Experimental Investigations of Axial Force Monitoring and Control for Friction Stir Welding Process

Friction stir welding( FSW) is a solid-state welding process that utilizes a rotating tool to induce gross material plastic deformation and join two parts together. A large number of studies have indicated that axial force control can be used to achieve good welding quality. However,in the welding process,due to workpiece's geometry error,improper clamping and other process variations,the axial force can vary significantly and produce welding defects.The control of force in the process of FSW is investigated. At first,the development and evaluation of a closed-loop control system is described,which is equipped with a custom real-time wireless force dynamometer for FSW. Then,an axial force controller is designed based on nonlinear force controllers for FSW. Experimental validations are carried out on an FSW platform. The experimental results demonstrate that the controller maintains the constant axial force and shows desirable dynamic behavior, even when the disturbance is encountered during the welding process.

Effect of Cooling Conditions on Mechanical and Microstructural Behaviours of Friction Stir Processed AZ31B Mg Alloy

Friction stir processing (FSP) is an important microstructural alteration process used recently in the engineering field. Grains alteration and hence the mechanical properties of the possessed zone are controlled by the temperature, heating and cooling rate. In this work, AZ31B magnesium samples were friction stir processed in three different cooling conditions like air, water and cryogenic (liquid nitrogen) cooling. 1000 rpm and 60 mm/min were kept constant as tool rotation speed and traverse speed respectively in all the three mediums. The consequence of these conditions on thermal fields, axial force, resulting grain structure and mechanical properties?was?studied. It is found that the cryogenic treated friction stir processed samples exhibit fine grain structures and hence offer better mechanical properties than the air and water cooled processed samples.

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding （FSW） process parameters on tensile strength of cast LM6 aluminium alloy. Joints were made by using different combinations of tool rotation speed, welding speed and axial force each at four levels. The quality of weld zone was investigated using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a rotational speed of 900 r/min, a welding speed of 75 mm/min and an axial force of 3 kN showed superior tensile strength compared with other joints. The tensile strength and microhardness of the welded joints for the optimum conditions were 166 MPa and 64.8 Hv respectively.

Optimization of friction stir welding parameters for improved corrosion resistance of AA2219 aluminum alloy joints

The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.

层间摩擦系数对非黏结柔性管抗拉铠装层轴压屈曲失效模式的影响研究

在柔性管运输、铺设安装和服役过程中,由于其抗拉铠装层钢带为柔性细长螺旋结构,当外部载荷超过临界值时,抗拉铠装层钢带容易发生屈曲失效。考虑非线性材料、几何大变形、层间接触和摩擦等非线性效应的影响,运用ABAQUS有限元软件建立了63.5mm典型非黏结柔性管8层完整结构模型,研究了在抗拉铠装层不同层间摩擦系数的情况下,非黏结柔性管在轴向压缩载荷作用下的力学性能和屈曲失效模式。研究结果表明,层间摩擦系数对非黏结柔性管的抗压刚度和抗拉铠装层屈曲失效模式有较大影响,层间摩擦系数以0.1和0.2为分界点,抗压刚度和屈曲失效模式均呈现出“三段式”变化规律。研究成果可为海洋非黏结柔性管的结构设计和屈曲失效评估提供技术参考。

螺栓设计参数对连接状态的影响及轴向力可视化方法研究

螺栓结构的连接状态与轴向力密切相关,而轴向力受多因素的影响,在拧紧或者松动过程中不断变化且无法做到无传感器实时监测。首先,基于螺栓的外螺纹轮廓方程,建立了精细化的螺栓有限元模型。其次,基于此模型研究了螺纹接触面摩擦因数、牙型角、螺距对于螺栓预紧过程及松动过程的影响规律。最后,关联松动角度和轴向力,结合深度学习目标检测算法,将螺栓的轴向力信息可视化。研究结果表明:在拧紧和松动过程中,螺栓轴向力实现了可观和可控,同时螺栓在预紧相同角度的情况下,其轴向力随着螺距和牙型角的增大而增加;其预紧力矩随着螺纹接触面摩擦因数和螺距的增大而变大,但会随着牙型角的增大而变小。

