边坡预应力锚杆蠕变的数值分析

运用非线性蠕变分析理论模型,采用MSC.MARC软件重点研究了锚杆的应力指数、蠕变系数和几何参数的变化对于锚杆应力松弛的影响.通过对预应力锚杆支护的边坡进行数值分析,探讨了锚杆的蠕变规律以及锚杆预应力松弛现象.锚杆的参数取不同数值时,比较数值模拟结果发现:锚杆的轴力和剪力主要分布在锚固段的前端;随着锚杆应力指数及蠕变系数的增加,蠕变应变增大,应力松弛加快.     

Nonlinear creep of unidirectional fibrous composites tensioned along the reinforcement

Creep strains in unidirectional organic-fiber-and organic-glass-fiber-reinforced plastics subject to tension in the reinforcement direction are predicted. Based on homogeneity condition and statistical criteria, it is shown that the creep of the composites is essentially nonlinear. To predict creep strains, use is made of a nonlinear creep model based on a modified Rabotnov’s similarity hypothesis for isochrones and of material constants determined from tests on specimens made of a composite as a whole and specimens made of its separate components, the mixing rule applied in the latter case. The calculated results and the experimental data are in satisfactory agreement __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 5, pp. 20–34, May 2007.     

砂岩短时单轴直接拉伸蠕变特性试验研究

采用自行设计加工的挂重型岩石材料直接拉伸装置,对重庆市某地红砂岩进行了短时分级加载单轴直接拉伸蠕变试验,并对该砂岩的蠕变特性进行了分析。结果表明,砂岩在该试验条件下具有明显的蠕变特性,其蠕变表现为衰减蠕变和稳态蠕变两个阶段,砂岩蠕变量与稳态蠕变速率随着荷载的增加而增加。应用三参量广义Kelvin模型与Burgers蠕变模型描述该砂岩的蠕变规律,结果表明,两个模型均可以准确描述该砂岩的蠕变特性,其中,Burgers蠕变模型效果更佳。本文所得结论可为从事相关研究的工作人员提供一定的借鉴。     

煤矿泥岩流变模型辨识及支护方法的确定

结合高家梁煤矿斜井泥岩的流变变形特征, 对泥岩进行分析建模, 设计有效的泥岩斜井支护措施. 通过对泥岩进行蠕变加卸载试验, 采用统一流变力学模型理论建立了能表现泥岩流变特性的弹性--黏性--黏弹性--黏弹塑性模型, 并确定了流变模型参数. 结合泥岩试验测得的泥岩力学特性和现场观测资料, 设计采用锚喷网联合支护方法, 并采用大型有限元软件ADINA进行数值模拟分析, 该支护方法能有效控制泥岩变形, 采用的锚喷网支护方法合理可靠.     

非平稳温度场影响下混凝土结构的随机徐变应力

大体积混凝土结构的徐变应力受多种随机因素的影响。文中视混凝土结构内部温度场为非平稳随机过程，对此非平稳温度场采用了时域上简化处理的方法。同时，为进一步考虑材料参数（如徐变度、弹模等）随机性的影响，文中将随机有限元法引入到混凝土结构随机徐变应力的计算中，提出了求解随机徐变应力的初应变随机有限元隐式解法。     

梁的循环弯曲蠕变脆断损伤失效分析和预测

提出了梁的循环弯曲蠕变损伤失效分析方法，推导了梁的循环弯曲蠕变损伤基本方程，以梁的弯曲惯性矩减少定义弯曲损伤变量，给出了便于工程应用的失效预测方程。     

基于纳米压痕法无铅焊锡连接各层材料力学性能的研究

利用SMT全自动回流焊机和高温恒温试验箱,制备出经2次回流焊时效20天的Sn-0.7Cu/Cu焊点试件.采用纳米压痕法,对其焊点金属间化合物力学性能进行测试.根据OliverPharr算法,利用接触刚度连续测量技术得到该化合物(IMC)的弹性模量及硬度,并与同种工况下的焊料及铜进行对比,发现其硬度明显大于二者.并得到了Sn-0.7Cu焊料、金属间化合物和Cu的室温蠕变速率敏感指数,对三者的蠕变性能做了对比分析,发现Sn-0.7Cu的室温蠕变速率敏感指数明显大于IMC和Cu.     

Creep relaxation and stress relaxation of PS-HI/SEBS blends

For the selection of the polymer materials and polymer blends for various fields of applications the stability of material under constant deformation and constant load are very important. In this paper, the copolymers high-impact polystyrene, PS-HI, styrene-ethylene/buthylene-styrene block copolymer, SEBS, and their blends PS-HI/SEBS were investigated. The investigations were done by DMA analysis. The secondary viscoelastic functions, creep, creep modulus, stress and flexural relaxation modulus were investigated in creep and stress relaxation experiment at temperatures 25, 35, 45, 55 and 65°C during 1 h. The master curves were created by time-temperature correspondence principle, TTC. The correlation of the secondary viscoelastic functions with time, temperature and content of the hard, PS, phase was discussed.     

Morphology and Properties of Poly(oxymethylene) Engineering Plastics

Comparative WAXD/SAXS/SEM/DSC structural studies of a series of semi-crystalline poly(oxymethylene) (POM) engineering plastics, including the commercial products, homopolymer Delrin^® and typical poly(oxymethylene-co-oxyethylene)s, and a few lab-made POM compositions, were performed. The latter differed in their content of functional additives (present in low concentrations) and POM molecular weight characteristics. In parallel, their densities, thermal behavior/laser-interferometric creep rate spectra (DSC/CRS) at 20-180 °C, as well as long-term creep resistance (LTCR) at 20 °C were studied. It has been found that introducing the nucleating agents and oxyethylene units resulted in formation of more fine spherulitic or practically non-spherulitic structure with close- or loose-packed lamellar stacks. The presence of both “thick” (5-10 nm) and “thin” (1.5-3 nm) lamellae in the weight ratio of ∼3:1 was shown in all cases. Close values of real POM crystallinities, not exceeding 50%, were obtained by WAXD and DSC. A predominant role of “straightened out” or slightly bent tie chains in disordered layers of isotropic POMs was presumed, resulting in segmental dynamics differently constrained by crystallites (DSC/CRS data). As a result, certain morphology - density - creep resistance correlations were found.