含矩形内部分层的复合材料层板的 状态分解-片条合成能量解法

根据叠加原理将含有矩形内部分层的层板在横向载荷作用下的受力状态进行分解, 从而 将分层问题归结为在分层表面上的附加剪切载荷作用下层板附加位移与附加应力的分析, 并据此 建立了一个仅包含分层区的力学模型。进而在层板分层区中切取平行于边界的切片, 将切片视为 含分层的层合梁, 其位移模态以相应层合梁的附加位移模态来表示。这样, 可构造层板分层区内满 足位移边界条件的位移场。最后, 应用最小势能原理确定位移幅值的闭合解。计算结果表明, 挠度 幅值远远大于中面位移幅值, 且与由双三角级数能量解法所得挠度幅值吻合很好。      

Experimental tests on the shear behaviour of dowels connecting concrete slabs to stone masonry walls

An experimental investigation has been conducted on the behaviour of dowels used to connect concrete slabs to stone masonry walls in order to transfer horizontal shear forces. A technique for embedding the dowels in the stone block without injection of grouting material or resin has been developed. Special experimental equipment has been designed in order to allow the execution ofin situ load tests on representative ancient buildings. Monotonic loading tests have been carried out on eight specimens with the purpose of measuring both stone block displacement and dowel deformation     

A solution of laminated cylindrical shells using an unconstrained third-order theory

An unconstrained third-order shear deformation theory is presented for the analysis of laminated anisotropic cylindrical shells. Based on the realistic through-thickness distribution of the in-plane displacements, a zig-zag function is used to approximate the piece-wise nature of the displacements. The zero-shearing condition on the laminate surfaces and continuous conditions for the transverse shear stresses on the inter-laminar surfaces have been considered for the final stresses calculation, the displacement functions remain to be unconstrained. This theory is very useful for the finite element analysis because it requests only C⁰ continuity for the assumed displacement fields. By comparing with three-dimensional elasticity theory for laminated orthotropic cylindrical shell, the performance of the present theory is verified. The problems solved in this paper illustrate that the present theory is very accurate for the thin and moderately thick shells.     

含非对称矩形分层的复合材料层合板状态分解-片条合成能量解法

根据叠加原理将横向载荷作用下的含有非对称矩形内部分层的层板进行状态分解,从而将分层问题归结为分层表面上的附加剪切载荷作用下层板附加位移与附加应力的分析,并据此建立一个仅包含分层区的简单的力学模型。进而在分层区中切取平行于边界的无限小的切片,将切片视为含分层的层合梁,其位移模态以相应的层合梁的附加位移模态表示。在此基础上构造层板分层区内满足位移边界条件的位移模态,最后用最小势能原理确定位移幅值的闭合解并且分析了分层区的应力场和能量释放率。      

Exploring a Multi‐modal Experimental Approach to Investigation of Local Embedment Behaviour of Wood under Steel Dowels

A multi‐modal experimental approach for analysing the embedment behaviour of timber connections with steel dowels is proposed in this study. In this approach, a standard mechanical embedment test on single‐dowel connections is combined with an optical measurement of surface deformations of the connection based on digital image correlation principle and an X‐ray micro‐computed tomography examination of the deformations in the dowel‐wood interface. The latter is conducted on cylindrical cores including the dowel hole, physically extracted from the loaded specimen at three characteristic points of the load‐deformation curves. The major challenge of this procedure is disrupted load transfer between the cylindrical core specimens and the external material they were plugged in for further analysis. Despite its challenges and limitations, the method revealed a potential for an unprecedented insight into the micromechanics of dowel connections and for effective correlation of the micro‐level observations with the external macroscopic load‐deformation characteristics.     

含椭圆形分层层板的状态分解-片条合成能量解法

根据叠加原理将含有椭圆形非穿透分层的层板在横向载荷作用下的受力状态进行分解,从而将分层问题归结为在分层表面上的附加剪切载荷作用下层板附加位移与附加应力的分析,并据此建立了一个仅包含分层区的力学模型。进而在层板分层区中切取平行于坐标平面的切片,将切片视为含分层的层合梁,其位移模态以相应层合梁的附加位移模态来表示。这样,可构造层板分层区内满足位移边界条件的位移场。最后,应用最小势能原理确定位移幅值的闭合解。计算结果表明,挠度幅值远远大于中面位移幅值,且与由双三角级数能量解法所得挠度幅值吻合很好。      

含矩形内部分层的复合材料圆柱壳块 三维问题的片条合成能量解法

根据叠加原理将含有矩形分层的复合材料圆柱壳块在横向载荷作用下的受力状态进行分解,将分层问题归结为在分层表面受附加剪切载荷作用时附加状态的分析,并据此建立了一个仅包含分层区的力学模型。通过切取纵横切片,利用含分层层合直梁与曲梁的附加位移,构造分层区附加位移模态。最后,应用最小势能原理确定位移幅值的闭合解。     

Experimental study on the effects of the boundary conditions on the deformations of composite plates

In this study, the effects of the boundary conditions on the out-of-plane displacements and through-the-thickness strain distribution of symmetric composite laminated plates are reported. The plates are subjected to bending by a central force and supported by two-line or four-point supports. The out-of-plane displacement field is measured using a full field electronic speckle pattern interferometry technique and the through-the-thickness distribution of the deformations by fibre Bragg gratings, embedded at selected locations during preparation of the plates. The experimental data are correlated with the results from elasticity-based 2D and 3D finite element models of the actual experimental configuration. The results clearly exhibit the effects of the boundary conditions on the deformation behaviour of the plates. Non-linear through-the-thickness strain distributions appear in the thick plate range. Aspects such as force and displacement distributions on the contact areas of both loading and supports are also considered.     

