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.     

复合材料贴补工艺参数的研究及优化模拟

贴补是复合材料修补中一种重要的修补方式,研究了贴补的补片直径和补片厚度对树脂基复合材料层压板弯曲强度恢复值的影响,确定了最佳的贴补工艺参数.并通过有限元分析建立了修补模型,对贴补工艺参数进行了优化.     

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.     

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。     

复合材料开孔层合板双轴拉伸的渐进损伤

应用连续介质损伤力学(CDM)理论,对受双轴拉伸载荷作用的复合材料开孔层合板有限元模型分别计算分析了1:1、2:1和3:1加载比下的渐进损伤,预测了损伤初始发生、延展到最后破坏的渐进损伤过程以及极限载荷.经试验验证三个不同加载比时的极限荷载计算值与试验数据均能较好吻合,纤维、基体、分层损伤演化过程的计算结果符合试验中观...     

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.     

On the Bearing Failure of Laminated Composite Pin‐Loaded Joints: Exploitation of Semi‐Analytical Solutions for the Determination of the Stress State

Abstract: The present work deals with the development and verification of a set of analytical solutions for the bearing failure of single lap composite joints, which are applied on a composite joint tested experimentally. The stress field originating from the solution is calculated and progressive failure criteria are applied, verifying their applicability as a fast way of calculating bearing failure of a joint. Additionally, the extracted stress field from the results is introduced as a load to the finite element model of the joint under evaluation, and the equivalency of this method is compared and proven against typical implicit non‐linear contact analysis. The major advantage of the proposed methodology is that the highly non‐linear contact problem is circumvented using the stress distribution at the hole boundary as an actual load and thus transforming the analysis to a linear one, providing considerable agreement to the exact high‐cost numerical solution.     

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.     

预腐蚀铝合金典型螺栓单搭接件疲劳寿命研究

模拟飞机服役环境,对航空LY12 铝合金板材典型螺栓单搭接试验件做了预腐蚀试验,然后通过疲劳试验得到了未腐蚀试验件和预腐蚀后试验件的疲劳寿命。通过对试验件分解检查,分析了腐蚀对航空LY12 铝合金典型螺栓单搭接件的影响。建立了考虑腐蚀影响的基于断裂力学的沉孔螺栓搭接件疲劳寿命计算模型,对预腐蚀搭接件的疲劳寿命进行了计算和分析。结果表明:螺栓孔附近和搭接面腐蚀较表面其他部位严重,腐蚀产物的膨胀作用下产生了“枕垫效应”;计算模型得到的疲劳寿命与试验寿命吻合较好,其中模型1 最大相对误差为36.7%,模型2 的最大相对误差为25.7%。搭接件不同的腐蚀程度要选择不同的计算模型才能得出精确的结果。在分析较严重的腐蚀对搭接件疲劳寿命影响时,应考虑搭接面的多腐蚀损伤。     

On the Variation of Clamping Force in Bolted Double Lap Joints Subjected to Longitudinal Loading: A Numerical and Experimental Investigation

Abstract: This study investigates the variation of clamping force and its concomitant effects on the performance of bolted double lap joints subjected to longitudinal loading. Two different amounts of clamping force were applied to bolted double lap joints made of Aluminium 2024‐T3, and variations of clamping force were measured under the application of longitudinal loading. Finite element modelling was also performed to compare with experiments. The results unanimously revealed a gradual initial reduction of clamping force followed by a significant increase as the longitudinal load was increased. Also affected, was the load transfer mechanism in the joint resulting in variation of friction force between the plates, but in a different trend compared to clamping force. Finally, the key parameters have been discussed and highlighted pertaining to the performance of the joint.     

Cumulative fatigue damage evaluations on spot‐welded joints using 590 MPa‐class automobile steel

This study focused on local strain behaviour near the slit edge of spot‐welded joints, where the fatigue crack initiated, and investigated methods of evaluating cumulative fatigue damage. A method of evaluating local strain amplitude by following modified Goodman's law gave almost the same result as an evaluation approach based on the external force and provided reasonable result on general strength design. An approach based on Smith–Watson–Topper's equation was easy to evaluate cumulative fatigue damage compared with the method based on modified Goodman's law and gave a good agreement with a criterion of the modified Miner's rule.     

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.     

考虑间隙配合的复合材料钉载分配均匀化方法

针对多钉连接中因复合材料脆性等因素导致结构中的钉载分配不均匀,以及接头在承载较大的钉位置易发生过早破坏的问题,提出了调整钉孔配合间隙改善钉载分配的不均匀性的优化方法。首先,基于弹簧质量模型,以钉孔间隙为设计变量,建立了多钉连接钉载分配的二次规划优化模型。然后,采用内点法对优化模型进行了求解,得到了优化模型的全局最优解。最后,以复合材料5钉双剪接头为例,对钉孔间隙进行了优化,将计算结果与有限元预测结果进行对比。结果表明:模型优化结果与有限元结果吻合较好,优化后最大钉载比例由41.1%降低到了20%。采用该模型可以高效、准确地实现复合材料多钉连接钉载分配比例的均匀化设计。      

Damage Mechanisms in Composite/Composite Bonded Joints Under Static Tensile Loading

This paper presents an experimental study of the initiation and development of damage in composite/composite joints. The materials studied are glass fibre reinforced polyester laminates and these are bonded together using an epoxy adhesive. Two types of joint interface are examined, assemblies between woven roving layers and between mat layers. The experimental techniques employed are dye impregnation, extensometry, visual observation and photoelasticimetry. It is shown that the nature of the surface layer does not influence the damage initiation load but does affect subsequent crack propagation. This revised version was published online in June 2006 with corrections to the Cover Date.     

C/SiC复合材料螺栓螺牙承载能力

为了对C/SiC复合材料螺栓螺牙的承载能力进行评估,采用有限元法和刚度折减方法对C/SiC复合材料螺牙抵抗拉脱的能力进行了研究。结果表明:当齿合螺牙数大于6时,再增加齿合螺牙数已不能有效地提高螺牙的初始拉脱载荷;增大螺距会降低螺牙初始拉脱强度,因而也不能显著地提高螺牙的初始拉脱载荷;在螺距与螺栓直径之比保持常数的情况下,螺牙的初始拉脱载荷与螺栓直径的平方成正比;而螺牙的极限拉脱载荷则近似正比于齿合螺牙数、螺距及螺栓直径。