板厚、温度和速度对单搭接胶接接头强度的影响

为了探讨单搭接胶接接头结构的破坏机理,采用Hopkinson拉杆实验技术,研究了板厚、温度和速度(试样端部的最大速度)对单搭接胶接接头强度的影响。实验结果表明,板越厚、温度越低、速度越大,接头的强度越大。运用有限元方法分析了胶层的应力分布,通过引入剥离应力对试样强度的影响因子,研究发现板越厚、温度越低、速度越大,剥离应力对接头强度的影响越小。     

胶接体系的胶接强度、粘结能及损伤破坏研究

胶接是指一种用粘合剂实现连接和固持的方法,胶接形式的金属薄板在汽车工业,建筑业以及航空航天领域有着广泛的应用.论文采用有限元模拟方法,研究了该胶接体系在受载状态下的滑剪破坏行为,重点关注了胶层粘结能,搭接长度,胶层厚度对胶接接头承载能力的影响,同时初步探讨了胶层的界面损伤情况.胶层粘结能的提高能够显著提高接头的承载能力.此承载能力受搭接长度和胶层粘结能的共同影响,较大的粘结能情况下,提高搭接长度能够显著提高接头的承载能力.胶层厚度对接头的承载能力也存在影响,在论文考虑的厚度范围内,提高厚度能够增强接头的承载能力.最后初步考虑了接头在达到载荷峰值时刻的胶层损伤情况.     

复合材料层合板单搭胶接力学性能检测技术与分析

胶接工艺缺陷对单搭胶接接头的拉伸剪切性能有着重要的影响。为了研究不同单搭接胶接层厚度对不同材质复合材料层合板胶接性能的影响规律,通过喷水穿透法超声C扫描对试样的剪切区域进行无损检测,并分别采用1mm、2mm、4mm的胶层厚度,以碳纤维/玻璃纤维复合材料层合板为被粘物,进行单搭胶接拉伸剪切性能试验。检测及试验结果表明:当胶层厚度h1mm时,对于相同材料的被粘物,胶层厚度越大,试件胶接接头剪切强度越小;相同的粘接剂厚度,以碳纤维增强复合材料板为被粘物的试件胶接接头剪切强度大于以玻纤增强复合材料板为被粘物的试件胶接接头强度;胶粘剂与碳纤维被粘物表面的润湿效果要优于胶粘剂与玻纤被粘物表面的润湿效果。     

复合材料-金属毛化接头的失效预测模型

针对复合材料与金属连接的一种新型连接形式－毛化接头,建立了其在拉伸载荷作用下的失效模式与破坏载荷的宏－细观预测模型。首先根据毛刺的分布选择合适的代表体积元,建立毛刺层单胞模型,施加周期性边界条件,通过有限元分析得到毛刺层的平均刚度参数。其次,基于累积损伤理论预测毛刺层的单胞强度,分析毛刺层的失效机理。最后,将毛刺层的等效材料参数赋予接头整体模型,预测接头的抗拉强度及失效模式。预测结果与试验值吻合良好。分析结果表明,毛化接头的承载能力和失效模式与毛刺的密度高度、搭接面积等因素密切相关,通过参数设计可获得较高的承载能力。     

内聚力模型的形状对胶接结构断裂过程的影响

内聚力模型被广泛应用于粘接结构的断裂数值模拟过程中,为深入分析不同形状内聚力模型与胶黏剂性质和粘接结构断裂之间的关系,本文分别采用脆性和延展性两种类型胶黏剂,对其粘接的对接试件进行了单轴拉伸、剪切实验,以及其粘接的双臂梁试件进行了断裂实验.3种类型的内聚力模型(抛物线型、双线型和三线型)分别模拟了以上粘接结构的断裂过程,并与实验结果进行对比.结果发现:双线型的内聚力模型适用计算脆性胶黏剂的拉伸与剪切的断裂过程;指数型内聚力模型较适合计算延展性胶黏剂的拉伸和剪切的断裂过程,临界应力、断裂能和模型的形状参数是分析拉伸和剪切的重要参数;双臂梁试件的断裂过程模拟结果发现,断裂曲线与胶黏剂性质有关,内聚力模型形状参数也有影响.通过实验与计算结果分析,双线型内聚力模型更适合脆性胶黏剂粘接的双臂梁断裂计算,而三线型更适合计算延展性胶黏剂粘接的双臂梁断裂过程,此研究结果对胶黏剂的使用和粘接结构的断裂分析有很重要意义.     

“三明治”结构强度弱化的反射特性研究

针对铝-胶层-铝结构强度弱化的超声检测问题,采用改进全局矩阵法推导了多层粘接结构中超声传播方程,通过降低胶层的剪切波波速来模拟粘接强度弱化,对不同频率、不同入射角情况下超声纵波入射“三明治”结构时的反射系数与粘接强度的关系进行了仿真计算.仿真结果为:超声纵波以0.5MHz入射,在入射角为65°~73°区域内进行扫描检测,通过角度分辨的方式对强度弱化区域进行定位.第一层与胶层之间的界面出现强度弱化时,检测条件为0.5MHz、65.9°的超声纵波;胶层与第三层之间的界面出现强度弱化时,检测条件为1.0MHz、62.9°的超声纵波.结果表明:在特定的频率和入射角进行组合情况下,采用超声纵波斜入射方法可实现对粘接结构界面的强度弱化区域的定位和粘接强度的定量检测.     

