多孔复合材料机械连接件弹性接触内力和应力分析

本文用有限元混合法给出了多孔复合材料机械连接件弹性接触内力和应力分析。文中详细讨论了销钉弹性、层合板铺设方式和摩擦对各孔钉载分配及孔边应力的影响,并给出了多孔连接件向单孔连接件简化的条件。     

饱和黏弹性土中圆柱形隧洞的振动特性

基于流体不可压缩饱和多孔介质理论,将衬砌视为具有分数导数本构关系的多孔黏弹性体,在频率域内研究了在内水压力作用下饱和黏弹性土和衬砌系统的振动特性。通过引入与孔隙流体体积分数有关的应力系数,合理地确定了隧洞边界衬砌和孔隙水共同承担的内水压力值。利用衬砌内边界上的边界条件以及衬砌和土体界面处应力和位移的连续性条件,给出了隧洞边界部分透水条件下饱和黏弹性土和分数导数型黏弹性衬砌系统简谐耦合振动时系统动力响应的解析解。结果表明:饱和黏弹土和衬砌结构的动力响应与衬砌材料的黏性有关;应力系数合理地确定了衬砌和孔隙水共同承担的内水压力值。     

PBL剪力连接件抗剪承载力试验研究EI北大核心CSCD

为建立组合桥梁中开孔钢板剪力连接件(PBL)剪力连接件的抗剪承载力计算公式,开展8个PBL连接件的单调加载推出试验。着重研究静载下不同承压方式、混凝土强度、开孔数量和贯穿钢筋直径对连接件抗剪承载力的影响。基于变形协调条件分析端部混凝土、孔内混凝土榫和贯穿钢筋对单孔连接件极限承载力的贡献;多孔连接件的抗剪承载力则在考虑应力重分布的基础上将单孔连接件承载力进行叠加。试验结果表明:提出的PBL连接件抗剪承载力计算模型物理意义明确,计算结果精度较高,可用于单排PBL剪力连接件的承载力计算。     

PBL剪力连接件抗剪承载力试验研究

为建立组合桥梁中开孔钢板剪力连接件（PBL）剪力连接件的抗剪承载力计算公式,开展8个PBL连接件的单调加载推出试验。着重研究静载下不同承压方式、混凝土强度、开孔数量和贯穿钢筋直径对连接件抗剪承载力的影响。基于变形协调条件分析端部混凝土、孔内混凝土榫和贯穿钢筋对单孔连接件极限承载力的贡献;多孔连接件的抗剪承载力则在考虑应力重分布的基础上将单孔连接件承载力进行叠加。试验结果表明：提出的PBL连接件抗剪承载力计算模型物理意义明确,计算结果精度较高,可用于单排PBL剪力连接件的承载力计算。     

装配式钢-混凝土组合梁高强螺栓剪力连接件力学模型

剪力连接件是装配式钢-混凝土组合梁的关键部件,其荷载-滑移曲线大致分为四个阶段,即滑移前摩擦阶段、滑移阶段、滑移后弹性阶段、滑移后塑性阶段。该文通过弹性地基梁理论和材料力学平面应力理论,建立了高强螺栓剪力连接件的受力模型,对前三个阶段的受力行为进行了理论解析分析,并通过多组试验数据对理论结果进行了验证,二者吻合良好。研究表明：剪力连接件在整个受力过程同时受弯矩、剪力和轴力的耦合作用,该文提出的力学模型能较为准确的模拟螺栓弹性阶段的极限值,能初步解释螺栓在弹性段抗剪性能随预拉力变化的原因;并得出了螺栓弹性段弯矩对其屈服极限影响有限的结论。     

柱状药包岩石中爆炸的数值模拟

利用ANSYS/LS-DYNA3D对柱状药包在半无限岩石介质中爆炸情况进行了数值模拟,对柱状药包的爆炸在岩石内产生的应力变化进行了分析。给出了岩石弹性区内一点的应力变化时程曲线;并借助球形装药的经验公式对柱状装药的情况进行了分析比较,结果表明,应力波的峰值基本一致。该时程曲线可以用于多孔爆破计算。     

