TC3钛合金电阻点焊工艺参数优化

钛合金点焊接头力学性能不仅由焊核大小决定,其焊核及热影响区晶粒粗化现象会显著影响其性能.为了优化1.3mm厚TC3钛合金点焊工艺,制得具有优异抗剪切及抗拉伸综合力学性能的钛合金点焊接头.采用二次回归旋转设计试验方案,基于响应面法建立了TC3钛合金电阻点焊工艺参数(焊接电流、焊接时间及焊接压力)与预测响应值(剪切失效载荷及十字拉伸力学性能)之间的数学模型.通过数学模型,得到优化电阻点焊工艺参数,实现点焊接头剪切性能及拉伸性能的最优组合,并通过试验验证了数学模型的准确性.为优化钛合金点焊接头力学性能提供了新的工艺途径.     

预涂导电密封胶的轨道车辆不锈钢车体电阻点焊工艺试验

根据某不锈钢车辆上下侧墙板搭接结构形式,采用涂导电密封胶的电阻点焊技术,实现结构连接的同时保证了车辆密封.为验证该工艺的可靠性,采用预涂导电密封胶的电阻点焊技术分别对三种搭接结构试件进行焊接试验.焊后根据相关标准分别对三种搭接结构进行电阻点焊接头试验,包括外观检验、剥离试验、剪切拉伸试验和金相检验,并对点焊接头的表面凹...     

301L/Q235B异种钢电阻点焊显微组织及拉剪性能

对等厚2 mm+2 mm的301L不锈钢冷轧板和Q235B低碳钢热轧板进行电阻点焊试验,通过显微组织分析、显微硬度分析和拉伸剪切试验,研究了点焊接头拉剪性能的影响因素,基于抗剪强度和断裂模式确定了最佳的电阻点焊工艺。结果表明,二者点焊熔核向不锈钢侧偏移,熔核中由于马氏体的产生其显微硬度最高;当界面熔核直径大于6.8 mm时,在拉剪载荷下可发生301L钢侧熔核拔出断裂;在焊接电流11 kA,电极压力11 kN,通电时间350 ms的工艺参数下,可获得拉剪性能最优的点焊接头。     

基于电极位移信号的电阻点焊质量预测模型

设计了电阻点焊过程动态参数监测系统，采集焊接电压、电流以及电极位移信号，建立以交流电阻点焊过程中的周波参数为输入空间，以试样的抗拉剪切强度为输出空间的点焊质量预测神经网络模型．为实现电阻点焊质量在线监控奠定了理论基础。试验结果证明了RBF神经网络用于这类应用场合的可行性和有效性。     

5052铝合金压印-电阻点焊复合连接可行性研究

为了提高压印连接接头的强度,改善电阻点焊对铝合金连接不稳定的问题,对5052铝合金压印-电阻点焊复合连接的可行性进行了探究性试验。在焊接时间和焊接压力保持不变的情况下,将焊接电流(23-27 k A)视为唯一变量,探究了焊接电流的最优值。利用超声波水浸聚焦入射法对复合连接接头的成形性进行了检测;使用MTS材料试验机对试样进行了拉伸-剪切试验,得到了压印-电阻点焊复合连接接头的最大静拉伸载荷、失效形式及能量吸收值。结果表明:压印-电阻点焊复合连接可以实现对5052铝合金接头的有效连接且接头形貌可以利用超声C扫描进行检测;在焊接时间和焊接压力不变的情况下,适当增大焊接电流,接头的最大静拉伸载荷和能量吸收能力均有所提高,焊接电流的最优值均为25 k A;当焊接电流继续增加,接头内部结构遭到破坏。     

镀锌钢-1420铝锂合金电阻点焊及压印接头连接强度对比

对镀锌钢-1420铝锂合金电阻点焊接头及压印接头进行强度对比,利用超声扫描显微镜,分析镀锌钢-1420电阻点焊接头的C扫描图像,得到电阻点焊焊核内部各个区域的特征;采用直接观测法观察镀锌钢-1420压印接头的成形质量;通过MTS材料试验机进行拉伸-剪切试验,得到电阻点焊接头和压印接头的静失效载荷、失效形式及能量吸收值。结果表明:电阻点焊和压印连接都能很好地对镀锌钢-1420进行连接;在镀锌钢-1420异种板材的拉伸-剪切试验中,电阻点焊接头的静拉伸载荷(4593.8 N)高于压印接头的静拉伸载荷(3119.3 N);电阻点焊接头的失效模式为部分界面撕裂,压印接头的失效模式为上板拉脱失效并伴随部分上板颈部断裂;镀锌钢-1420压印接头的能量吸收值(4.757 J)要大于电阻点焊接头的能量吸收值(3.861 J),压印接头有良好的能量吸收能力,缓冲吸震性强。     

