外载荷作用下夹层梁的理论弯曲计算分析

利用弹性体的剪应变与位移的几何方程,推导出了夹层梁的弯曲微分方程,研究了夹层梁的弯曲挠度计算问题。采用该弯曲微分方程可以方便计算出外载荷作用下夹层梁的弯曲挠度,而弹性理论对外载荷作用下夹层梁的弯曲计算仅能给出一题一解,本文方法则克服了弹性理论的缺陷。有关试验结果验证了该方法的计算精度较高。     

剪切对泡沫夹层结构梁弯曲性能的影响

本文以受剪后横截面仍为一平面但与轴线不再垂直为基本假设,采用能量法建立了一种对泡沫夹层结构梁的弯曲性能进行分析的方法。通过对比试验数据以及有限元的计算结果,得到用该方法可较为准确地预测泡沫夹层结构梁的挠度。通过分析,得到了剪切对泡沫夹层结构梁挠度的影响程度随着梁的跨高比的增大而减小,同时讨论了梁横截面正应变及正应力的分布情况。     

面板厚度对复合材料夹层梁整体及局部弯曲力学性能影响

考虑芯材局部压陷效应,对泡沫夹芯复合材料夹层梁整体及局部弯曲力学性能进行研究。分析了上面板厚度对夹层梁整体及局部弯曲力学性能影响规律。首先,对三种不同厚度上面板夹层梁进行三点弯曲试验,结果表明,夹层梁破坏模式为芯材压陷破坏和芯材剪切破坏;上面板厚度越大,夹层梁极限承载力越大;增大上面板厚度能有效减弱加载点位置芯材局部压陷效应。其次,基于考虑芯材竖向压缩变形的高阶剪切变形理论,对试验梁整体及局部弯曲受力机理进行分析,得到夹层梁上、下面板不同位置挠度及应变的分布规律。最后,对不同试验梁极限承载力进行理论分析,并与试验结果对比。     

泡沫塑料夹层梁弯曲试验和理论分析

本文对泡沫塑料夹层梁的试验结果进行了理论分析。挠度和剪应力的理论计算值与实测值很符合,面板应力的理论计算值比实测值大,经修正后的理论计算值与实测值吻合,可供夹层结构产品设计时使用。本文也指出泡沫塑料夹层梁弯曲的非线性特点,产品设计时应计及此特性。     

整体中空夹层复合材料弯曲刚度研究

基于整体中空夹层复合材料的织物结构特点以及对经纬向弯曲变形现象的分析,建立两种夹层梁模型,分别推导了经向与纬向弯曲刚度的解析表达式。通过理论解、有限元解以及试验值的对比,验证了模型的合理性和准确性。在此基础上,运用本文理论方法探讨了纱线密度对整体中空夹层复合材料弯曲刚度的影响。研究表明,随着纱线密度的增加,整体中空夹层复合材料经纬向弯曲刚度均呈线性增加;经向弯曲刚度的影响因素按影响程度从大到小依次为经纱、绒经、纬纱;纬向弯曲刚度的影响因素按影响程度从大到小依次为纬纱、经纱、绒经;和纬向弯曲相比,绒经对经向弯曲刚度的影响更大。     

芯材密度对复合材料夹层梁弯曲力学性能影响

研究了聚氨酯泡沫密度对复合材料夹层梁弯曲力学性能的影响。首先,对5种不同密度(48~413kg/m3)泡沫芯材复合材料夹层梁进行三点弯试验研究,结果表明,夹层梁极限承载力随芯材密度的增大而增大;当芯材密度大于等于199kg/m3时,继续增大泡沫密度,夹层梁极限承载力增加速度变慢;随着芯材密度的增加,夹层梁破坏模式由芯材压陷变为面板受压屈服破坏。其次,基于考虑芯材竖向压缩变形的高阶剪切变形理论,对不同试验梁弯曲受力机理进行弹性分析,得到夹层梁上、下面板挠度变化及应变分布规律,并与试验结果对比,验证了理论分析方法的正确性。最后,对试验过程中夹层梁典型的破坏模式进行极限承载力分析,提出其极限承载力计算公式,并与试验结果对比,结果吻合良好。     

