Progressive failure of bamboo-steel adhesive bonding interface subjected low-energy impact and tension in sequence

Bamboo–steel composite structure is a newly developed structure, composed of bamboo plywood and cold-formed thin-walled steel bonded by structural adhesive. This paper configured a three-dimensional (3D) numerical model to characterize the progressive failure of bamboo–steel adhesive bonding interface subjected low-energy impact and tension in sequence. A 3D cohesive zone model (CZM) with reloading trapezoid softening law was adopted to characterize the debonding behavior of the bamboo–steel interface. Investigations on the debonding damage propagation of the bamboo–steel interface subjected low-energy impact and tension after impact were completed, and the influence factors of the residual tensile strength were studied.     

动态热力学分析法评估短纤维/橡胶复合材料界面粘合效果

采用动态热力学分析法评估短纤维／橡胶复合材料（SFRC）界面层的粘合效果。其基本原理为；使用动态热力学分析仪测定SFRC的损耗因子（tanδ），依据公式计算出表征材料界面粘合强度的参数α。试验结果表明。α值越大，材料的界面粘合效果越好，SFRC的拉伸强度、撕裂强度和耐磨性能也越好，但拉断伸长率减小。该方法具有操作简单、数据精确和周期短等优点。     

Influence of surface treatment on the durability of stainless steel sheets bonded with epoxy

Fifteen different surface treatments were used to bond AISI 304 stainless steel. The objectives of the programme were to select treatments able to produce durable adhesive bonds and to contribute to the understanding of interface bonding phenomena and of phenomena responsible for debonding while ageing. Peel and sheer tests were carried out to assess the behaviour of the bonded joints at the initial state and after ageing. The test results indicate that only two treatments, sulphuric chromic acid anodization and nitric acid anodization, exhibit a high performance level after exposure to a moist environment. The chemical and physical properties of surfaces were determined. The surface morphology was observed with a scanning electron microscope, and chemical composition was studied by X-ray photoelectron spectroscopy and secondary ion mass spectrometry. A correlation between bond durability, surface morphology, and oxide film composition was established.     

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.

In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.     

Extraction of rate-dependent fracture properties of adhesive interface involving large-scale yielding

Interface debonding is one of the major failure modes for the adhesive joints of polymer–matrix composites. The interfacial fracture properties of adhesive interfaces involving large-scale yielding is difficult to determine. A hybrid method that combines modified data reduction and inverse analysis was used to determine the fracture energy of the composite propellant/insulation interface at different loading rates. The modified data reduction adopts effective crack length to account for the effect of the fracture progress zone and avoid monitoring the crack length. These estimated values of the fracture energy were then calibrated by inverse analysis based on the Hooke–Jeeves algorithm in which the interface layer is characterized by a cohesive zone model. The whole process of inverse analysis is conducted automatically without any intervention by procedures. Experimental and numerical results indicate that the proposed data reduction provided fracture energy sufficiently similar to those obtained by the inverse analysis. Moreover, the fracture energy of the propellant/insulation interface was found to rely heavily on the loading rate with a non-monotonic trend.     

螺旋桨用榉木层板胶粘剂性能测试及工艺研究

为了解决木质螺旋桨的稳定性与变形问题,选用自制的聚氨酯(PU)胶粘剂对榉木层板进行胶接后再加工成螺旋桨。分别对胶接件的力学性能、耐热性、耐寒性、耐水性和耐湿热老化性能等进行了测定,探索了自制PU胶粘剂的最佳工艺条件,并进行了常温、高低温处理后的发动机试车试验。结果表明:自制PU胶粘剂具有较高的综合力学强度及稳定性能(其平均常温拉伸剪切强度和压缩剪切强度分别为8.13 MPa和15.00 MPa,平均高低温拉伸剪切强度和压缩剪切强度分别超过6.50 MPa和7.10 MPa;在水中浸泡20 h或湿热环境中放置24 h后,其平均压缩剪切强度分别为5.85 MPa和11.75 MPa),完全满足木质螺旋桨的使用要求。     

Development of a Failure Model for the Adhesively Bonded Tubular Single Lap Joint

The accurate calculation of the stresses and torque capacities of adhesively bonded joints is not possible without understanding the failure phenomena of the adhesive joints and the nonlinear behavior of the adhesive.

