Micromechanics-Based Predictions on the Overall Stress-Strain Relations of Cement-Matrix Composites

A micromechanics-based model is proposed to determine the nonlinear stress-strain relations of cement-matrix composites at different concentrations of inclusions (aggregates). We first conducted some experiments to uncover the stress-strain behavior of the cement paste with a water-to-cement ratio of 0.45, and those of the mortar with the same cement paste but at three different volume concentrations of aggregates. The behavior of the cement paste is then simulated by Burgers’ rheological model. In the development of the composite model, we extend the linear elastic response to the nonlinear one through the replacement of elastic moduli by the corresponding secant moduli. The nonlinear stress-strain curves of the cement-matrix composite are then determined from those of the cement paste and inclusions. It is shown that the predicted stress-strain curves of the mortar are in close agreement with the experimental curves up to an aggregate volume fraction of 49% or 60?wt?%.     

堆石粗粒土多级加荷三轴试验分析

通过分析堆石粗粒土一个试样多级加荷三轴试验方法 ,将其分为不固结类的连续与固结类的不连续加荷。前者仅适用于σ3≤ 1 .2 MPa的低围压 ,后者必须考虑固结排水引起的应力回弹量。不连续加荷的固结方式对强度指标的影响仅限于 C值 ,内摩擦角Φ值基本保持不变。建议对土工试验规程中有关粗粒土的多级加荷三轴试验作重新修订     

An Elementary Plate Theory Prediction for Strain Energy Release Rate of the Constrained Blister Test

A technique based on elementary plate theory is proposed for estimating the strain energy release rate of the constrained blister specimen for the case of a relatively stiff blister adherend. The results of finite element analysis for an aluminum specimen confirm the applicability of the elementary plate theory approach for the constrained blister test. The paper also proposes an experimental scheme which could be automated to measure the necessary parameters to determine the strain energy release rate of the constrained blister specimen.     

应用于低阶四面体单元应力、应变有限元分析的稳定混合方程

介绍了一个解决四面体单元大小变形问题的稳定混合有限元方程。该方程的独特性在于它的普遍性,也就是这个方程可以应用于任何形状的材料模型,对模型的几何或材料参数没有任何限制为了克服体积测量的困难,在混合方程里采用线性位移和应力场。通过采用Bubble函数提高形变张量比值来达到其稳定性,由ANSYS的用户执行单元完成。基于ANSYS平台,通过对比预期结果和二次四面体单元、六面体单元混合方程的计算结果可以得到单元的属性。计算结果表明,新方程在解决复杂工程中所起的作用重大。     

钢结构在地震荷载作用下的大塑性交变应变测试方法研究

针对钢结构在抗震性能试验中，测试大塑性交变应变时存在一些问题研制出了一种新型试件光栅-胶性超微粒光栅，使交变性大应变可用云纹法准确而方便的获得．通过实验验证，其应变测试范围为-40％-40％，并应用到工字型钢柱的抗震性能试验中去，获得了满意的结果．     

Strain measurement standards—an outline

Strain measurement techniques are being used more frequently today to check that manufactured components are at a safe stress level in service. Designers are also requiring strain gauge tests on prototypes to confirm that the theoretical calculations are realistic and designs are economic.
Against this background the measurement engineer finds himself under pressure to produce test results quickly and sometimes to justify them. Strain measurement standards would have an important role in convincing customers that tests have been carried out in an approved manner and could be the measurement engineer's defence in the case of disputed results.
A suggested range of standards and codes of practice is described, from the anticipated BSI Standard on Strain Gauge Calibration to a proposed standard on strain gauge application and possible specifications on instrumentation for static and dynamic measurement. The need for strain measurement technician training and possible participationin the National Testing Laboratory Accreditation Scheme, NATLAS, is also discussed.     

Damage Constitutive Equations and its Application to Fiber Reinforced Composites under Transverse Impact

Two continuous field variables, called as continuity tensor and damage variable tensor, are used to describe the anisotropic responses of an elastic-brittle material under transverse impact load. Based on the continuum damage mechanics, anisotropic damage constitutive equations in both full and incremental forms are proposed here. The expressions of effective elastic module tensor, damage variable tensor and damage propagation force tensor are further derived, and the methods for determining the tensors are explained in detail. An example of strain and damage response of a fiber reinforced composite laminated plate under transverse impact load is employed to demonstrate the application of this theory. In the example, the damage variable coupled with geometric large deformation of laminated plate is also considered. The calculating results illustrate the influence of damage on strain field in the impacted laminated plate.     

Analysis and discussion of the modulus–strain curves of poly(ethylene terephthalate) and polyamide industrial yarns

The stress–strain and modulus–strain curves from the treatment of tensile test data are more complete and suitable for examining the mechanical properties of fibers than just the stress–strain curve. This article analyzes typical modulus–strain curves of poly(ethylene terephthalate) and polyamide fibers through the physical structure changes in these fibers during stretching and discusses how to enhance the modulus for industrial use. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 859–862, 2005     

The influence of defects on device performance of MBE-grown Si homojunction and strained Si1-xGex/Si heterostructures

Different Si homojunction and strained Si_1-xGe_x/Si heterojunction diodes and bipolar transistors have been fabricated by Si-MBE. The effect of annealing on Si homojunction diodes and transistors are studied. It is found that annealing generally improves the Si device performance, such as the ideality factor and breakdown characteristics. The influence of⁶⁰Co γ irradiation on the Si_1-xGe_x/Si diode performances are investigated by studying the temperature dependence of their electrical characteristics, and the results are correlated with the quality of the MBE-films. γ irradiation causes a drop in material conductivity due to the generation of atom-displacement defects in the whole volume of the wafers and increases the defect density at hetero-interfaces. The forward I-V curves of Si_1-xGe_x/Si devices may shift towards lower or higher voltages, depending on the film quality and the irradiation dose. The increase of defect density in strained Si_1-xGe_x/Si films appears to occur easier for the films with lower quality. Electrical measurements and calculations show that the defect-associated tunneling process is important in current transport for these MBE grown Si homojunction and strained Si_1-xGe_x/Si heterojunction devices, which have initially medium film quality or have been treated by irradiation.     

Mechanical behaviour of SSRT specimens optimized for IGSCC concerns

Simulating testing conditions leading to evaluate the intergranular stress corrosion cracking sensitivity of structural alloys is crucial to estimate the lifetime of in-service components. Former studies have pointed out that a simple modification of the design of slow strain rate tensile specimens was particularly convenient for evaluating the susceptibility to intergranular stress corrosion cracking of nickel-base alloys. The aim of the present work is to characterize and model the mechanical behaviour of such specimens. Validation of proposed modelling relies mainly on tensile tests carried on specimens equipped with strain gages. One of the striking results is that, for a given displacement rate of the heads of the specimen, a much slower strain rate can be obtained locally in comparison with the strain rate of an equivalent smooth specimen.