湿热循环老化对异种基材接头力学性能影响研究

开展钢/铝粘接接头在湿热环境下的耐久性研究,选择0°单搭接接头、45°嵌接接头和90°对接接头,研究不同老化周期对接头粘接强度、失效位移、失效模式和接头刚度的影响,最后使用最小二乘法拟合出剩余强度与老化周期之间的关系曲线。研究结果表明:随着老化周期增加,粘接强度逐渐降低,经过60周期老化,45°接头粘接强度衰减最多,0°接头失效形式由内聚失效转变为界面失效为主的混合失效,45°接头失效形式由内聚失效转变为界面失效,90°接头失效模式由内聚失效转变为内聚失效为主的混合失效;老化后0°和45°接头刚度显著降低,但90°接头刚度几乎没有变化;指数函数与试验数据吻合较好。该规律可作为粘接强度预测模型,指导胶粘剂的工程应用。     

铜电极与碳纤维/环氧复合材料粘接研究

研究铜电极与碳纤维/环氧复合材料的粘接工艺,比较铜的表面处理方法对于粘接强度和导电性的影响,并验证粘接的可靠性.首先分别用机械打磨、化学表面处理、表面电镀方法对铜片进行处理,然后通过铜粉导电胶与碳纤维/环氧复合材料粘接,测试粘接强度及电阻率,再通过湿热老化实验,对粘接的可靠性进行比较.测试结果表明,经化学表面处理的铜片与碳纤维/环氧复合材料粘接强度达到1.34 MPa,老化后强度保留率为76%;电阻率为4.19 Ω*m,老化后电阻率增加率为4.8%.从而确定化学表面处理方法得到的粘接强度和导电效果较佳.     

吸湿与干燥对车用聚氨酯胶粘剂接头失效的影响

为研究单一湿度和干燥恢复对聚氨酯粘接接头失效的影响,选择常温浸泡环境对粘接接头进行0(未老化)、10、20和30 d的老化作用,在潮湿和干燥两种状态下对粘接接头进行准静态失效测试,分析失效载荷和失效模式的变化规律,揭示聚氨酯粘接接头的失效机理。研究结果表明:在潮湿状态下的粘接接头失效载荷和接头刚度随着浸泡时间逐渐下降,但是下降趋势逐渐减缓,失效断面由内聚失效转变为混合失效,说明粘接接头在潮湿状态下的性能变化主要由胶层吸湿和界面失效引起;经过干燥之后,粘接接头的失效载荷和接头刚度都得到了恢复,且略高于未老化接头,失效模式又恢复为内聚失效,说明干燥之后粘接接头性能的提高主要由后固化引起。因此,提高车辆聚氨酯粘接结构在潮湿状态下的力学性能的关键在于提高粘接界面的力学性能。     

影响汽车板材粘接性能的研究进展

主要介绍了胶粘剂的性能,以及不同因素(如表面处理、胶层厚度、粘接体系的内应力、粘接接头的形状与尺寸和湿热环境等)对汽车新型轻质板材胶接件粘接性能的影响。最后对汽车新型轻质板材的粘接技术进行了展望。     

固体火箭发动机粘接界面湿热老化特性探究

对常用的加速老化寿命模型进行了归纳、总结,在分析其原理的基础上,针对固体火箭发动机粘接界面在湿热环境下的失效机理,提出合适的湿热老化寿命模型,可作为固体火箭发动机粘接界面湿热环境适应性研究的理论依据。     

湿热环境对铝合金接头性能的影响

选择单搭接接头,研究高铁车窗使用胶粘剂的耐候性,分别进行不同循环老化周期耐候性试验,研究不同老化周期对粘接性能的影响。通过对老化前后粘接接头准静态拉伸试验,确定其衰减比率和失效模式,并使用扫描电镜对失效接头断面进行表征。最后使用最小二乘法拟合出剩余强度与老化周期之间的关系曲线。研究结果表明:随着老化时间的增加,粘接强度退化明显,说明环境因素对粘接强度产生巨大影响。     

一种室温快速固化的高强度环氧胶的研制

以聚硫醇固化剂为基本原料,酚醛环氧树脂与端环氧基封端丁腈橡胶为增韧剂,制备了一种室温快速固化、耐高温、耐湿热且韧性较好的环氧结构胶。研究了酚醛环氧树脂与增韧剂对胶粘剂粘接性能、耐高温和耐湿热老化性能的影响。结果表明,酚醛环氧树脂的引入,提高了体系的耐温性能,尤其是高温老化与湿热老化后的粘接强度显著增强;端环氧基封端丁腈橡胶增韧剂的适量加入,提高了环氧胶的韧性与粘接强度。     

