考虑各向异性对软土隧道沉降的影响

采用不同本构模型对盾构开挖第4阶段的沉降进行了模拟,模型分别为考虑各向异性的本构模型（EVP-SCLAY1模型）和各向同性模型（MC模型和MCC模型）,将这3个模型的计算结果与实测数据之间进行了对比,结果显示,在模拟盾构开挖引起的沉降范围以及地表沉降时,各向异性模型模拟结果与实测结果更加吻合,而MC模型预测结果最差。     

混凝土构件正常使用极限状态的可靠度计算

以混凝土构件混凝土表面出现锈胀裂缝作为混凝土构件的正常使用极限状态 ,建立了混凝土构件在正常使用情况下的极限状态方程 ,应用可靠度程序进行计算 ,讨论了正常使用情况下各个因素对混凝土构件可靠指标的影响     

Displacements and stresses due to a vertical point load in an inhomogeneous transversely isotropic half-space

We present the solutions for displacements and stresses subjected to a vertical point load in a continuously inhomogeneous transversely isotropic half-space with Young's and shear moduli varying exponentially with depth. Planes of transverse isotropy are assumed to be parallel to the horizontal surface. The solutions for the half-space are obtained by superposing the solutions of two full spaces, one with a point load in its interior and the other with opposite traction of the first full space along the z=0 plane. The Hankel transform in a cylindrical co-ordinate system is employed for deriving the solutions. However, the resulting integrals for displacements and stresses involve polynomial, exponential function, and Bessel function that cannot be given in closed form; hence, numerical techniques are adopted in this work. In order to check the accuracy of numerical procedures, the comparisons are carried out with the homogeneous solutions of Liao and Wang, and the calculated results agree with those to nine decimal places. Furthermore, two illustrative examples are presented to elucidate the effect of inhomogeneity, and the type and degree of rock anisotropy on the vertical surface displacement and vertical normal stress in the inhomogeneous isotropic/transversely isotropic rocks subjected to a vertical concentrated force acting on the surface. The calculated results show that the induced displacement and stress are decisively influenced by the inhomogeneity, and the degree and type of material anisotropy. The proposed solutions can more realistically simulate the actual stratum of loading problem in many areas of engineering practice.     

On estimating the interface normal and curvature in piecewise linear interface calculation-volume of fluid approach for three-dimensional arbitrary meshes

Volume of fluid (VOF) method with its Piecewise Linear Interface Calculation (PLIC) reconstruction algorithm is one of the most popular approaches in numerical simulation of interfacial flows with a wide range of applications in different areas. In an effort to evaluate the similarity of the PLIC-generated planes in comparison with the exact interface, a point-cloud, based on the polygon centers of PLIC planes is extracted, which later is used to form a triangular grid that represents the estimated interface. The main objective of this article is to evaluate the interface geometrical properties based on the extracted triangular grid of the interface. The methods presented in this article, characterized by a higher spatially convergence ratio, are compared with the commonly used methods. The proposed methods are tested for two 3-dimensional general test cases, where an evident improvement is seen in calculation accuracy and spatial convergence of the errors of interface normal vector and curvature.     

An Investigation into the Effect of Normal Load Frequency on Fretting Fatigue Behavior of Al7075-T6

Most previous studies on fretting fatigue have been accomplished under constant normal loading and less attention has been paid to cyclic normal loading. An innovative test apparatus was specially designed and manufactured for fretting fatigue tests under cyclic loading in this work and the fretting fatigue behavior of Al7075-T6 was investigated at different normal load frequencies. A finite element model was developed to study the effect of normal load frequency on the contact stress distribution. It was found that the cyclic normal load has a more damaging effect on fretting fatigue life compared to constant normal load, particularly at lower frequencies. The results showed that at the normal load frequency of f = 1 Hz, fatigue life decreased by 52% in the high cycle fatigue regime and 28% in the low cycle fatigue regime. The experimental results also indicated that at the normal load frequency of 80 Hz, the fretting fatigue life converged to its corresponding life under constant normal load condition. The fracture surface and the fretting area of the specimens were examined using both optical and scanning electron microscopy (SEM). The experimental observations showed that the dominant partial slip condition with a wider slip region compared to constant normal loading, severe delamination, and higher oxidation rate due to the normal load release at each cycle, are the most important reasons for significant reductions in fretting fatigue life, under cyclic normal loading, especially for low normal load frequencies.     

