T-Stress of a Bi-Material Strip Under Generalized Edge Loads

An expression for the T-stress in a bi-material strip with a semi-finite interfacial crack is derived for general edge loads using a conservation integral method. The expression is explicit except for two non-dimensional constants, which are determined from a finite element analysis and which are tabulated as a function of the Dundurs’ parameters and the thickness ratio of the strip.     

GFRP约束微珠泡沫柱准静态受压性能

本研究对2根微珠泡沫柱及5根玻璃纤维复合材料(GFRP)约束微珠泡沫组合柱开展准静态轴压试验,探讨了GFRP层数、横向纤维与纵向纤维比例、泡沫密度等参数对组合柱极限承载力和吸能效应的影响,并与静态试验结果进行对比,研究不同加载速率对构件受压性能的影响规律.结果表明:准静态压缩作用下GFRP层数和泡沫密度的增加均提高了构...     

Local Finite Element and Experimental Limit Loads of Cracked Piping Elbows Under Opening Bending

Abstract: Finite element (FE) and experimental data of cracked, 88.9 mm outside diameter, 5.49 mm thick, short radius, carbon steel piping elbows under displacement controlled, opening bending are reported. Short and long defects with depth-to-thickness ratios ranging from shallow to through-wall, axially or circumferentially centred about the bend crown centreline or intrados respectively, are considered.
The FE predicted general deformation mechanisms and overall strain distributions compare well with the experimental observations. Also, the strains agree well with the experimental values away from the defects. However, in the immediate vicinity of the defect, the FE strain data give much more detail about the initiation and spread of plasticity as the loading is increased towards plastic collapse of the component, but specific integration point strain data reveals that the variations are large and that steep strain gradients are evident even within individual elements. This explains the poor comparisons with experimental data in these regions. Using the above type of data, in conjunction with the twice-elastic slope (TES) method for the determination of plastic loads for the cases investigated, it has been shown that values lower than those obtained from similar global measurements (load-displacement plots) are consistently obtained.     

On the Interface Crack Between Two Elastic Layers Under General Edge Loads

Stress intensities (energy release rate and stress intensity factors) and T-stresses are obtained in closed form for an interface crack between two elastic layers under general edge loads. The solutions derived are favorably compared with those from the literature.     

A Numerical Simulation of Time-Dependent Interface Failure Under Shear and Compressive Loads in Single-Fiber Composites

We performed a numerical simulation of a time-dependent interfacial failure accompanied by a fiber failure, and examined their evolution under shear and compressive loads in single-fiber composites. The compressive load on the interface consists of Poisson’s contraction for matrix resin subjected to longitudinal tensile load. As time progresses, compressive stress at the interface in the fiber radial direction relaxes under the constant longitudinal tensile strain condition for the specimen, directly causing the relaxation of the interface frictional stress. This relaxation facilitates the failure of the interface. In this analysis, a specific criterion for interface failure is applied; apparent interfacial shear strength is enhanced by compressive stress, which is referred as quasi-parabolic criterion in the present study. The results of the stress recovery profile around the fiber failure and the interfacial debonding length as a function of time simulated by the finite element analysis employing the criterion are very similar to experimental results obtained using micro-Raman spectroscopy.     

Approximate Evaluation for Effective Elastic Moduli of Cracked Solids

A system of equations for effective elastic moduli of 2-D cracked solids is presented by combining the energy balance equation proposed by Shen and Yi (2000) with the integral equations which control the problem of an infinite solid with a finite number of cracks in a sub-region. Then, using Kachanov's method (Kachanov, 1987) for the solutions of the integral equations, 2-D effective bulk and shear moduli for solids with randomly distributed cracks are evaluated.     

Modeling the Response of 3D Textile Composites under Compressive Loads to Predict Compressive Strength

The compression response of 3D woven textile composites (3DWC) that consist of glass fiber tows and a polymer matrix material is studied using a combination of experiments and finite element based analyses. A previous study reported by the authors consisted of an experimental investigation of 3DWC under high strain rate loading, Pankow, Salvi, Waas, Yen, and Ghiorse (2011). Those experimental results were explained by using the finite element method to analyze the high rate deformation response of representative volume elements (RVEs) of the 3DWC, Pankow, Waas, Yen, and Ghiorse (2012). In this paper, the same modeling strategy is used to examine the quasi-static, compressive deformation response of 3DWC. The effect of using different numbers of the textile repeat unit architecture in the RVE, on the predicted compression strength, is examined. The transitions in failure modes that are seen in experiments are seen to be captured by the model that is presented here.     

