由压痕蠕变试验确定材料的蠕变性能参数

研究由平头压痕蠕变试验来确定受压材料蠕变性能参数的可行性。利用有限元蠕变分析确定在定压痕应力下的压痕蠕变率,重点放在稳定压痕蠕变率和受压材料蠕变性能参数的关系上。详细地研究了压头形状、大小和宏观约束对压痕蠕变响应的影响:当压头的尺寸和受压材料为同一数量级时,宏观约束将有十分明显的影响。提出两种方法来由压痕蠕变试验来确定受压材料蠕变性能参数,并给出了算例,结果有利于准确认识平头压痕蠕变试验,从而拓宽其应用范围。     

基于TFN-隶属度软化的露天矿岩体质量评价方法研究

为了解露天矿岩体质量,从露天矿某竖向范围的围岩、矿体顶板、矿体和矿体底板四个特征位置进行取样确定一定范围内的露天矿质量.岩石抗压强度R_c、黏聚力C、内摩擦角φ和岩体变形模量E作为评价的指标体系,并形成单因素指标岩体分类的五个级别.通过TFN确定指标的相对权重.提出隶属度软化方式,在确定样本对某级别的隶属度的同时,考虑其与相邻两级别隶属可能性,即隶属度软化,以方便样本的多指标评价.评价最大隶属度级别即是样本所属级别,最终根据各个样本的质量等级和综合评判规则判断露天矿岩体质量.实验表明:提出的方法比RMR、Q和可拓学评价得到的样本质量评级略低,能考虑当地工程经验,并偏于安今.     

基于联系矩阵的围岩稳定性组合评价模型

围岩稳定性评价受诸多类型因素影响,是一个复杂不确定系统问题.为克服基于单一信息评价方法只能从特定角度分析围岩稳定性问题的缺陷,应用集对分析耦合理论探讨了可统一与融合各类信息特点的围岩稳定性组合评价新模型,以充分利用各类评价方法所包含的有用信息和避免单一方法预测错误的风险.该模型首先基于各种典型评价方法独立分析围岩稳定性,然后将获得的评价结果两两构成集对进行同异反分析,以构建联系矩阵和合理确定权重,最后基于组合原理综合评定围岩稳定性类别.实例应用结果表明,该模型用于围岩稳定性评价是有效可行的,且能综合各类评价方法的优点与提高预测精度,也为类似评价问题提供了参考.     

Creep of polyolefins

Conclusions 1. In their deformation properties the polyolefins studied are substances of a single class even under creep conditions. The principal factor which distinguishes the behavior of one polyolefin from another is the critical values of the specific volume V_o. At an identical value of V-V_o (at corresponding temperatures) the creep process is identical in polyolefins of different density.2. Change in the specific volume of polyolefins takes place upon the action, not only of temperature, but also of stress, and also as a result of thermooxidative processes, which exert a strong effect on the creep of these substances.A report presented at the Third All-Union Conference on Polymer Mechanics, Riga, 1976.M. I. Kalinin Leningrad Polytechnic Institute. Translated from Mekhanika Polymerov, No. 1, pp. 22–26, January–February, 1978.     

残余寿命熵的上界

讨论寿命分布混合的类不变性问题,改进了文[1]中的相关结果.此外,基于寿命分布类的特性研究了不同于[4]的另一类残余寿命熵的特性,并在一定的条件下得到残余寿命熵的上界.     

寿命分布的PP图

本文介绍了三种寿命分布的PP图,并比较了PP图和QQ图,得出PP图是一种更加直观的、更具解释性的拟合优度检验图;     

Creep stability of polymer rods

The author examines the problem of the buckling of a hinger rod of rigid homogeneous polymer material under constant load. The results of an experimental investigation are presented. The theoretical calculations are based on the nonlinear generalized Maxwell equation. A numerical solution has been obtained on a computer. The results of this solution are compared with the experimental data. An analytic solution that makes it possible to estimate certain limiting values is obtained for the linearized equation.Mekhanika Polimerov, Vol. 4, No. 1, pp. 145–150, 1968     

Creep of thermally cycled polyethylene

A method for determining creep strains of polymer tube specimens (in three mutually perpendicular directions) tested at constant and cyclically changing temperatures is described. The equipment for the programmed variation of specimen temperature and for the application of complex loads is described. The application of the method is illustrated by the results of creep tests on tube specimens of low-density polyethylene (LDP). The creep strain _c of thermally cycled specimens is noticeably larger than that of specimens tested isothermally at the median temperature of a given thermal cycle, and in time it becomes larger than the strain of specimens tested isothermally at the maximum cycle temperature.Mekhanika Polimerov, Vol. 3, No. 4, pp. 676–685, 1967     

Creep of plastics with spherical inclusions

A new variant of the theory of creep of plastics with spherical inclusions or pores is proposed on the basis of approximate equations for the integral parameters and the Volterra principle. Rabotnov's theory of viscoelasticity is used to describe linear creep of the matrix. The remaining components of the composite are assumed to be elastic. The complete system of operator equations of the linear viscoelasticity of plastics with spherical inclusions is obtained on the basis of the hypothesis of elastic deformation of the composite and hydrostatic pressure. Sample calculations are performed. A. A. Blagonravov Institute of Mechanical Engineering, Russian Academy of Sciences, Moscow. Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 668–675, September–October, 1996.     

Creep Stability of Thin-Walled Composite Structures

The studies on the long-term stability of composite plates and shells under limited creep carried out mainly by the research associates of the Institute of Polymer Mechanics are reviewed. The statement of the stability problems is discussed, according to which a viscoelastic structural member can be regarded as stable if a disturbance in the form of a small initial deflection asymptotically tends with time to a small constant value. In the case of stability, as evidenced by experiments, the increase in the axisymmetric components of the initial deflection, dominating in the early stage, die down with time. On the contrary, the amplitudes of nonaxisymmetric initial imperfections grow at an increasing velocity. Analytical investigations show that the initial imperfections, when expanded into Fourier series, have a spectrum of short- and long-term critical forces. The deflection components having a critical force exceeding the external load are damped out, whereas those having a smaller critical force increase infinitely. The accelerated growth in the deflection, after a time, leads to transient buckling of the shell into a new stable equilibrium form. The problems of optimization of the structure and geometry of thin-walled composite constructions, with constraints on their long-term stability and critical time, are discussed.