Experimental and Finite Element Method Studies of J-Lead Solder Joint Reliability

A comprehensive experimental and numerical study of solder joints for plastic leaded chip carrier (PLCC) 84-Pin, 1.27 mm pitch was carried out. The reliability of solder joints was assessed through accelerated thermal cycling at the temperature range of - 55℃-125℃. The samples were taken out to observe the evolution in microstructure, such as grain coarsening, initiation and propagation of cracks. It was found that the Pb-rich phases segregated gradually and formed a continuous layer adjacent to the intermetallic compound (IMC) layer with increasing the number of thermal cycles, resulting in cracks near the solder/lead interface. The response of stress and strain was studied using nonlinear finite element method (FEM), and the results agreed well with the experimental data.

EXPERIMENTAL RESEARCH AND NONLINEAR FINITE ELEMENT ANALYSIS ON NEW TYPE JOINT BETWEEN COLUMN AND STEEL BEAM OF CONCRETE-FILLED RECTANGULAR STEEL TUBULAR

Experimental results of new type joints between the column and the. steel beam of concrete-filled rectangular steel tubular （CFRT） under reversed cyclic loads are presented. The earthquake resistant capacity of the joint is influenced by infilled concrete, stiffener length and relative dimensions of column and beam. It is found that the hysteresis curves obtained in the experiment are full and the joints have a good energy dissipation capacity. The nonlinear finite element models are also used to analyze the hysteresis behavior of the joints under reversed cyclic loads using ANSYS 8.0. The influences of the stiffener length and the infilled concrete are analyzed. Analytical results show that the stiffener length and the infilled concrete are critical for the joints. Furthermore, the skeleton curves of the finite element models are in good agreement with those of experiments.

Finite Element Modeling and Modal Analysis of Complicated Structure with Bolted Joints

A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among these models, the coupled bolt model provides the best accurate responses compared with the experimental results. The contact bolt model shows the best effectiveness and usefulness in view of operational time. The bolt models proposed in this study are adopted for a dynamic characteristic analysis of a large diesel engine consisting of several parts which are connected by many bolts. The dynamic behavior of the entire engine structure was investigated by experiment. The coupled bolt model and the contact bolt model were applied to model the assembly of engine with high preload. The experimental results are in good agreement with the finite element method （FEM） results. Compared with the other models, the contact bolt model presented in this paper is more effective and useful in view of operational time and experience of analysts.

Finite-Element Analysis of Parts Stress State of Tight Joint Assembled by Press Fitting

This paper includes descriptions of the stress distribution regularities in the tight joint parts, regularities of the stress state changes in the contact region along coupling length, stress concentration factors, levels of additional stresses caused by press fitting. Distributions of stress intensity, axial stress, contact pressure, tangent stress in parts and in contact zone along coupling length are considered. Calculation results obtained by three approaches: Lame relationships, FEM without considering assembly method, FEM with considering press fitting process are analyzed and compared. The adequacy of research carried out is confirmed.

Anybody仿真太极不同步法时股骨及下肢骨主要关节的应力特征

背景:Anybody骨肌建模系统,使用数学建模技术模拟人体骨骼、肌肉和环境的关系,可对人体的逆向动力学进行研究,得出下肢关节力等指标。目的:分析练习太极拳动作时下肢骨主要关节的应力分布规律,为其科学训练和锻炼价值提供依据。方法:在北京体育大学武术学院选取8名太极拳健将级运动员进行7组步法动作和右腿股骨CT的数据采集。使用BTS红外捕捉系统、Kistler三维测力台采集太极(八法五步)7组步法动作的运动和力学数据,利用Anybody 7.2骨肌模型的多体动力学仿真技术计算下肢关节动力学参数,结合Workbench 19.2对股骨进行应力计算分析。结果与结论:①利用Workbench软件分析得出了7组步法动作的股骨应力结果,7组动作的应力峰值由大至小顺序是:退步捋势(22.00 MPa)、退步採势(19.379 MPa)、左右移步挤按(9.35 MPa)、左右移步肘靠(6.30 MPa)、进步掤势(4.68 MPa)、进步挒势(2.57 MPa)、中定独立势(0.31 MPa)。②在7组步法动作中2种向后退步动作股骨应力最大(P<0.05),且在7组动作运动过程中的股骨最大应力位置均不同。③上述结果证实,在太极(八法五步)7种步法动作练习时,股骨应力阈值和最大应力位置会随着5种方向(7组动作)运动不同而变化,通过连续训练能够全面地刺激股骨体,进步动作对于股骨体正面和外侧上端影响较大,退步动作对股骨体后面和内侧影响较大,左右横向步法动作主要是股骨体两侧对称受力。④初学者要根据不同步法动作的受力特点来进行针对训练,进步动作和退步动作训练时要注重太极拳的旋转用力以及左右横移步法动作训练时的内侧对抗用力,根据自身薄弱问题,对太极拳训练步法有所侧重,进而达到更好的锻炼效果。

