单向复合材料横向裂纹黏弹性损伤演化模型

建立一个考虑基体黏弹性的纤维增强聚合物单向复合材料在产生横向裂纹时的损伤演化模型,有效地预测了单向复合材料横向拉伸行为。假设呈现威布尔分布的缺陷会在变形的驱动下演化为损伤,并以此为基础建立了单向复合材料横向损伤演化模型。通过此模型,时间-温度叠加原理（TTSP）得到了更具有物理基础的解释。最后,通过具体例子阐述了此模型的应用,并通过试验对模型预测结果进行了验证。本模型有效地预测了单向复合材料横向拉伸行为。由于单向复合材料横向性能存在脆性,此模型还无法准确预测失效和强度。      

Constitutive modeling for large deformation behavior of thermoplastic olefin

A constitutive model has been developed to capture the rate-dependent large deformation behavior of the polypropylene (PP)/elastomer/inorganic filler ternary phase thermoplastic olefin (TPO). As the TPO exhibits elastic behavior of each constituent phase during elastic deformation and shear yielding of PP matrix after linear elastic loading. The elastic modulus of the composite is predicted using micromechanics theory. The viscoplastic behavior of TPO is described by a model which includes rate and temperature dependent yield, strain softening, and strain hardening. The material properties of the model are obtained from the uniaxial tensile test and then the model is examined for its ability to predict the response in deformation. It is proved that the large deformation features of the TPO composites are well described by the constitutive model.     

铜包铝复合材料轧制变形过程模拟及轧制力计算公式

基于对铜包铝双金属复合材料轧制变形过程进行的有限元模拟,建立了双金属复合材料轧制变形分区模型,可分为弹性区、单材料塑性区、后滑区、揉轧区和前滑区.以铜的体积分数为变量,对不同铜含量的铜包铝复合材料的轧制过程进行模拟,在单一材料轧制力理论计算公式的基础上,提出了双金属复合材料轧制力的理论计算公式,通过对铜包铝复合材料轧制的试验和不同压下率下的铜包铝双金属复合材料轧制成形的有限元模拟,对所推导出的轧制力公式进行了验证.     

超前微桩复合土钉支护稳定及变形简化计算方法

超前微桩复合土钉支护是一种经济有效的基坑支护形式, 但对其设计分析方法的研究远落后于工程实践。该文在对此种复合土钉支护的构造及工作性能进行简要分析的基础上, 对其整体稳定验算方法和变形计算方法进行讨论, 借鉴已有的一些相关研究提出了相应的简化计算方法。针对其整体稳定验算, 提出考虑微桩-土相对刚度采用不大于2.5倍特征长度上土体被动抗力来考虑微桩作用的建议, 从而给出一种较为简便的整体稳定验算方法, 就一些实际工程的计算对比表明所建议的方法合理可行。针对其坑壁位移计算, 在仔细分析此种支护体系受力变形机理的基础上, 基于基坑支护计算的增量法及弹性地基梁求解的链杆法, 提出一种思路清晰的简化计算方法, 给出了具体的计算模型、参数确定方法及问题求解方法, 并通过与有限元计算及工程实测的对比对所提出的方法进行了检验。     

Modeling of magnetostriction in particulate composite materials

By combining a magnetostrictive material with a polymer or a metal, the magnetostrictive composites can have a reasonably large magnetostriction response for various sensor and actuator applications. In this paper, a relatively simple model for studying the magnetostrictively induced deformation behavior of magnetostrictive composites is presented. For illustrative purposes, we calculate the magnetostriction responses of composites containing Terfenol-D and nickel. Through numerical calculation, we have obtained the macroscopic longitudinal strains parallel to the applied magnetic field for Terfenol-D/glass composite and both longitudinal and transverse strains for the nickel/epoxy composite. Comparison with experimental data for both material systems shows our model is applicable up to very high volume fraction of magnetostrictive inclusions.     

Analytical modeling of low velocity impact on carbon nanotube-reinforced composite (CNTRC) plates

In this paper, a new analytical model for behavior of carbon nanotubes reinforced composite plates under low velocity impact has been presented. Nanotubes aligned, straight and randomly oriented are distributed on rectangular simply supported composite plate. The Mori–Tanaka model is used to obtain effective mechanical properties of composites reinforced with nanotubes consisting of aligned, straight and randomly oriented carbon nanotubes embedded in a polymer matrix. The analytical model based on the first-order shear deformation theory and spring-mass model. The results of analytical model are compared with the results of low velocity impact on fiber-reinforced polymer composites. The results show that the deflection and energy absorption of plate in a randomly oriented distribution is more than aligned straight of carbon nanotubes in the composite layers.     