柱状药包岩石中爆炸的数值模拟

利用ANSYS/LS-DYNA3D对柱状药包在半无限岩石介质中爆炸情况进行了数值模拟,对柱状药包的爆炸在岩石内产生的应力变化进行了分析。给出了岩石弹性区内一点的应力变化时程曲线;并借助球形装药的经验公式对柱状装药的情况进行了分析比较,结果表明,应力波的峰值基本一致。该时程曲线可以用于多孔爆破计算。     

钢筋套筒灌浆连接性能试验研究及筒壁应力分析

完成了12个钢制套筒灌浆连接件的拉拔试验,系统研究了其破坏过程与破坏形态、荷载-位移曲线、套筒应变等,重点分析了锚固长度、钢筋直径对筒壁应力的影响。运用厚壁圆筒理论,明确套筒灌浆连接件中钢筋与灌浆料以及套筒之间的传力过程,并基于轴向拉力建立了筒壁纵、横向应力的计算模型。研究表明：套筒灌浆连接件破坏过程分为弹性、屈服、强化、颈缩四个阶段,屈服强度和极限强度与钢筋材性相近。随钢筋锚固长度增加,筒壁应力略有减小,且随着钢筋直径增加,筒壁的应力明显增大。同时,建议筒壁应力计算值与试验值吻合较好,可为钢筋套筒灌浆连接设计与研究提供借鉴。     

剪切连接件的受力机理理论分析与试验验证

基于剪切连接件（SLD）的典型构造建立力学模型,应用弹性力学半逆解法对其腹板的应力分布进行求解,并对剪切连接件的初始刚度K、屈服后刚度K'、屈服荷载F_y、屈服位移u_y等关键性能指标进行了理论分析。针对以往屈服点确定方法存在的不足,提出了一种基于Bouc-Wen模型和模拟退火算法的等效屈服点确定方法。最后采用单调拟静力加载试验进行验证。研究结果表明：剪切连接件腹板应力分布和各项力学性能指标的理论解与有限元分析结果及试验实测结果吻合较好;该文提出的屈服点确定方法能够有效识别剪切连接件的相关力学性能指标,且拟合曲线与单调加载试验曲线良好吻合。理论分析成果将为剪切连接件的工程设计、性能评估及后续研究提供理论参考。     

多相非饱和多重孔隙介质的有效应力定律

多孔介质的有效应力定律广泛应用于流固耦合变形分析问题。该文考虑孔隙的重数、孔隙流体的相数、各向异性、非饱和、基质吸力等条件,提出了广义多相非饱和多重孔隙介质的有效应力定律。在固体相及各流体相线弹性变形的假设下,首先通过应力状态分解、边界条件叠加方法,得到了不考虑基质吸力的多相等效饱和各向异性多重孔隙介质的有效应力。考虑到非饱和多孔介质中两相界面张力引起的基质吸力,在线弹性变形基础上,叠加了基质吸力引起的变形部分,推导得到非饱和多孔介质的有效应力定律的一般形式。将所得公式根据实际需要进行简化处理,可以得到目前常用的有效应力定律的表达形式,充分说明了该文所得结论的合理性。     

Über die Gebrauchseigenschaften von Schraubenverbindungen in Magnesiumbauteilen

Usage properties of bolted joints in magnesium parts The following paper presents a survey on the results of the research project “Usage properties of bolted joints in magnesium parts”. By the use of component orientated specimen geometries parameter for the use of bolted joints in and with magnesium cast parts are determined in a most realistic way. Therefore investigations on magnesium alloy sockets with thread and sockets with clearance hole in combination with steel and aluminium alloy fasteners have been carried out. The focus of the investigations is set on the minimum thread reach and the interfacial load on one hand and on the other on the relaxation behaviour. Geometry, load and temperature are variied. The investigated materials are characterized with regard to their suitability of certain environments.     

