Mode III fracture behavior of laminated composite with edge crack in torsion

A three-dimensional (3-D) finite element analysis was performed on a [90,(+45/−45)_n,(−45/+45)_n,90]_s class of laminated composites under the edge crack torsion (ECT) test configuration. Finite element delamination models were established and formulas for calculating the Mode III fracture toughness from 3-D finite element models were developed. The relations between the interlaminar fracture behavior and various configuration parameters were investigated and the effects of point loads, ends, geometry, Mode II interference, and friction were evaluated. Results showed that with proper selection of ECT specimen configuration and layup, the delamination could grow in pure Mode III in the middle region of the specimen. Specimen end effect played an important role in the ECT test. A Mode II component occurred in the end regions but it did not interfere significantly with the Mode III delamination state. Specimen dimension ratio, layup, and crack length exhibited significant effect on the interlaminar fracture behavior and the calculated strain energy release rates. However, friction between crackfaces was found to have negligible effect on the interlaminar properties.     

On the Size of RVE in Finite Elasticity of Random Composites

This paper presents a quantitative study of the size of representative volume element (RVE) of random matrix-inclusion composites based on a scale-dependent homogenization method. In particular, mesoscale bounds defined under essential or natural boundary conditions are computed for several nonlinear elastic, planar composites, in which the matrix and inclusions differ not only in their material parameters but also in their strain energy function representations. Various combinations of matrix and inclusion phases described by either neo-Hookean or Ogden function are examined, and these are compared to those of linear elastic types.     

Micromechanics of particle-reinforced elasto-viscoplastic composites: Finite element simulations versus affine homogenization

The micromechanics of elasto-viscoplastic composites made up of a random and homogeneous dispersion of spherical inclusions in a continuous matrix was studied with two methods. The first one is an affine homogenization approach, which transforms the local constitutive laws into fictitious linear thermo-elastic relations in the Laplace–Carson domain so that corresponding homogenization schemes can apply, and the temporal response is computed after a numerical inversion of Laplace transform. The second method is the direct numerical simulation by finite elements of a three-dimensional representative volume element of the composite microstructure. The numerical simulations carried out over different realizations of the composite microstructure showed very little scatter and thus provided – for the first time – “exact” results in the elasto-viscoplastic regime that can be used as benchmarks to check the accuracy of other models. Overall, the predictions of the affine homogenization model were excellent, regardless of the volume fraction of spheres, of the loading paths (shear, uniaxial tension and biaxial tension as well as monotonic and cyclic deformation), particularly at low strain rates. It was found, however, that the accuracy decreased systematically as the strain rate increased. The detailed information of the stress and strain microfields given by the finite element simulations was used to analyze the source of this difference, so that better homogenization methods can be developed.     

Numerical simulation of thermo-mechanical fatigue properties for particulate reinforced composites

In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites. The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermo-mechanical behavior. Some related conclusions are obtained by examples of numerical simulation.The project supported by the Special Funds for the National Major Fundamental Research Projects (2004CB619304), the National Natural Science Foundation of China (10276020 and 50371042), the Key Grant Project of Chinese Ministry of Education (0306)     

利用宽带音频扫描加载实现复合材料结构质量检测的数字散斑错位术研究

本文系统地分析了数字散斑错位术相关条纹的形成机理，并结合此项技术提出一种新的加载方式——宽带音频扫描加载，同时从理论上剖析了该加载方式的可行性，从而构造出一种新的无损测试系统．采用该检测系统对带有预制不同形状和尺寸缺陷的复合材料模型进行检测验证，发现该技术使用方便，检测时不受环境的影响，可以实现现场在线原位实时检测，并能够得到非常真实的检测结果，从而可以实现更为精确的定量计算．     

Non-linear strain rate dependent micro-mechanical composite material model for finite element impact and crashworthiness simulation

The present study aims at implementation of a strain rate dependent, non-linear, micro-mechanics material model for laminated, unidirectional polymer matrix composites into the explicit finite element code LSDYNA. The objective is to develop an accurate and simple micro-mechanical, rate dependent material model, which is computationally efficient. Within the model a representative volume cell is assumed. The stress-strain relation including rate dependent effects for the micro-model is derived for both shell elements and solid elements. Micro-failure criterion is presented for each material constituent and failure mode. The implemented model can deal with problems such as impact, crashworthiness, and failure analysis under quasi-static loads. The developed material model has a wide range of applications such as jet engine jackets, armor plates, and structural crashworthiness simulation. The deformation response of two representative composite materials with varying fiber orientation is presented using the described technique. The predicted results compare favorably to experimental values.     

Hill condition and overall properties of composites

Summary We discuss the Hill principle's role and applications in modern micromechanics of industrial composite materials. Uniform boundary conditions, fundamental in micromechanics, are introduced as a class of Hill solutions. Mixed uniform conditions, basic for experimental testing, are analysed. Domains of application of the Hill principle are reviewed, like homogeneization of heterogeneous media, definition of effective properties and size effect in heterogeneous materials. Generalization of the Hill condition is realized for arbitrary materials, in particular for nonlinear inelastic composites with imperfect interfaces. Received 9 September 1997; accepted for publication 23 December 1997     

Microstructure and fracture characteristic of Mg–Al–Zn–Si3N4 composites

Magnesium matrix composites reinforced by three dimensional (3-D) network structure were fabricated by pressure-less infiltration technology. The 3-D network structure reinforcement and its composites exhibited special topology structure and different fracture characteristic. Metal matrix fractured in a ductile mode is manifested by small dimples and craters on the fracture surface. When the volume fraction of reinforcement is not in excess of 6%, the composite had an improved fracture toughness. This is because of the relatively homogeneous Si₃N₄ particles distributed in the metal matrix and the occurrence of interface reaction product such as MgAlO₂ spinel phase. With the increases of volume fraction of reinforcement (>6%), the fracture toughness decreases slowly at the initial stages and then decreases rapidly towards the end. Therefore, the main fracture failure mechanisms consist of crack nucleation, growth, coalescence and crack propagation.     

双向固定网格渐进结构优化方法

近年来发展的渐进结构优化方法是一种有前途的结构拓扑和形状优化方法.本文在渐进结构优化方法的框架内建立了统一敏感度的概念,并基于固定网格有限元技术,发展了一种新的增加材料技术,提出了双向固定网格渐进结构优化方法.将该方法应用于复合材料壳结构开孔形状优化,以孔周等Tsai-Hill强度值作为优化目标,可以得到合理的最优解,证明了双向固定网格渐进结构优化方法的适用性.不同的初始点能得到几乎相同的最优解,展示了本文方法良好的全局最优性.     

Nonlinear composites: a linearization procedure,exact to second-order in contrast and for which the strain-energy and affine formulations coincideComposites non linéaires : un schéma exact au second ordre pour lequel la formulation en énergie de déformation coı̈ncide avec la formulation affine

This Note presents a new approximate scheme for nonlinear composites. The approximation which is made preserves certain features of the original second-order scheme of Ponte Castañeda, exactness to second-order in the contrast and existence of an effective energy, but improves on one drawback, which is the gap between the strain-energy formulation and the affine formulation. A numerical example shows the accuracy of the present method. To cite this article: N. Lahellec, P. Suquet, C. R. Mecanique 332 (2004).