考虑裂纹效应的弹性板振动分析模型

针对含裂纹板的动力学问题,提出了一种耦合裂纹效应的弹性板动力学建模方法。该方法依据变形等效原则用虚拟外部载荷代替裂纹作用,并通过力学平衡原理建立了耦合裂纹项的弹性板运动方程,且基于Rice和Levy应力关系式推导出裂纹项表达式;在此基础上,结合Galerkin法和Berger经验,把含裂纹弹性板振动系统简化成一单自由度非线性振动模型进行动力学特性分析。通过算例探讨了裂纹尺度、阻尼以及激励力位置对弹性板振动特性的影响。结论表明,裂纹尺度和板尺寸对振动非线性作用明显,动应力幅值受阻尼与激励力位置的控制。     

Stressed State of a Viscoelastic Layer on the Rigid Foundation Under the Action of Concentrated Cyclic Loads

Materials Science - By using a generalized two-parameter model, we study main regularities of the deformation of an infinite viscoelastic layer on the rigid foundation under the action of...     

Elastodynamic Response of Cracked Orthotropic Strip Under Impact Loading

The paper presents the elastodynamic response of an infinite orthotropic strip of finite width containing a central crack opened by suddenly applied stresses. Integral transforms are employed to reduce the transient problem to the solution of a pair of dual integral equations in the Laplace transform plane solved by iterations in the low frequency case. Analytic expressions for the dynamic stress intensity factors are obtained. Numerical results for two particular materials are given. The influence of different orthotropic constants on the magnitude of the overshoots in the stress intensity factors K ₁(t) and K ₂(t) are found.     

The Topology Optimization Under the Static Loads

The method of the structural topology optimization is often used to design machine in the early stage of the mechanical design. And one mechanical structure use the topology design to produce a new still and lightweight assembly.     

Optimization of Sandwich Composites Fuselages Under Flight Loads

The sandwich composites fuselages appear to be a promising choice for the future aircrafts because of their structural efficiency and functional integration advantages. However, the design of sandwich composites is more complex than other structures because of many involved variables. In this paper, the fuselage is designed as a sandwich composites cylinder, and its structural optimization using the finite element method (FEM) is outlined to obtain the minimum weight. The constraints include structural stability and the composites failure criteria. In order to get a verification baseline for the FEM analysis, the stability of sandwich structures is studied and the optimal design is performed based on the analytical formulae. Then, the predicted buckling loads and the optimization results obtained from a FEM model are compared with that from the analytical formulas, and a good agreement is achieved. A detailed parametric optimal design for the sandwich composites cylinder is conducted. The optimization method used here includes two steps: the minimization of the layer thickness followed by tailoring of the fiber orientation. The factors comprise layer number, fiber orientation, core thickness, frame dimension and spacing. Results show that the two-step optimization is an effective method for the sandwich composites and the foam sandwich cylinder with core thickness of 5 mm and frame pitch of 0.5 m exhibits the minimum weight.     

Fracture of an Elastic rib Reinforced Plate Weakened by a Circular Cracked Hole

The present paper considers an important for engineering application problem of fracture of an elastic plate weakened by a circular hole with radius and emanating from its countur a crack of length. Refere the plate to the system of coorinates or in complex variables with an origin at the centre of the hole and axis directed along the crack, Fig.1.     

