复合材料接头三维有限元应力分析

本文介绍了复合材料三维单元刚度矩阵,用三维有限元方法计算了复合材料层压耳片接头拉伸、剪切、弯曲载荷的问题,给出了孔边应力分布及弯曲时层间剪应力分布。结果表明,当载荷平行于铺层且沿厚度均匀分布时,应力沿厚度方向变化不大,主要与铺层角度有关,当载荷不平行铺层时,层间剪切应力和拉伸应力较大,是接头破坏的主要原因。     

预应力锚索锚固段剪应力分布特性研究

基于弹性理论，利用弹性半空间体在边界上受法向集中力作用的布西内斯克应力解，建立了弹性理论空间模型，对预应力锚索锚固段剪应力沿长度方向的分布规律进行模型研究。得到剪应力沿锚固段轴向的分布曲线，求出了剪应力分布曲线的特征点；并通过与现场试验结果对比，验证了该模型的合理性，得出锚固段周边剪应力分布的合理结论。     

循环载荷下层间界面反平面剪切破坏的解析解:2.再加载及综合响应分析

本研究利用“剪切梁”模型,研究了在定常侧压力和周期性的反平面剪切载荷共同作用下,层间界面的破坏规律。本文为本研究的第二部分。对应一个完整的载荷周期,解析地给出了界面层上剪应力及位移场在再加载过程中的分布规律及演化规律。计算结果表明,由于裂纹前方损伤过程区的存在,当再加载过程不能覆盖卸载过程造成的损伤区时,会产生新的“应力锁死”现象。文末对结构整体的载荷－位移行为的分析,揭示了周期载荷作用下的两种结构响应模式：１）　接触塑性安定;２）　增量破坏。     

循环荷下层间界面反平面剪切破坏的解析解：2.再加载及综合响应分析

本研究利用“剪切梁”模型,研究了在定常侧压力和周期性的反平面剪切载荷共同作用下,层间界面的破坏规律。本文为本研究的第二部分。对应一个完整的载荷周期,解析地给出了界面层上剪应力及位移场在再加载过程中的分布规律及演化规律。计算结果表明,由于裂纹前方损伤过程区的存在,当再加载过程不能覆盖卸载过程造成的损伤区时,会产生新的“应力锁死”现象。文末对结构整体的载荷-位移行为的分析,揭示了周期载荷作用下的两种结构响应模式：1)接触塑性安定：2)增量破坏。     

复合材料夹层板单向受弯应力分析

基于非线性软质芯材位移模式的高阶剪切变形Zigzag夹层板理论,运用有限元方法分析了木质芯材-玻璃纤维增强聚合物（Glass Fiber Reinforced Polymer,下文缩写为GFRP）面板增强层、木芯材-GFRP竹混合增强层、以及泡沫芯材-GFRP面板增强层三种由真空导入工艺制作的复合材料夹层板;以米塞斯应力屈服准则为依据计算了特征点极限荷载,提出层间应力差作为树脂层的计算依据;考虑到根据本构模型直接由有限元法求得的位移获得的横向剪应力精度较低,采用基于应力平衡方程的最小二乘法计算了夹层板横向剪应力。对比实验和等效截面法的分析结果表明,基于非线性软质芯材位移模式的高阶剪切变形zigzag理论有限元分析法对于硬质和软质芯材复合材料夹层板都是十分有效的、实用的分析方法,适合于精细化分析和设计;等效截面法对于硬质芯材复合材料夹层板具有一定准确性,适合于初步分析和设计。     

爆破动荷载作用下边坡锚杆加固效果分析

岩质基坑边坡的加固措施常采用全长粘结式锚杆。为了研究在爆破动荷载作用下的锚杆加固效果,根据南溪长江大桥北岸锚碇基坑北侧边坡的爆破开挖情况,采用FLAC3D对基坑边坡加设锚杆前后的动力响应进行了计算。应用Bishop-拟静力法计算基坑边坡的动力稳定性系数。通过分析计算结果得出以下主要结论:加设锚杆后可以改善边坡的应力分布,减弱边坡坡脚处的应力集中现象,防止由于应力集中而导致的局部破坏;在爆破动力作用下,锚杆的轴力和砂浆剪应力均随时间的增加而增大,且增大的速率基本相同;加设锚杆后边坡的动力稳定性系数由0.98提高到1.33,提升幅度为36%。     

一种反映横向剪应力分布的层合板模型

本文提出一种新的三阶位移模型.在这个模型中,位移连续,而横向剪应力沿板厚成抛物线分布,从而完全满足了层间连续的条件,反映了横向剪应力的变化.一类准确解的例子表明,它比文献[3,4]中的三阶模型具有更高的位移和应力精度.      