SY-D15表面处理剂的性能研究

SY-D15表面处理剂具有良好的综合性能,对于不同的复合材料胶接体系都能够显著提高粘接强度,SY-14A胶粘剂-5405/HT3复合材料胶接体系和SY-24C胶粘剂-3218/SW-280A复合材料胶接体系的粘接强度能够提高30%以上,胶接接头具有优异的耐介质、耐热和耐湿热老化等耐久性能。     

一种水工钢闸门用环氧砂浆垫料

提供了一种压缩强度较高、黏度较低的水工钢闸门环氧砂浆垫料,研究了该垫料的工艺性、粘接性和耐湿热老化性。结果表明,当压缩强度达到100 MPa时,自制固化剂配方的环氧砂浆混合黏度为6 000 m Pa·s;7 d常温养护下的相对最大伸长率为0.65%,拉伸粘接强度为3.5 MPa;90 d湿热老化剪切强度为21.9 MPa,湿热老化降低率为9.9%。     

温湿度变化对固体火箭发动机粘接界面的影响

固体火箭发动机的粘接界面通常在贮存和使用过程中容易受到多种环境因素的影响。采用加速老化的方法研究钢壳体发动机粘接界面在湿热老化条件下的性能变化。双因素显著性分析可对界面扯离力的测试影晌进行量化评估。结果表明湿热环境下界面力学性能下降明显,湿度变化为主要原因。     

Strength prediction of adhesively bonded carbon/epoxy joints

A finite element approach has been used to obtain the stress distribution in some adhesive joints. In the past, a strength prediction method has not been established. Therefore in this study, a strength prediction method for adhesive joints has been examined. First, the critical stress distribution of single-lap adhesive joints, with six different adherend thicknesses, was examined to obtain the failure criteria. It was thought that the point stress criterion, which has been previously used for an FRP tensile specimen with a hole, was effective. The proposed method using the point stress criterion was applied to adhesive joints, such as single-lap joints with short non-lap lengths and bending specimens of single-lap joints. Good agreement was obtained between the predicted and experimental joint strengths.     

In situ cure monitoring of adhesively bonded joints by dielectrometry

Since the reliability of adhesively bonded joints is much dependent on the curing status of thermosetting adhesives, the in situ cure monitoring during the cure of adhesive joints could improve the quality of adhesively bonded joints as it enables one to control the cure parameters. In this work, a dielectric method which measures the dissipation factor of the adhesive during the cure of joints and converts it into the degree of cure of the adhesive was devised. Steel adherends were used for the adhesively bonded joints because the steel adherends worked as the electrodes for the measurement of dissipation factor without additional electrodes. The relation between the dissipation factor and the degree of cure of adhesive was investigated, which could eliminate the temperature effect on the dissipation factor that is largely affected by the degree of cure and temperature of adhesive. Comparing the results obtained by the method developed with those by DSC (differential scanning calorimetry), it was found that the dissipation factor showed a trend similar to the cure rate of the adhesive.     

Spot Welding–Adhesive Joints: Modelling and Testing

Modelling and testing of hybrid joints obtained by combination of two simple techniques, i.e., by application of spot welding and adhesive, is reported. The joints were subjected to uniaxial tension. The experiments were performed for: 1) a pure joining of the parts by spot welding and 2) spot welding–adhesive joining of the structural elements. A new experimental method was elaborated with application of two digital image correlation (DIC) systems. The method allowed for online monitoring of the deformation process of the joined elements with complex shapes. Modelling of the hybrid joints response to mechanical loading was performed by ABAQUS code. Damage process in the adhesive layer was taken into account. The obtained results lead to the conclusion that the strengthening of joints by the application of adhesive significantly improves static strength and energy absorption. The visible degradation process of the adhesive layer which started prior to the maximum value of force carrying the hybrid joint was obtained.     

Piezoelectric monitoring of the reliability of adhesive joints

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. In order to validate the method, the piezoelectric properties of the adhesive were measured during the fatigue test. Electrically conducting adherends were used as electrodes without embedded sensors, and the adhesively bonded joint was modeled as the equivalent parallel circuit composed of electric charge and capacitance. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.     

Prediction of crack length and crack growth rate of adhesive joints by a piezoelectric method

As adhesive joints have been widely used for fastening thin adherends, the damage tolerance design of adhesive joints has become important, and the estimation of initiation and propagation of a fatigue crack in the adhesive has become necessary. However, the measurement of crack length of tubular joints has been difficult because the observation of crack initiation and growth in the adhesive layer by conventional methods is not easy. In this work, a prediction method for the fatigue crack length in the adhesive layer of tubular single-lap adhesive joints was developed by the piezoelectric method. In order to obtain the relationship between the fatigue crack length and the piezoelectric signal, finite element analysis was conducted and verified by experiments. The damage of the adhesive joints was monitored by the piezoelectric method during torsional fatigue tests on tubular single-lap adhesive joints. Using the damage monitoring signals and the relationship between the fatigue crack length and the piezoelectric signal, a method for predicting fatigue crack growth in the adhesive layer of tubular single-lap adhesive joints was developed.     