Crack–surface displacements for cracks emanating from a circular hole under various loading conditions

The purpose of this paper is to calculate and develop equations for crack–surface displacements for two‐symmetric cracks emanating from a circular hole in an infinite plate for use in strip‐yield crack‐closure models. In particular, the displacements were determined under two loading conditions: (1) remote applied stress and (2) uniform stress applied to a segment of the crack surface (partially loaded crack). The displacements were calculated by an integral‐equation method based on accurate stress–intensity factor equations for concentrated forces applied to the crack surfaces and those for remote applied stress or for a partially loaded crack surface. A boundary‐element code was also used to calculate crack–surface displacements for some selected cases. Comparisons made with crack–surface displacement equations previously developed for the same crack configuration and loading showed significant differences near the location where the crack intersected the hole surface. However, the previous equations were fairly accurate near the crack‐tip location. Herein an improved crack–surface displacement equation was developed for the case of remote applied stress. For the partially loaded crack case, only numerical comparisons were made between the previous equations and numerical integration. A rapid algorithm, based on the integral‐equation method, was developed to calculate these displacements. Because cracks emanating from a hole are quite common in the aerospace industry, accurate displacement solutions are crucial for improving life‐prediction methods based on the strip‐yield crack‐closure models.     

钢筋销栓模型及其在深梁分析中的应用

本文提出了一个用于有限元分析的钢筋销栓作用模型。该模型采用分布模式来处理钢筋的横向销栓力和横向变形,以便与钢筋的整体式模型和混凝土的分布裂缝模型相协调。在有限元分析中采用了位移控制的割线刚度迭代法,可以进行荷载位移曲线下降段的分析计算。对深梁试件的分析表明,本文提出的钢筋混凝土模型可以准确分析试件的荷载变形特性。同时发现,纵向主筋的销栓作用对深梁的承载力和变形能力都有重要的影响。     

Dynamic stability behavior of damped laminated beam subjected to uniformly distributed subtangential forces

The dynamic stability behavior of damped laminated beam with various boundary conditions subjected to the uniformly distributed subtangential forces is investigated using the finite element formulation. The formal engineering approach of the mechanics for the thin-walled laminated beam based on kinematic assumptions consistent with Vlasov beam theory is used. An extended Hamilton’s principle is employed to obtain the mass-, damping-, elastic stiffness-, geometric stiffness matrices, and the load correction stiffness matrix due to the subtangential forces, respectively. The method for the evaluation of critical values for divergence and flutter of the nonconservative systems is briefly introduced in case of considering and neglecting damping effects. Throughout numerical examples, the influence of various parameters on the dynamic stability behavior of the nonconservative laminated beam is newly investigated: (1) the variation of the divergence and flutter loads due to the nonconservativeness with respect to the fiber orientation, (2) the effect of boundary condition on the instability region of the divergence-flutter system, and (3) the influence of external and internal damping on the flutter load.     

复合材料层合板壳热弹性动力响应

本文提出了一个复合材料层合扁壳的位移场。据此导出了在力载和热载作用下的板壳运动方程。该位移场满足层间位移和横向剪应力的连续性,较充分反映了横向剪切对层合板壳力学行为的影响,但位移场的变量和运动方程均为五个,与一阶剪切变形理论相同。文中以暂态响应为例考察了横向剪切变形对层合板壳动力响应的影响,显着改善了解的精度。      

Buckling of symmetric cross-ply square plates with various boundary conditions

The buckling analysis of cross-ply laminated square plates subjected to three types of in-plane forces and various edge boundary conditions is presented on the basis of a unified five-degree-of-freedom shear deformable plate theory. The employment of the appropriate “shear deformation shape functions” in the theory leads to certain shear deformable plate theories developed previously, also, fulfills the requirement of the continuity conditions among the layers. The governing equations of buckling behaviour of completely simply supported cross-ply laminated plates are solved analytically. For the plates with different combinations of free, clamped and simply supported boundary conditions at their edges, the Ritz method is applied by assuming the displacement components as the double series of simple algebraic polynomials. The numerical results obtained on the basis of various plate theories for uniaxial, biaxial compression and compression–tension types of loading and different length-to-thickness ratios are presented and compared with the ones available in the literature.     

