铺层方式对CFRP-Al单搭接接头胶接性能的影响

使用热压罐制备[45/-45]_4s、[0/90]_4s和[0/45/-45/90]_2s三种铺层方式的CFRP层合板,然后在室温下与Al胶接制备出单搭接试样。使用电子万能试验机、数字图像相关法(DIC)和扫描电子显微镜(SEM)等手段测量胶接接头的拉伸载荷-位移曲线和应变分布并观察断口形貌。基于试验数据分析不同铺层方式下CFRP-Al单搭接接头的拉伸性能,研究了铺层方式对CFRP-Al单搭接接头胶接性能的影响和铺层方式胶接接头的破坏机制。结果表明,在拉伸过程中[45/-45]_4s试样出现塑性变形阶段其拉伸位移最大,而[0/45/-45/90]_2s和[0/90]_4s试样的拉伸位移较小且发生了脆性断裂。铺层方式从[45/-45]_4s到[0/45/-45/90]_2s再到[0/90]_4s,试样的极限载荷和纤维束断裂数量增加、层间剪切力减小、应变集中程度和分层破坏程度降低。     

铺层方式对CFRP-铝合金单搭接胶接接头低速冲击损伤及剩余拉伸性能的影响

采用热压罐成型方法制备铺层方式为[+45/-45]_4s、[0/+45/-45/90]_2s和[0/90]_4s的碳纤维复合材料层合板,通过胶黏剂与铝合金板进行粘接获得异质材料单搭接胶接接头。利用落锤冲击试验机和万能电子试验机分别对三种接头进行低速冲击与冲击后静态拉伸测试,获得接头接触力-时间曲线和拉伸强度。通过CT扫描技术和数字图像相关(DIC)方法表征接头冲击损伤模式及表面应变演化过程,研究了铺层方式对接头抗冲击性能、冲击损伤模式以及剩余拉伸性能的影响。结果表明,复合材料铺层方式为[+45/-45]_4s时,接头在冲击载荷作用下具有较高的抗冲击性能,但胶层界面脱粘损伤较为严重。与胶层界面脱粘相比,接头剩余强度对层合板分层损伤更为敏感。相较于[+45/-45]_4s,[0/+45/-45/90]_2s和[0/90]_4s铺层方式接头的胶层界面脱粘范围与冲击后失效载荷退化程度较小,同时接头冲击后拉伸载荷主要集中于临近胶层的0°铺层且失效模式较为复杂...     

复合材料层合板阶梯形挖补胶接修理渐进损伤分析

建立了复合材料层合板阶梯形挖补胶接修理构型的渐进损伤分析三维有限元模型, 同时考虑了复合材料母板、 补片和胶层的损伤扩展以及它们之间的相互影响。层合板采用含正交各向异性损伤的连续介质损伤力学(CDM)本构方程进行描述, 材料积分点处的损伤状态采用二阶张量形式的内部状态变量表征。胶层采用含各向同性损伤的CDM本构方程进行描述, 材料积分点处的损伤状态采用常数形式的损伤变量表示。计算结果与试验数据符合较好, 说明该模型可较好预测挖补胶接修理的复合材料层合板拉伸强度及其失效模式。     

复合材料层合板的铺层几何对结构声传输的影响

采用基于复合材料一阶剪切理论－Mindilin理论的板单元和基于Rayleigh表面分方程的边界元,对嵌在无限障板上的复合材料层合板在低频简谐平面声波斜入射情况下,建立了考虑流体结构耦合的传声计算模型,并利用该模型计算研究了对称角铺设、反对称角铺设和正交铺设等不同铺设方式对层合板传声损失的影响以及在板侧流体介质分别为空气和水时层合板的传声特性,指出层合板的铺层几何对其传声损失有较大影响,应在设计中引起注意。     

搭接长度对CFRP单搭接胶接接头拉伸性能及破坏特征的影响

采用碳纤维增强复合材料(CFRP)基板制备不同搭接长度的单搭接胶接接头,并利用数字图像相关方法(DIC)、万能电子试验机等测试手段,对胶接接头失效载荷、断裂过程和应变场变化等进行表征,研究搭接长度对单搭接接头拉伸性能、断裂过程、应变分布以及破坏特征的影响.结果表明:随搭接长度增加,接头平均剪切强度先明显降低,后趋于稳定.拉伸过程中由偏心载荷所引起的接头次弯曲效应愈加显著,搭接区域端部变形程度逐渐增大,接头初始破坏位置由搭接区域端部中的一端向两端转变.接头正面和侧面端部的应变集中区域由非对称分布向对称分布过渡.接头受剥离力逐渐增大,层间主要失效形式由剪切向剥离破坏转变,接头破坏模式经历了由界面和轻微纤维撕裂到混合失效再到层间分层的过程.     

