铝合金焊点疲劳性能及其影响因素分析

研究了铝合金AA5754和AA6111-T4焊点的疲劳性能,获得了不同厚度及试件类型的焊点疲劳数据;研究了试件类型不同时焊点的疲劳失效模式,讨论了焊点疲劳裂纹的扩展形式;分析了铝合金焊点疲劳寿命的影响因素。结果表明:焊点疲劳失效模式主要有两种,分别是母材“眉状”裂纹断裂和焊点熔核界面断裂;母材对焊点疲劳寿命影响不大;循环载荷比对焊点寿命有一定的影响,增大载荷比导致焊点疲劳寿命略有下降;试件类型对焊点寿命有很大的影响,应在设计中避免焊点承受剥离载荷。     

铝合金点焊拉剪接头疲劳性能及寿命分析

研究了铝合金AA5754点焊拉剪接头的疲劳性能,获得了不同厚度试件的载荷寿命曲线。研究了铝合金焊点的疲劳失效模式,讨论了焊点疲劳裂纹的扩展形式,并测量了裂纹扩展路径与点焊熔核界面之间的角度。分析了点焊拉剪试件在同时承受I型和II型载荷时,疲劳裂纹的扩展方向,并与测量值进行了比较。利用疲劳破坏后沿铝板厚度方向的实际裂纹长度修正了裂纹尖端的局部应力强度因子,提出了评价焊点寿命的疲劳参量K(i),并对试验数据进行了分析比较。结果证明K(i)可以有效关联试件尺寸效应和焊点疲劳寿命,能够用于预测焊点疲劳寿命。     

平衡轴力作用下K节点焊缝周围应力分布规律

首先建立了焊接K节点的有限元分析模型,计算了承受平衡轴力作用下的K型管节点在焊缝周围的应力分布情况.然后通过对420个K节点模型进行的参数分析,研究了表征K节点的几个主要几何参数对热点应力分布规律的影响.通过模型分析,发现在平衡轴力作用下K型管节点焊缝周围应力分布情况是要受几何参数影响的.在几何参数不同的情况下,热点应力的位置会在冠点和鞍点之间发生移动.由于热点应力处是疲劳裂纹出现的位置,因此K节点疲劳断裂过程是要受到几何参数影响的.     

两级加载下ST12点焊接头的疲劳累积损伤

近几十年来,关于点焊问题,国内外学者从焊接性、影响因素到拉伸疲劳特性等方面展开了大量试验及理论研究,进行了一些关于强度问题的理论研究分析。本文以承受拉剪作用的ST12点焊接头作为研究对象,通过两级加载试验,分析了载荷顺序、平均应力和过载效应等因素对电焊接头寿命的影响。     

兆瓦级风机机架焊缝疲劳分析

在风力发电机机架的焊缝疲劳分析时,目前应用最广的方法为表面外推热点应力法.表面外推热点应力法直接应用热点应力作为疲劳应力控制参量,板厚尺寸和载荷模式效应通常按经验修正公式考虑,焊趾缺口效应在热点应力S-N曲线中统计考虑.以某兆瓦级风机焊接机架为例,首先建立机架的有限元分析模型,计算得到热点的应力,其次通过将载荷历程与其进行通道合并,并运用雨流计数法计算得到等效疲劳应力,最后结合焊缝的S-N曲线进行焊缝的疲劳强度评定及寿命预测.     

45钢焊接接头组织和性能的定量分析

用金相分析技术和微型剪切试验方法对45钢的电子束焊和氩弧焊焊接接头各区进行了组织分析和力学性能的定量分析，结果表明：两种接头热影响区和焊缝的显微组织，力学性能均优于基材，45钢采用电子束焊和氩弧焊都可获得优良的焊接接头。     

多点焊拉剪搭接接头构件的最佳焊点间距研究

通过研究多点焊搭接构件的静强度与疲劳强度，探讨了焊点间距对强度的影响，并且用弹性力学模型分析了板中焊点附近的应力状态，与实验结果能较好地对应。     

基于MSC.NASTRAN的点焊模型及其比较分析

点焊是汽车车身结构常用的一种连接方式,为对这种结构进行有限元分析必须建立相应的点焊模型。本文介绍了MSC.NASTRAN中常用的3种点焊模型,并用一个例子说明了不同的点焊模型对分析结果的影响。     

基于激光位移传感器的角焊缝位姿检测

针对工字梁、箱梁等焊接结构自动化生产中工件偏移和偏转问题,提出了一种基于激光位移传感器的角焊缝位姿检测方法。建立了角焊缝位姿的弧长模型,分析了角焊缝位姿对弧长的影响规律;基于傅里叶分析,提出了角焊缝位姿解耦算法,实现了对角焊缝横向偏差、纵向偏差、坡口角度和工件偏转角度的检测;通过对存在坡口间隙和定位焊缝的角焊缝进行位姿检测试验。结果表明,所提出方法具有检测误差小、抗干扰能力强等优点,在焊接自动化生产中具有良好的应用前景。     