Residual Stiffness of Cracked Cross-Ply Composite Laminates Under Multi-Axial In-plane Loading

In this paper, the Equivalent Constraint Model (ECM) together with a 2-D shear lag stress analysis approach is applied to predict residual stiffness properties of polymer and ceramic matrix [0/90 _n /0] cross-ply laminates subjected to in-plane biaxial loading and damaged by transverse and longitudinal matrix cracks. It is found that the longitudinal Young’s modulus, shear modulus and major Poisson’s ratio undergo large degradation as the matrix crack density increases, with Poisson’s ratio appearing to be the most affected by transverse cracking. In cross-ply laminates with thick 90° layer strip-shaped delaminations begin to initiate and grow from the tips of matrix cracks at the 0°/90° interface. These delaminations contribute to further stiffness degradation of such laminates, and hence have to be taken into account in failure analysis models. The thickness of the 90° layer plays an important role; the thicker the 90° layer, the bigger stiffness reduction suggesting a size (volume) effect at ply level. In SiC/CAS cross-ply laminates reduction in the longitudinal modulus occurs mainly due to transverse cracks, while the shear modulus appears to be the most affected by the presence of longitudinal cracks. The shear modulus reduction ratio predicted previously by a semi-empirical formula is, in the most of cases, within 10% of the current ECM/2-D shear lag approach value. In some cases, though, the error of the semi-empirical finite element expression can be as big as 20% since it fails to capture damage mode interaction.     

气幕对弹性球壳振动影响的探讨

对气幕中弹性薄球壳的振动进行理论分析，以探讨气幕对结构振动的影响。分析表明：气幕对结构强迫振动响应的影响，相当于给结构增加了附加质量（气幕压缩性的影响）和附加阻尼（气幕阻尼的影响），它们与气幕自身的参数及激振频率有关。     

夹层材料裂纹体疲劳载荷作用下的J积分研究

通过弹塑性有限元方法研究了裂纹平行于界面时夹层材料在平行于界面时夹层材料在Ｉ型疲劳功载荷作用下扩展裂纹的Ｊ积分的适用性，结果表明，在疲劳裂纹的起裂阶段，Ｊ积分具有良好的守恒性，而在随后的疲劳裂纹扩展过程中，由于裂纹尖端区域残留应力的影响，Ｊ积分具有明显的路径依赖性。     

Elastic Wave Propagation in a Class of Cracked,Functionally Graded Materials by BIEM

Elastic wave propagation in cracked, functionally graded materials (FGM) with elastic parameters that are exponential functions of a single spatial co-ordinate is studied in this work. Conditions of plane strain are assumed to hold as the material is swept by time-harmonic, incident waves. The FGM has a fixed Poisson’s ratio of 0.25, while both shear modulus and density profiles vary proportionally to each other. More specifically, the shear modulus of the FGM is given as μ (x)=μ ₀ exp (2ax ₂), where μ ₀ is a reference value for what is considered to be the isotropic, homogeneous material background. The method of solution is the boundary integral equation method (BIEM), an essential component of which is the Green’s function for the infinite inhomogeneous plane. This solution is derived here in closed-form, along with its spatial derivatives and the asymptotic form for small argument, using functional transformation methods. Finally, a non-hypersingular, traction-type BIEM is developed employing quadratic boundary elements, supplemented with special edge-type elements for handling crack tips. The proposed methodology is first validated against benchmark problems and then used to study wave scattering around a crack in an infinitely extending FGM under incident, time-harmonic pressure (P) and vertically polarized shear (SV) waves. The parametric study demonstrates that both far field displacements and near field stress intensity factors at the crack-tips are sensitive to this type of inhomogeneity, as gauged against results obtained for the reference homogeneous material case     

Creep of Textile-Reinforced Composite Under Static and Cyclic Loads

Strength of Materials - The paper considers the creep of a textile-reinforced thermoplastic composite with a glass filler under the action of a combined short-term cyclic and long-term static...     

Edge-Cracks in Single Crystals Under Monotonic and Cyclic Loads

Basic solutions are obtained for edge-cracks lying along the primary slip plane in a single crystal. The study is motivated by Stage I fatigue crack growth wherein crack orientation is controlled by the slip direction and continued growth is dependent on the crack overcoming barriers to slip. Plasticity is assumed to occur as slip along planes inclined at 45^ to the surface. Problems where slip is limited to persistent slip bands are considered side-by-side with the problem where slip is not confined. Results for both monotonic and cyclic loadings are presented, with emphasis on the crack tip opening and sliding displacements. Both small and large scale yielding are considered. Preliminary results are given for interaction with barriers to slip, such as a grain boundary. This revised version was published online in July 2006 with corrections to the Cover Date.