Effect of wear on EHD film thickness in sliding contacts

A theoretical solution to the elastohydrodynamic (EHD) lubrication problem in sliding contacts, which takes into consideration the effect of the change in shape of the gap due to wear on the load‐carrying capacity, is presented. The model of such a contact is based on assumptions of Grubin and Ertel (von Mohrenstein). The resultant dimensionless Reynolds and film profile equations have been solved numerically for a number of cases with several values of thickness of the worn layer. Iteration of the EHD film thickness is performed by means of the secant method. Values of the calculated dimensionless film thickness are presented as a function of dimensionless wear. The conclusions concern the influence of the linear wear on the film thickness in heavily loaded sliding contacts. Copyright © 2006 John Wiley & Sons, Ltd.     

Thermophysical properties from the equation of state of Mason and co-workers

The theory gives formulas for calculating the three temperature-dependent parameters of the equation of state from the intermolecular potential. But the second virial coefficient also serves to predict the entire equation of state in terms of two scaling parameters and, hence, a number of other thermodynamic properties including the Joule-Thomson inversion curve, bulk modulus. secant bulk modulus, and inverse isobaric expansivity among others. Agreement with experimental data is quite good. Paper dedicated to Professor Edward A. Mason.     

Incremental‐secant modulus iteration scheme and stress recovery for simulating cracking process in quasi‐brittle materials using XFEM

In this paper, an incremental‐secant modulus iteration scheme using the extended/generalized finite element method (XFEM) is proposed for the simulation of cracking process in quasi‐brittle materials described by cohesive crack models whose softening law is composed of linear segments. The leading term of the displacement asymptotic field at the tip of a cohesive crack (which ensures a displacement discontinuity normal to the cohesive crack face) is used as the enrichment function in the XFEM. The opening component of the same field is also used as the initial guess opening profile of a newly extended cohesive segment in the simulation of cohesive crack propagation. A statically admissible stress recovery (SAR) technique is extended to cohesive cracks with special treatment of non‐homogeneous boundary tractions. The application of locally normalized co‐ordinates to eliminate possible ill‐conditioning of SAR, and the influence of different weight functions on SAR are also studied. Several mode I cracking problems in quasi‐brittle materials with linear and bilinear softening laws are analysed to demonstrate the usefulness of the proposed scheme, as well as the characteristics of global responses and local fields obtained numerically by the XFEM. Copyright © 2006 John Wiley & Sons, Ltd.     

有关传递矩阵法特征值问题的研究

在用传递矩阵法1求解多圆盘转子系统的特征值问题时,经常会出现数值不稳定和误差较大的现象。将求传递矩阵特征值的割线法进行改进,使得计算结果的误差变得较小,计算结果的可靠性增强。最后通过实例证实本算法的优越性。     

骨料对混凝土力学性能的影响分析

利用颗粒流方法,实现了相同条件下混凝土的骨料大小和空间位置对其破坏形态、应力-应变曲线、峰值应力和割线模量的影响规律研究.通过对比砂浆与骨料的不同质量比(5∶5,4∶6,3∶7,2∶8)以及不同级配(一级配、二级配、三级配、四级配)骨料的混凝土单轴压缩仿真试验结果,发现骨料有阻止混凝土裂纹扩展的作用,且骨料越大,阻止混凝土裂纹扩展的作用越强,而微裂纹多绕骨料产生和发展;砂浆中加入骨料对混凝土强度和变形特性具有明显的改善作用,相对于砂浆的峰值应力5.2MPa和割线模量30.7GPa而言,在砂浆与骨料质量比为5∶5和4∶6时,不同级配混凝土的峰值应力约增加22%~48%、割线模量增加-8%~99%,其平均值基本维持在6.5MPa和7.2MPa,37.4GPa和42.6GPa;在砂浆与骨料质量比为3∶7和2∶8时,不同级配混凝土的峰值应力急剧增加40%~228%、割线模量急剧减小79%~92%,其平均值分别为9.2MPa和15.4MPa,15.8GPa和4.4GPa.当砂浆与骨料的质量比相同时,骨料级配越高,越容易形成架空结构,造成局部不稳定,影响骨料增强效果;级配相同时,混凝土强度随骨料质量占比的增大而增大,且其应力-应变曲线呈现出单峰到双峰再到单峰的变化趋势,这说明骨料空间结构的稳定程度决定了混凝土应力-应变曲线的形状变化.     

水泥土力学性能的试验分析

通过一系列水泥土工程力学性能试验,得到了水泥土的基本力学参数.对试验结果进行回归分析后,给出了水泥土抗压强度的影响因素及其与抗压强度的关系、变形模量与抗压强度的关系、抗剪强度与正应力的关系、水泥土应力-应变曲线的回归方程以及不同水泥掺量和龄期的水泥土抗压强度推算公式.     

高层框架-抗震墙结构在地震作用下内力重分布的近似计算

根据钢筋混凝土框架及抗震墙的模型试验数据 ,确定了各种变形阶段框架及抗震墙的割线刚度 ;并分析了多高层建筑结构侧移的成分 ,以及引起震害的侧移 ,将不同变形阶段框架及抗震墙的割线刚度、目标位移的控制值与引起震害的侧移值相联系 ,按割线刚度、采用矩阵位移法对高层框架 -抗震墙结构进行分析。从而得到遭遇本地区多遇地震、设防烈度地震及罕遇地震时 ,结构的弹塑性变形 ,框架、抗震墙及连梁的刚度退化程度 ,以及水平地震作用在框架和抗震墙之间分配规律的变化     

软土地层咬合桩成桩施工引起的邻近建筑沉降分析

以某轨道交通深基坑工程中钻孔咬合桩挡土结构为背景工程,针对软土地区咬合桩成桩施工引起邻近建筑沉降这一工程问题,对咬合桩的施工工艺流程及其对地层的扰动机理进行了分析,并结合成桩过程中的工程实测资料对成桩施工引起的临近建筑沉降规律进行了分析,提出了减少咬合桩施工引起的沉降、保护周围房屋建筑的措施。     

地基沉降量计算方法分析研究

对目前采用的最终沉降量计算方法进行了分析比较，通过工程实例，验证了割线模量法计算最终沉降量的可行性，提出了宜采用割线模量法估计最终沉降置的建议。     

咬合桩支护结构的抗弯承载特性研究

钻孔咬合桩作为一种较为新颖的基坑挡土墙形式,其抗弯承载力特性对于基坑挡墙的设计来说至关重要。在室内试验的基础上,根据缓凝时间要求,确定C30超缓凝混凝土的配比;通过相似模型试验对咬合桩支护结构在考虑素桩作用下的抗弯承载力特性进行研究,揭示了咬合桩从弹性到塑性破坏不同阶段荤素桩力学行为,提出了其抗弯承载力计算方法.进一步结合上海地铁某咬合桩试验段,通过实测钢筋应力和测斜曲线推算了不同工况下咬合桩抗弯承载力的发挥情况.实测情况表明,考虑素桩作用的抗弯承载力设计是合理的。