基于锥形孔的干涉配合铆接应力特性研究

针对干涉配合铆接过程中铆钉孔上端变形明显、干涉量大、应力集中等现象,提出了一种带锥度的新型铆钉孔铆接方案,以改善板材应力分布和降低铆接过程中产生的残余应力。基于有限元方法,对准静态铆接过程进行模拟仿真,得到了锥形孔与常规孔铆接后的Mises应力以及铆接头径向和周向残余应力变化规律。结果表明,锥形孔试件沿径向和周向残余应力均低于常规铆钉孔试件的应力。随着锥度增大,沿板厚方向的径向和周向残余应力逐渐降低;沿铆钉孔径向,锥形孔接头径向残余应力明显降低,周向残余应力与常规孔接头残余应力基本一致。对比仿真和试验得到的力-位移曲线、镦头尺寸和相对干涉量变化情况,结果表明,试验和仿真模拟的力-位移曲线最大误差为7.03%;镦头尺寸最大误差为6.93%;3个铆接件与仿真得到的接头平均相对干涉量误差为5.01%。改变预制孔的锥度可以降低铆接后铆接头的残余应力,有效改善了铆接过程中的应力集中。

中性盐雾环境对异种材质自冲铆接接头静力学性能的影响

为了探究异种材质自冲铆接接头在中性盐雾腐蚀环境中的暴露时间对其静力学性能的影响,制备了DA-SPR接头和BA-SPR接头,并采用5%的NaCl中性盐雾腐蚀液分别进行了不同试验周期(0、168、336、504和840 h)的腐蚀试验。通过静拉伸试验、失重法等手段研究了中性盐雾腐蚀试验对接头静力学性能的影响规律,并利用场发射扫描电子显微镜对拉伸失效接头进行观察。试验结果表明:DA-SPR接头的最大拉伸静载荷值随着盐雾时间的增加持续减小,而BA-SPR接头最大拉伸静载荷值则随着盐雾时间的增加出现先增大后减小的变化趋势。在整个盐雾试验周期内,所有DA-SPR接头的能量吸收值都大于同腐蚀试验周期的BA-SPR接头。中性盐雾试验并没有改变DA-SPR接头的拉伸失效形式,而BA-SPR接头的拉伸失效形式虽都为上下板分离失效,但随着BA-SPR接头在中性盐雾试验环境中暴露时间的增加,铆钉由留在上板侧逐渐变化为铆钉从上板脱离,并出现铆钉头部的边缘处与钉身撕裂的情况。暴露在中性盐雾环境中的试样单位面积的腐蚀失重符合幂指数函数的变化规律,且有BA-SPR接头表层的腐蚀物锈层将加速其腐蚀,BA-SPR接头的腐蚀速率始终大于相同盐雾试验周期的DA-SPR接头。

一种基于AEKF的铆接件视觉伺服精确装配方法

针对工业生产中存在多轴孔铆接件因铆钉数量多、铆钉与铆孔间隙小、铆钉分布不规则等特点,致使装配过程约束复杂,装配精度要求高,难以实现铆接工艺智能化以提升装配效率问题,提出一种基于自适应扩展卡尔曼滤波的铆接件视觉伺服精确装配方法。为实现铆接件装配时的高精度定位,在传统扩展卡尔曼滤波的基础上,引入自适应噪声估计器,消除未知环境下的系统噪声对图像雅可比矩阵估计精度的影响,保证视觉伺服过程中图像雅可比矩阵的高精度估计;为保证铆接件装配时视觉伺服运动轨迹平滑稳定,设计滑模控制器,对铆接件进行轨迹跟踪,同时引入最小二乘法对铆接件图像特征深度信息进行实时在线估计,实现铆接件的高精度装配;以6自由度机器人建立仿真模型,结果表明在分布不规则的铆钉中选取4个铆钉的圆心点特征作为控制输入,通过设计的视觉伺服控制器能够完成铆接件的高精度多轴孔装配,提高了铆接工艺中关键工序的智能化水平。

基于改进YOLOv8n的雨天场景中飞机铆钉检测方法

为解决雨天场景中飞机表面附着与铆钉大小、形状相似的水滴而导致机务工程师在绕机检查过程中易出现铆钉误检的问题,提出1种基于改进YOLOv8n的飞机铆钉小目标检测方法。首先,改进C2f层,融入动态蛇形卷积,以捕捉复杂多变的全局形态特征;其次,在主干网络中嵌入可变形注意力机制,自适应调整对不同区域的关注度;然后,增加1个160×160的小目标检测层,提高小目标的检测能力;最后,使用斯库拉交并比(SIoU)边界框损失函数,提升模型训练速度和推理准确性,基于自建的飞机铆钉和雨滴数据集进行消融实验和对比实验。研究结果表明:本文所提算法在雨天场景下的铆钉检测精确度、召回率、mAP值分别较YOLOv8n提升7.4,4.0,7.8百分点,较其他主流算法也有显著提升。研究结果可为特殊天气下的飞机铆钉检测提供理论基础。

