单面贴补修理后层合板的拉伸性能

对含孔损伤复合材料层合板单面贴补后进行拉伸试验研究。测量了层合板的应变分布、修理后层合板中心点的离面位移及拉伸强度等, 考察了补片的厚度、大小等因素对修理效果的影响。结果显示, 增加补片的厚度和直径能够提高母板的承拉能力, 但是增加补片的厚度会导致层合板离面位移增大。对无侧边支持的单面贴补层合板进行计算分析时, 必须考虑偏心载荷引起的弯矩的影响。在此基础上, 采用分层损伤判据建立了三维有限元模型, 对单面贴补层合板的破坏机理和拉伸强度进行了计算和分析。结果表明, 修理后层合板的拉伸破坏是由补片或母板内与胶接面相邻的层间分层引起的; 计算结果与试验结果一致。      

拉伸载荷下贴补复合材料层合板的渐进损伤分析

基于连续介质损伤力学和粘聚区模型建立了贴补复合材料层合板的渐进损伤分析模型,计算了拉伸载荷下修补结构的极限强度。数值仿真结果和实验结果吻合较好,验证了该模型的有效性。基于建立的模型研究了贴补复合材料层合板的损伤演化过程,并讨论了补片参数对修补结构拉伸性能的影响。研究结果表明：补片参数对贴补复合材料层合板的破坏模式与损伤演化过程有显著影响;不同破坏模式下,补片参数的改变对修补结构极限强度的影响效果不同。研究结果可为复合材料层合板的贴补设计提供部分理论参考。     

复合材料织物层合板挖补修理软件实现与试验验证

针对单向拉伸载荷作用下复合材料织物层合板胶接挖补修理结构,改进现有解析模型,建立适用于无附加层、附加1层和附加2层结构的阶梯型挖补修理结构和斜切型挖补修理结构的解析分析模型。给出求解算法,定义准确度用于评价数值计算精度,最终实现开发一套界面友好的复合材料胶接挖补修理设计与分析软件。该软件可以求解单向拉伸载荷作用下,复合材料胶接修理结构内部的剪应力场/剪应变场分布,评价搭接板受载情况,并预测结构失效载荷与失效模式。研究中采用T300/CYCOM-970织物作为母板与补片材料,METLBOND1515-4M作为胶层材料,设计进行了一系列阶梯型及斜切型挖补修理验证试验。试件失效载荷与软件计算结果吻合良好,阶梯型最大相差5.7%,斜切型最大相差14.0%。该软件可以对复合材料织物层合板胶接挖补修理进行高效、准确的初步辅助设计与分析。     

复合材料层压板单面贴补修理建模分析研究

胶接修理技术是一种优质、高效、低成本的结构修理技术.针对复合材料层板的胶接贴补修理进行计算模拟分析,并与实验结果相对比.采用ABAQUS有限元软件对层压板的损伤板和单面贴补修理板进行有限元建模,分析修补前后的应力分布情况,计算出失效强度与完好板进行对比,得出修补后的强度恢复率.     

复合材料开孔平板结构强度数值仿真及试验验证

复合材料结构损伤是导致结构失效的重要原因之一.本工作基于有限元分析软件ANSYS,结合渐进损伤分析方法建立了非线性渐进损伤分析模型,分析了复合材料开孔平板结构在拉伸载荷作用下的损伤模式和强度特性,并用试验验证了程序的有效性.使用蒙特卡洛方法分析了结构响应点与复合材料刚度参数的相关性,得到了关键参数对开孔平板结构拉伸承载能力的影响.最后等比例加载拉伸和弯曲载荷,对比其极限载荷值的大小,分析了不同载荷耦合作用下结构强度特性研究的必要性.结果表明,该方法对复合材料构件的损伤形式和强度预测精确度比较高,并定量分析了拉伸方向的弹性模量对最大破坏载荷的影响,为误差分析提供了一定的研究基础.     

层压板双面挖补修理的拉伸性能研究及参数分析

对含穿透型损伤层压板双面挖补胶接修补件的拉伸性能及主要影响参数进行了试验研究。结果表明: 双面挖补后的失效拉伸强度恢复率能够达到80%; 当挖补斜度1∶40、 覆盖层取3层、 且靠近母板的铺层方向与母板的最外层的铺层方向保持一致时, 强度恢复率较大; 使用双面挖补后, 母板厚度、 母板铺层方式对强度恢复率的影响不大。同时应用有限元软件ABAQUS, 采用三维实体单层设置建模方式对双面挖补层压板的拉伸性能进行了数值模拟, 模拟计算结果与试验结果基本相符。      

复合材料胶接修理层合板拉伸性能及影响参数

胶接修理是效率较高、应用较广的复合材料结构修补技术。对采用不同参数进行挖补和贴补修理的复合材料层合板的拉伸性能进行实验研究。结果表明:挖补修理实验件的强度恢复率约为66%~91%,贴补修理实验件的强度恢复率约为44%~61%。在挖补修理实验件中,减小挖补斜度、采用双面挖补、使用热压罐固化,在贴补修理实验件中,采用双面贴补、增大补片尺寸,均可得到更高的强度恢复率。在实验基础上建立的有限元模型,能够有效预测实验件的失效载荷、破坏模式,并可分析实验件的应力分布和渐进损伤过程,为设计修理方案提供参考。     