In this paper, an adhesive failure model of the adhesively bonded tubular single lap joint with steel-steel adherends was proposed to predict the torque capacity accurately.

The model incorporated the nonlinear behavior of the adhesive and the different failure modes in which the adhesive failure mode changed from bulk shear failure, via transient failure, to interfacial failure between the adhesive and the adherend, according to the magnitudes of the residual thermally-induced stresses from fabrication.     

结构胶在航空工业中的研究现状及进展

随着航空工业的迅猛发展,结构胶在航空工业中的使用日益广泛。综述了结构胶在航空领域中的研究进展,阐述了国内外航空用结构胶的近况,详细分析了目前客机中结构胶的需求及其应用的关键技术,并对今后航空用结构胶的发展趋势进行了展望。     

化学植筋的设计与施工

介绍了植筋的设计,施工方法及施工过程中的注意事项。     

Progressive failure and experimental study of adhesively bonded composite single-lap joints subjected to axial tensile loads

Experimental tests and finite element method (FEM) simulation were implemented to investigate T700/TDE86 composite laminate single-lap joints with different adhesive overlap areas and adherend laminate thickness. Three-dimensional finite element models of the joints having various overlap experimental parameters have been established. The damage initiation and progressive evolution of the laminates were predicted based on Hashin criterion and continuum damage mechanics. The delamination of the laminates and the failure of the adhesive were simulated by cohesive zone model. The simulation results agree well with the experimental results, proving the applicability of FEM. Damage contours and stress distribution analysis of the joints show that the failure modes of single-lap joints are related to various adhesive areas and adherend thickness. The minimum strength of the lap with defective adhesive layer was obtained, but the influence of the adhesive with defect zone on lap strength was not decisive. Moreover, the adhesive with spew-fillets can enhance the lap strength of joint. The shear and normal stress concentrations are severe at the ends of single-lap joints, and are the initiation of the failure. Analysis of the stress distribution of SL-2-0.2-P/D/S joints indicates that the maximum normal and shear stresses of the adhesive layer emerge on the overlap ends along the adhesive length. However, for the SL-2-0.2-D joint, the maximum normal stress emerges at the adjacent middle position of the defect zone along the adhesive width; for the SL-2-0.2-S joint, the maximum normal stress and shear stress emerge on both edges along the adhesive width.     

钢/塑复合管用热熔胶的制备与性能研究

以PE(聚乙烯)接枝母料、线性低密度聚乙烯(LLDPE)为主要原料,石油树脂为增黏树脂,苯乙烯-乙烯-丁二烯-苯乙烯嵌段共聚物(SEBS)为改性剂,采用单因素试验法优选出制备钢/塑复合管用HMA(热熔胶)的最佳配方。结果表明:增黏树脂的引入能明显提高HMA的剥离强度和熔体指数,并且胶接层的破坏形式为内聚破坏;SEBS类弹性体的引入能显著提高HMA的剥离强度,但熔体指数明显降低,而且胶接层的破坏形式是黏附破坏;当m(PE接枝母料)∶m(LLDPE)∶m(石油树脂)∶m(SEBS)=30∶45∶15∶10时,HMA的综合性能相对最好,其剥离强度为397 N/cm、熔体指数为2.3 g/10 min且胶接层的破坏形式是内聚破坏。     

Microstructure and mechanical properties of diffusion bonded W/MA956 steel joints with a titanium interlayer by SPS