A Comparison Between the EN 383 and ASTM D5764 Test Methods for Dowel‐Bearing Strength Assessment of Wood: Experimental and Numerical Investigations

Abstract: The purpose of this paper is to provide a comparison between embedding tests covered by the EN383 and ASTM D5764 standards, highlighting some difficulties regarding the application of the referred standards. These embedding tests are essential to evaluate the embedding strength of wood, which is required for the assessment of joints strength. The proposed comparison is based either on experimental data and numerical simulations through the finite element (FE) method. Tests were performed on maritime pine wood (Pinus pinaster Ait. species) according to the longitudinal and radial directions, allowing the comparison of the embedding strength and elastic foundation modulus. Three dimensional FE models of the tests were built using contact elements technology and assuming the steel dowel and wood as linear elastic isotropic and orthotropic materials, respectively. The contact modelling is a challenging topic for which this paper also proposes some guidance. The test configuration proposed in the EN383 standard for assessment of the embedment strength in compression is more susceptible to the dowel bending than the half‐hole test configuration proposed in the ASTM D5764 standard. The numerical simulation of the EN383 embedding test raises some additional difficulties regarding the dowel boundary conditions.     

Efficient laminated composite beam element subjected to variable axial force for coupled stability analysis

A numerically efficient laminated composite beam element subjected to a variable axial force is presented for a coupled stability analysis. The analytical technique is used to present the thin-walled laminated composite beam theory considering the transverse shear and the restrained warping-induced shear deformation based on an orthogonal Cartesian coordinate system. The elastic strain energy and the potential energy due to the variable axial force are introduced. The equilibrium equations are derived from the energy principle, and explicit expressions for the displacement parameters are presented using the power series expansions of displacement components. Finally, the member stiffness matrix is determined using the force–displacement relations. In order to verify accuracy and efficiency of the beam element developed in this study, numerical results are presented and compared with results from other researchers and the finite beam element results, and the detailed finite shell element analysis results using ABAQUS; especially, the influence of variable axial forces, the fiber orientation, and boundary conditions on the buckling behavior of the laminated composite beams is parametrically investigated.     

Large deflection behaviour of thick composite plates

A rectangular quadratic finite element which includes large displacements, strains and rotations is developed in this paper. The effect of extra quadratic terms in the strain—displacement relationships on the large deflection of angle-ply plates is examined first. It is further shown that the fibre orientation and the boundary condition have a predominant effect on the nonlinear deflection of a unidirectional laminate. Basic work relating to the large deflection behaviour of thin and think antisymmetric and unsymmetric layered plates is also reported. Results are presented for simply supported and clamped boundary conditions.     

Orientation of bars glued on glued laminated products: Parallel vs. perpendicular

This paper presents the results of a comprehensive experimental study of joints made with threaded steel bars glued with epoxy in both parallel and perpendicular directions to the timber fibres. Two types of wooden products, namely, glulam and laminated veneer lumber (LVL), were used due to their widespread use in notable timber engineering designs. Experimental results showed that the behaviour of glued joints with bars parallel and perpendicular to the timber fibres differed, depending on the slenderness of the joint. It was also observed that specimens made with LVL had lower strength than those made with glulam, regardless of whether the anchors were parallel or perpendicular to the fibres.     

Influence of loading rate on bond behaviour of reinforcing steel and prestressing strands

Pull-out tests with short embedment length were carried out within a wide range of loading rates. The highest loading rate which could be achieved on a Split-Hopkinson-bar equipment was about 500,000 times the loading rate in a static test. The test variables were the steel type, the concrete quality and the loading rates. It turned out that plain reinforcing bars and prestressing strands were insensitive to variations in the loading rate, whereas deformed bars showed a significantly higher bond resistance with increasing loading rate. This influence is more pronounced according as the concrete quality is lower and the bar displacements are smaller. An explanation of the phenomena is suggested.     

Influence of boundary conditions for a thin laminated rotating cylindrical shell

A study on the influence of boundary conditions for a thin laminated rotating cylindrical shell is presented. The analysis is carried out using Love-type shell theory and solved using Galerkin's method. The displacement fields employed consist of beam functions in the axial direction and fourier functions in the circumferential direction. Extensive results on the influence of boundary conditions and contour plots for the nodal displacements are presented. The analysis has been examined by comparing results with those available in the literature.     

Plastic damage analysis of oil and gas pipelines with unconstrained and constrained dents

Indentation resulting from mechanical damage is one of the main causes of pipeline rupture failure. The primary objective of this case study is to analyze the plastic damage of the pipelines with unconstrained and constrained dents using the existing plastic damage model, namely, the ductile failure damage indicator (DFDI) model. As part of this study, an attempt is made to clarify the influence of the constraint on the behavior of the pipeline. The investigation indicates that the plastic damage of the pipeline interior walls outweighs that of the pipeline exterior walls and cracks start frequently from the pipe interior walls. The position of the maximal circumferential plastic damage deviates from the deepest position of the dent when the critical displacement loading arriving due to the circumferential deformation of the pipeline. The total plastic damage of the unconstrained dented pipeline only depends on the initial displacement loading because the working pressure has very little influence on its behavior under the unconstrained condition. However, the total plastic damage of the constrained dented pipeline depends on the initial displacement loading and the working pressure because the working pressure has a significant effect on its behavior under the constrained condition. Under the same condition, the constrained dented pipeline is easier to crack compared to the unconstrained dented pipeline. In this paper, the model, results and the findings are summarized and discussed.