Friction surfacing of AISI 316 over mild steel: A characteriation study

An attempt has been made with overlaying of stain-less steel on mild steel by the technique of friction surfacing. This investigation elaborates the excellence acquired by different combination of the process parameters used in friction surfacing specifically traverse speed of the cross slide, speed of rotation of the spindle and the uniaxial compressive load. Excellent overlaying has been obtained amongst the chosen materials. To which, the coating can be done with various set of process parameters. It has been observed that the bond strength of the coating was found to be at a maximum of 502 MPa by ram tensile test.Based upon this results the surface methodology was characterized with scanning electron microscope.For authenticating the results, the coated specimen was subjected to salt spray test. The bonding microstructure was characterized using optical microscopy and X-ray diffraction. Corrosion resistance of surfaced coatings was found to be more inferior to that of mechtrode material and greater with the substrate.

一种航天器运动机构O形轴向动密封摩擦阻力研究

针对航天器一种常用的多道冗余O形轴向动密封摩擦阻力偏大的问题,对密封圈压缩率、金属配副表面摩擦因数、装配状态等因素进行仿真和试验研究。通过试验获得密封圈压缩率与摩擦阻力的关系;建立密封圈橡胶材料与轴孔摩擦仿真模型,通过分析获得O形密封圈与不同金属副动摩擦因数可能存在关系,并通过轴孔模拟试验验证仿真结果。通过密封圈磨损部位及应力分析,探究密封圈磨损原因。结果表明:摩擦阻力随密封圈压缩率的增大呈非线性增大趋势,且压缩率越大,摩擦阻力增幅越明显,因此降低密封圈压缩率可有效降低摩擦阻力;影响密封结构摩擦阻力的关键因素在于轴与密封圈之间的摩擦因数,通过在轴表面涂覆润滑膜层,可有效降低主轴摩擦因数,从而降低摩擦阻力。

软土中单侧边载作用下桩基负摩阻力研究

软土中因土体压缩性较高,在边载状况下易产生桩基负摩阻力,从而对工程产生安全隐患。本文通过有限元法对软土中受边载作用的桩基础所受到的桩基负摩阻力进行数值模拟,分析了不同边载等级、不同边载位距对软土中桩基负摩阻力、中性点位置和桩身轴力的影响。结果表明,在边载等级增加时,软土中桩身轴力有明显上升趋势,并随桩体埋深增加呈非线性趋势增长,而桩基负摩阻力随深度变化呈现非线性减小的趋势,桩体的下拉力增加,边载效应增强;同等级边载效应时,当边载与桩基之间的距离增加时,软土中桩基负摩阻力逐渐减小,中性点位置位于桩体靠近底部位置处,并随边载位置改变而受到一定影响。

轴向振动对近水平孔管柱减摩及屈曲的影响

为了解决近水平长钻孔孔内管柱受压后摩阻增大甚至管柱屈曲变形的问题,提出了轴向振动减摩和防屈曲方法。首先,建立了轴向振动减摩的力学分析模型,分析了振动减摩的内在力学机制;其次,建立了振动减摩的有限元模型,研究了激振力、激振频率对于减摩效果的影响关系,并通过现场试验进行了验证。研究结果表明:单个振动周期内管柱与孔壁摩阻存在方向变换现象,降低了单个振动周期内的平均摩阻;激振力越大,减摩效果越好;轴向振动的幅值和频率达到一定门限值后能够有效防止管柱屈曲变形,降低管柱摆动;对于长为200 m、直径为89 mm的通缆钻杆管柱,当激振力大于等于5 kN时,能够大幅度减小管柱与孔壁摩阻,防止管柱屈曲;平均摩阻与振动频率呈倒对数关系,随着激振频率的增大,平均摩阻先减小而后趋于稳定,当激振频率大于等于6 Hz后减摩效果趋于稳定。该研究结果对于减摩防屈曲钻具的研制以及钻孔工程施工具有指导意义。