Diffusion bonding is an effective technique for joining dissimilar metals. In this paper, tungsten and MA956 steel were diffusion-bonded by Spark Plasma Sintering (SPS) technique with titanium (Ti) foil as an interlayer. The bonded joints were evaluated by metallographic analysis and mechanical tests, and the results reveal that all W/Ti/MA956 joints were well bonded by efficient SPS technique. Microstructure analysis showed that W-Ti solid solution formed at W/Ti interface; reaction phases at Ti/MA956 steel interface varied with the joining temperature, e.g. intermetallics phases FeTi for 850?°C, FeTi, Fe₂Ti and Cr₂Ti for 900?°C and 950?°C joining temperature. The peak value of microhardness occurred at the interfaces of Ti/MA956 steel owing to the formation of intermetallic compound. All specimens of shear testing fractured at the Ti/MA956 steel interface close to MA956, and the average shear strength of joints was 182?MPa, 228?MPa and 164?MPa bonded at 850?°C, 900?°C and 950?°C respectively.     

一系弹簧橡胶与金属粘接失效的仿真分析

概述双涂型胶粘剂粘接原理和橡胶与金属粘接失效模式,针对某型一系橡胶弹簧(一系弹簧),采用Sigmasoft仿真软件对胶料充模和保压硫化过程进行分析与计算。研究表明:一系弹簧橡胶与金属粘接失效的根本原因为外套径向尺寸公差较大,径向封胶效果不佳,外套边缘硫化压力小;将一系弹簧外套径向封胶改为垂向封胶,并将原来的两瓣模结构改为整体模结构,一系弹簧外套边缘硫化压力增大,可以彻底解决橡胶与金属粘接失效问题。     

不同固化剂下低摩尔比脲醛树脂热行为及胶接胶合板性能

通过对3种固化剂下5种低摩尔比脲醛树脂进行热分析和胶合板制造实验,研究了摩尔比、游离甲醛含量、固化剂种类等对低摩尔比脲醛树脂胶粘剂固化反应起始温度、峰顶温度、终止温度和胶合板胶合强度及其甲醛释放量的影响。实验结果表明:1)与传统的氯化铵固化剂相比,过硫酸铵催化的脲醛树脂的热分析曲线的起始温度和峰顶温度都很低,显示出良好的固化促进作用;2)以过硫酸盐作固化剂时,低摩尔比脲醛树脂固化过程中起始温度和峰顶温度受摩尔比的影响较小;3)摩尔比为1．0的脲醛树脂胶接胶合板的胶合强度也能够满足GB／T 9846．3-2004Ⅱ类胶合板的要求;4)用过硫酸盐作固化剂制备的胶合板的甲醛释放量较低。     

Processing and property of carbon-fiber aluminum-foam sandwich with aramid-fiber composite adhesive joints

Thin tissues (or called webs) of short aramid fibers were added at the adhesive joints between carbon-fiber face sheets and aluminum-foam core to form aramid-fiber ‘composite adhesive joints’ for improving the interfacial bonding strength of sandwich structures and therefore other structural properties. In-plane critical compression loads and failure modes of carbon-fiber aluminum-foam sandwich beams with short aramid-fiber composite adhesive joints are investigated and discussed in this study. Improvements in critical compression loads were achieved for all specimens with aramid-fiber composite adhesive joints of different densities. It is suggested that the composite adhesive joints using low-density short aramid fibers is effective in promoting reinforcements against cracking and delamination at the interface between carbon-fiber face sheets and aluminum-foam core. The underlying interfacial strengthening and toughening mechanisms were discussed and analyzed based on observations from optical image and scanning electron microscopy.     

Experimental investigation and prediction of bonding strength of Oriental beech (Fagus orientalis Lipsky) bonded with polyvinyl acetate adhesive

Adhesive bond strength of solid wood plays a key role in the efficient use of wood in a large number of engineering applications. In this study, the effects of amount of adhesive, pressing pressure, and pressing time on bonding strength of beech wood bonded with polyvinyl acetate adhesive were investigated and predicted by developing an artificial neural network (ANN) model. Experimental results have showed that bonding strength of wood samples increased generally by increasing amount of adhesive, pressing pressure, and pressing time. Besides, ANN analysis has yielded highly satisfactory results. The designed neural network model allows predicting the bonding strength of wood samples with mean absolute percentage error of 2.454% and correlation coefficient of 97.8% for testing phase. It is clear from the results that the model has a good learning and generalization ability. This model therefore can be used to predict bonding strength of beech samples bonded with polyvinyl acetate adhesive under given conditions. Consequently, this study provides beneficial insights for practitioners in terms of the safe and efficient use of wood as an engineering material in applications related to the strength of the bond between wood and adhesive.     