Numerical modelling of resonance mechanisms in jointed rocks using transfer functions

Resonance effects in parallel jointed rocks subject to stress waves are investigated using transfer functions,derived from signals generated through numerical modelling.Resonance is important for a range of engineering situations as it identifies the frequency of waves which will be favourably transmitted.Two different numerical methods are used for this study,adopting the finite difference method and the combined discrete element-finite difference method.The numerical models are validated by replicating results from previous studies.The two methods are found to behave similarly and show the same resonance effects;one operating at low frequency and the other operating at relatively high frequency.These resonance effects are interpreted in terms of simple physical systems and analytical equations are derived to predict the resonant frequencies of complex rock masses.Low frequency resonance is shown to be generated by a system synonymous with masses between springs,described as spring resonance,with an equal number of resonant frequencies as the number of blocks.High frequency resonance is generated through superposition of multiple reflected waves developing standing waves within intact blocks,described as superposition resonance.While resonance through superposition has previously been identified,resonance based on masses between springs has not been previously identified in jointed rocks.The findings of this study have implications for future analysis of multiple jointed rock masses,showing that a wave travelling through such materials can induce other modes of propagation of waves,i.e.spring resonance.

Research on Simulation Methods of Electric Field Intensity on Surface of 10 kV Cable Joint

The electric field intensity (EFI) is important characteristic quantity for evaluating the internal insulation state of cable joints. Based on finite element method, this paper proposes two EFI research methods, field-circuit coupling method and equivalent circuit method. The average EFI of the inner surface of the outer semi-conducting shield can be calculated from the current in the measuring circuit. The relative error between these two methods is about 15%, which roughly proves the consistency of the two methods. Further practical application research enables online monitoring of cable joints.

Sensitivity Analysis of Buried Jointed Pipelines Subjected to Earthquake Waves

In this study, a number of nonlinear time-history dynamic analyses are conducted on a part of Tehran water distribution network to investigate its functionality during transient large ground motions. The network is of 950-meter length, consisting of ductile iron pipes segments of 6-meter length. Pipes are modeled using beam elements and springs characterize the connections. Considering the time lag between support inputs, and the nonlinear soil-pipe interaction, by scaling the amplitude of the Tab as earthquake record, incremental dynamic analysis is carried out on the network in two orthogonal directions and the sensitivity of the network response is examined. Furthermore, the effects of variations in soil damping and soil spring stiffness are also studied in the network analysis. Finally the effect of changes in angle between incoming wave and pipeline is considered on a simplified network. Results show that the points other than critical ones at network intersections remain almost intact and when the angle of incidence is 30 degrees the stress and rotation peak.

考虑坝-基-库水相互作用的拱坝底缝开裂模拟

针对拱坝裂纹扩展问题,以某拱坝为例,建立了大坝-地基-库水系统的三维有限元模型.在此基础上,基于全耦合的拱坝-地基-库水模型,利用扩展有限元法(extended finite element methods,XFEM)对地震作用下的底缝开裂进行了模拟分析.研究中,在坝体上游底部设置了不同位置的人工短缝,以探讨拱坝在强震条件下的底缝开裂响应.结果表明:横缝削弱了坝体的整体性,增大了坝体的位移响应,但增设横缝可有效减小坝体的应力响应;在坝体底部设置人工短缝显著降低了坝踵的应力响应;拱坝的横缝对底缝开裂影响显著,能限制底缝的横向扩展,减少坝体的开裂损伤.