加载角度对6082铝合金自冲铆接接头疲劳性能及失效模式的影响

以6082铝合金自冲铆接为研究对象,采用拉伸试验、疲劳试验、扫描电镜观测等手段研究了接头疲劳裂纹扩展机理和微动磨损行为。结果表明:相较于0°、45°,加载角度90°的接头具有最优的静力学性能;在同一载荷水平下,接头疲劳寿命随加载角度的增大而增大;高周疲劳下的接头失效为下板开裂失效,低周疲劳下的接头失效为上板开裂和铆钉断裂;微动磨损影响接头疲劳裂纹的萌生位置和扩展路径,接头加载角度影响接头不同区域的微动磨损程度,加载角度90°的铆钉头部与上层板接触区域、加载角度0°的下板与铆钉腿表面接触区域的微动磨损最严重。

热铆温度对20Mn2冷拉盘条钢锚杆疲劳性能的影响

为选择合适的20Mn2冷拉盘条钢锚杆热铆温度以保证冷拉盘条锚栓的疲劳性能,分别对200℃(低温热铆)、500℃(中温热铆)、800℃(高温热铆)3种热铆温度工艺下的冷拉盘条锚杆进行疲劳试验,分析热铆温度对冷拉盘条锚杆疲劳性能影响。结果表明:不同热铆温度工艺下冷拉盘条锚杆疲劳性能差异明显,其中500℃热铆温度工艺疲劳性能最优。

不同孔径、孔型对环槽铆钉连接副预紧力的影响研究

目前轨道交通装备、铁路桥梁、钢结构站房建筑等节点连接主要有焊接、螺栓连接、环槽铆钉连接三种连接方案,其中焊接、螺栓连接已大规模应用数百年,相关的研究内容已趋于完善。但环槽铆钉连接为新型连接型式,国内相关研究较少,本文就不同孔径、孔型对环槽铆钉预紧力力学性能的影响开展了研究,为各领域技术人员使用环槽铆钉产品提供技术参考。

碳纤维复合材料胶铆混合结构拉伸失效研究

随着复合材料在轨道交通领域的广泛应用,形成了一系列复合材料车体、设备舱等结构,其车体装配方式已由金属焊接方式过渡到铆接、栓接以及混合连接的结构方式,连接的可靠性直接决定车体服役性能。鉴于此,本文制备了青岛1号线车体的典型碳纤维复合材料胶铆混合结构,进行了静载拉伸试验,分析了不同胶铆混合接头的承载能力、失效模式。研究结果表明,胶铆混合连接结构在拉伸载荷下,胶层首先在拉伸引起的偏心载荷下产生微裂纹,沿载荷方向两侧边缘向内部逐步扩展而后失效。胶层大部分失效后,铆钉和板材主要承载,复合材料/金属混合连接结构失效形式为铆钉断裂,而复合材料胶铆混连结构的失效形式表现为复合材料分层、纤维断裂、基体开裂的渐进破坏及铆钉拉脱。

Design of Drilling and Riveting Multi-functional End Effector for CFRP and Aluminum Components in Robotic Aircraft Assembly

To fulfill the demands for higher quality,efficiency and flexibility in aviation industry,a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer(CFRP)and aluminum components for a robotic aircraft assembly system.To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials,additional modules are incorporated on the end effector aside of the basic processing modules for drilling.And all of these processing modules allow for a onestep-drilling-countersinking process,hole inspection,automatic rivet feed,rivet geometry check,sealant application,rivet insertion and installation.Besides,to guarantee the better quality of the hole drilled and joints riveted,several online detection and adjustment measures are applied to this end effector,including the reference detection and perpendicular calibration,which could effectively ensure the positioning precision and perpendicular accuracy as demanded.Finally,the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm,aperpendicular accuracy within 0.3°,a diameter tolerance of H8,and a countersink depth tolerance of±0.01 mm.Moreover,it could drill and rivet up to three joints per minute,with acceptable shearing and tensile strength.

Prediction of Cross-Tension Strength of Self-Piercing Riveted Joints Using Finite Element Simulation and XGBoost Algorithm

Self-piercing riveting(SPR)has been widely used in automobile industry,and the strength prediction of SPR joints always attracts the attention of researchers.In this work,a prediction method of the cross-tension strength of SPR joints was proposed on the basis of finite element(FE)simulation and extreme gradient boosting decision tree(XGBoost)algorithm.An FE model of SPR process was established to simulate the plastic deformations of rivet and substrate materials and verified in terms of cross-sectional dimensions of SPR joints.The residual mechanical field from SPR process simulation was imported into a 2D FE model for the cross-tension testing simulation of SPR joints,and cross-tension strengths from FE simulation show a good consistence with the experiment result.Based on the verified FE model,the mechanical properties and thickness of substrate materials were varied and then used for FE simulation to obtain cross-tension strengths of a number of SPR joints,which were used to train the regression model based on the XGBoost algorithm in order to achieve prediction for cross-tension strength of SPR joints.Results show that the cross-tension strengths of SPR steel/aluminum joints could be successfully predicted by the XGBoost regression model with a respective error less than 7.6%compared to experimental values.