循环压拔荷载作用下桩基础模型试验研究

随着大型建筑物不断兴起,桩基础作为西部地区基础常用形式之一,在承受上拔力作用时发挥着不可替代的作用。为了探明桩基础在循环荷载作用下的承载特性,在黄土高原区某典型黄土地基上,对单桩进行抗拔试验、循环压拔试验和循环抗拔试验。重点分析循环压拔加载路径下桩顶轴向位移和桩侧摩阻力的分布规律,阐述桩基承载力在不同循环次数以及循环荷载时的变化规律。结果表明:循环荷载和循环次数都是影响桩顶轴向位移变化的重要因素,并引入弱化因子来定量描述循环次数的影响;荷载越大,桩侧摩阻力越大,循环荷载下桩侧摩阻力整体呈下降趋势;压拔循环加载会在一定程度上减少对桩土之间接触的破坏,桩基承载力的损失也会更少,试验对竖向循环压拔荷载作用下的桩基础承载能力研究具有深刻的工程实践意义。

不同荷载作用下桥梁摩擦桩承载特性研究

研究桥梁钻孔灌注摩擦桩的承载特性及桩身力学性质的分布规律对桥梁的安全稳定运行具有重要意义。以重庆三店互通式1号桥梁桩基为研究对象,根据桥梁桩基特点设计室内试验,依次进行了灌注摩擦桩单桩承载力、桩身轴力以及侧摩阻力等桩基性能研究,并将试验结果与数值模拟结果以及理论公式计算结果进行对比验证。研究表明:持力层岩性对桥梁灌注摩擦桩桩顶沉降量存在影响,持力层岩土性能越高,则桩顶沉降量越小;桩身轴力及摩阻力的变化幅度均随着桩顶荷载的增加呈先增大后减小的规律,且桩身中部所受到的摩阻力最大;经理论公式和有限元分析的验证,本次试验结果整体上偏差率较小,3种分析计算方法均可较好地得出灌注摩擦桩桩身轴力变化规律。研究结果可为桥梁运营后期的病害防治提供重要的理论支撑。

涡旋压缩机轴向密封机构结构设计及摩擦学性能研究

涡旋压缩机运行过程中轴向间隙导致的气体泄漏以及密封材料与涡旋盘端板之间的摩擦损耗极大地降低了压缩机的工作效率,对其工作性能产生了不利影响。为了减少动、静涡旋盘之间的气体泄漏以及摩擦磨损,提出一种磁悬浮轴向密封机构,通过对其进行受力分析,得到动涡旋盘所受背压腔气体力的压力差,并以受力结果为指导进行不同石墨含量填充的PTFE密封材料的磨损试验,探究轴向密封材料的摩擦学性能。结果表明:该轴向密封装置能够有效降低轴向间隙引起的径向泄漏,使用石墨填充量为25%的PTFE密封材料搭配所设计的新型磁悬浮轴向密封机构能够实现较好的密封和减摩效果。

冲刷条件下在役桥梁桩基础竖向承载特性研究

为了分析冲刷条件下桥梁桩基础的承载特性,文中分析了不同冲刷深度下承台以及各个位置桩的轴力及摩擦力分布情况。结果表明,当冲刷深度为1倍桩径时,桩体回弹量为6 mm,桩体位移的下降速率为0.005 mm/kN;当冲刷深度为6倍桩径时,桩体回弹量达到了23 mm,桩体位移的下降速率为0.0103 mm/kN;即冲刷深度越大,桩体的回弹量越高,桩体位移下降速率越大。轴力以及桩侧摩阻力均表现为角桩>边桩>中间桩,且随着桩体深度的增加,三者之间的轴力及桩侧摩阻力差距不断缩小。

大直径铝合金波纹管复合整体制造工艺研究

为了得到具有大直径、高膨胀率、低壁厚减薄率的铝合金波纹管,提出了一种复合整体制造工艺,其核心思想是利用搅拌摩擦焊接获得大直径铝合金初始管坯,随后采用轴向压形法成形出所需的连续波形。首先开展平板焊接试验,确定搅拌摩擦焊接最佳工艺参数。通过实验与数值模拟分析结合的方式,基于ABAQUS有限元分析软件,建立了波纹管轴向压形过程的有限元模型,并基于波纹管轴向低压压形过程中的形状精度及壁厚分布情况,分析了不同成形工艺参数对波纹管成形过程的影响,获得了成形内压与轴向进给间最佳的匹配关系。最后开展静力试验考核。结果表明,采用该复合整体制造工艺可以获得满足设计要求的大直径大膨胀率铝合金波纹管,并且具有低成本、高效率优势。