复合材料层合板胶接贴补修理渐进损伤分析

建立了复合材料层合板胶接贴补修理构型渐进损伤分析的三维有限元模型, 其中层合板和胶层分别采用正交各向异性损伤和各向同性损伤的连续介质损伤力学模型, 整个分析过程中同时考虑层合板和胶层的损伤形成和扩展以及它们之间的相互影响, 单向压缩载荷作用下的层合板贴补修理构型的试验数据验证了该模型的有效性, 采用该模型分析了不同的贴补修理参数对修补强度的影响。 结果表明: 当层合板补片较薄时, 补片损伤是导致修补结构失效的主要原因; 当补片较厚时, 胶层失效是导致修补结构失效的主要原因, 此时补片厚度增加并不能显著增大修补结构的极限强度。在复合材料贴补修理时需要对补片和胶层进行详细优化设计。      

纳秒激光调控CFRP复合材料表面润湿性及其对胶接性能的影响

采用纳秒激光对碳纤维增强树脂基(CFRP)复合材料进行表面预处理,调控其表面成分、粗糙度和表面润湿性,然后采用SEM、接触角测量仪、光学轮廓仪、XPS等表征CFRP复合材料的表面微观形貌、接触角、粗糙度和化学成分,并通过拉伸剪切实验评价和分析激光表面处理对CFRP复合材料胶接强度的影响规律和机制.结果表明:优化激光表面...     

铺层拼接层合板的抗拉强度

针对复合材料结构设计中遇到含铺层拼接的层合板强度预测问题,本文设计了含铺层交错拼接区的碳/双马复合材料层合板试件,采用拉伸试验方法测定了该材料的力学性能,得到了不同拼接长度层合板的抗拉强度。试验结果表明,铺层拼接状态差异对复合材料层合板的承载能力有显著影响,文中根据试验结果建立了抗拉强度随拼接长度变化的经验公式,为复合材料层合板结构的铺层设计和强度分析提供了理论依据。     

搭接长度对Z-pins增强陶瓷基复合材料接头连接性能的影响

本文对搭接长度分别为15mm,20mm,23mm,37ram,60mm的Z-pins增强陶瓷基复合材料接头在单向载荷作用下的连接性能进行了试验研究和数值模拟.试验结果表明接头的最终失效形式有两种:(1)搭接长度大于、等于20mm的接头由搭接板断裂而失效;(2)搭接长度等于15mm的接头由搭接面的脱胶而失效.在搭接长度为20mm～60mm之间,接头的最大破坏载荷与搭接长度之间呈线性关系变化.采用有限元的方法对搭接接头的破坏过程进行了数值模拟,模拟结果与试验结果吻合较好,进而得到了介于上述两种破坏模式之间的搭接接头的搭接长度.     

搭接长度对玻璃钢复合材料拉伸强度的影响探究

我们通过对搭接长度对玻璃钢复合材料拉伸强度的分析与研究,得出搭接的度数的重要性。这也为其他工程提供了一些建设性的意见。     

Evaluation of adhesively bonded joint strength of CFRP with laser treatment

Pulsed laser surface treatment was applied to carbon fiber-reinforced plastics (CFRPs) to enhance the work efficiency as well as to establish the stable clean process of surface pre-treatment during the bonding process of CFRP structures. Surface analyses were conducted to CFRP treated by various laser conditions in order to find the optimal laser process. Adhesively bonded specimens were fabricated using CFRPs subjected to laser treatment, and adhesive lap shear strength of CFRPs bonded with adhesive films was evaluated compared with the abrasive paper treatment. Surface conditions, adhesive strength, and adhesive fracture mode depended on the treatment parameters, and adhesive strength similar to abrasive paper treatment could be obtained in the specimens with appropriate laser treatment. It was concluded that laser surface treatment can be applied to the surface treatment process of CFRP bonded structures.     

交变载荷对CFRP复合材料-铝合金粘接接头剩余强度的影响

为了给碳纤维增强聚合物（CFRP）复合材料粘接结构的安全设计及应用提供参考,针对CFRP复合材料-铝合金对接接头,研究了拉-拉交变载荷作用下的疲劳寿命特性及剩余强度变化规律。设计专用夹具,完成接头的制作及固化,并测试其拉伸、剪切准静态失效强度,在此基础上进行不同载荷水平下的疲劳寿命测试。选取特定载荷水平,测试不同循环次数后的接头剩余强度,并对失效形式进行观察分析。结果表明:CFRP复合材料-铝合金对接接头强度-寿命（S-N）曲线在单对数坐标上符合线性函数规律;随着交变载荷循环周期的增加,接头剩余强度呈先慢后快的下降趋势,而且在较大的载荷水平下,下降幅度更为明显;经历交变载荷循环前、后接头失效形式发生改变,由局部CFRP复合材料表层撕裂转变为局部界面破坏。结合试验测试所获得的初始失效准则,并引入疲劳退化因子,建立内聚力模型对交变载荷作用下的粘接接头强度衰减进行数值模拟,结果表明所建立模型能够有效预测交变载荷作用下的接头剩余强度。      

