Three-dimensional finite element analysis of composites with coated spherical inclusions

A three-dimensional finite element analysis has been used to determine the internal stresses in a three-phase composite. The stresses have been determined for a variety of interphase properties, the thicknesses of the interphase and the volume fractions of particles. Young's modulus has been calculated from a knowledge of these stresses and the applied deformation. The calculations show that stress distributions in the matrix and the mechanical properties are sensitive to the interphase property in the three-phase composites. The interfacial stresses in the three-dimensional analysis are in agreement with results obtained by an axisymmetric analysis. The predicted bulk modulus in three-dimensional analysis agrees well with the theoretical solution obtained by Qui and Weng, but it presents a great divergence from that in axisymmetric analyses. An investigation indicates that this divergence may be caused by the difference in the unit cell structure between two models. A comparison of the numerically predicted bulk and shear modulus for two-phase composites with the theoretical results indicates that the three-dimensional analysis gives quite satisfactory results.

An experimental-study of the bending behavior of call hybrid composites

The bending behavior and damage characteristics of CALL (Carbon fiber/epoxy/AL Laminate) hybrid composites have been studied by moire interferometry. The shear strain distribution along the cross-section and the forms of damage of bending beams are obtained. The results show that the magnitude of the shear strain in a carbon/epoxy layer is obviously larger than that in a corresponding aluminum layer and the shear strain distribution of a CFRP layer along the cross-section conforms basically to a parabolic distribution curve, as for the shear strain distribution in aluminum layers along the cross-section. Shear damage, either in the interfaces or in carbon-fiber/epoxy laminae, and tensile failure of CFRP laminae in the tension surface represent, respectively, the damage forms of the longitudinal and transverse bending specimen.

Orthotropy rescaling and implications for fracture in composites

For most practically important plane elasticity problems of orthotropic materials, stresses depend on elastic constants through two nondimensional combinations. A spatial rescaling has been found to reduce the orthotropic problems to equivalent problems in materials with cubic symmetry. The latter, under favorable conditions, may be approximated by isotropic materials. Consequently, solutions for orthotropic materials can be constructed approximately from isotropic material solutions or rigorously from cubic ones. The concept is developed to gain insight into the interplay between anisotropy and finite geometry. The inherent simplicity of the solutions allows a variety of technical problems to be addressed efficiently. Included are stress concentration related cracking, effective contraction of orthotropic material specimens, crack deflection onto easy fracture planes, and surface flaw induced delamination.

The influence of buoyancy on the oscillatory thermocapillary convection with small bond number

This work is an experimental study of unidirectional bamboo-epoxy laminates of varying laminae number, in which tensile, compressive, flexural and interlaminar shear properties are evaluated. Further, the disposition of bamboo fibre, the parenchymatous tissue, and the resin matrix under different loading conditions are examined. Our results show that the specific strength and specific modulus of bamboo-epoxy laminates are adequate, the former being 3 to 4 times that of mild steel. Its mechanical properties are generally comparable to those of ordinary glass-fibre composites. The fracture behaviour of bamboo-epoxy under different loading conditions were observed using both acoustic emission techniques and scanning electron microscopy. The fracture mode varied with load, the fracture mechanism being similar to glass and carbon reinforced composites. Microstructural analyses revealed that natural bamboo is eligibly a fibre composite in itself; its inclusion in a plastic matrix will help solve the problems of cracking due to desiccation and bioerosion caused by insect pests. Furthermore, the thickness and shape of the composite can be tailored during fabrication to meet specific requirements, thereby enabling a wide spectrum of applications.

A note on fracture toughnesses of unidirectional composites

presented in a general form where more reasonable relations for the two-phase

Inhomogeneous isoparametric elements for stress analysis of composites

The concept of inhomogeneous element is proposed and the formulations of the inhomogeneous isoparametric elements for stress analysis of four kinds of problems are derived. As an example of applications of the inhomogeneous elements, the stress distribution in a cone-like composite syntheticrope termination is calculated.

