Comparative Studies on the Mechanical Properties of a Thermoset Polymer in Tension and Compression

Results of an experimental investigation into the mechanical properties of a polyester resin in tension and compression are reported. Features of the stress-strain curves obtained are discussed. Data on the elastic modulus, Poisson ratio, and volume strains are obtained. The results of creep behavior of the material in tension and compression are also presented. It is found that the time-dependent creep obeys a power law, but the nonlinear stress dependence can be described by using the hyperbolic sine function. The effect of load type (tension or compression) on the nonlinearity of the creep is analyzed. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 5, pp. 633–650, September–October, 2005.     

Calculation of the Ultimate State of Reinforced Plastics and Unoriented Polymers in Asymmetric High-Cycle Tension–Compression

The fatigue failure of reinforced plastics and unoriented polymers under a joint action of static and high-cycle loadings is considered. The fatigue failure strength is estimated from stress range diagrams with a static tensile component. The models of ultimate state are constructed based on the hypothesis of existence of a unified ultimate diagram invariant with respect to the number of cycles to failure. The unified diagram is given by a transcendental power function whose exponent characterizes the sensitivity of the material to the stress-cycle asymmetry. The models of ultimate state make it possible to span practically all forms of ultimate diagrams of composite and polymer materials, including concave, rectilinear, S-shaped, and convex ones.     

Modeling the Nonlinear Deformation and Damage of Carbon-Aramid Fabric Composites in Tension

Mechanics of Composite Materials - To model the deformation of fabric polymer composite materials highly nonlinear in tension along the warp/weft threads, an analytical approach is proposed. Based...     

单轴作用下岩土材料的双重介质本构模型

基于弹塑性力学和损伤力学理论,将岩土材料视为孔隙-裂隙双重介质,假设孔隙介质不发生损伤,而裂隙介质随应变的增加发生损伤,建立了单轴作用下岩土类材料的双重介质本构模型隐式表达式,并利用Newton迭代法得出了材料的全程应力-应变曲线．分析结果表明,岩土材料中裂隙空间展布的多态性（均匀展布、集中展布和随机展布）是岩土材料本构关系千变万化的根本原因．由于双重介质本构模型将岩土材料的弹性主体（孔隙介质部分）和损伤主体（裂隙介质部分）分化开来,对于研究岩土或含损伤材料的破坏具有实用价值和理论意义．     

Torsion and Extension of a Tube with Different Moduli in Tension and Compression

The problem of the torsion and extension of a circular cylindricaltube is studied for small strain theory for a material whichhas different moduli in extension and compression. The solutionis completed in detail for an incompressible solid circularcylinder.     

Relationships Between Student,Teacher, and School Characteristics and Mathematics Achievement

A variety of factors contributes to student achievement in mathematics, including but not limited to student behaviors and student, teacher, and school characteristics. The purpose of this study was to explore which of these factors have an impact on student mathematics achievement. The target population for this study was North Carolina Algebra II students. Analyses of variance models were examined for group differences and a Three‐level Hierarchical Linear Modeling method was employed to examine individual predictors of student achievement in mathematics. Statistically, significant differences were found between students of different ethnicities, socioeconomic statuses (SES), and parental education levels. No gender effects were statistically significant. All teacher‐level variables investigated were found to be statistically significant, impacting student achievement in mathematics. School size and SES were not found to significantly contribute to student achievement. More research on the relationships between these factors shown to make statistically significant differences on mathematics achievement is needed to further explain several phenomena that this research reveals.     

Anchoring and a Load Transfer Technique in Uniaxial Tension of Unidirectional High-Strength Composites

A simplified analytical method for calculating the stress-strain state in uniaxial tension of unidirectional composite specimens with glued wedges is developed. A numerical analysis of the influence of geometry and mechanical parameters of the specimens on the maximum stresses is carried out. The calculations are refined by finite-element modeling. Tests of the specimens have proved the suitability of the suggested technique of anchoring and load transfer in uniaxial tension of unidirectional high-strength composites.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 319–334, May–June, 2005.     

Synthesis and Characterization of Jute- and Chicken-Feather-Fiber-Reinforced Polymer Hybrid Composites

Mechanics of Composite Materials - The properties of jute- and chicken-feather-fiber (CFF)-reinforced polymer hybrid composites have been investigated experimentally. The scanning electron...     

Research in the Limiting Efficiency of Plastic Deformation of Multilayer Tension (Compression) Bars

A method is proposed for calculating the limiting loads of multilayer bars in plastic deformation. The regularities of changes in the efficiency factor (EF) of plastic deformation in relation to the elastic moduli of the materials of which the bars are composed, the stress which causes the material plasticity, and variations in the cross-sectional areas of layers are examined. Mathematical expressions are derived which allow one to easily calculate the EF for arbitrary values of variable parameters and to find the limiting values of EF when one of the parameters is changed. The equivalent tension diagram for a multilayer bar is obtained in relation to the strength and stiffness of materials and their number and cross-sectional areas.     

Effect of Splitting of Polymer Fibers on the Strength of Unidirectional Composites

Mechanics of Composite Materials - With the example of Aramid fibers, it is shown that the model of acumulation of fiber breaks in composites cannot explain their observed tensile strength...     

Description of the Structure of the Polymer Matrix of Particulate-Filled Polymer Composites as a Thermal Cluster: the Critical Indices

The adequacy of the model of a thermal cluster for describing the structure of the polymer matrix of particulate-filled composites is shown. The equality of the critical indices _T = of thermal and percolation clusters is realized in the composites at a nonzero molecular mobility, which is characterized by the fractal dimension D of the chain fragment between entanglements. The variation interval of D for the polymer matrix of a composite is smaller than for the initial polymer because of the influence of the filler on its structure.     

张量A和A~k的Z-特征值的关系及其应用

给出了张量A和A的k次幂A~k的Z-特征值的关系,作为应用,给出了弱对称非负张量Z-谱半径的新下界估计式,改进了某些已有结果.     

弯曲厚矩形板精确角点静力条件的推导

本文根据最小势能原理[1]严格地导出弯曲厚矩形板精确的角点静力条件。