emission in rock fracture

The acoustic emission (AE) features in rock fracture are simulated numerically with discrete element model (DEM). The specimen is constructed by using spherical particles bonded via the parallel bond model. As a result of the heterogeneity in rock specimen, the failure criterion of bonded particle is coupled by the shear and tensile strengths, which follow a normal probability distribution. The Kaiser effect is simulated in the fracture process, for a cubic rock specimen under uniaxial compression with a constant rate. The AE number is estimated with breakages of bonded particles using a pair of parameters, in the temporal and spatial scale, respectively. It is found that the AE numbers and the elastic energy release curves coincide. The range for the Kaiser effect from the AE number and the elastic energy release are the same. Furthermore, the frequency-magnitude relation of the AE number shows that the value of B determined with DEM is consistent with the experimental data.     

考虑无缺陷退货的在线商品信息发布策略

消费者网络购物面临的不确定性往往导致非质量原因的退货。合理发布产品信息,并提供退货保障,是网络零售商促进消费者购买和提高利润的有效策略。基于消费者效用理论和博弈论,构建了产品信息影响消费者购买和退货模型,研究了零售商在垄断和竞争情形下的产品信息发布决策问题,发现垄断性零售商的最优信息发布策略和竞争性零售商在发布产品信息量和信息内容方面的均衡策略均取决于产品价值和退货成本特征,提出了不同市场结构下基于产品特征的在线商品信息发布策略。     

基于故障树分析的堰塞湖溃坝概率估计方法

堰塞湖排险的一个关键问题是如何针对实施不同应对措施情况下的堰塞湖溃坝概率进行估计,这是一个值得关注的重要研究课题。本文提出了一种基于故障树分析(FTA)的堰塞湖溃坝概率估计方法。首先,通过堰塞湖排险问题的实际背景分析,基于FTA构建了堰塞湖溃坝故障树的基本架构;然后,通过相关领域知识、历史案例分析、专家主观判断和多位专家主观判断信息的融合,可以确定实施某一应对措施情形下故障树中各基本事件在不同时段内发生的概率;进一步地,依据构建的故障树和基本事件发生的概率,给出了在不同时段内堰塞湖溃坝事件发生的概率的估计方法。最后,通过一个实例分析说明了本文所提出方法的可行性与有效性。     

高温后钢管活性粉末混凝土的动态力学性能

采用霍普金森压杆装置对高温后钢管活性粉末混凝土(reactive powder concrete-filled steel tube,RPC-FST)进行冲击压缩实验,分析了应变率效应及温度效应对试件动态力学性能的影响。结果表明:高温(200、300 ℃)后RPC-FST仍具有较好的抗冲击能力、延性和完整性;冲击荷载作用下,RPC-FST的应变率效应明显弱于RPC的应变率效应;随着过火温度的提高,RPC-FST的峰值应力逐渐增大,变形能力增强,抗冲击能力提高。动力提高系数随过火温度的提高而增大,说明高温后RPC-FST的应变率效应更显著。     

超高强度平头圆柱形弹体对低碳合金钢板的高速撞击实验

为分析不同组分低碳合金钢板抗超高强度低碳合金钢弹体的高速撞击性能及破坏模式,以两种典型防弹特种钢SS、AS以及常见的Q235A钢为研究对象,通过静态拉伸、静态压缩及动态压缩测试,获得静态拉伸和压缩性能参数以及1 000~6 000 s-1应变率范围内的力学行为,分析了材料组分与力学性能的相关性。采用弹道枪加载撞击方法,获得了两种超高强度合金钢平头圆柱形弹体对3种钢板(14.5~15.9 mm厚)的弹道极限速度,通过分析获得了不同工况下的极限比吸收能,讨论了合金钢板在弹体高速撞击下破坏模式的差异,分析了材料力学性能与破坏模式的相关性。研究表明:3种合金钢板抗弹体撞击性能与材料屈服强度正相关,但其性能间的差异远小于屈服强度间的差异;在超高强度合金钢平头圆柱形弹体的高速撞击下,3种钢板的失效机制与其力学性能密切相关,Si和Mn含量高的AS钢呈硬脆性特征,其断裂失效主要取决于材料的剪切强度,而Si和Mn含量较低的SS钢和Q235A钢具有良好的塑性,其断裂失效主要取决于材料的压缩强度和剪切强度。     

Long-term failure of a layered viscoelastic composite material with a crack under a time-dependent load

The long-term failure of a layered viscoelastic composite caused by precritical propagation of a coin-shaped crack is studied. It is assumed that the crack is located inside a viscoelastic layer (the layer of binder) parallel to the layer orientation. The crack development due to stretching of the composite massive by uniformly distributed external forces increasing with time is described. It is assumed that these forces act perpendicularly to the plane of crack propagation. The investigation is carried out within the framework of Boltzmann-Volterra linear theory for resolving integral operators with difference kernels describing the deformation of a material with time-dependent rheological properties. An irrational function of the viscoelastic integral operator is presented in the form of a proper continued fraction and transformed using the method of operator continued fractions. Numerical solutions are obtained for resolving integral operators with the kernel in the form of Rabotnov exponential-fractional function. The kinetics of crack growth with a prefailure zone commensurable with the crack length is described. A comparison with the results obtained in terms of the concept of thin structure of the crak tip is given.Timoshenko Institute of Mechanics, Ukrainian National Academy of Sciences, Kiev, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 4, pp. 545–558, July–August, 2000.     

The effect of hydrostatic pressure on the crack resistance of particulate reinforced composite materials

The effect of hydrostatic pressure on the fracture toughness of disperse-reinforced composite materials is investigated. It is shown that increased hydrostatic pressure leads to an increase in the critical value of the stress intensity factor and, as a consequence, to an increase in the crack propagation rate. In this case, the pressure-time analogy method can be used to describe the effect of hydrostatic pressure on the characteristics of the crack resistance. This method enables us to represent the experimental data obtained in the form of a generalized dependence of the fracture toughness on the reduced loading rate. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 1, pp. 121–126, January–February, 2000.     

伴随微孔洞生长的裂纹弹塑性定常扩展

裂纹在韧性材料中扩展时,将们随着微孔洞的萌生和生长,孔洞的萌生和深化将直接影响着材料的总体断裂韧性和强度,以往的研究主要集中在将裂纹的扩展刻划为微孔洞的萌生、生长和汇合这样一个过程。从传统的断裂过程区模型出发研究微孔洞的萌生和生长对材料总体断裂韧性的影响,通过采用Ｇｕｒｓｏｎ模型,建立塑性增量本构关系,然后针对定常扩展情况直接进行分析,孔洞对材料断裂韧性的影响由本构关系刻划,而在孔洞汇合模型中,上     

高边坡岩体渐进性破坏粘弹塑性有限元数值模拟

根据边坡实际地质模型 ,基于弹塑性与粘弹 -粘塑性理论的本构方程 ,通过有限元模拟分析 ,定量地揭示和模拟再现了高边坡岩体破裂、变形、破坏及失稳前后锁固段岩体渐进性破坏的机制和过程 ,探讨了高压水流作用下滑坡启程剧动的破坏机理。