Effect of temperature on the joint strength of a silyl-modified polymer-based adhesive

Temperature is a very important factor that must be fully considered in the study on the adhesive joint strength. In this paper, a silyl-modified polymer-based adhesive ISR 70-08 which is widely used in engineering was studied. Dog-bone specimens were fabricated and tested at ?40°C, room temperature (RT), and 90°C. Results show a decrease in the main mechanical properties with increasing temperature. Butt joints (BJs), single-lap joints (SLJs), and Scarf joints (SJs) were fabricated and tested at different temperatures. A quadratic polynomial expression was an ideal choice to express the joint strength as a function of temperature which was obtained using the least-squares method. Temperature combinations of ?40°C, 0°C, and 90°C were obtained to study the effect of temperature on the joint strength more easily for this adhesive. A three-dimensional surface, consisting of temperature, adhesive angle, and joint strength was presented to facilitate the application of bonding structures in engineering     

Yield behavior of rubber-modified epoxy adhesives under multiaxial stress conditions

In rubber-modified epoxy resins, a damage zone is generated in the vicinity of the crack tip due to the cavitation of rubber particles, which improves fracture toughness dramatically. Hence, in evaluating the stress distribution in adhesive joints with rubber-modified adhesives, the void formation and growth should be taken into account. In most studies, however, the adhesive layer is still considered as a continuum material governed by the von Mises yield criterion. For many ductile materials, Gurson's model is used for the stress analysis, in which the void formation and growth is taken into account. In a previous study, using adhesively bonded scarf and torsional butt joints, the effect of stress triaxiality on the yield stress in the adhesive layer was investigated. In this study, these experimentally-obtained yield stresses were compared with those obtained by a finite element method, where Gurson's constitutive equations were applied to the adhesive layer. As a result, the calculated yield stresses agreed well with the experimentally-obtained yield stresses. This indicates that Gurson's model is a useful tool for estimating stress distributions in adhesive joints with rubbermodified adhesives.     

Characterization and prediction of fracture properties in hygrothermally degraded adhesive joints: an open-faced approach

One of the challenges in the application of structural adhesive joints is the prediction of their long-term durability. During the service life, moisture diffuses into the adhesive layer and eventually degrades its fracture properties. Environmental degradation should thus be taken into consideration in the design and analysis of adhesive joints. This work first provides an overview, summarizing the recent efforts regarding the hygrothermal exposure of adhesive joints, accelerated aging methods, water diffusion modeling, and characterization of fracture properties in adhesively bonded joints. The second part presents a recent degradation methodology by which the fracture toughness evolution of adhesive joints can be predicted using fracture test data obtained using the accelerated open-faced degradation method.     

Investigation of the creep behavior of graphene oxide nanoplatelet-reinforced adhesively bonded joints

In this paper, the effect of adding graphene oxide nano-platelets (GONPs) into the adhesive layer was investigated on the creep behavior of adhesively bonded joints. The neat and GONP-reinforced adhesive joints were manufactured and tested under creep loading with different stress and temperature levels. 0.1?wt% GONPs revealed the highest improvement on the adhesive joint creep behavior amongst the studied weight percentages. Furthermore, the effect of GONPs on the creep behavior of adhesive joints was more significant at higher temperatures. It was found that adding 0.1?wt% of GONPs into the adhesive layer imposed reductions of 21%, 31% and 34% in the elastic shear strains and reductions of 24%, 31% and 37% in the creep shear strains of SLJs under testing temperatures of 30, 40 and 50?°C, respectively. The Burgers rheological model was employed for simulating the creep behavior of the neat and GONP-reinforced adhesive joints. The Burgers model parameters were obtained as functions of testing temperature, creep shear stress and GONP weight percentage using a response surface methodology. Reasonable agreement was obtained between the modeled and experimental creep behaviors of the adhesive joints.     

Effect of Temperature on the Joints Strength of an Automotive Polyurethane Adhesive

In this paper, the performance of an automotive polyurethane adhesive was studied through adhesive joints tests. Butt joints and single lap joints were fabricated and tested at seven temperature measuring points (TMPs). It is shown that both the tensile strength and lap shear strength decrease with the increasing of temperature. Quadratic polynomial expression obtained by the least square method can represent the tensile and lap shear strength as a function of temperature very well. ?40°C, 0°C, and 90°C were selected as the most ideal TMPs for this adhesive through the comparison of the residual sums of squares of 35 fitting curves with different combination of TMPs. Scarf joints with adhesive angles of 60° and 30° were fabricated and tested at ?40°C, 0°C, and 90°C. It also showed a decrease in joint strength with the increasing temperature. Joint strength as a function of adhesive angle is presented. It was found to closely follow a linear behaviour. A three-dimensional surface, consisting of temperature, adhesive angle, and joint strength, is presented finally to facilitate the design of automotive bonding structures.