板翅式换热器夹层结构等效模型研究及数值分析

依据薄板小挠度弯曲变形理论和正交各向异性夹层板弯曲变形理论,对板翅式换热器这种特定的金属夹层结构进行等效模型研究,通过建立有限元等效模型的方法研究板翅式换热器的力学参数。使用有限元前处理软件Patran对换热器夹层结构进行几何简化并独立成具有代表性的胞元,在多种边界条件下,提取胞元的应变分量和弯曲内力。结合夹层板应力与应变的本构关系计算刚度矩阵,从而求出宏观等效弹性常数。通过该方法可以将板翅式换热器夹层板等效成连续材料的单层板单元,最后将等效计算模型的力学参数用于板翅式换热器的模态分析,并与模态实验分析结果进行对比,验证等效分析方法的合理性和有效性。     

钢纤维对钢筋混凝土梁弯曲韧性与疲劳损伤的影响

通过钢筋混凝土梁弯曲静载和等幅疲劳试验,研究了钢纤维对钢筋混凝土梁挠度、弯曲韧度、刚度以及刚度损伤累积的影响.结果表明:在弯曲静载试验中,梁的挠度随着钢纤维体积率的增加而逐渐减小,弯曲韧度逐渐增大;在疲劳试验中,各梁挠度增长和刚度损伤累积随着荷载循环次数增加均呈现三阶段变化规律,说明钢纤维掺入不会改变钢筋混凝土梁疲劳损伤发展规律,但会改变梁挠度和刚度的大小,随着纤维掺量增加,梁的挠度逐渐减小,刚度逐渐增加,抵抗变形能力增强.     

计入横向剪切时层合梁的弯曲弹性解

本文根据一阶横向剪切变形理论，导出了对称层合梁的挠曲线微分方程，求解了层合染在简单载荷作用下的挠度曲线和应力，横向剪切对挠度和应力的影响依赖于层合梁的材料常数，约束类型，载荷种类和跨高比，计算结果表明，横向剪切对层合梁挠度影响颇为显著，且当层合梁跨高比大于18时，可忽略横向剪切效应。     

纤维复合材料层间剪切摸量测试

1概述随着纤维复合材料产品的广泛应用,且产品设计均采用计算机,特别是航天航空部门、军工产品,计算越来越精确,因此,对材料性能要求更全面,如要求测出复合材料层板的G13、G23等性能(1)。根据我们的长期实践经验及理论分析,可以应用GB/T1456三点外伸梁弯曲法来测试复合材料层板的G13、G23等(2)。三点外伸梁弯曲法的特点是,可以用梁外伸端的位移(挠度)独立地计算出梁材料的弯曲弹性模量。由梁当中的挠度及外伸端的位移(挠度)可以一次计算出梁材料的层间剪切模量,不必像文献(3)等解联立方程,其优越性极显著(4)。2试验过程2.1试样尺寸试样形…     

Effect of shear deformation on interfacial stresses in plated beams subjected to arbitrary loading

Bonding a fibre reinforced polymer (FRP) composite or metallic plate to the soffit of a reinforced concrete (RC), timber or metallic beam can significantly increase its strength and other aspects of structural performance. These hybrid beams are often found to fail due to premature debonding of the plate from the original beam in a brittle manner. This has led to the development of many analytical solutions over the last two decades to quantify the interfacial shear and normal stresses between the adherends. The adherends are subjected to axial, bending and shear deformations. However, most analytical solutions have neglected the influence of shear deformation of the adherends. For the few solutions which consider this effect in an approximate manner, their applicability is limited to one or two specific load cases. This paper presents a general analytical solution for the interfacial stresses in plated beams under an arbitrary loading with the shear deformation of the adherends duly considered. The shear stress distribution is assumed to be parabolic through the depth of the adherends in predicting the interfacial shear stress and Timoshenko's beam theory is adopted in predicting interfacial normal stress to account for the shear deformation. The solution is applicable to a beam of arbitrary prismatic cross-section bonded symmetrically or asymmetrically with a thin or thick plate, both having linear elastic material properties. The effect of shear deformation is illustrated through an example beam. The influence of material and geometric parameters of the adherends and adhesive on the interfacial stress concentrations at the plate end is discussed.     