An Overview of Self-piercing Riveting Process with Focus on Joint Failures, Corrosion Issues and Optimisation Techniques

Self-piercing riveting(SPR)is a cold forming technique used to fasten together two or more sheets of materials with a rivet without the need to predrill a hole.The application of SPR in the automotive sector has become increasingly popular mainly due to the growing use of lightweight materials in transportation applications.However,SPR joining of these advanced light materials remains a challenge as these materials often lack a good combination of high strength and ductility to resist the large plastic deformation induced by the SPR process.In this paper,SPR joints of advanced materials and their corresponding failure mechanisms are discussed,aiming to provide the foundation for future improvement of SPR joint quality.This paper is divided into three major sections:1)joint failures focusing on joint defects originated from the SPR process and joint failure modes under different mechanical loading conditions,2)joint corrosion issues,and 3)joint optimisation via process parameters and advanced techniques.

Approach to Interference Riveting Process Control of Aircraft Automatic Drilling and Riveting

Interference fit riveting is an effective way to improve the fatigue life of aircraft.The accurate control of riveting interference of aircraft automatic drilling and riveting equipment is achieved by process parameters including upsetting force and upset head height.It is valuable for aircraft manufacturing engineering.An approach to interference riveting process control based on the analysis of interference riveting stress field is proposed.According to assembly structure,the upsetting force is calculated by the material property and interference fit level,and the upset head height is deduced by the upsetting force.The experimental result shows that the interference fit level can be controlled accurately by the upsetting force and upset head height,and then,the quality of aircraft automatic riveting can be improved.The proposed approach is verified by the good match between the predicted result and the experimental result.

A Comparative Study of Friction Self-Piercing Riveting and Self-Piercing Riveting of Aluminum Alloy AA5182-O

In this paper,self-piercing riveting(SPR)and friction self-piercing riveting(F-SPR)processes were employed to join aluminum alloy AA5182-O sheets.Parallel studies were carried out to compare the two processes in terms of joint macrogeometry,tooling force,microhardness,quasi-static mechanical performance,and fatigue behavior.The results indicate that the F-SPR process formed both rivet–sheet interlocking and sheet–sheet solid-state bonding,whereas the SPR process only contained rivet–sheet interlocking.For the same rivet flaring,the F-SPR process required 63%less tooling force than the SPR process because of the softening effect of frictional heat and the lower rivet hardness of F-SPR.The decrease in the switch depth of the F-SPR resulted in more hardening of the aluminum alloy surrounding the rivet.The higher hardness of aluminum and formation of solid-state bonding enhanced the F-SPR joint stiffness under lap-shear loading,which contributed to the higher quasi-static lap-shear strength and longer fatigue life compared to those of the SPR joints.

Microstructure evolution of AA5052 joint failure process and mechanical performance after reconditioning with tubular rivet

To extend the service life of the clinched joint,a reconditioning process conducted with an additional tubular rivet was proposed in this work.Different reconditioning forces were employed to produce dissimilar reconditioned joints by experimental method.The experimental results indicated that the neck fracture was the common failure mode of both original clinched and reconditioned joints.Compared with the original clinched joint,the shearing strength of the reconditioned joint produced by a reconditioning force of 40 kN increased from 1810.5 to 1986.47 N,and the energy absorption increased from 2.34 to 3.46 J.The range of effective reconditioning force was from 35 to 40 kN and 40 kN was the best choice for reconditioning the AA5052 failed joints.The mechanical properties of the reconditioned joints are obviously better than those of the original clinched joints,which fully demonstrates that the reconditioning method proposed in this work has a broad prospect of industrial application.

Friction-based riveting technique for AZ31 magnesium alloy

A new friction-based riveting technique, Rotating Hammer Riveting(RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a pre-heating operation. Due to preliminary twinning and followed by dynamic recrystallization, AZ31 Mg grains in the rivet head were refined during RHR, which enhance the formability of Mg rivets by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top AZ31 Mg sheet, which eliminates a significant pathway for corrosion.

