5052铝合金胶接接头静强度及疲劳性能研究

运用实验方法研究了胶接接头的静强度及其疲劳性能。对胶接接头进行静力学实验,并在此基础上选用6种不同载荷水平对胶接接头进行疲劳实验,获得了接头的载荷-寿命(F-N)曲线。试验结果表明:胶接接头静强度为同尺寸铝合金板静强度的77.5%,说明胶接接头有较高的静强度。当疲劳载荷水平大于最大静载荷平均值的50%时,接头F-N曲线呈线性趋势变化;随着疲劳载荷水平的不断提高,接头失效形式更多地表现为混合破坏。通过分析疲劳失效接头刚度变化可知:在各疲劳载荷水平下,接头刚度的线性趋势变化在整个疲劳周期内占很大比例,疲劳载荷水平越低,接头刚度降低越慢;接头刚度的变化表明在接头内产生了裂纹并逐步扩展。     

爆炸复合321/Q370qD双金属板对接接头的疲劳性能

采用轴向脉动拉伸疲劳试验,研究了爆炸复合321/Q370qD双金属板对接接头的疲劳性能。通过数理统计计算,获得了50%及97.7%两个置信度下试验材料的S—N曲线方程及据此确定的疲劳强度(2×10~6次),两个置信度下的疲劳强度均高于设计指标。对疲劳试样断口进行了观察,结果显示:疲劳裂纹大都起始于复合板对接接头的基层,个别起始于复层;裂纹稳定扩展区具有明显的疲劳辉纹,瞬断区具有典型的韧窝特征。断裂力学分析表明:疲劳裂纹起始于复合板不同组分的驱动力与复合板对接接头不同组分的循环屈服强度和弹性模量的乘积有关。     

Experimental and Numerical Investigation of Strain Distributions Within the Adhesive Layer in Bonded Joints

Abstract: We present the results of investigations into the strain distributions in the adhesive layers of epoxy‐bonded aluminium–aluminium and aluminium–carbon fibre reinforced polymer (Al/CFRP) double‐lap shear joints. The area of the adhesive at the end of the overlap region, where high stresses are predicted and failure generally initiates, has been studied at high magnification. 2‐D maps of the longitudinal and engineering shear strains in this region have been obtained experimentally by using high magnification moiré interferometry (HMMI). These results have been compared with the strain maps predicted by 3D elastic and elasto‐plastic finite element (FE) modelling. Excellent agreement is seen between the experimentally measured and FE‐predicted strain distributions, thus validating both methods. In some cases, quantitative comparison of the strains along certain profiles is compromised by noise in the measurements, especially for the Al/CFRP joints, which experienced lower overall strains. The source of such errors is discussed in the paper.     

胶接接头界面理论及其表面处理技术研究进展

胶接是用胶粘剂将被粘物表面连接在一起,形成可承受外载的胶接接头的过程,是涉及材料粘附、高分子材料老化机理、表面技术、力学性能测试等多个学科领域的边缘学科.介绍了与胶接接头界面紧密相关的弱界面层理论和润湿理论等领域的研究进展,总结了胶接接头表面处理方面的主要方法.     

Experimental study on the whole‐life heterogeneous ratchetting and ratchetting‐fatigue interaction of SUS301L stainless steel butt‐welded joint

Uniaxial fatigue tests of butt‐welded joint, made from SUS301L stainless steel, were carried out under asymmetric stress‐controlled cyclic loading conditions in this work. The effects of stress amplitude and mean stress on the whole‐life heterogeneous ratchetting and fatigue life of the butt‐welded joint were investigated, respectively, for the specified subzones. The experimental observations show that the whole‐life inhomogeneous ratchetting strain concentrating in a specific fusion zone (denoted as the FZ‐1 subzone) of the welded joint becomes more significant as the stress level increases; the fatigue failure also occurs in the FZ‐1 subzone, and the fatigue life depends on both the applied mean stress and stress amplitude and is determined by the combination of ratchetting damage and fatigue one in the localized FZ‐1 subzone.     

单个冲击对不锈钢管道焊接头低周疲劳寿命的影响

完成了单个冲击对１Ｃｒ１８Ｎｉ９１不锈钢管道焊接头试样低周疲劳寿命影响的试验研究。单个试验最大瞬时峰值应变率达４８０ｓ＾－１。试样未经消除焊接残余应力。采用成组法试验（每组７个试样）,对称加载模式,总应变幅为０．００２２８。结果表明,冲击影响受到焊接残余应力和冲击塑性导入机制的耦合作用。焊接残余应力与冲击应力叠加将增加材料损伤,而冲击塑性导入将减缓疲劳损伤和降低疲劳寿命分散性。前者扼制后者。考虑疲     

固溶氢对TA15钛合金电子束焊接头疲劳扩展寿命的影响

对TA15钛合金电子束焊接试样充氢,研究了氢对其显微组织形态和接头疲劳扩展寿命的影响。结果表明:充氢含量低于0.105%时,氢以固溶态存在于合金中,并未形成氢化物;母材抗疲劳扩展的能力高于焊缝区;随着充氢含量的增加,接头的疲劳寿命大幅下降。其原因是,微量氢的存在降低了TA15合金的韧性,固溶氢提高了疲劳裂纹的扩展速率。氢在边界处的聚集加速了焊接接头内裂纹沿马氏体束边界的扩展,导致在断口形成了团结构这一特殊组织形态。     