内翻U形外包钢组合梁正截面抗弯承载力分析

为研究新型内翻U形外包钢混凝土组合梁正截面抗弯承载力及其构造要求,以已有内翻U型外包钢混凝土组合连续试验梁为参照,建立该组合连续梁非线性有限元模型,模拟组合连续梁有限元模型的荷载跨中挠度曲线,并与相关试验结果对比,验证了该组合梁有限元模型的建模方法和参数选取的合理性与有效性。应用建立的组合连续梁有限元模型,分析了内翻外包钢混凝土组合梁正截面抗弯承载力的主要影响参数。综合内翻U型外包钢混凝土组合连续梁正截面抗弯承载力试验和模拟结果,提出采用简化塑性理论计算组合梁正截面抗弯承载力计算时,组合梁正截面抗弯承载力塑性理论计算值应乘0.96的修正系数。0.96倍组合梁正截面抗弯承载力塑性理论计算值与组合梁有限元模型模拟计算值相比较,发现二者十分接近,偏于安全,提出的组合梁正截面抗弯承载力修正简化塑性理论计算值具有足够的准确性和可靠性。     

吸附制冷用混合吸附剂导热性能的研究

用水溶液挤压法制备了24个CaCl2/ENG成型混合吸附剂样品,利用目前闪光扩散法测量导热系数最先进的仪器——LFA447激光导热仪对样品进行了导热系数的测试。研究表明:挤压法制备的样品垂直于压力方向上的导热系数高于平行于压力方向上的,大约是其1.1~1.2倍,具有各向异性;在一定范围内,随着固化密度的增加导热系数不断增加,随着氯化钙和膨胀石墨质量比的减小导热系数也不断增大;在氯化钙和ENG的质量比为2∶1,固化密度从600kg/m3增加到700kg/m3的过程中导热系数增加得最为明显,固化密度和膨胀石墨的含量对成型吸附剂样品的导热系数的影响有耦合作用。     

铋掺杂对铌酸钾钠无铅压电陶瓷结构和性能的影响

用常压烧结法制备铋掺杂铌酸钾钠无铅压电陶瓷(K0.5Na0.5)1-3xBixNbO3(KNBN)。研究不同铋掺杂量对KNN陶瓷结构、形貌、致密度及电学性能的影响。结果表明:在1 120℃烧结的含铋量为1%(摩尔分数)的陶瓷表现出最好的铁电和压电性能及较好的介电性能,即压电常数最大121pC/N,P-E回线形状达到饱和,且剩余极化为12.67μC/cm2,矫顽场Ec为13.58kV/cm,介电常数为575,损耗为5.82%(频率为1kHz)。陶瓷样品在131℃从正交结构转变到四方结构,Curie温度为400℃。     

师范院校无机元素化学的教学改革与探讨

针对师范院校应用化学、化学等专业在元素化学课程的教学过程中存在的问题,并结合教学及科研经历,从如何激发学生的学习动力、提高学生的学习兴趣、开发学生的创新潜能、培养学生的自主学习能力等方面进行初步探讨,并提出相应的改革措施。     

磺化硅胶催化合成乙酸正辛酯的研究

磺化硅胶是一种以化学键键合而成,性能稳定的固体酸催化剂。文章以冰醋酸和正辛醇为原料,磺化硅胶为催化剂,合成了乙酸正辛酯,并获得了最佳合成条件:n(乙酸)∶n(正辛醇)=1∶1.2,回流时间为50 min,催化剂用量为反应物总质量的0.8%,乙酸正辛酯的酯化率可达97.5%,催化剂重复使用5次后的酯化率仍达91.1%。磺化硅胶对乙酸正辛酯的合成具有良好的催化活性。