Fatigue strength evaluation of self-piercing riveted joints of AZ31 Mg alloy and cold-rolled steel sheets

The application of magnesium alloys to automobiles is increasing due to their superior specific strength and specific stiffness.In this study,an upper sheet of AZ31 magnesium alloy and a lower sheet of cold-rolled steel were joined by self-piercing riveting(SPR),a method commonly used to join automotive panels.A cross-shaped specimen was fabricated with a punching force of 35 kN,which exhibited the best joint strength for the SPR joint specimen geometry.Monotonic and fatigue strengths were evaluated using cross-shaped specimens at loading angles of 0°,45°,and 90°.The load amplitude corresponding to the fatigue endurance limit was assumed to be at 106 cycles,and the fatigue ratios(=fatigue endurance limit/static strength)at the loading angles of 0°,45°,and 90°are 22%,13%,and 9%,respectively.For all three loading angle specimens,fatigue cracks initiated at the triple point where the rivet shank,the upper sheet and the lower sheet are in contact with each other,with the cracks propagating through the thickness of the upper sheet and ultimately leading to fracture.The fatigue lifetimes were evaluated through the von-Mises stress,maximum principal stress,and equivalent stress intensity factor.It was found that the fatigue lifetimes could be evaluated most appropriately through the maximum principal stress.

Study of galvanic corrosion and mechanical joint properties of AZ31B and carbon-fiber–reinforced polymer joined by friction self-piercing riveting

A new testing methodology was developed to quantitively study galvanic corrosion of AZ31B and thermoset carbon-fiber–reinforced polymer spot-joined by a friction self-piercing riveting process.Pre-defined areas of AZ31B in the joint were exposed in 0.1 M NaCl solution over time.Massive galvanic corrosion of AZ31B was observed as exposure time increased.The measured volume loss was converted into corrosion current that was at least 48 times greater than the corrosion current of AZ31B without galvanic coupling.Ninety percent of the mechanical joint integrity was retained for corroded F-SPR joints to 200 h and then decreased because of the massive volume loss of AZ31B。

Mechanical joint performances of friction self-piercing riveted carbon fiber reinforced polymer and AZ31B Mg alloy

Carbon fiber reinforced polymer(CFRP) and AZ31B Mg alloy were joined by the friction self-piercing riveting(F-SPR) with different steel rivet shank sizes. With the increase of rivet shank size, lap shear fracture load and mechanical interlock distance increased. Ultrafine grains were formed at the joint in AZ31B as a result of dynamic recrystallization, which contributed to the higher hardness. Fatigue life of the CFRP-AZ31B joint was studied at various peak loads of 0.5, 1, 2, and 3 kN and compared with the resistance spot welded AZ31B-AZ31B from the open literature. The fatigue performance was better at higher peak load(>2 kN) and comparable to that of resistance spot welding of AZ31B to AZ31B at lower peak loads(<1 kN). From fractography, the crack initiation for lower peak load(<1 kN) case was observed at the fretting positions on the top and bottom surfaces of AZ31B sheet. When peak load was increased, fretting between the rivet and the top of AZ31B became more dominant to initiate a crack during fatigue testing.

Friction self-piercing riveting(F-SPR)of aluminum alloy to magnesium alloy using a flat die

Friction self-piercing riveting(F-SPR)process based on a pip die has been invented to solve the cracking problems in riveting high-strength and low-ductility light metals,such as magnesium alloys,cast aluminum,and 7 series aluminum alloys.In this paper,in order to solve quality issues caused by the misalignment between rivet and pip-die in F-SPR,a flat-die based F-SPR process was proposed and employed to join 1.27 mm-thick AA6061-T6 to 3 mm-thick AZ31B.The results indicate that a 1.0 mm die distance is effective to avoid rivet upset and insufficient flaring.As the feed rate increases,the heat input in the whole process decreases,resulting in a larger riveting force,which in turn increases both the bottom thickness and interlock amount.Besides,solid-state bonding,including Al-Mg intermetallic compounds(IMCs),Al-Mg mechanical mixture,and Al-Fe atom interdiffusion was observed at the joint interfaces.The upper Al layer was softened,but the lower Mg layer was hardened,and both sheets exhibited a narrowed affected region with the increase of feed rate,while the rivet hardness shows no obvious change.Three fracture modes appeared accompanying the variations in lap-shear strength and energy absorption as the feed rate increased from 2 mm/s to 8 mm/s.Finally,the F-SPR process using a flat die was compared to those using a pip die and a flat bottom die to show the advantage of flat die on coping with the misalignment problem.

Study on the EM Scattering of Rivets on the Plate

The electromagnetic (EM) scattering by rivets on the conducting plate isstudied for the first time by using electric field integral equation (EFIE) in conjunction with themoment method. The surfaces of the rivets and the plate are partitioned into triangular cells, thecurrent distribution on the patches is represented by sub-domain type basis function, the EFIE istranslated into matrix equation by the Galerkin method, then the current coefficient is obtained.The results show the properties of radar cross section (RCS) varying with the incident angle whenthere are rivets on the plate.