颗粒增强铝基复合材料断裂韧性与拉伸延性的解析模型

基于Eshelby等效夹杂理论及Weibull统计分布,发展了SiCp/Al金属基复合材料断裂韧性与拉伸延性的力学模型.模型的计算表明:当复合材料受外力时,SiC颗粒所受的力与外加应力呈线性关系.随着外加应力的增加,SiC颗粒所受的力也线性增加.同时,外力作用下SiC颗粒的断裂分数服从Weibull统计分布,即SiC颗粒的总体含量越高,其断裂分数就越高.模型关于约化拉伸延性和断裂韧性的计算与实验结果较为吻合.模型的解析和实验结果都表明:拉伸延性与断裂韧性随SiC颗粒体积分数的增加而减小.在相同体积分数的情况下,拉伸延性与断裂韧性随SiC颗粒尺寸的增加而减小.     

挖补修理复合材料层合板拉伸性能研究

在试验研究的基础上,建立三维损伤累积模型研究拉伸载荷下挖补修理复合材料层合板的损伤扩展及其最终破坏规律,并讨论挖补角对挖补修理结构拉伸性能的影响,计算结果和试验结果吻合良好。研究结果表明:挖补胶层中的损伤首先发生在胶层连接0°铺层的地方,然后向四周扩展,当损伤扩展到整个胶层面积约40%时,挖补层合板的应力-位移曲线发生较大的刚度下降,此时的载荷为胶层失效载荷。母板和补片在胶层发生损伤前就出现了少量损伤,在胶层完全破坏前,损伤会沿胶界面扩展;在胶层完全破坏后,损伤会沿母板最窄处向两侧自由边快速扩展,而补片在胶层失效后就停止损伤;胶层失效载荷随挖补角的增大而减小,但挖补角的增大会使胶层破坏后母板的承载能力增加,从而使挖补层合板的最终破坏载荷反而增加。在工程应用中,挖补角的选择应综合考虑结构设计要求、工艺和功能等多方面的因素。     

Analysis of adhesive bonded composite lap joints with transverse stitching

The effect of transverse stitching on the stresses in the adhesive is investigated using an adhesive sandwich model with nonlinear adhesive properties and a transverse stitching model for adhesive bonded composite single-lap and double-lap joints. Numerical results indicate that, among all stitching parameters, thread pretension and stitch density have significant effect on the peel stresses in the adhesive; increase in the thread pretension and the stitch density leads to a decrease in peel stress in the adhesive, while an increase in other parameters generally results in a negligible reduction in peel stress. The effect of stitching was found to be negligible on the shear stresses in the adhesive. Thus it is concluded that stitching is effective for the joints where peel stresses are critical and ineffective for those where shear stresses are critical.     

Fatigue behaviour of double lap riveted joints assembled with and without interfay sealant

Fatigue tests on ‘double shear’ riveted specimens were carried out. Material was aluminium alloy, 7075‐T73, thickness 3 mm. Specimen surfaces were protected by chromic acid anodization and epoxy primer. The mating surfaces of some specimens were sealed by a two‐component manganese‐dioxide cured, polysulfide compound. Specimens were pre‐assembled by inserting a temporary spring fastener in a pilot hole. The holes were reamed to the final diameter after sealant curing; then the Hi‐Loks were installed. Comparative fatigue tests were carried out on dry assembled specimens. Quite surprisingly, the fatigue resistance of sealed specimens was very low when compared with the results of dry assembled specimens. Hysteresis cycles measured in sealed and un‐sealed specimens clearly indicated a lubricant effect of the sealing layer, which justified the results obtained. Additional tests were performed on specimens assembled by applying different clamping force during the sealant curing time. The results obtained indicated an independence of the fatigue resistance on this parameter. Different failure modes were observed in sealed and un‐sealed specimens: fatigue cracks nucleated outside the hole at a location in the shadow of the rivet in the un‐sealed joints, while fatigue cracks nucleated at both sides of the holes in sealed joints. Finite element calculations carried out under different values of the friction coefficient between the mating surfaces confirmed the different location of the fatigue critical areas in sealed and un‐sealed specimens.     

Failure prediction and strength improvement of uni-directional composite single lap bonded joints

A methodology is presented for the failure prediction of the composite single lap bonded joints considering both the composite adherend and the bondline failures. An elastic-perfectly plastic model of the adhesive and a delamination failure criterion were used in the methodology. The failure predictions using the finite element analysis and the proposed methodology were performed. The failure prediction results such as failure mode and strength showed very good agreements with the test results for the joint specimens with various bonding methods and parameters. Based on the numerical investigation, the optimal joint strength condition was found and a new joint strength improvement technique was suggested. The suggested technique was verified to have a significant effect on the joint strength improvement.     