温度循环载荷对柔性接头界面损伤的影响

固体火箭发动机在生产、运输和储存的过程中会受到环境湿热和老化载荷的作用,导致柔性接头界面的力学性能产生退化.为研究柔性接头界面力学性能退化对界面损伤的影响规律,基于双线性内聚力模型建立了一种描述界面力学性能退化的数学模型.以某柔性接头为研究对象,为便于研究,以温度循环载荷代替环境老化载荷开展了界面损伤分析,并采用ABAQUS 6.14进行了仿真.结果 表明,与后法兰粘接的界面损伤程度最大.当温度循环周期达到672次时,界面13和界面14的损伤程度分别由初始状态的2.9％和4.3％增加到5.2％和8.2％,增幅分别高达81.2％和91.7％.同时,温度循环载荷会加速柔性接头的界面损伤.该界面力学性能退化模型可为柔性接头老化研究提供参考.     

剪胶接结构的混合模式断裂分析

给出了Ｇｏｌａｎｄ－Ｒｅｉｓｓｅｎｅｒ型剪接结构的Ｊ积分表达在被粘物体小转角和胶层很薄的假设下与路径无关。Ｊ积分代表胶层厚度与胶层内最大能量密度的乘积。对单剪接接头，本文计算了裂纹在胶层内和界面上两种情况下的局部Ｉ型和Ⅱ型应力强度因子之比，即局部载荷相角，从而给出了单剪接接头的断裂判据。     

单搭接胶接接头拉伸剪切性能的数值模拟与实验研究

采用数值模拟和光测技术对单向拉伸载荷作用下单搭接胶接接头中的剪切性能进行分析,研究了不同厚度胶层中切应力的变化规律。用有限元方法(FEM)对不同胶层厚度的试件进行建模,得到了拉伸载荷下胶粘剂中的切应力分布及其统计参数。利用数字图像相关(digitalimage correlation,DIC)方法对试件的变形场进行测量。结果表明,当胶粘剂的厚度较小时,胶粘剂中的切应力的分布统计参数随着其厚度的增加会有显著的变化,但是当厚度超过一定的数值时,统计参数对厚度的变化不再敏感。     

胶层吸湿对单搭接接头影响的数值模拟

在建立胶桔剂吸涅本构模型的基础上,用弹塑性有限元法研究了聚丙烯酸酯胶层吸涅程度对单搭接接头上胶层中应力分布的影响.结果表明:随着胶层吸湿程度增加,单搭接接头上胶瘤处的峰值应力显著降低.对水分从搭接区两侧渗入胶层的总宽度变化时胶层中的应力分布作了研究,发现随渗入总宽度的增加,胶层中的等效应力Seqv峰值下降.因水分渗入后引起胶层溶胀,在胶瘤过渡到中间胶层的拐角处会产生严重变形,可能导致该处发生脱粘.     

腐蚀环境下复合材料修补件力学特性研究

采用复合材料补片胶接修补含裂纹LY12CZ铝合金板,开展了试验室大气环境和加速预腐蚀环境下复合材料修补件静强度拉伸和疲劳裂纹扩展对比试验研究.结果表明,复合材料补片均能显著提高损伤结构的拉伸强度和疲劳寿命,且短周期的预腐蚀环境对修补件两种力学特性的影响可以忽略不计.同时,基于Paris公式和Rose分析模型,建立了常规环境和预腐蚀环境下疲劳裂纹扩展寿命预测模型,通过与试验结果的对比证明了该模型的工程有效性.     

Progressive fracture of adhesively bonded composite structures

Progressive damage and fracture of adhesively bonded graphite/epoxy composite structures are evaluated via computational simulation. Load induced damage in both the adhesive bond and the adjoining laminate is considered. An integrated computer code is used for the simulation of structural degradation under loading. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulations. Results show in detail the damage progression sequence and structural fracture resistance during different degradation stages. Design implications with regard to damage tolerance of adhesively bonded joints are examined. Influence of the type of loading as well as adhesive thickness on damage initiation and progression for an adhesively bonded composite structure are investigated.     

Cohesive zone model for high-cycle fatigue of adhesively bonded joints under mode I loading

A cohesive zone model adequate for simulating the behaviour of adhesively bonded joints subjected to high-cycle fatigue and pure mode I loading is presented. The bilinear cohesive zone law with linear softening relationship was considered. The main advantage of the proposed formulation is the use of a unique damage parameter accounting for cumulative damage resulting from static and fatigue loading. The method was implemented in a user subroutine of the commercial finite element software Abaqus®. Two-dimensional numerical simulations of the double cantilever beam test using different representative combinations of the modified Paris law coefficients were performed. It was verified that the results of the model simulate with excellent agreement the several Paris laws used as input, thus demonstrating the good performance of the method as a predictive tool.     