变截面直杆轴向拉压时的剪应力

本文对变截面杆在轴向拉压时的各横截面应力计算提出了各点除有不为常量的正应力外， 存有不为常量的剪应力，并论证了该剪应力沿截面高度，沿轴线长度向的分布规律，提出了剪应力计算公式。     

基于裸光纤光栅传感技术GFRP抗浮锚杆荷载传递机制的原位试验研究

基于3根全螺纹GFRP抗浮锚杆现场拉拔破坏性试验,成功地将植入式裸光纤光栅传感技术应用于抗浮锚杆拉拔试验中,研究了全长黏结GFRP抗浮锚杆在各级荷载作用下的承载特性、荷载传递特征及破坏机制。研究表明:植入式裸光纤光栅传感技术有其独特的优越性,不会对锚杆自身造成损伤;GFRP抗浮锚杆破坏以杆体基体材料剪切破坏为主,锚固长度为5.0 m,ϕ28 mm锚杆极限抗拔承载力为400 kN,能够满足工程需求;锚杆的轴向应力主要集中在距孔口约3.0 m的区域,且随着锚固深度的增加迅速衰减;剪应力峰值出现在距离孔口以下约0.8 m的位置,随着荷载的增加,剪应力曲线的峰值逐渐增大并向深部移动。在此基础上,进一步分析论证了GFRP抗浮锚杆的破坏机制,为GFRP抗浮锚杆的工程应用提供了理论依据。     

循环载荷下层间界面反平面剪切破坏的解析解:1.卸载行为

本研究利用“剪切梁”模型,研究了由定常侧压力和周期性的反平面剪切周期载荷共同作用下,层间界面的破坏规律。本文为本研究的第一部分,解析地给出了界面层上剪应力及位移场在卸载(反向加载)过程中的分布规律及演化规律。计算结果表明,由于裂纹前方损伤过程区的存在,卸载是非弹性的,伴随有损伤和摩擦两种耗散机制;另外,当卸载过程不能覆盖加载过程造成的损伤区时,会产生“应力锁死”现象,从而导致结构在以后的加载过程中可能产生冲击载荷。     

海洋平台受损构件的承载能力与加固分析

采用了数值有限元和弹塑性理论解析方法,对某海洋平台结构受大型船舶冲撞的斜撑受损构件进行承载能力分析,同时对灌浆卡箍维修方案进行了理论分析与数值计算,分析评价了灌浆卡箍的修理方法。利用混凝土强度理论von Mises破坏准则,建立灌浆卡箍的轴向受拉、轴向受压和面内弯矩作用下的非线性有限元模型进行计算,与理论分析所得的承载能力设计值比较表明,灌浆卡箍的轴向抗拉、抗压承载能力要比原钢管强,但其抗弯承载能力不如原钢管。对照APIRP2A规范提供的设计值进行分析比较表明,其加固方案是安全的,用它进行海洋平台结构受损构件的承载能力及加固分析是可行的。     

考虑剪切作用的盾构隧道管片接头力学模型研究

目前使用较广泛的盾构隧道管片接头研究模型往往视切向为刚性,大多考虑了轴力与弯矩的共同作用而忽视了剪力作用。然而剪切力可能会使接头位置发生剪切位移,严重时可能引起管片剪切破坏、隧道错台等。该文将轴向、切向和转动三个方向的位移作为已知荷载,分别推导接头区域内螺栓与混凝土结构的刚度矩阵,然后对刚度矩阵进行合成,得到管片接头考虑剪切时的力学模型。并以狮子洋盾构隧道工程为依托,对比了有限元法与该模型的计算结果。研究表明,模型与有限元法计算的结果规律相同,两者具有较好的一致性。该文建立的模型考虑了轴向、剪切及弯曲三个方向上荷载的耦合作用,使之更符合接头的实际情况。研究成果对补充管片接头力学模型有一定参考价值。     

新型单边拧紧高强度螺栓摩擦型连接扭矩系数及抗剪性能试验研究

为促进钢结构装配式建筑和可拆卸钢结构的连接技术发展,该文介绍了一种基于传统高强度螺栓的新型单边连接方式,并设计了5个摩擦型连接接头试件。通过开展抗剪试验,研究了其扭矩系数、抗滑移系数、抗剪承载力、抗剪机理等,并与《钢结构设计标准》(GB 50017—2017)的相关设计方法进行了对比分析。采用有限元软件ABAQUS建立了高强度螺栓连接接头试件的有限元模型,验证了有限元模型的准确性和适用性,并对该新型螺栓连接接头进行了参数分析。结果表明,该文提出的新型单边拧紧高强度螺栓摩擦型连接方式安装简单、易于施工和拆卸,抗剪连接破坏前螺栓预拉力损失值在15%~20%,其抗滑移系数、抗剪承载力仍可按照现行标准进行设计计算。研究成果能够为此类新型单边连接技术的工程应用提供基础。     