变刚度复合材料开孔板拉伸行为数值模拟及试验验证

纤维曲线铺放是提高复合材料构件力学性能的有效方法之一。本文针对复合材料开孔板铺放轨迹进行了研究,利用B样条曲线插值拟合获取了开孔板最大主应力铺放轨迹,并通过离散网格法建立了变刚度开孔板模型,通过引入Tsai-Wu损伤失效判据以及常刚度退化准则,进行了拉伸失效数值模拟及损伤失效分析,并分别铺放了两组常刚度和变刚度开孔板试验样件,进行了拉伸对比试验。结果表明：数值模拟与实验数据吻合较好,变刚度开孔板相比常刚度开孔板,拉伸强度提升了26.92%,且两者损伤失效演化过程显著不同。     

An analytical model for the prediction of load distribution in highly torqued multi-bolt composite joints

This paper presents the development of an enhanced analytical approach for modelling the load distribution in multi-bolt composite joints. The model is a closed-form extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The enhancement accounts for static friction effects between the laminates, a primary mechanism of load transfer in highly torqued bolted joints. The method is validated against detailed three-dimensional finite element models and where possible, experimental results. The effect of varying bolt-torque and bolt-hole clearance on the load distribution in a three-bolt, single-lap joint is investigated and the method proves to be robust, accurate and highly efficient. Finally, the method is employed in a parameter study, where increasing bolt torque levels can be used for achieving a more even load distribution in multi-bolt joints.     

Effect of hole lubrication on the fretting fatigue life of double shear lap joints: An experimental and numerical study

In this research the affect that lubrication at a hole and pin connection has on the fatigue life of a double shear lap joint is studied both experimentally and numerically. The study focuses on the joint middle plate item, which is connected via a central hole to the outer plates by means of a clearance fitting pin, thereby placing the hole in double shear. In the experimental work three identical batches of fatigue specimens, which are made from aluminum alloy 2024-T3, were fatigue tested. In the first batch the surface of the fastener hole was not lubricated whilst the hole in the other two batches was lubricated – each batch using a different lubricant. The three batches of double shear lap joint specimens were fatigue tested and their S–N curves established. The results show that the specimens in which the holes were lubricated have better fatigue lives than the non-lubricated hole specimens. In the numerical study, FE simulations were performed to include hole lubrication effect on the stress distribution by using different friction coefficient at the interface of the hole and its fastener (pin). The FE results have helped to gain an understanding of the reasons for fatigue life improvement and also have helped to quantify the level of improvement.     

An analytical model for the prediction of through-thickness stiffness in tension-loaded composite bolted joints

This paper presents the development of an analytical model for replicating the through-thickness stiffness of single-bolt, single-lap composite joints subjected to secondary bending. The model is an extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The model accounts for extension of the bolt, the stiffness of the clamped region of the joint due to bolt torque, as well as the flexural stiffness and anticlastic curvature within the laminates. In order capture bolt extension and the stiffness of the clamped region, a closed form approach is used. An approximation approach is used to model flexural stiffness and anticlastic curvature within the laminates. The method is validated against detailed three-dimensional finite element models of bolted composite plates and good agreement was obtained. The method is subsequently employed to calibrate the through-thickness stiffness of single-bolt, single-lap joints in highly-efficient numerical models.     

复合材料3钉单搭连接有限元模拟与钉载分布

进行了复合材料一铝合金三钉单搭连接单向拉伸试验,测量了层合板面内位移、应变和离面位移随载荷的变化关系,建立了复合材料多钉单搭连接的三维累积损伤有限元模型,计算与试验对比结果表明,该模型可模拟大范围损伤发生之前的承载特性。采用试验和数值模拟相结合的方法研究了复合材料一金属三钉单搭连接钉载分布情况,结果表明：试验用复合材料-铝合金三钉单搭连接,螺栓1承载比例最高,螺栓3次之,中间螺栓的承载比例最低,并且螺栓承载比例在加载过程中基本保持不变;随着金属连接板刚度的增加,螺栓1的承载比例增加,螺栓3承载比例降低,中间螺栓2的承载比例变化较小,层合板离面位移减小;金属板配合间隙变化对钉载分布影响很小,但层合板的离面位移随配合间隙的增大而增大。     

Failure load evaluation and prediction of hybrid composite double lap joints

Hybrid joints are a combination of adhesive bonding and mechanical fastening and are known to combine the advantages of both joint types. In this paper, we evaluate and compare the strengths of mechanical joints, adhesive joints and hybrid composite joints. We manufactured and tested 10 hybrid joint specimens with different width-to-diameter (w/d) ratios, edge-to-diameter (e/d) ratios and adherend thicknesses. Additionally, the strengths of the hybrid joints were predicted using the Failure Area Index (FAI) method and the damage zone method, and we compared our theoretical predictions with our experimental results. From these data, we were able to predict hybrid joint strengths to within 23.0%.