Experimental relaxation behavior of chopped-strand mat glass-fiber reinforced polyester beams in 3 point bending

A dimensionless relation of the form for collating fatigue crack starting growth data is proposed in which Δkth represents the stress intensity factor range at the threshold. Based on experimental results, this relation attains the value of 0.6 for a fatigue crack to start growth in the Austenitic stainless steel investigated in this work. Metallurgical examinations were also carried out to show a transgranular shear mode of cyclic cleavage and plastic shear.

Static and fatigue failure behavior of carbon-fiber reinforced epoxy composite-materials with edge notch

A study of carbon fiber reinforced epoxy composite material with 0° ply or ±45°ply(unnotched or with edge notch) was carried out under static tensile and tension-tensioncyclic loading testing. Static and fatigue behaviour and damage failure modes in unnotched/notched specimens plied in different manners were analysed and compared with each other.A variety of techniques (acoustic emission, two types of strain extensometer, high speed pho-tography, optical microscopy, scanning electron microscope, etc.) were used to examine thedamage of the laminates. Experimental results show that when these carbon/epoxy laminateswith edge notch normal to the direction of the load are axially loaded in static or fatiguetension, the crack does not propagate along the length of notch but is in the interface (fiberdirection). The notch has no substantial effect on the stresses at the unnotched portion. Thedamage failure mechanism is discussed.

SiC_p/6151Al复合材料的微结构效应

利用分离式Hopkinson压杆和MTS通用材料试验机研究了SiC_p/6151Al颗粒增强复合材料在不同应变率下的变形行为和增强颗粒的尺寸对复合材料微结构及变形行为的影响。结果表明，对于在不同应变率下的SiC_p/6151Al复合材料，增强颗粒尺寸大小的流动应力高于增强颗粒尺寸的流动应力。根据位错强化理论中的Hall-Petch关系对这个结果进行了解释。首次在实验上观测到增强颗粒对复合材料微损伤-微带形成的影响，并根据微带（microband）形成的双位错墙理论（double dislocation walls）, 分析了增强颗粒对复合材料微带损伤及力学性能影响的微结构效应。

冲击剪切载荷下SiC_P/6151Al复合材料变形局部化及增强颗粒尺寸效应

利用特殊设计的“hat shape”试样，在分离式Hopkinson压杆和MTS通用材料试验机上实验研究了颗粒尺寸和应变率对颗粒增强金属基复合材料（SiC_P/6151Al）变形局部化行为的影响。结果表明：颗粒尺寸对复合材料的变形强化与变形局部化行为有显著影响。具体表现为：颗粒越小，复合材料流动应力越高，即强化效果越好；另一方面，对受载试样的微观检测发现，颗粒越小，复合材料剪切变形局部分越明显。同时发现，冲击载荷（高应变率）下复合材料更容易发生变形局部化。

冲击载荷下纤维复合材料裂纹起裂的实验研究

采用SHTB技术对纤维增强复合材料裂纹动态起裂行为进行了实验研究。使用应变片方法确定了裂纹的起裂时间，结合有限元数值模拟得到了裂纹的起裂韧性；同时观察了裂纹在冲击载荷作用下的裂纹起裂和扩展方式，分析了纤维的铺层角度对裂纹起裂和扩增的影响。

颗粒增强复合材料的界面开裂与尺度效应

采用基于Huang等提出的塑性应变梯度传统理论发展的有限元方法，模拟了颗粒增强金属基复合材料的界面开裂与颗粒尺度效应．分别针对考虑颗粒与基体间界面开裂和不开裂两种情况进行分析，并将考虑界面开裂的模拟结果与实验结果进行比较，证明了模型的有效性，同时也获得应变梯度理论中所包含的材料特征尺度参量的取值．

Randomized, double-blind, placebo-controled clinical trial of sublingual immunotherapy in natural rubber latex allergic patients

Trial registration number: CTRN12611000543987