地震作用下顺倾岩体边坡锚固界面剪切作用分析

基于FLAC 3D软件,尝试修正的cable单元建立全长黏结锚杆锚固顺倾岩体边坡数值分析模型,改进剪应力提取方法,分别模拟分析了锚杆-注浆体界面上和注浆体-岩体界面上的剪切作用及其演化。研究发现:注浆体-岩体界面上比杆体-注浆体界面上的剪应力小得多,且均以锚杆上的中性点为界方向相反,分布很不均匀,中性点附近大,锚杆两端小,随边坡地震响应增强锚固界面脱粘并向锚杆两端发展,直至全部脱粘致使锚固破坏。获得了地震波作用下边坡两锚固界面上剪应力及其分布和脱粘破坏过程,揭示了锚固界面上的剪切相互作用和锚固破坏机制,并得到了试验印证。为边坡锚固设计和施工提供了参考。     

Dual boundary element method modelling of aircraft structural joints with multiple site damage

The computation of crack growth from a bolt or rivet hole in a structural joint practically requires that the geometry be approximated to some degree. In this paper a simplified quasi-2D stress analysis method, using the boundary element method is presented, where the load transfer rate and the contact stresses at the hole edge for the full 3D geometry are fairly well approximated. Coupled with a dual boundary element formulation for the crack propagation problem, this model is used to evaluate stress intensity factors for through cracks emanating from holes in several double shear lap joint configurations. As the calculated stress intensity factors compare well with experimental data, this procedure is considered to approximate satisfactorily the load transfer rate and the contact stresses at the hole edge of the full 3D geometry, when secondary bending is not a factor.     

Two-dimensional axisymmetric winding model for finite deformation

A two-dimensional axisymmetric winding model for wound rolls of thin web is developed. The model accounts for radial and axial displacements and radial, circumferential, axial and shear stresses. The roll build-up is modeled as an incremental accretion process. The material behaviour of the roll is considered as hyperelastic, orthotropic and radially nonlinear. The numerical solution is developed using the finite element method and the total Lagrangian formulation. The model is applied to the winding of paper rolls. It is shown that centrifugal forces may considerably affect the resulting stress distributions. For nonzero Poisson’s ratios significant edge effects in the roll stresses are found. In particular, high shear stresses and shear stress gradients are discovered in the vicinity of the core near the roll ends. A remarkable stress leveling phenomenon is found where the effect of a non-constant incoming web tension is evened out in the roll axial direction.     

Finite element analysis of substation composite insulators

Composite insulators are rapidly replacing their porcelain counterparts in electrical substation applications. These insulators consist of a glass-reinforced polymer (GRP) rod, with two metal end fittings radially crimped onto the ends of the rod during assembly. In this paper, axisymmetric finite element models are developed to evaluate the mechanical performance of composite insulators under externally applied axial compression. The analyses are performed by assuming both a perfectly bonded interface between the composite rod and the end fittings, and an imperfect interface which permits large relative sliding with Coulomb friction. Results indicate that the perfect interface model is unrealistic since it predicts singular stresses at the interface comer and an overall linear structural response. On the other hand, the imperfect interface model is found to simulate accurately the structural non-linearity caused by relative sliding of the GRP rod within the end fittings. The imperfect interface model has therefore been used to evaluate the effects of interface friction, and the extent of crimping, on the maximum load-bearing capacity of substation composite insulators.     

The measurement of the distribution of residual stresses through the thickness of a welded joint

A new method for the measurement of residual stresses in welded joints of complex cross section is described. The method involves the measurement of strain changes in the body as a narrow slot is cut in the plane of interest, in small increments of depth. A finite element model of the cross section is used to relate the strain changes at the measurement points to the residual stresses across the slot plane.
The accuracy of the method is demonstrated by using it to measure a known residual stress field in a cold bent bar. The method has been used in combination with a block removal technique to measure the through wall distribution of axial residual stresses at a circumferential butt weld in a cylinder with a protruding root bead. It could also be applied to the measurement of residual stresses in other joint configurations, such as fillet welds or T-butt welds.     

Dynamics of a functionally graded material axial bar: Spectral element modeling and analysis

Functionally graded material (FGM) bars in axial motion (hereafter called “FGM axial bars”) have great potential for applications in many engineering fields. Therefore, it is important to develop a reliable mathematical model that can provide very accurate dynamic and wave propagation characteristics in FGM axial bars, especially at high frequencies. As an extension of our previous work, we present a spectral element model for a modified FGM axial bar model wherein nonuniform lateral contraction in the thickness direction is taken into account. We assume that material properties of the modified FGM axial bar model vary in the radial direction according to the power law. The performance of the proposed spectral element model is validated through comparison with solutions from a conventional finite element model, and with the results from the previous FGM axial bar model. In addition, the effects of lateral contraction on the dynamic and wave propagation characteristics in example FGM axial bars are numerically investigated.