胶焊单搭接头静拉伸力学行为的研究

对比考察了胶接、电阻点焊和胶焊接头的静拉伸剪切强度和断裂特征。结果表明,典型的胶焊接头载荷位移曲线呈双峰形态,兼具纯胶接和纯电阻点焊接头的特征;曲线上第一载荷峰值略低于单纯胶接接头的断裂载荷,第二载荷峰值与单纯电阻点焊接头的强度基本一致。     

胶焊单搭接头静拉伸力学行业的研究

对比考察了胶接,电阻点焊和胶焊接头的静拉伸剪切强度和断裂特征。结果表明,典型的胶焊接头载荷位移曲线呈双峰形态,兼具纯胶接和纯电阻点焊接头的特征;曲线上和一载荷峰值略低于单纯胶接接头的断裂载荷,第二载荷峰值与单纯电阻点焊接头的强度基本一致。     

不同电阻点焊方法对轨道车辆用不锈钢接头质量与性能的影响

分别采用阿普拉斯焊接工艺、中频逆变点焊工艺对1.0 mm厚SUS301L-ST与1.5 mm厚EN1.4318+2G轨道车辆用奥氏体不锈钢进行电阻焊接,焊后根据相关标准进行点焊接头的外观质量、断面质量观察,剪切拉伸、轴向拉剪疲劳试验与分析.结果 表明,与中频逆变点焊接头相比,阿普拉斯焊接接头外观质量得到大幅提升,达到无...     

轨道客车用不锈钢等离子填丝搭接焊接头力学性能研究

针对板厚3mm SUS301L-MT与板厚5mm SUS304不锈钢板材搭接方式,分别采用等离子填丝焊工艺和电阻点焊工艺进行焊接,分析比较等离子填丝焊和电阻点焊两种方法搭接接头的准静态剪切拉伸性能和剪切拉伸疲劳性能。试验结果表明:在确定的焊接工艺参数条件下,等离子填丝焊和电阻点焊接头均符合铁道客车用不锈钢焊接接头的设计要求,且与电阻点焊接头相比,等离子填丝焊接头的剪切拉伸载荷提高约1.3倍,在循环寿命为2×106条件下的疲劳极限提高67.1%。     

Development of simple shear test for the measurement of work hardening

The simple shear test achieves large deformation without plastic instability in comparison with the uniaxial tensile test or the plane strain tensile test. However, the strain measurement can be very time consuming if the appropriate apparatus is not available. Moreover, the effect of specimen geometry on the measured work hardening has not been well investigated. The present work describes a simple shear test and a new strain extensometer based on a rotary angle transducer. FEM simulations and experimental work were carried out to evaluate the effect of specimen geometry on shear strain distribution, to study the effect of material parameters on the measured work hardening, and to correct the edge effect based on the geometry of test specimen. The correction method proposed for the simple shear test was validated experimentally.     

热输入对超高强钢DP1000激光焊接接头微观组织和断裂机制的影响

利用光学显微镜（OM）、扫描电子显微镜（SEM）观察超高强双相钢DP1000激光焊接接头微观组织的变化,通过显微硬度的测试、拉伸试验研究其不同热输入下焊接接头的力学性能.结果表明,随着热输入的增加,由回火区和两相区组成的软化区的组织发生了明显的变化,软化区内平均硬度值减小,其宽度尺寸增加,导致拉伸试样的断裂位置发生变化.当热输入不高于52 J/mm,焊接试样的抗拉强度是母材的97.75%,软化区宽度最大约为506 μm,断裂发生在母材上;当热输入达到72 J/mm,软化区宽度约为621 μm,断裂发生在软化区内.     

Damage and fracture mechanism of 6063 aluminum alloy under three kinds of stress states

To study the damage and fracture mechanism of 6063 aluminum alloy under different stress states,three kinds of representative triaxial stress states have been adopted,namely smooth tensile,notch tensile,and pure shear.The results of the study indicate the following.During the notch tensile test,a relatively higher stress triaxiality appears in the root of the notch.With the applied loading increasing,the volume fraction of microvoids in the root of the notch increases continuously.When it reaches the critical volume fraction of microvoids,the specimen fractures.During the pure shear test,the stress triaxiality almost equals to zero,and there is almost no microvoids but a shear band at the center of the butterfly specimen.The shear band results from nonuniform deformation constantly under the shear stress.With stress concentration,cracks are produced within the shear band and are later coalesced.When the equivalent plastic strain reaches the critical value（equivalent plastic fracture strain）,the butterfly specimen fractures.During the smooth tensile test,the stress triaxiality in the gauge of the specimen remains constant at 0.33.Thus,the volume of microvoids of the smooth tensile test is less than that of the notch tensile test and the smooth specimen fractures due to shearing between microvoids.The G-T-N damage model and Johnson-Cook model are used to simulate the notch tensile and shear test,respectively.The simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well.In addition,the empirical damage evolution equation for the notch specimen is obtained from the experimental data and FEM simulations.     

