Micromechanics of Damage Accumulation in a 2.5D Woven C-Fiber/SiC Ceramic Composite

The morphology of a C/PyC/SiC ceramic composite is studied and its microdamage mechanisms are revealed. Some models based on the micromechanical fracture mechanics are proposed to describe the possible damage processes. The influence of the observed microdamage on the stiffness reduction is studied. It is shown that the delamination between the layers and the cracks in the coating alone cannot explain the stiffness reduction observed in tests. Debonding between the SiC coating and pyrocarbon is suggested as another mechanism of the stiffness reduction.     

Micromechanical Modeling of Woven Fiber Composites for the Construction of Effective Anisotropic Polyconvex Energies

In computer simulations where constitutive equations are considered polyconvex energies can preferably be used because the existence of minimizers is then automatically guaranteed. In this work we investigate the capability to simulate woven fiber composites using polyconvex energies. A virtual experiment of the microstructure of the considered composite is performed and the results are used for the specification of an effective macroscopic anisotropic polyconvex model. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental and Numerical Study of the Open-Hole Tensile Strength of Carbon/Epoxy Composites

Open-hole tension tests are a part of the qualification process for composite parts that need to be joined to other parts in aircraft structures [1]. With each new material, a new set of tests is required. To reduce costs, it is desirable to develop analysis tools for the prediction of damage and failure in such tests, so that the amount of testing can be reduced and predictions can be made about material behaviour early in the design process. In this paper, an experimental and numerical study is presented on the notched (open-hole) strength of high-strength carbon/epoxy composites (HTA/6376). Open-hole tension tests have been performed on specimens with three different lay-ups — quasi-isotropic, zero-dominated, and cross-ply — in accordance with procedures in available standards. The data observed are being used to develop several methods for predicting the notched strength, and results from one such method using a progressive damage analysis are presented with comparisons with experiments. The predictions of specimen stiffness and failure load were found to agree well with experiments. To gain insight into the failure process, damage progression maps are shown.     

Simulation and Modeling the Mechanical Behavior of Textile Reinforced Composites by Combining the Binary Model and X-FEM

This paper presents a new efficient modeling strategy based on the combination of Binary Model and X–FEM. It is applied to represent the inner architecture of textile reinforced composites where the fabric is characterized by a complex geometry. Homogenization methods are used to compute the effective elastic material properties. Thereby, the discrete formulation of periodic boundary conditions is adapted. Finally, the results in terms of effective material properties reveal a good agreement with parameters obtained by experimental tests. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于有限元的金属基短纤维复合材料MMC的一种统计蠕变模型

在有限元分析的基础上建立了一个单向应力状态下金属基短纤维复合材料(MMC)的统计蠕变模型.首先建立细胞模型并进行有限元分析,得到了单向应力状态下材料细观尺寸及载荷方向对宏观蠕变响应的影响规律.通过在细胞模型中增加一界面层(考虑材料特性和厚度)来研究基体和纤维的界面对MMC宏观蠕变响应的影响.基于细胞模型的数值结果,提出了一适用于纤维平面随机分布的随机统计模型,该模型考虑了纤维的断裂.通过试验获得纤维的统计分布规律.分析结果表明随机统计模型可以满意地描述试验结果.进一步讨论了材料细观尺寸,纤维的断裂特性以及界面层的材料特性和厚度对MMC宏观蠕变响应的影响.     

单轴拉伸条件下细观非均匀性岩石损伤局部化和应力应变关系分析

岩石在拉应力状态下的力学特性不同于压应力状态下的力学特性．利用细观力学理论研究了细观非均匀性岩石拉伸应力应变关系包括:线弹性阶段、非线性强化阶段、应力降阶段、应变软化阶段.模型考虑了微裂纹方位角为Weibull分布和微裂纹长度的分布密度函数为Rayleigh函数时对损伤局部化和应力应变关系的影响,分析了产生应力降和应变软化的主要原因是损伤和变形局部化.通过和实验成果对比分析验证了模型的正确性和有效性．     

Mixing Properties and Central Limit Theorem for a Class of Non-Identical Piecewise Monotonic C2 — Transformations

For a sequence T⁽¹⁾, T⁽²⁾,…of piecewise monotonic C² - transformations of the unit interval I onto itself, we prove exponential ψ- mixing, an almost Markov property and other higher-order mixing properties. Furthermore, we obtain optimal rates of convergence in the central limit Theorem and large deviation relations for the sequence f_k oT(k?1)o…oT⁽¹⁾, k=1, 2, …, provided that the real-valued functions f₁, f₂,…on I are of bounded variation and the corresponding probability measure on I possesses a positive, Lipschitz-continuous Lebesgue density.     

A note on the C2/G/1 queue and the C2/G/1 loss system

In this note, we consider the steady-state probability of delay (PW) in the C₂/G/1 queue and the steady-state probability of loss (p_loss) in the C₂/G/1 loss system, in both of which the interarrival time has a two-phase Coxian distribution. We show that, for c_X ²<1, where c_X is the coefficient of variation of the interarrival time, both p_loss and PW are increasing in β(s), the Laplace–Stieltjes transform of the general service-time distribution. This generalises earlier results for the GE₂/G/1 queue and the GE₂/G/1 loss system. The practical significance of this is that, for c_X ²<1, p_loss in the C₂/G/1 loss system and PW in the C₂/G/1 queue are both increasing in the variability of the service time. This revised version was published online in June 2006 with corrections to the Cover Date.     

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...     

Modeling the drainage and groundwater table above the collecting pipe through 2D groundwater models

In order to understand the effects of the landfill operation on groundwater flow behavior, 2D horizontal groundwater simulation model was carried out. The model saved the memory of computer and time consumption comparing with 3D groundwater flow model. However, the most difficulty is the assignment of collecting pipe boundary in the study site. Therefore, 2D vertical model was applied to calculate the change of groundwater table above the collecting pipe. This paper paid attention to examine the validation of the assignment of the collecting pipe boundary by applying the results of 2D vertical model. 2D horizontal model was coupled with the recharge model to solve the partial differential equation of groundwater flow. Finite difference method and iterative successive over relaxation were applied. The drainage volume of leachate collection was summed up in the whole landfill site and compared with the average volume of treated waste water. The study demonstrated that the results of 2D vertical model validated and can be applied to 2D horizontal groundwater flow simulation.