Influence of adhesion area,applied voltage,and adherend materials on residual strength of joints bonded with electrically dismantlable adhesive

ABSTRACT

The separation characteristics of an electrically dismantlable adhesive, ElectRelease, were experimentally investigated. The adhesive has a strength that decreases by applying voltage. The residual strengths of cylindrical butt joints bonded with the adhesive were measured after voltage application. Various experiments were carried out in order to investigate the influences of the bonding area and the type of adherend materials on the residual strength by changing the dimensions and material of the adherends. The influence of constant voltage and current applications was also examined. As a result, it was confirmed that the residual strength of a joint does not depend significantly on the bonding area but on the type of adherend material. The residual strength was able to be determined and predicted by using an areal density of the total charge passing through the bonding area. Higher applied voltage was able to accelerate the decay of the residual strength and shorten the time for a given decrease in strength. The constant current application also induced a decrease in joint strength, which also corresponded to the total charge that could easily be calculated from a duration for current application.     

PET化学结构与热力学行为的关系

采用差热分析和红外光谱分析、粘均相对分子质量测定的方法,研究了PET的相对分子质量、端羟基和端羧基含量等化学结构与其玻璃化转变、冷结晶、热结晶行为、熔融行为的关系。结果表明:由于玻璃态中分子链段的局部有序性,PET呈现出双玻璃化转变和双冷结晶峰;随着相对分子质量减小,端羟基和端羧基含量相对增加,PET的玻璃化转变温度升高,冷结晶能力和热结晶能力增强,熔点升高,有利于形成结构完善的增强微纤。相对分子质量和端羧基、端羟基含量对热结晶行为影响的程度比对冷结晶行为的大得多,热结晶过程也由均相成核到既有异相成核,又有均相成核,到以异相成核为主。     

A two-dimensional stress analysis and strength evaluation of band adhesive butt joints subjected to tensile loads

The stresses in band adhesive butt joints, in which two adherends are bonded partially at the interfaces, are analyzed, using a two-dimensional theory of elasticity, in order to demonstrate the usefulness of the joints. In the analysis, similar adherends and adhesive bonds, which are bonded at two or three regions, are, respectively, replaced by finite strips. In the numerical calculations, the effects of the ratio of Young's moduli for adherends to that for adhesives, the adhesive thickness, the bonding area and position, and the load distribution are shown on the stress distributions at interfaces. It is seen that band adhesive joints are useful when the bonding area and positions are changed with external load distributions. Photoelastic experiments and the measurement of the adherend strains were carried out. The analytical results are in a fairly good agreement with the experimental results. In addition, a method for estimating the joint strength is proposed by using the interface stress distribution obtained by the analysis. Experiments concerning joint strength were performed and fairly good agreement is found between the estimated values and the experimental results.     

Extension of a one-dimensional finite element model program for analysing elastic-plastic stresses and progressive failure of adhesive bonded joints

A program for stress analysis of adhesive bonded joints within an elastic range was extended to consider the elastic-plastic stress state in an adhesive layer and its progressive failure. The program is based on the one dimensional finite element method. The von Mises yield criterion and the Mohr-Coulomb failure criterion are used in the program. Numerical analysis of a single lap joint subjected to four-point bending load was conducted and its result was compared with the experimental result. Good agreements were obtained between both results except for the final failure load. The present extension has some advantages. The stress singularity in the adhesive layer at the lap end or crack tip can be avoided due to the simple assumption for adhesive strains. Shorter computing time by the present method than by other general two- or three-dimensional finite element model programs should be much emphasized as one of the advantages.