轴向柱塞泵低压待机工况摩擦副功率损失研究

柱塞泵是特种车辆液压装置动力核心,在待机工况下,由于压力的降低,润滑性能会下降,摩擦副功率损失变大,不仅不节能,而且影响设备寿命和可靠性。为使轴向柱塞泵在低压待机时在节能、寿命、可靠性等方面都具有较好表现,针对某型号轴向柱塞泵开展配流副和滑靴副压紧系数理论研究及低压待机工况功率损失试验研究,并对工程实践和结构优化提出实质性建议。分析得出随着泵出口压力的降低,配流副和滑靴副的压紧系数逐渐增加,当出口压力低于2 MPa时,压紧系数急剧增加,会导致摩擦功率损失增加。通过对柱塞泵进行功率损失试验和100 h低压工况耐久试验得出,当出口压力低于2MPa时,柱塞泵的摩擦功率损失增大0.8kW,同时配流副和滑靴副有较严重磨损,与理论研究相符;若柱塞泵长期工作在此状态,会导致摩擦副严重磨损、柱塞泵寿命降低。建议主机在低压待命时,柱塞泵出口压力要高于2MPa。

桩端采空区对嵌岩桩承载力的影响

针对桩端采空区对嵌岩桩的设计(如承载性能和长期服役性能)提出的挑战,以杜家山特大桥采空区嵌岩桩为原型,进行缩尺模型试验,研究采空区到桩端不同距离以及采空区是否注浆的单桩承载力。计算比例参数,并选择合适的试验材料进行模型构建;通过多级荷载试验,获得采空区到桩端不同距离以及注浆后桩顶沉降、桩基础轴力、桩端阻力和桩侧摩阻力的变化特征;并对比分析了无采空区嵌岩桩的承载特征。结果表明,随着采空区到桩端距离的减小,桩端持力层的承载能力减小,不利于模型桩的承载力;注浆后,桩端持力层的承载能力明显增加,导致模型桩的桩顶沉降显著减少,承载能力显著提高。

竖向载荷下桥梁桩基承载特性研究

为分析竖向荷载作用下桥梁桩基础的承载特性,文中以某桥梁工程为例,通过静载试验分析了单桩及群桩的荷载-位移曲线、单桩桩身轴力以及桩侧摩阻力随桩深的变化规律。结果表明,随着桩身深度的增加,桩身侧摩阻力呈现先增加后降低的趋势,曲线存在反弯点,发生在桩深为30cm的位置;随着加载水平的增加,桩身侧摩阻力不断增加。桩的数量越多,桩基的沉降量越小,承载力越好。九桩的最大桩顶沉降量为20mm,卸载后的恢复沉降量为8.5mm;六桩的最大桩顶沉降量为25mm,卸载后的恢复沉降量为12.1mm;四桩的最大桩顶沉降量为28mm,卸载后的恢复沉降量为18.5mm。

轴向柱塞泵微织构配流副摩擦特性研究

在配流副表面加工微织构并研究其减摩特性。采用正交试验方法进行配流副仿真研究,得到各因素对配流副摩擦影响顺序为:转速>油膜厚度>深度>形状>直径>面积率,得出最优参数组合为:直径400μm、深度200μm的圆球形凹坑、凹坑面积率6%、油膜厚度15μm、转速1500 r/min.分析了微织构配流副的速度场、压力场、动压承载力,并对全油膜进行了仿真。搭建了轴向柱塞泵的配流副摩擦试验系统,在不同负载压力4 MPa、8 MPa、12 MPa和工作流量10 L/min、20 L/min、35 L/min下,对最佳参数的微织构配流副进行摩擦特性试验,试验结果表明,微织构配流盘的摩擦扭矩值比光滑配流盘小,与全油膜仿真结果相验证。最大差值为1.53 N·m,最大减摩率为12.47%.

大厚度湿陷性黄土场地群桩基础负摩阻力分析

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