液体垫片对复合材料单搭接螺栓接头力学性能的影响

复合材料构件由于存在制造误差,装配时常常产生间隙,消除间隙的一种基本手段是向其中填充液体垫片。以复合材料单搭接螺栓连接接头为研究对象,设计了拉伸实验,选取一种改进的失效准则与对应的材料退化准则建立了渐进损伤有限元分析（FEA）模型,在此基础上研究了液体垫片对复合材料单搭接接头强度、刚度等力学性能的影响及复合材料孔内损伤演化的过程,此外还研究了液体垫片孔边的应力-应变状态。由实验与有限元结果可以得出：随着液体垫片厚度的增加,接头的拉伸刚度与峰值载荷均有所降低;相同载荷下复合材料孔内损伤加剧,孔内单元产生初始损伤时对应的载荷降低;但液体垫片厚度的增加可以降低垫片孔边的应力与塑性应变峰值,并使其分布更加均匀化,改善液体垫片孔边受力状态。     

复合材料单螺栓双剪搭接干涉配合疲劳强度评价

该文采用有限元软件ANSYS,建立了复合材料单螺栓双剪搭接干涉配合的三维有限元模型,研究了当连接模型中施加了预紧力时,预紧力对干涉配合的影响.首先分析了无载荷作用下复合材料板在干涉配合孔边切向应力分布特点;之后比较了双剪搭接在10kN 和15kN 两种远程纵向载荷作用下,孔边切向应力的分布情况.结果表明：远程纵向循环载荷作用下,预紧力能有效均匀各板所受载荷,并可消除在无预紧力时中板上的局部应力集中点,而且适当增大预紧力能提高干涉配合连接的效率;此外研究显示双剪搭接连接在不同的载荷下,疲劳危险点也不同;最后研究了复合材料干涉配合连接时,各板的交叉区域孔边切向应力分布,因此得出各板在高低不同的载荷下疲劳危险点的分布.     

螺栓与孔间隙对单搭单螺栓连接板模态频率的影响

由于装配需要或者制造误差等因素的影响,连接板的螺栓与螺栓孔之间不可避免地存在间隙,而且间隙的变化对连接板的模态频率有一定的影响。通过研究螺栓与孔间隙对单搭单螺栓连接板模态频率的影响机制,讨论一种基于变通孔直径的螺栓连接动力学设计方法。首先,基于ABAQUS软件和Python语言,建立了包含变通孔直径的单搭单螺栓连接板有限元计算模型;然后,探讨了螺栓连接板在一端固支、两端固支两种边界条件下螺栓与孔间隙变化对连接板模态频率的影响机制;最后,提出了一种基于变通孔直径的螺栓连接板动力学设计方法。结果表明:当通孔直径为螺栓直径的1.02~1.20倍时,通孔直径的变化对螺栓连接板各阶固有频率的影响可忽略;通孔直径大于螺栓直径的1.21倍时,其变化对连接板模态频率有明显的影响,且影响程度各异。研究表明在特定激励环境下可通过改变通孔直径来改变系统模态频率,从而避免结构共振。该方法为螺栓与孔间隙对复杂螺栓连接系统固有频率的影响分析提供了参考,也为螺栓连接系统的抗振疲劳设计问题提供了思路。     

Strength prediction in CFRP woven laminate bolted double-lap joints under quasi-static loading using XFEM

The current paper is concerned with modelling damage and fracture in woven fabric composite double-lap bolted joints that fail by net-tension. A 3-D finite element model is used, which incorporates bolt clamp-up, to model a range of CFRP bolted joints, which were also tested experimentally. The effects of laminate lay-up, joint geometry, hole size and bolt clamp-up torque were considered. An Extended Finite Element (XFEM) approach is used to simulate damage growth, with traction–separation parameters that are based on previously reported, independent experimental measurements for the strength and toughness of the woven fabric materials under investigation. Good agreement between the predicted and measured bearing stress at failure was obtained.     