CFRP层合板单搭胶接接头胶板界面剥离强度仿真分析

基于异材界面奇异应力场理论,以CFRP层合板单搭胶接结构为对象,通过有限元和实验的方法分析了结构承载时板胶结合界面上出现的应力分布,锁定界面剥离强度关键区域,通过网格无关的有限元应力比值法提升仿真求解精度,最大限度还原板胶界面应力分布,着重探讨了多层各向异性CFRP板与传统均质材料在仿真过程和结果的差异,及搭接长度、胶层厚度、结构胶参数等对板胶界面应力分布及起裂点位置的影响,为板胶界面剥离应力的优化、胶接工艺的改进和单搭胶接接头强度的提升提供理论支撑。结果表明:各层参数不同的CFRP板胶界面承载时,剥离应力的最大处需由三个维度共同约束,其中两个维度的约束结果与均质材料相同,极值位于板胶界面垂直于拉伸方向的边缘,实际结构中失效的起始亦常见于此处,第三维度受层合板多层异性影响,该边缘上应力最大的点既不位于该边缘的中点也不位于界面角部,具体位置由材料参数和胶接结构共同影响。

输电塔钢管角钢组合节点承载能力模拟分析与计算方法研究

依托输电线路实际工程,选取输电铁塔主材与横担连接处钢管角钢组合节点为研究对象,采用数值软件ABAQUS建立了钢管角钢组合节点精细化有限元模型,并通过静力加载试验验证了有限元模型的合理性;随后模拟分析了组合节点的传力机理和应力分布,明确了不同参数对组合节点受力特性的影响规律。结果表明,钢管、中环板与竖向板相交区域出现应力集中且最大应力达到屈服强度,并向四周扩散且逐渐减小,中环板和竖向板的厚度是影响组合节点极限承载力的关键因素。采用有效宽度法计算了中环板和竖向板的承载能力,建立了不同板件的内力占比计算式,基于此,提出了组合节点承载力计算方法。所提出的极限承载力计算方法与数值模拟结果的误差在13%以内,验证了计算方法的合理性,可为钢管角钢组合节点的结构设计与分析提供参考。

采用钢管榫卯节点连接的节段预制拼装桥墩抗震性能研究

为分析钢管榫卯节点连接构造对节段预制拼装桥墩抗震性能的影响,以福建省某互通立交桥匝道桥为背景进行研究。首先进行钢管榫卯节点连接的足尺节段预制拼装桥墩试设计,采用MIDAS Civil软件建立实桥模型,对试设计的足尺节段预制拼装桥墩开展静力承载力验算;然后按1∶3.75比例缩尺,设计、制作1根整体现浇桥墩(RC)试件和1根钢管榫卯节点连接的节段预制拼装桥墩(PSBP-MTJ)试件,开展拟静力试验;最后对比分析两试件的破坏模式、滞回曲线、骨架曲线与延性、累积滞回耗能、刚度退化与残余位移。结果表明:两试件的破坏模式类似,均为整体压弯型破坏,PSBP-MTJ试件塑性铰区因墩底灌浆套筒的存在而上移;两试件滞回曲线饱满无捏缩,耗能能力相当;PSBP-MTJ试件水平承载能力较RC试件提高约19%;PSBP-MTJ试件的拼装节段之间无剪切滑移出现,预应力筋延缓了其刚度退化,显著提高了其自复位性能,其残余位移仅为RC试件的67%,且残余位移与最大位移比值显著小于未采用无粘结预应力筋连接试件。