Measurement of adhesive shear properties by short beam shear test based on higher order beam theory

This paper refers to the measurement of the shear properties of adhesive bonding by a new beam theory using the short beam shear (SBS) test configuration. A novel higher-order sandwich beam theory has been developed to analyze the adhesive bonded beam that consists of two adhered laminates and a single layer of adhesive in between. The closed form analytical solution for the SBS test model of the adhesively bonded beam is obtained in terms of deflection and stress distribution. The present theory has been used for calculating the adhesive shear modulus from the structural compliance. The initiation of stiffness degradation for the short beam shear test model was used as the critical load value for deriving the adhesive shear strength. A finite element model is built for validating the present model, and to evaluate its suitability for measuring adhesive shear properties. The present theory shows better accuracy for measuring the shear modulus than existing theories for both thin and thick adhesive layers. The measured strength values are more accurate than those obtained from the single lap joint shear test model. This theory can be used for adhesive materials with linear elastic deformation behavior.     

横向腹板增强复合材料夹层梁受弯性能试验研究

通过四点弯试验研究横向腹板增强复合材料夹层梁受弯性能,得到不同腹板间距、厚度对夹层梁弯曲破坏模式、刚度、极限承载力及延性性能的影响规律。结果表明:横向腹板能改变夹层梁的破坏模式,无腹板增强夹层梁破坏模式为芯材剪切破坏,横向腹板增强夹层梁破坏模式为多区格渐进破坏模式;相对于无腹板增强夹层梁,横向腹板能显著增强复合材料夹层梁的延性特性,最高达229%,腹板间距越小,夹层梁延性性能越好。     

Interface Stress Response of Laminated Plates Subjected to Static and Impact Loads

This paper deals with the stress analysis of laminated sandwich beams subjected to static loads and impact loads. When the laminated sandwich beams are subjected to static loads, stress distribution at the interfaces is analyzed, by using two-dimensional theory of elasticity, as a contact problem. When the laminated sandwich beams are subjected to impact loads, the interface stress response is analyzed using FEM (DYNA3D). Experiments were conducted. A fairly good agreement is seen between the analytical and the experimental results. The effects of the ratios of Young's moduli for each beam on the interface stress response are clarified.     

Modeling and optimization of the sandwich beam specimen in three-point bending for adhesive bond characterization

Standard tests for adhesive bond characterization suffer for several deficiencies. The simplest specimens to make and test are lap joint geometries (e.g. single, double, symmetric, etc.) that generate complex stress distributions with irregularities and even singularities of the stress state. Those with the stress state closer to pure shear (e.g. napkin ring or Arcan) are difficult to make and require special test fixtures. This paper examines the stress state in the adhesive of a simple beam specimen obtained by bonding two flat plates one upon the other and loading the final sandwich in three-point bending. An elementary theory is used to optimize the specimen for in-situ measurements of either shear strength or shear modulus of the adhesive. The accuracy of the model is validated with finite element analyses, showing good agreement between the analytical and finite element model and also providing suggestions for the best geometry to be adopted for practical implementation of the test.     

An improved four-parameter model on stress analysis of adhesive layer in plated beam

The prediction of stresses in an adhesive layer is helpful in revealing the mechanism of debonding failure in plated beams. This study proposes an improved analytical model for the stress analysis of an adhesive layer in a plated beam. The beam and the soffit plate are individually modelled as a single Timoshenko sub-beam with separate rotations, while the adhesive layer is modelled as a two-dimensional elastic continuum in plane stress, which considers different adherend-adhesive interface stresses. The internal forces of the adhesive layer are assumed to satisfy the Timoshenko beam theory, and the shear deformation and bending moment of the adhesive layer can be considered. The internal forces and displacements of the adhesive layer are fully considered in the displacement compatibility equations, and deformable interfaces are assembled so that the effect of interface stresses on local deformation is captured. Based on equilibrium equations and displacement continuity, the governing differential equations of beam forces are derived, and then the analytical solutions of interface stresses and stresses along the thickness of the adhesive layer are obtained. Comparisons of the results of the finite-element analysis and the existing four-parameter model solutions show that the present model is reasonable. The influence of adhesive thickness on stress distributions in adhesive layers is also investigated.     