Photoelastic investigation of bolted joints in composites

In this paper, the methods of photo-orthotropic elasticity are applied to the study of bolted joints in composites. The photoelastic models are E-glass fibre-reinforced epoxy strips loaded through a cylindrical pin, simulating bolt loading without lateral pressure. A special loading arrangement is devised so that the photoelastic response around the hole is not obscured. Quasi-isotropic and unidirectionally-reinforced specimens are tested, with ratios of end distance to hole diameter varying from 2 to 6. Photoelastic isochromatic fringe patterns are presented along with the shear stress distribution for the quasi-isotropic models.     

A global bolted joint model for finite element analysis of load distributions in multi-bolt composite joints

This paper presents the development and validation of a global bolted joint model (GBJM), a highly efficient modelling strategy for bolted composite joints. Shell elements are used to model the composite laminates and the bolt is represented by a combination of beam elements coupled to rigid contact surfaces. The GBJM can capture effects such as bolt–hole clearance, bolt-torque, friction between laminates, secondary and tertiary bending in the laminates as well as the load distribution in multi-bolt joints. The GBJM is validated using both three-dimensional finite element models and experiments on both single- and multi-bolt joints. The GBJM was found to be robust, accurate and highly efficient, with time savings of up to 97% realised over full three-dimensional finite element models.     

The effect of electroless Ni–P coatings on the fatigue life of Al 7075-T6 fastener holes with symmetrical slits

In this paper, the fatigue behaviour of Al 7075-T6 fastener holes with symmetrical through slits was studied. The holes were coated with electroless nickel (EN) plating with a high phosphorous content of 10–13 wt% and a thickness of 40 μm. Uncoated open-hole, EN coated open-hole, uncoated bolted hole and EN coated bolted hole specimens were fatigue tested. Bolted samples were clamped with a high tightening torque of 7 Nm. The established S–N curves showed 282–1348% improvements in the fatigue life due to the combined effect of EN coating and bolt clamping, depending on the level of maximum alternating stress. Excellent adhesion was observed between the coating and the aluminium substrate along the crack path. Tensile tests results showed a considerable reduction of 54% in the ductility of the coated material while both the yield and ultimate strengths were found to slightly increase by approximately 6% in comparison with the uncoated aluminium alloy.     

Experimental and numerical analysis of aluminum-aluminum bolted joints subject to an indentation process

The increasing interest of the industry (especially automotive, aviation and marine) in the fastener joints (riveted, bolted, etc.) between metallic materials, has re-opened the study on the possibility to improve the performance of the drilled structure using plastic deformation processes.Indentation process, performed before the drilling operation, creates circumferential compression stresses around the hole which increase significantly the mechanical performance of the drilled structures.In this paper, static and the fatigue performances of aluminum–aluminum (AW 6082-T6) single-lap bolted joints are studied. In particular, the study compares the mechanical strength of only drilled single-lap bolted joints (OD specimens) and single-lap bolted joints subject to an indentation process (IP specimens). In order to determine the cycles to failure and the corresponding Wöhler diagram, several fatigue tests are performed. The analyses allow to determine the mechanical performance and the failure mode of the analyzed joints.Several numerical analysis, conducted in ANSYS environment on three-dimensional models of the single-lap joint, are focused on the evaluation of the residual stress on the indented plate and, in particular, to compare the stress distribution on both type of analyzed joints.     

配合方式对复合材料单钉单剪螺栓连接接头刚度的影响及其机制

针对单钉单剪复合材料螺栓连接,研究了间隙与干涉2种配合方式对接头刚度的影响及其机制。通过与试验结果的对比,验证了所采用的有限元方法的有效性。结果表明:对于复合材料单钉单剪螺栓连接,间隙配合导致接头刚度变小, 3%钉直径的间隙量导致接头刚度下降16%~17%,并且随着间隙量的增大,接头刚度基本呈线性下降;而对于装配过程中没有产生孔边分层损伤的干涉配合连接件, 0.5%钉直径的干涉量使得接头刚度增加了约15%。配合方式不同,连接件孔周接触应力峰值方向及厚度方向接触应力分布不均匀的程度不同,进而影响了接头刚度。