Experimental and computational study on thermo‐mechanical fatigue life of aluminium alloy piston

To assess the life of a new diesel aluminium alloy piston under thermal shock loads, thermo‐mechanical fatigue (TMF) testing was conducted to characterise the TMF properties of the piston alloy, and an empirical model based on the constraint ratio concept was proposed to predict the TMF life of the piston. Considering that the empirical model required expensive experimental support, a platform with high‐frequency induction heating was established to simulate the force on the piston under thermal shock loads to calculate the piston life using the thermal shock test. Additionally, a finite element method was developed to compute the distributions of temperature, strain, and stress during this process. The characteristics of crack initiation and propagation in TMF test rods and piston mock‐ups were also investigated. The results showed that the TMF test rod suffered brittle fracture with brittle quasi‐cleavage features. The microcracks mainly occurred in primary Si particles due to stress concentration around the primary Si particles induced by the difference between the thermal expansion coefficients of Si and Al. From a macro perspective, the piston initially cracked at the rim above the pinhole, where the stress is larger than that along other directions. From a micro perspective, the protrusions of various sizes on the piston rim were induced by the compression stresses at high temperature. The piston cracks usually initiate around primary Si particles, propagate along the edge of primary Si in a straight line, bifurcate and then stop at a certain depth. If the piston was only heated, cracks or plastic deformations were not produced. The piston life can be assessed using the proposed empirical model based on the constraint ratio concept or thermal shock testing based on the developed platform. The difference between the predicted and experimental life was not greater than 7%.     

Experimental analysis of the friction coefficient effect of the zinc‐lamella coated fasteners on bolt preload and tightening moment

Basic parameters of the bolt‐nut joints, which are ones of the most important elements of assembly processes, are the torque, bolt preload and friction coefficients between bolt and nut interfaces. In bolted joints tightened with torque and angle‐controlled method, friction coefficients of the fasteners are highly significant because they affect final torque and bolt preload values directly, creating a large uncertainty in regard to meet the minimum requirements on preloads considering the safety of joints and further systems, in case of this study, the vehicles being assembled. Also, the range of the lower and upper limits of friction coefficients of the coated fasteners affect process quality considerably in bolted joints tightened with torque and angle‐controlled technique. In this study, the effect of the friction coefficients on the bolt preload and final torque values in the vehicle chassis joints, which are created using torque and angle‐controlled tightening, were investigated experimentally. Therefore, bolt specimens which have both low and high friction coefficients, were tightened by the torque and angle‐controlled tightening method especially using high angle torque parameters on the vehicle chassis test bench. The torque and preload values obtained have been compared to each other and correlated in terms of the friction coefficients occurred.     

The Effects of Electrode Force on the Mechanical Behaviour of Resistance Spot‐Welded 5083‐O Aluminium Alloy Joints

Abstract: In this study, the effects of electrode force on the static and fatigue strength of spot welded joints of 5083‐O aluminium alloy sheets were investigated. The thickness of the sheet joints was 1.5 mm. Tensile‐shear joints with one spot weld were considered and three different load levels for electrode force were selected as 2500 N, 3000 N and 3500 N while the welding time and electric current were fixed during resistance spot welding process. Also, micro‐structures and micro‐hardness of cross‐sectional area of the test samples were investigated. The results show that increasing the electrode force from 2500 N to 3000 N has no major impact on the nugget size and fatigue strength of the specimens, but increasing the electrode force from 3000 N to 3500 N, despite reducing in the diameter of the nuggets, increases the fatigue life of the joints significantly. The results also indicate that increasing the electrode force increases the life associated with the crack initiation phase of total fatigue lifetime.     

Graphene/Polyaniline/Poly(4‐styrenesulfonate) Hybrid Film with Uniform Surface Resistance and Its Flexible Dipole Tag Antenna Application

A graphene/polyaniline/poly(4‐styrenesulfonate) (G/PANI/PSS)‐based conducting paste is successfully fabricated by introducing a PANI/PSS nanofiller into a multilayer graphene matrix by mechanical blending. As a compatibilizer, the PSS binder increases the dispersibility, interfacial interactions, and mechanical interlocking between the multilayer graphene matrix and PANI, thereby allowing surface resistance with narrow distribution. High concentrations of this PSS binder, obtained using ex situ polymerization, further improve the adhesion of the hybrid film to a flexible substrate. The minimum surface resistance of the screen‐printed G/PANI/PSS hybrid film is approximately 10 Ω sq^?1 for a 70 μm uniform thickness. When bent to angles of ?30°, the flexible hybrid film exhibits an approximately 6% decrease in surface resistance. The surface resistance after 500 bending cycles increases by only 10 Ω sq^?1, which is 14 times that of smaller, graphene‐based thin films. The micropatterned, screen‐printed G/PANI/PSS hybrid film is evaluated as a practical dipole tag antenna. High‐resolution patterns are formed in the hybrid film by the inherently high surface tension and the properties of grains within the domain‐based structure. The G/PANI/PSS‐based dipole tag antenna has a bandwidth of 28.7 MHz, a high transmitted power efficiency of 98.5%, and a recognition distance of 0.42 m at a mean frequency of 910 MHz. These characteristics indicate that the G/PANI/PSS‐based dipole tag antenna could be used as a signal‐receiving apparatus, much like a radio‐frequency identification tag, for detecting nearby objects.