THE BEHAVIOUR OF ADHESIVELY BONDED BEAMS VERSUS THEIR WELDED EQUIVALENT

The study aims to produce a design guide for the calculations of stresses and deflections of adhesively bonded beams fabricated from steel adherends using a structural epoxy adhesive. Such design calculations already exist for welded but not for bonded beams. Small models based on beams with a T-section profile, at various beam lengths, are formulated. A key to these calculations is the determination of the adhesive/adherend interface factors/coefficients, to correct the estimated values of stress and deflection from three-point bending conditions. This article presents the methodology for evaluating bonded beams in relation to equivalent welded (solid) beams. This includes mechanical testing, an analytical method based on beam and sandwich theory, and finite element techniques. Results from these techniques are presented and compared and values of the coefficients for T-section beams are determined.     

The behaviour of adhesively bonded beams versus their welded equivalent

The study aims to produce a design guide for the calculations of stresses and deflections of adhesively bonded beams fabricated from steel adherends using a structural epoxy adhesive. Such design calculations already exist for welded but not for bonded beams. Small models based on beams with a T-section profile, at various beam lengths, are formulated. A key to these calculations is the determination of the adhesive/adherend interface factors/coefficients, to correct the estimated values of stress and deflection from three-point bending conditions. This article presents the methodology for evaluating bonded beams in relation to equivalent welded (solid) beams. This includes mechanical testing, an analytical method based on beam and sandwich theory, and finite element techniques. Results from these techniques are presented and compared and values of the coefficients for T-section beams are determined.     

Microstructural characterization and failure analysis of 2D C/SiC two-layer beam with pin-bonded hybrid joints

In this paper, the microstructural characteristics and mechanical behavior of 2D C/SiC two-layer beams with pin-bonded hybrid joints were investigated. The pin joints were incorporated into the two-layer beam during the assembling stage, and the adhesively bonded joints can be introduced by subsequent chemical vapor infiltration (CVI) process. For 2D C/SiC two-layer beam it was confirmed that the distribution of the adhesively bonded joints was random. Based on the partial interaction composite beam theory, a simplified method was proposed to characterize the effect of adhesively bonded joints on the bending stiffness of the 2D C/SiC two-layer beam. The stress distribution around the pin joints was described by finite element modeling. It was found that the radial stress, the hoop stress and the in-plane shear stress around the pin joints were unique in their distributions. Under the action of these stresses, two kinds of failure modes can be initiated: one is the debonding of the pin–hole interface, and the other is the fracture of the 2D C/SiC plate. Based on the stress results, an empirical failure criterion was present to predict the ultimate failure of the 2D C/SiC two-layer beam.     

Strain‐rate and temperature effects on the deformation of polypropylene and its simulation under monotonic compression and bending

Monotonic compressive loading and bending tests are conducted for solid polypropylene (PP) under constant or time‐varying strain‐rates and temperatures of 10, 25, 40°C. The observed compressive stress‐strain responses under constant conditions have revealed that the inelastic deformation behavior is remarkably dependent on loading rates and temperatures of normal use. The examination of such inelastic behavior has indicated that the strain‐rate effects correspond with the temperature effects based on the concept of time‐temperature equivalence. The viscoplastic constitutive theory based on overstress (VBO) has successfully reproduced the experimental responses with stress‐jumping phenomena using the equivalent time. Four‐point bending tests are performed under monotonic loading and holding for PP beams at three different temperatures. The observed deformation behavior has shown that the Bernoulli‐Euler hypothesis is valid. The VBO model and beam bending theory has generated the basic equations for PP beams, showing an analogy with the uniaxial one. In the numerical analysis, the equations are transformed into nonlinear ordinary differential equations with use of Gaussian quadrature for the spatial integrals. The comparison of numerical and experimental results has suggested some modifications for actually loaded moment taking the effect of deflection and friction into consideration. Finally, the numerical calculation has simulated the experimental time‐histories of curvatures fairly well.