Design and analysis of a smart composite pipe joint system integrated with piezoelectric layers under bending

Incorporating with the high electro-mechanical coupling performance of piezoelectric materials, design and analysis of an adhesively bonded smart composite pipe joint system were conducted. In this joint system, piezoelectric layers were integrated into the joint coupler in order to reduce stress concentration in the joint adhesive layer. To theoretically verify the composite action and efficiency of the integrated piezoelectric layers, an electro-mechanical model based on the first-order shear deformation theory was established. This model was able to clarify the energetic characteristics of the proposed joint system on the improvement in the joint strength, which was under the action of a bending moment at the joint ends. The state-space method was utilized to obtain the final analytical solutions, including the peel and shear stress distributions in the adhesive layer. Finally, some numerical examples were calculated to evaluate the effect of the detailed stacking sequence and size of the integrated piezoelectric layers on reducing the stress concentration in the adhesive layer as well as the applied electric fields. These numerical results validated the integrity of the developed adhesively bonded smart composite pipe joint system.     

FRP加固金属裂纹板的断裂力学分析

传统的金属结构加固方法会形成新的疲劳源,而粘贴FRP加固则具有明显的优势．提出了“三维实体-弹簧-壳元”有限元模型,金属板采用三维实体单元, FRP采用壳单元,用弹簧单元来模拟FRP与金属板之间的胶层,对金属裂纹板粘贴FRP加固后的性能进行了线弹性断裂力学分析,并对影响金属板裂纹前缘应力强度因子的参数进行了讨论．分析结果表明,采用高弹性模量的FRP和增加FRP的厚度对改善加固效果非常明显．     

Process zone in the Single Cantilever Beam under transverse loading - Part II: Experimental

This paper describes an experimental arrangement to evaluate stress/strain fields in the process zone of asymmetric adhesively bonded joints. A transparent polycarbonate flexible beam was bonded to an aluminium alloy rigid block with an epoxy adhesive in a Single Cantilever Beam (SCB) configuration. The flexible adherend was loaded in the direction parallel to the initial crack front at constant rate. To monitor strains induced by bending and shear along the beam, electric strain gauges were attached to the upper surface of the flexible adherend. Thus strain distribution was measured above the bonded surface, which could be used to monitor crack propagation and investigate stress redistribution in the process zone. A Timoshenko beam lying on a Pasternak elastic foundation model was used for the analysis of experimental findings. Subsequently, the Digital Image Correlation technique was used to measure the flexible substrate in-plane displacement field in the vicinity of the crack front and to assess the specimen kinematics. We found that strain gauge instrumentation of the fracture mechanics specimen was a very sensitive technique for experimental analysis of crack propagation under complex loading, offering fine investigation of stress distribution in the cohesive zone.     

Energy release rate and phase angle of delamination in sandwich beams and symmetric adhesively bonded joints

Delamination in sandwich structures along the interface between the face sheet and the core, or along the adherend/adhesive interface in adhesively bonded joints, is one of the most common failure modes of this type of tri-layer structure. This delamination is usually modeled as an interface crack problem, for which the energy release rate and phase angle can be calculated using interface fracture mechanics solutions. Existing interface fracture mechanics solutions, however, ignore the effect of transverse shear deformation, which can be significant for short crack. In an effort to overcome this shortcoming, this study presents new analytical solutions for the energy release rate and for the phase angle of the interface crack in sandwich structures or adhesively bonded joints. Since the new solutions incorporate relative rotation at the tip of the delamination, transverse shear effects are taken into account in this study. Typical delaminated sandwich and adhesively bonded joint specimens are analyzed by using the new solutions, as well as by the existing solutions. The energy release rate predicted by the present model agrees very well with that predicted by FEA, and furthermore it is considerably more accurate relative to existing models. As the existing model neglects the transverse shear force, it underestimates the total energy release rate. A stress field analysis is also conducted in this study in order to clarify some misunderstandings in the literature on the determination of the phase angle of adhesively bonded joints using an interface stress-based method.     

CFRP-混凝土界面粘结的疲劳性能试验研究

外贴FRP是重要的混凝土结构加固技术,但目前对外贴FRP加固混凝土结构的疲劳性能研究尚不充分,尤其对FRP-混凝土粘结界面的疲劳退化规律和破坏模式的研究更为缺乏。本文采用双面剪切试件,通过2个静载试件和4个疲劳试件的试验研究,考察了粘结长度和胶层厚度等因素对FRP-混凝土界面粘结疲劳性能的影响。通过分析沿粘结长度的FRP应变分布在疲劳循环过程中和疲劳后静载过程中的变化情况,讨论了不同粘结长度和粘结胶层厚度条件下的粘结界面疲劳退化规律和疲劳后静载性能。试验结果表明:胶层树脂-混凝土粘结界面是发生疲劳剥离破坏的薄弱环节;胶层厚度增大时,由于疲劳引起的界面损伤累积发展显著减小,疲劳后静载中胶层厚度较大试件的粘结承载力也更大;粘结长度增大时,界面粘结呈现更为明显的损伤退化,但由于试验粘结长度小于有效粘结长度,疲劳后的静粘结承载力仍更大。