双相钢/铝合金激光胶接焊胶层作用分析

通过双相钢/铝合金激光胶接焊和激光焊接的对比分析,揭示钢上、铝下搭接激光胶接焊时胶层作用。对焊接过程进行等离子体形貌同步拍摄和焊接光谱采集并分析,与激光焊接比较,发现激光胶接焊时等离子体的颜色明亮,形态密度大,与试样板材表面呈一定角度,胶层分解产物利于改善下层铝合金表面高反射率的状况,等离子体对激光能量的吸收减少;而光谱相对强度和光致等离子体电子密度增加,胶层的存在增加试件对激光的吸收率;焊接成形试验发现胶层可起增加焊接熔深和熔宽的作用;剪切试验结果表明胶层提高焊接接头的平均抗剪强度。由于添加胶层加快上层双相钢冷却速度,增加下层铝合金对激光能量的吸收,导致下层Al向上层钢侧的扩散受到抑制,而熔宽两侧熔融态Al体积分数增多,焊接熔宽加大,增加钢、铝横向结合面积,提高焊合率,此外剪切力的外加载荷由焊缝和胶层共同承担,因此添加胶层改善了钢/铝焊接接头的力学性能。     

Analytical studies for buckling and vibration of weld-bonded beam shells of rectangular cross-section

An approach to analytical solution is presented for vibration and buckling of thin-walled tubular beam shells typical of automotive structures, which are fabricated by joining sheet metal stampings along the two longitudinal edges with periodic spot welds, adhesive bonding, or combination of spot welds and bonding, known as weld bonding. Solutions are obtained for such beam shells of rectangular cross-section with two opposite ends simply supported. The beam shell is modeled as an assembly of the constituent walls and Levy-type formulation is used to obtain a series solution for the transverse displacement of each of the walls. The challenge of expressing the discrete point support conditions at the spot welds by a continuous function is addressed using the flexibility function approach used in literature. The flexibility function, used earlier to represent the flexibility distribution along weld-bonded edges of rectangular plates with periodic spot welds, is used here. The characteristic equations are obtained by satisfying the displacement, slope, shear, and moment equilibrium at the mating edges of the walls including the two weld-bonded edges and the compatibility conditions at the spot-weld locations. This approach to analytical solution, described here for thin-walled beam shells of rectangular cross-section, can be suitably adopted for more general cross-sections and joints along non-symmetric edges. A parametric study is undertaken to show the effect of aspect ratio of the beam shell, adhesive joint parameters, and the number of spot welds on the elastic buckling loads and the natural frequencies. Such parametric studies can be of use to designers in arriving at an optimal joint configuration of weld-bonded beam shells from buckling and vibration considerations.     

Investigation on the resistance spot-welded austenitic/ferritic stainless steel

In this work, the effect of weld current on joining capability of austenitic stainless steel (AISI 304) and ferritic stainless steel (AISI 430) sheets with application of resistance spot welding process was investigated. Macrostructure, microstructure, microhardness, tensile shear strength, and failure mode of welded materials were evaluated for different weld currents. The values of weld current were 2.5, 3.75, and 5 kA. It was found that when the weld current increased, the nugget size and the weld strength were increased. Two distinct failure modes including interfacial and pullout were observed during tensile shear test. Finally, an adequate weld current was obtained.     

MW级风机塔筒门框焊缝的强度分析

运用有限元分析软件ANSYS建立某MW级风力发电机塔筒门框的有限元模型,分析了其在极限载荷下的静强度; 同时采用热点应力法对门框焊缝进行疲劳分析,基于临界面理论计算热点应力,并利用雨流计数法和Palmgren-Miner线性累积损伤理论计算了门框焊缝的疲劳损伤,结果表明,门框焊缝的极限强度和疲劳强度均满足使用要求。     

三维四向编织复合材料接头承载能力分析

针对三维四向编织复合材料单耳承力接头,用细观力学和均匀化方法分析三维编织复合材料的细观结构,用MATLAB程序对复合材料弹性性能进行参数化求解,利用ANSYS估算两种几何尺寸试样的破坏载荷.有限元计算结果与试验值有较好的吻合,显示文中方法可以满足工程设计和分析的要求.     

Rigid-plastic collapse of compression-bent shallow shells

Limit analysis solutions are given for simply supported shallow spherical shells under combined external loading. The effect of transverse shear on collapse loads is examined in the paper. Lower bound and exact load interaction curves at collapse are given for several shell configurations. The shell material is assumed rigid-plastic and yields according to the von Mises criterion. The results indicate that the lower bound approach gives acceptable results when extremely shallow shells are considered. It is also shown that the reduction of collapse loads due to transverse shear is of the same order as found for circular plates.     