后摆心潜入式喷管柔性接头力学特性数值仿真

针对后摆心潜入式喷管柔性接头在燃气压力与摆动联合载荷下,弹性件与增强件的力学特性计算问题,建立了对称刚体-柔性体结合的几何模型;采用了有限元方法,获取了柔性接头在燃气压力、摆动载荷及联合载荷下应力、弹性比力矩分布规律。研究表明:随着燃气压力增大,弹性比力矩降低;随摆角增大,弹性比力矩增大。文中的数值仿真方法,可以应用于柔性接头力学特性的计算,为柔性接头强度的安全性评估提供指导。

SnAgCu/SnBi混装焊点的热循环可靠性研究

Sn-Bi和Sn-Ag-Cu混装焊点是利用低熔点的Sn-58Bi锡膏将高熔点的Sn-3.0Ag-0.5Cu(SAC305)的小球回流焊接在印制电路板(PCB)上,从而实现高温芯片的低温焊接工艺.文中研究了SnAgCu/SnBi混装焊点在热循环条件下的可靠性并通过有限元模拟揭示了混装焊点热循环可靠性的应变演变行为.热循环试验发现混装焊点的寿命要优于SAC305无铅焊点.有限元计算表明,结构混装焊点内SnBi钎料层的添加能够减小最大非弹性应变范围,从而提升混装焊点的热循环可靠性.

面向电流信息与模态分析的工业机器人关节振动求解研究

在工业机器人健康监测中,针对需采用振动传感器对机器人各关节逐一检测而引起测试成本剧增问题,提出一种基于电流信息与模态分析的关节振动求解方法,该方法可由关节电流经模态转换直接获取关节振动信息。首先,将关节电流信息引入,建立基于关节电流的工业机器人振动模型。然后,由有限元法进行模态分析获取机器人前6阶振型,便于后续模态试验优化测点布置。接着,在力锤激励试验中,基于优化后的测点,测取工业机器人系统质量、刚度等模态参数。之后,将驱动力矩与模态参数带入该模型进行龙格库塔数值求解,得到机器人各关节振动响应。最后,在指定关节转角运行的关节单动与联动实测振动数据验证了本文提出算法的正确性。

基于响应面法与MOGA算法的竹集成材榫接合椅子节点力学分析及优化

竹集成材是符合“双碳”目标的可持续发展绿色材料,具有“以竹代木”的巨大潜力。本研究借助竹集成材优良材料性能,基于榫卯结构特性,以竹集成材榫接合椅子为例,运用有限元法(FEM)进行椅子静载荷及耐久性分析,探究竹集成材榫接合椅子及榫接合节点力学特性,搭建响应面模型求解竹集成材T型椭圆榫接合节点榫卯尺寸与其最大等效应力、总形变和最小安全系数的关系,并运用MOGA多目标遗传算法以形变最小化、安全系数最大化为优化目标,进行榫卯尺寸优化。结果表明:竹集成材榫接合椅子静载荷分析所得椅子最大等效应力为6.818 MPa,位于座面大边与椅后腿榫接合节点;最大等效应变值为4.245×10^(-3),位于椅子扶手与椅后腿榫接合节点;椅子发生的最大形变为4.433 mm,分布在椅子靠背位置。椅子耐久性分析所得最大等效应力及最大等效应变均位于椅子扶手与椅后腿榫接合节点,分别为4.999 MPa和3.113×10^(-3);椅子整体发生的最大形变为3.251 mm,位于椅子靠背上端。由竹集成材T型榫接合节点响应面分析可知,椭圆榫接合节点的最大等效应力及最大形变随着榫头厚度a及榫头长度l的增大而减小,安全系数随之增大,榫卯尺寸对T型榫接合节点力学强度的影响以榫头厚度a和榫头长度l为主,榫头宽度b影响不显著。运用MOGA算法优化竹集成材椭圆榫尺寸,优化结果与实际试验结果的相对误差为3.93%,相对误差较小,证明优化方法及结果有效。本研究为竹集成材椭圆榫的加工生产提供参考,并为竹集成材榫接合椅子的榫卯尺寸设计提供科学优化方法。