Modeling the tensile stress–strain response of carbon nanotube/polypropylene nanocomposites using nonlinear representative volume element

This paper presents a finite element model for predicting the mechanical behavior of polypropylene (PP) composites reinforced with carbon nanotubes (CNTs) at large deformation scale. Existing numerical models cannot predict composite behavior at large strains due to using simplified material properties and inefficient interfaces between CNT and polymer. In this work, nonlinear representative volume elements (RVE) of composite are prepared. These RVEs consist of CNT, PP matrix and non-bonded interface. The nonlinear material properties for CNT and polymer are adopted to solid elements. For the first time, the interface between CNT and matrix is simulated using contact elements. This interfacial model is capable enough to simulate wide range of interactions between CNT and polymer in large strains. The influence of adding CNT with different aspect ratio into PP is studied. The mechanical behavior of composites with different interfacial shear strength (ISS) is discussed. The success of this new model was verified by comparing the simulation results for RVEs with conducted experimental results. The results shows that the length of CNT and ISS values significantly affect the reinforcement phenomenon.     

Meso-modelling of Non-Crimp Fabric composites for coupled drape and failure analysis

To date macro-analysis methods have been invariably used to analyse textile composite structures for forming and mechanical performance. Techniques such as geometric ‘mapping’ for the draping of textile fabrics and classical laminate analysis combined with simplified failure criteria to determine mechanical performance have formed the basis of most of these methods. The limited accuracy of the physical laws applied is appropriate to macro-analysis methods in which the fibre-matrix composite is treated as homogeneous medium. Today, however, modern high performance computers are opening new possibilities for composites analysis in which far greater detail of the composite constituent materials may be made. This paper presents Finite Elements techniques for the draping simulation of textile composites, specifically biaxial Non Crimp Fabrics, in which the complex deformation mechanisms of the dry tows and stitching may be properly modelled at the individual tow and stitch meso-level. The resulting ‘deformed’ Finite Element model is then used to provide a basis for accurate simulation of the impregnated composite structure. The modelling techniques for both draping and structural analysis are present, together with validation results for the study of a relatively large-scale hemisphere composite part.     

Progressive damage modeling for large deformation loading of composite structures

A nonlinear constitutive model for large deformation loading at different strain rate condition was developed to represent tensile progressive damage of the nonlinear large deformation rate dependent behavior of polymer-based composite materials. The material was characterized by using off-axis composite specimens at different strain rates. A new failure criterion was proposed for the analysis of different loading directions and strain rates. Based on a method of combining the nonlinear constitutive theory and the proposed failure criterion for different strain rates, the progressive damage behavior of large deformation composites was represented. The strength of the material was also successfully represented with a single material constant.     

Low-Velocity Impact Damage Simulation of Biaxial Warp-Knitted Flexible Composite with Simplified Microstructure Model

Applied Composite Materials - In this paper, the low-velocity impact deformation behavior of biaxial warp-knitted flexible composite was investigated. A simplified finite element model (FEM) of the...     

A mean-field micromechanical formulation of a nonlinear constitutive equation of a two-phase composite

In this paper, a mean-field micromechanical approach has been employed to formulate a nonlinear constitutive equation and yield conditions of a two-phase composite considering plastic and creep deformation of constituent phases. The derived constitutive equation is expressed in a piecewise linear-rate form, so it can be easily combined with common structural analyses such as a finite element analysis as well as lamination theories for typical continuous fiber-reinforced composite structures. The model has taken into account the threshold creep of constituent phases and diffusional mass transfer at the inclusion/matrix interface, which play a significant role in high-temperature deformation of short-fiber-reinforced metal matrix composites. A numerical study on anisotropy in Bauschinger effect and thermal-cycling creep of SiC whisker/Al matrix composites has been made based on the developed model.     

