Thermal expansion of an SiC particle-reinforced aluminum composite

Using a push-rod dilatometer, we measured between 76 and 390 K the thermal expansion of a particle-reinforced-composite wrought plate obtained by powdermetallurgy methods. The particles, 30% by volume, consisted of monocrystals of -SiC with sizes near 10 m. The matrix consisted of a 6061 aluminum alloy with original particle sizes near 20 m. We found the perpendicular thermal expansivity, ₃, higher by 26% than the in-plane thermal expansivity, ₁-₂. These values differ from a rule-of-mixture prediction by –3 and –23%, respectively. All three _i, components lie outside the Rosen-Hashin bounds. Levin's isotropic model agrees within 10% with the ₁-₂-₃ average. Both the anisotropy and the bounds violation result from microstructural nonhomogeneity arising from processing. Rosen and Hashin's transverse-isotropicsymmetry relationships account approximately for these effects by introducing the anisotropic elastic constants. Using neutron diffraction, we determined that the SiC particles are textureless.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

冷弯薄壁受压C形截面局部屈曲荷载和承载力

为研究板组效应对冷弯薄壁受压C形截面局部屈曲荷载和承载力的影响,对组成其截面各板件局部屈曲时的变形协调情况进行理论分析,提出考虑该效应的腹板局部屈曲计算模型,基于能量法和静力平衡条件推导了冷弯薄壁受压C形截面局部屈曲荷载的解析解,并分别与有限条法和中国规范GB 50018—2002规定的方法进行对比.将所推导的解析解引入直接强度法,对21根冷弯薄壁C形受压短柱试验的承载力进行计算,并分别与承载力试验结果和按GB 50018—2002规定方法计算的承载力进行对比分析.结果表明:在屈曲荷载方面,本文推导的解析解合理可靠,而按中国规范规定的方法则存在系统误差,当截面高宽比小于4.5时,其结果偏于保守,当截面高宽比大于4.5时,其结果偏于不安全;在承载力方面,按本文方法计算的承载力与试验结果较为接近,合理可靠,而按中国规范规定方法计算的承载力较保守,并且随着截面宽高比的增大,保守趋势不断增大.     

Simulation of Fatigue Stiffness Degradation in Prestressed Concrete Beams under Cyclic Loading

In order to investigate and research the fatigue cracking of prestressed concrete fatigue properties and loading and stiffness degeneration process,cyclic loading tests were carried out on six prestressed concrete beams and the stiffness degradation under fatigue was investigated. A simulation model of stiffness degradation is proposed based on the stiffness analysis of the fatigue-damaged section. The elastic modulus of damaged concrete and the effective residual area of steel were introduced as well as an adjusted three-stage concrete fatigue damage evolution model. The strip method was used to analyze concrete damage due to changing stress along the depth of the beam section. The simulation and test results were compared and a method of predicting fatigue deflection was presented based on the simulation model. The predicted results were compared with that of the neural network method. It is in good agreement for the simulation results with the test results. It is only less than 5% error for the simulation model which can reveal the two-stage degradation of prestressed concrete beams under cyclic loading. It is more precise for the simulation prediction method under proper conditions.     

水平弹性支撑抛物线拱在均布荷载与热载荷作用下的屈曲特性

分析了水平弹性支撑抛物线拱在均布荷载与热负荷共同作用下的屈曲特性,通过变分原理推导了弹性支撑抛物线拱的非线性平衡方程,得到了外荷载与径向位移和轴力的关系,用数值法分析了弹性支撑抛物线拱在均布荷载与热负荷共同作用下屈曲特性。     

基于弹性网络模型的蛋白质结构-功能关系

蛋白质结构-功能关系研究是结构生物学领域的热点问题之一,具有重要的理论和实际应用价值.弹性网络模型(elastic network model,ENM)是获取蛋白质结构本身固有动力学性质,进而揭示其生物学功能的有效方法,在蛋白质结构-功能关系研究中得到了广泛应用.简要介绍了ENM的基本原理及其在蛋白质结构-功能关系中的应用,主要包括蛋白质功能性运动分析和关键位点识别等.     

基于SVM的PC刚构桥施工期时变可靠度

为了研究早龄期混凝土材料时变性能,通过现场24组主梁同步养生试块力学试验结果,得到了早龄期混凝土弹性模量的时变规律.基于支持向量机(support vector machine,SVM)建立了施工期预应力混凝土(prestressed concrete,PC)刚构桥标高控制可靠度模型,结合蒙特卡洛法计算了PC刚构桥标高控制可靠指标.结果表明:主桥同样状态下,混凝土弹性模量与龄期之间的关系呈现幂函数关系,PC刚构桥中悬臂阶段与最大悬臂阶段应以不同的自由端挠度偏差容许值控制,中悬臂阶段自由端挠度偏差容许值最大不高于4 mm,最大悬臂阶段自由端挠度偏差容许值最大不高于20 mm.     

蛋白质折叠的计算机模拟研究进展

蛋白质折叠是结构生物学领域有待解决的重要科学问题,计算机模拟方法是研究蛋白质折叠的主要手段之一.对蛋白质折叠的计算机模拟研究进展进行了简要介绍,主要内容包括:全原子分子动力学模拟、Gō模型以及弹性网络模型的主要思路及其在蛋白质折叠研究中的应用.     

某超高层框筒结构的抗震性能分析

本文以某超限框架-核心筒结构为例,通过对该结构在多遇地震下的弹性分析、设防烈度下的等效弹性计算以及罕遇地震下等效弹性分析和弹塑性分析,并对开洞楼层的楼板应力分析,检验其抗震性能。分析结果表明,通过加强措施后,能达到期望的性能目标,可供同类工程参考。     

机械弹性车轮随机振动理论与数值分析

针对现有轮胎模型不再适用于机械弹性车轮的振动分析的问题,依据其结构特点和铰链组单向传力特性,提出弹性绳索简化模型,推导弹性绳索刚度表达式、总等效刚度表达式以及系统频响函数,建立完整的振动分析数学模型.基于弹性绳索数学模型,进行C级随机不平路面输入激励下的随机振动分析,得到轮毂中心时域位移响应和频域功率谱密度响应.有限元仿真试验结果表明:机械弹性车轮共振频率为19~21 Hz,验证了弹性绳索模型的正确性.     

弹性支承梁在均布冲击荷载下的振动解耦

应用传统振动理论求解弹性支承梁的动力响应常需要借助数值方法来实现,而数值计算中的截断误差会造成数据失真和伪阻尼现象.为此,在传统弹性梁振动理论基础上,通过变换振动系统的位移表达,推导出了弹性支承梁在均布矩形脉冲和三角形脉冲两类冲击荷载下的耦合振动解析解.通过与有限元方法计算结果的比较,证明了解析解的正确性.该解析解与传统结构动力学的表达一致,可以直观反映出梁体与支座弹簧的耦合振动特征,且不会出现伪阻尼造成数据失真.算例分析表明:梁端设置弹簧以提高梁的抗冲击性能时,应综合考虑梁体材料特性及支座弹簧的刚度,设置较大刚度的支座弹簧不能有效提高梁的抗冲击性能,而对于应变率敏感的梁体材料,在梁端设置刚度较小的支座弹簧可以提高梁的抗冲击性能.