热循环条件下BGA叠层焊点可靠性研究及参数优化

构建叠层焊点最优结构参数,提高BGA叠层焊点热循环条件下的可靠性具有重要的意义。建立有限元模型,分析叠层焊点在热循环条件下应力应变,运用田口正交法和曲面响应法,将焊点的高度、直径、间距、阵列作为实验设计的变量,关键焊点最大等效塑性应变作为优化目标。结果表明:焊点阵列对优化目标的影响权重最大,优化后的BGA叠层焊点结构参数如下,田口正交法:单层焊点高度为0.38 mm,焊点间距为0.55 mm,焊点直径为0.44 mm,焊点阵列为8×8;曲面响应法:单层焊点高度为0.387 mm,焊点间距为0.573 mm,焊点直径为0.446 mm,焊点阵列为8×8。对优化前后的寿命进行预测,优化后的叠层焊点寿命约是优化前的3.75倍。

圆化离散单元法的改进及其在岩体断裂过程中的应用

为精确模拟岩体断裂的演化过程,将有限单元法与圆化多面体离散元法相结合,提出一种用于模拟断裂全过程的三维可变形圆化多面体离散单元法。为模拟块体的真实破坏状态,该方法将每个岩体颗粒都离散成有限单元,沿有限单元的边界嵌入无厚度节理单元,最后采用判断节理单元状态的方式来捕捉断裂过程产生的裂缝,岩体颗粒与断裂表面之间的接触相互作用通过圆化多面体离散元法求解。通过5个算例说明新方法的准确性和有效性,可用于模拟准脆性材料的断裂全过程,且能够捕捉裂缝萌生和扩展以及块体之间的碰撞和变形。

分缝护栏致空心板梁桥L型裂缝预应力控制方法研究

为提高护栏分缝桥梁的耐久性和承载力,以台金高速公路杨司高架桥预制空心板梁桥为背景,研究通过施加预应力控制因护栏分缝引起L型裂缝的有效性,并针对既有桥梁加固和新建桥梁设计提出通用的有效方法。采用Abaqus软件建立既有桥梁和新建桥梁的有限元模型,研究车道荷载作用产生的应力放大效应;分析预应力筋布置高度和长度对边梁梁底应力的影响及对既有桥梁护栏分缝导致的预应力损失;在此基础上,提出L型裂缝的预应力控制方法。结果表明:边梁应力放大系数随桥梁跨径和护栏高度的增加而增大,其取值范围为[1.42,2.14];预应力筋布置高度越低,边梁跨中梁底应力越大;预应力筋布置长度越短,既有桥梁梁底应力越大,对新建桥梁应力没有影响;分缝护栏对既有桥梁施加预应力产生损失,对新建桥梁不会产生预应力损失;在边梁跨中施加相应的预应力,可有效抵消跨中的应力集中效应,防止主梁跨中产生L型裂缝。

考虑结合面特性影响的机床整机有限元静力学分析模型

针对机床数字化设计中典型结合面建模精度误差较大的问题,提出了一种采用虚拟材料等效结合面静力学特性的方法,建立了考虑结合面特性影响的机床整机有限元静力学分析模型,并完成了相应的静刚度测试实验。首先,综合考虑了弹塑性变形机制和摩擦力的影响,提出了一种新的结合面法向和切向刚度的分析模型;其次,根据不同类型结合面的特点,采用虚拟材料模拟结合面的刚度特性,建立了刚度特性与虚拟材料弹性模量和泊松比的关系,并将其应用于精密数控机床整机的静刚度分析;最后,开展了整机工艺系统的静刚度测试实验,得到了主轴末端X、Y、Z三个方向的刚度分别为26.60 N/μm、41.87 N/μm和40.17 N/μm,并将其与仿真数据进行了对比。研究结果表明:不考虑结合面影响的模型相对误差将近17%,而考虑结合面影响的模型相对误差在5%以内,验证了考虑结合面特性影响的机床整机有限元静力学分析模型的有效性;采用虚拟材料等效结合面静力学特性的方法可作为机床数字化设计的一种可行的方法。