高温老化对玄武岩纤维增强树脂复合材料-铝合金单搭接接头失效的影响

为了研究持续高温环境对车用新材料粘接结构力学性能的影响,加工了铝合金-铝合金（Al-Al）和玄武岩纤维增强树脂复合材料-铝合金（BFRP-Al）单搭接接头,在高温（80℃）环境下进行了0天（未老化）、5天、10天、15天的老化实验,并对胶粘剂和BFRP复合材料进行了DSC和FTIR测试,分析高温老化后胶粘剂、BFRP复合材料的玻璃化转变温度（T_g）和化学成分变化,通过准静态拉伸测试获得老化后接头的失效载荷,并对其失效模式进行分析。研究结果表明:高温环境下,胶粘剂会发生后固化及氧化反应,BFRP复合材料发生热分解及氧化反应;Al-Al接头的失效载荷随老化周期的增加而不断增大,老化前后的失效模式均为内聚失效,其性能变化主要由胶粘剂决定;BFRP-Al接头的失效载荷先增加后减小,不同老化周期的接头均发生内聚和撕裂的混合失效,其性能变化由胶粘剂和BFRP复合材料共同作用决定,且随着老化周期的增加,BFRP复合材料撕裂面积不断增大,BFRP-Al接头的失效模式越来越倾向于玄武岩纤维/树脂界面的破坏,BFRP复合材料老化对接头失效载荷的影响越来越显著。      

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.     

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.     

The effects of size and stacking sequence of composite laminated patch on bonded repair for cracked hole

The performance of a bonded repair for cracked holes has been studied using the three dimensional finite element method, linear elastic fracture mechanics and strain energy density theory. Increasing the composite patch size reduces the strain energy level at the crack tip; increasing the patch length normal to the crack is a better choice. The stacking sequences of the laminated patch have little influence on the strain energy distribution in the vicinity of the crack. To repair the cracked holes of aircraft components subjected to variable direction loading during flight, the orientations of the patch ply, 90° and ±45° with respect to the crack direction, are the optimum selection in bonded repairs.     

The effect of fibre alignment on composite strength: II. The strength of angle-ply laminates

Experiments have been carried out on relatively wide angle-ply laminate samples with very short gauge lengths. These proved to be very much stronger than samples tested in earlier work, and which form the basis for our present design with these materials. It is highly likely that the early results for strength were more indicative of edge effects than true laminate strength. This is confirmed by data from tests on pressurized tubes. A review of the literature on this shows that such tests produced results which can be an order of magnitude higher than the early laminate tests. Thus our design calculations could well be severely underestimating the potential strength of angle-ply laminates. This may be having serious consequences for the aerospace industry, through the use of design criteria for strength which may be too conservative. Single-fibre experiments may pave the way for more realistic estimates of angle-ply laminate strengths. These indicate that a simple one-third power rule can be used to estimate the potential strength. However, this is purely ad hoc at present, and needs to be put on a firmer footing through both theoretical and experimental studies. Furthermore, if this approach is adopted, edge effects will still have to be allowed for, and estimated on the basis of the aspect ratio of the part.     

Analysis of adhesively bonded joints: a finite element method and a material model with damage

This paper deals with the derivation of a finite element (FE) method for an adhesively bonded joint which consists of two relatively thin bodies, joined by an even thinner adhesive layer. It is based on a model of the compound joint where the three bodies involved are described as material surfaces. A geometrically two‐dimensional model, where the middle surfaces of the upper and lower body are represented as geometrically coinciding surfaces, is obtained. An elastic–plastic material model with damage is used for the adhesive layer, and an important implication is that the (quasi‐static) propagation of the local failure zone in the adhesive layer in a structure can be simulated. Consequently, the failure load is obtained as a computational result and no failure criterion is needed. The problem is discretized, and a surface model, where only a single surface needs to be FE‐meshed, is obtained. A single‐lap joint is analysed and good agreement is obtained when compared to an analysis using a fine mesh with brick element. Furthermore, the failure load is computed and compared with experiments. The derived FE method opens up the possibility to efficiently model and analyse the mechanical behaviour of large bonded structures. Copyright © 2005 John Wiley & Sons, Ltd.     

金属裂纹板复合材料单面胶接修补结构应力分析

考虑金属裂纹板复合材料单面胶接修补结构的几何非线性和边界条件,建立了考虑弯曲变形单面修补结构力学分析模型,计算出承受面内载荷时修补结构的弯矩和挠度,将补片自由端和金属板裂纹处的弯矩作为胶层应力控制微分方程的边界条件,推导出剪应力和剥离应力的解析解,及裂纹张开位移的表达式,并与有限元数值结果进行对比。分析结果表明,胶接修补结构应力分析理论模型和相关简化假设合理、正确。利用所建立的解析模型研究了金属裂纹复合材料单面胶接修补结构的应力分布特点及胶层主导破坏模式的失效机制,为胶接修补结构的承载能力分析以及结构改进设计提供了一定的理论依据。