Interfacial characterization of resistance spot welded joint of steel and aluminum alloy

The dissimilar material resistance spot welding of galvanized high strength steel and aluminum alloy had been conducted. The welded joint exhibited a thin reaction layer composed of Fe2Al5 and Fe4Al13 phases at steel/aluminum interface. The welded joint presented a tensile shear load of 3.3 kN with an aluminum alloy nugget diameter of 5.7 ram. The interfucial failure mode was observed for the tensile shear specimen and fracture occurred at reaction layer and aluminum alloy fusion zone beside the interface. The reaction layer with compounds was the main reason for reduction of the welded joint mechanical property.     

纳米晶体镍片剪切带演化的实验研究

以高纯度、高致密度的纳晶金属镍片为研究对象,利用数字图像相关方法研究了其在单轴准静态拉伸载荷下的剪切带化变形行为,系统分析了纳晶金属镍片中剪切带的萌生及演化规律,定量分析了剪切带形核、扩展和失效的重要节点,讨论了纳晶镍剪切带的物理特征。结果显示:剪切带的演化发展是纳晶镍试样塑性变形的主要形式,是纳晶镍试样具有较低延性的原因。     

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied. Various microstructural analyses were performed using the techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization. The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates. The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40:1. Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40:1. The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio. Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%, compared with those of the cast specimen.     

高层建筑深基础周围岩体在不同加载速率的细观特性研究

为研究高层建筑深基础周围岩体在加载机制下的细观力学特性,文章以辽宁某在建房建项目为工程背景,采用颗粒流数值模拟方法对该深基础围岩(砂岩)在不同加载速率下进行单轴压缩试验研究。结果表明:随着加载速率的逐渐增大,砂岩的单轴抗压强度、弹性模量、峰值径向应变和轴向应变均呈逐渐增大的趋势;相同加载速率下,试样表现出显著的拉伸破坏模式。随着加载速率的逐渐增大,砂岩破坏时随产生的裂隙数呈逐渐减小变化趋势,加载速率由0.5 mm/s增大至2.5 mm/s,拉伸裂隙减幅为9.65%,剪切裂隙减幅为17.05%,表明加载速率对剪切裂隙的影响更加显著。     

Finite Element Analysis of the Microstructure–Strength Relationships of Metal Matrix Composites

The influence of the shape and spatial distribution of reinforced particles on strength and damage of metal matrix composite （MMC） is investigated through finite element method under uniaxial tensile, simple shear, biaxial tensile, as well as combined tensile/shear loadings. The particle shapes change randomly from circular to regular n-sided polygon （3 ≤ n ≤ 10）; the particle alignments are determined through a sequentially random number stream and the particle locations are defined through the random sequential adsorption algorithm. The ductile failure in metal matrix and brittle failure in particles are described through damage models based on the stress triaxial indicator and maximum principal stress criterion, respectively, while the debonding behavior of interface between particles and matrix is simulated through cohesive elements. The simulation results show that, under different loadings, interface debonding is the dominated failure mechanism in MMCs and plastic deformation and ductile failure of matrix also play very important roles on the failure of MMCs.     

Measurement of In-Plane Shear Strength of Carbon/Carbon Composites by Compression of Double-Notched Specimens

The compression of a double-notched specimen was used to determine the in-plane shear strength (IPSS) of a carbon/carbon composite in the paper. The effects of the notch distance (L), thickness (T), and notch width (W) and supporting jig on the IPSS of the double-notched specimens were investigated numerically and experimentally. The fracture surfaces were examined by a scanning electron microscope. It was found that the IPSS varied with L. Thin specimen yielded low strength. W has little effect on IPSS. The main failure modes include the matrix shear cracking, delamination, fracture and pullout of fibers or fiber bundles. Meanwhile, a supporting jig can provide lateral support and prevent buckling, therefore lead to the failure in a shear mode.     

Effects of expulsion in spot welding of cold rolled sheet steels

The effects of expulsion on microstructure and tensile shear strength of spot welds have been investigated for a high-strength cold rolled sheet steel. Spot welds with expulsion are characteristic for a “double im-age” near the fusion line, an equiaxed dendritic grain zone along the faying surface, and deep indenta-tions on the outer surfaces. Microstructural examinations and tensile shear tests of spot welding specimens were conducted to determine the correlation between microstructure and strength. It was found that the equiaxed dendritic structure was associated with significant solidification cracking. Frac-tography on tensile specimens reveals that brittle failure is associated with an equiaxed microstructure. Furthermore, the surface indentation will change the stress at the nugget edge, and deep surface inden-tations are expected to promote premature failure.