Transverse impact damage and energy absorption of 3-D multi-structured knitted composite

Knitted composites have higher failure deformation and energy absorption capacity under impact than other textile structural composites because of the yarn loop structures in knitted performs. Here we report the transverse impact behavior of a new kind of 3-D multi-structured knitted composite both in experimental and finite element simulation. The knitted composite is composed of two knitted fabrics: biaxial warp knitted fabric and interlock knitted fabric. The transverse impact behaviors of the 3-D knitted composite were tested with a modified split Hopkinson pressure bar (SHPB) apparatus. The load–displacement curves and damage morphologies were obtained to analyze the energy absorptions and impact damage mechanisms of the composite under different impact velocities. A unit-cell model based on the microstructure of the 3-D knitted composite was established to determine the composite deformation and damage when the composite impacted by a hemisphere-ended steel rod. Incorporated with the unit-cell model, a elasto-plastic constitute equation of the 3-D knitted composite and the critical damage area (CDA) failure theory of composites have been implemented as a vectorized user defined material law (VUMAT) for ABAQUS/Explicit. The load–displacement curves, impact deformations and damages obtained from FEM are compared with those in experimental. The good agreements of the comparisons prove the validity of the unit-cell model and user-defined subroutine VUMAT. This manifests the applicability of the VUMAT to characterization and design of the 3-D multi-structured knitted composite structures under other impulsive loading conditions.     

Prediction of anisotropic behavior of nano/micro composite based on damage mechanics with cell modeling

New advanced composite materials have recently been of great interest. Especially, many researchers have studied on nano/micro composites based on matrix filled with nano-particles, nano-tubes, nano-wires and so forth, which have outstanding characteristics on thermal, electrical, optical, chemical and mechanical properties. Therefore, the need of numerical approach for design and development of the advanced materials has been recognized. In this paper, finite element analysis based on multi-resolution continuum theory is carried out to predict the anisotropic behavior of nano/micro composites based on damage mechanics with a cell modeling. The cell modeling systematically evaluates constitutive relationships from microstructure of the composite material. Effects of plastic anisotropy on deformation behavior and damage evolution of nano/micro composite are investigated by using Hill's 48 yield function and also compared with those obtained from Gurson-Tvergaard-Needleman isotropic damage model based on von Mises yield function.     

Fracture Analysis of Composites in High-speed Tension

In this paper the results of a high-speedtension experiment of the SiC_w/Al compositehave been reported and a simplified theoreticalmodel has been developed to study the fracturemechanism of composites in high-speed tension.This theoretical model provides a new explanationfor the increase of dynamic fracture strengthof composites in high-speed tension.     

Intra/inter-ply shear behaviors of continuous fiber reinforced thermoplastic composites in thermoforming processes

The thermoforming of continuous fiber reinforced thermoplastic (CFRTP) composite panels generally involves significant in-plane shear deformation. In the present work, the in-plane shear behavior of woven thermoplastic composites (Carbon/Polyphenylene Sulfide) over a range of processing temperatures is studied by bias-test experiments at different velocities. The experimental data of force versus displacement and force versus shear strain are presented for different extension velocities and temperatures. A thermo-visco-elastic model for numerical simulations of woven thermoplastic composite forming is proposed considering the influences of temperature and of strain rate. We applied a large displacement three-dimensional cohesive element with eight nodes which has been used for crack analysis in fracture mechanics by other authors, to investigate the inter-ply shear mechanism of woven thermoplastic composites. Applying three-dimensional cohesive elements, multi-plies forming simulations are performed to show inter-ply slip behaviors at different temperatures. The proposed models can be useful to predict from the properties of reinforcement and resin the intra/inter-ply shear behaviors of woven thermoplastic composites at high temperatures if experimental characterization of composite laminate behaviors is difficult to conduct.     

Effect of Variation in Matrix Constitution on the Work Hardening Behavior of a Peak Age Hardened SiC Reinforced Aluminum Based Metal-Matrix Composite

An understanding of the work hardening behavior of particulate reinforced metal -matrix composites is crucial in optimizing the parameters for deformation processing of these materials. In the case of particulate reinforced composites with an age hardenable aluminum alloy matrix, the microstructure and mechanical properties can be altered by a suitable aging treatment as well as by changing the content of alloying elements in the matrix. In this study MMCs with different levels of Cu in the matrix were prepared and aged to peak hardness. A modified continuum model was then used to relate the work hardening behavior of the composites to microstructural parameters. The model is shown to be accurate for all the composite materials investigated in the present study.     

帘线／橡胶复合材料疲劳测试方法

利用自建的试验系统,采用单向聚酯帘线／橡胶复合材料模拟汽车子午胎的胎体,研究了疲劳载荷下橡胶复合材料的变形和损伤累积特性,讨论了两徊加载方式对疲劳性能的影响,结果表明：定载荷疲劳测试优于伸长疲劳测试,为评价轮胎的疲劳特性,预报轮胎的疲劳寿命提供了有效手段。