3D upper bound limit analysis of multi-leaf masonry walls

A full three dimensional (3D) heterogeneous approach for FE upper bound limit analyses of in- and out-of-plane loaded masonry walls is presented. Under the assumption of associated plasticity for the constituent materials, mortar joints are reduced to interfaces with a Mohr–Coulomb failure criterion with tension cut-off and cap in compression, whereas for bricks a Mohr–Coulomb failure criterion is adopted. Four-noded tetrahedron elements with linear interpolation of the velocities field are used for bricks discretization, whereas possible jumps of velocities at the interfaces between adjoining elements can occur. Triangular elements with linear interpolation of the jump of velocities field are used both for joints reduced to interfaces and internal bricks interfaces. In this way, an improvement of the numerical model in terms of collapse load is obtained.In order to test the reliability of the model proposed, two examples consisting of an English bond shear panel and a simply supported rectangular stretcher bond slab are discussed. Results obtained are compared with experimental data available and previously presented numerical models. The comparisons show both that reliable predictions of collapse loads and failure mechanisms can be obtained by means of the numerical procedure proposed and that full 3D models should be employed in presence of loads eccentricities and/or multi-leaf walls out-of-plane loaded.     

基于均匀化循环理论的车身焊点布局优化方法

提出一种基于焊点间距参数化的焊点布置优化方法,首先采用均匀分配理论建立几个不同焊点间距布置的有限元模型,进而根据循环迭代原理确定基于焊点等间距分布的迭代形式,并进行分析求解,最后以白车身刚度和车身关键区域最大应力值为约束条件,以焊点数量最小为设计目标,对焊点布置方案进行优化。该方法既保证了车身结构的性能要求,又保证了焊点均匀分布,提高了优化设计结果的工程实用性。     

微波组件模块组装焊点及其可靠性

介绍微波组件的应用及其组装焊接的重要性,提出组装焊接中焊点的特点,并对焊点失效进行详细机理分析,阐述机械应力和热应力对焊点失效的影响,在焊接工艺和焊点设计方面找到抗失效断裂的有效措施,从而保证焊点的质量,提高微波组件的可靠性。     

搅拌摩擦焊缝类型对接头拉伸性能及断裂特征的影响

采用三种不同针长的搅拌头对6082-T6铝合金板材进行焊接,获取三种类型的焊缝,即未透对接焊缝、已透对接焊缝和对-搭组合焊缝,通过对焊缝金相观察、拉伸测试和断口分析,得到焊缝类型对接头拉伸性能及断裂特征的影响规律。不同类型焊缝的表面成形区别不大,但内部成形各有特点。未透对接焊缝根部界面处形成未焊合缺陷;已透对接焊缝中无缺陷;对-搭组合焊缝后退侧和前进侧形成“钩状”缺陷。拉伸测试表明,未透对接接头拉伸性能最低,裂纹在未焊合处产生并沿焊核区扩展,接头下部呈现剪切断裂特征,接头上部呈现准解理和剪切混合断裂特征;已透对接接头拉伸性能最高,断裂位置位于前进侧热机影响区,断口呈现出典型的剪切断裂特征;对-搭组合接头拉伸性能居中,裂纹在前进侧“钩状”缺陷处产生并沿焊核区扩展,断口形貌与未透对接接头相似。     

Refill Friction Stir Spot Welding Al Alloy to Copper via Pure Metallurgical Joining Mechanism

The current investigation of refill friction stir spot welding(refill FSSW) Al alloy to copper primarily involved plunging the tool into bottom copper sheet to achieve both metallurgical and mechanical interfacial bonding. Compared to conventional FSSW and pinless FSSW, weld strength can be significantly improved by using this method. Nevertheless, tool wear is a critical issue during refill FSSW. In this study, defect-free Al/copper dissimilar welds were successfully fabricated using refill FSSW by only plunging the tool into top Al alloy sheet. Overall, two types of continuous and ultra-thin intermetallic compounds(IMCs) layers were identified at the whole Al/copper interface. Also, strong evidence of melting and resolidification was observed in the localized region. The peak temperature obtained at the center of Al/copper interface was 591℃, and the heating rate reached up to 916 ℃/s during the sleeve penetration phase. A softened weld region was produced via refill FSSW process, the hardness profile exhibited a W-shaped appearance along middle thickness of top Al alloy. The weld lap shear load was insensitive to the welding condition, whose scatter was rather small. The fracture path exclusively propagated along the IMCs layer of Cu_9Al_4 under the external lap shear loadings, both CuAl_2 and Cu_9Al_4 were detected on the fractured surface on the copper side. This research indicated that acceptable weld strength can be achieved via pure metallurgical joining mechanism, which has significant potential for the industrial applications.