Finite element simulation for mechanical response of surface mounted solder joints under different temperature cycling

Nonlinear finite element simulation for mechanical response of surface mounted solder joint under different temperature cycling was carried out. Seven sets of parameters were used in order to evaluate the influence of temperature cycling profile parameters. The results show that temperature cycling history has significant effect on the stress response of the solder joint. Based on the concept of relative damage stress proposed by the authors, it is found that enough high temperature holding time is necessary for designing the temperature cycling profile in accelerated thermal fatigue test.

Finite Element Simulation of Processes Involving Moving Heat Sources. Application to Welding and Surface Treatment

A wide range of welding and surface treatment processes involve the use of a heat source which is moving at a constant speed over the component. The numerical simulation of such processes implies a transient analysis using a very refined mesh in order to follow properly the path of the heat source. The 3D-mesh size can be very large if one consider the welds length or the heat-treated surface size in industrial components. To reduce the computational time to acceptable values, several techniques have been investigated. The first type is to use analytical methods such as Rosenthal equations. The second type of solutions consists in performing a transient analysis using adaptive meshing. But, for a large proportion of the involved processes, practical experience demonstrates the existence of quasi steady state conditions over the major part of the heat source path. Numerical algorithms have therefore been developed to directly compute the steady temperature, metallurgical phase proportion and stress distributions. This paper gives a general overview of the different numerical methods used to simulate welding and surface treatment processes with a special emphasis on the steady state calculation. The benefits and limitations of each of them are discussed and applications are presented.

Damage prediction for magnesium matrix composites formed by liquid-solid extrusion process based on finite element simulation

A damage prediction method based on FE simulation was proposed to predict the occurrence of hot shortness cracks and surface cracks in liquid-solid extrusion process.This method integrated the critical temperature criterion and Cockcroft & Latham ductile damage model, which were used to predict the initiation of hot shortness cracks and surface cracks of products, respectively.A coupling simulation of deformation with heat transfer as well as ductile damage was carried out to investigate the effect of extrusion temperature and extrusion speed on the damage behavior of Csf/AZ91D composites.It is concluded that the semisolid zone moves gradually toward deformation zone with the punch descending.The amplitude of the temperature rise at the exit of die from the initial billet temperature increases with the increase of extrusion speed during steady-state extrusion at a given punch displacement.In order to prevent the surface temperature of products beyond the incipient melting temperature of composites, the critical extrusion speed is decreased with the increase of extrusion temperature, otherwise the hot shortness cracks will occur.The maximum damage values increase with increasing extrusion speed or extrusion temperature.Theoretical results obtained by the DeformTM-2D simulation agree well with the experiments.

Treatment of discontinuous interface in liquid-solid forming with extended finite element method

Extended finite element method(XFEM) is proposed to simulate the discontinuous interface in the liquid-solid forming process.The discontinuous interface is an important phenomenon happening in the liquid-solid forming processes and it is difficult to be simulated accurately with conventional finite element method(CFEM) because it involves solid phase and liquid phase simultaneously.XFEM is becoming more and more popular with the need of solving the discontinuous problem happening in engineering field.The implementation method of XFEM is proposed on Abaqus code by using UEL(user element) with the flowchart.The key is to modify the element stiffness in the proposed method by using UEL on the platform of Abaqus code.In contrast to XFEM used in the simulation of solidification,the geometrical and physical properties of elements were modified at the same time in our method that is beneficial to getting smooth interface transition and precise analysis results.The analysis is simplified significantly with XFEM.

Numerical simulation of materials-oriented ultra-precision diamond cutting:review and outlook

Ultra-precision diamond cutting is a promising machining technique for realizing ultra-smooth surface of different kinds of materials.While fundamental understanding of the impact of workpiece material properties on cutting mechanisms is crucial for promoting the capability of the machining technique,numerical simulation methods at different length and time scales act as important supplements to experimental investigations.In this work,we present a compact review on recent advancements in the numerical simulations of material-oriented diamond cutting,in which representative machining phenomena are systematically summarized and discussed by multiscale simulations such as molecular dynamics simulation and finite element simulation:the anisotropy cutting behavior of polycrystalline material,the thermo-mechanical coupling tool-chip friction states,the synergetic cutting responses of individual phase in composite materials,and the impact of various external energetic fields on cutting processes.In particular,the novel physics-based numerical models,which involve the high precision constitutive law associated with heterogeneous deformation behavior,the thermo-mechanical coupling algorithm associated with tool-chip friction,the configurations of individual phases in line with real microstructural characteristics of composite materials,and the integration of external energetic fields into cutting models,are highlighted.Finally,insights into the future development of advanced numerical simulation techniques for diamond cutting of advanced structured materials are also provided.The aspects reported in this review present guidelines for the numerical simulations of ultra-precision mechanical machining responses for a variety of materials.

Numerical study of three-dimensional free surface dynamics

The dynamic problem of three-dimensional free surface is numerically studied in this paper. The ALE （Arbitrary Lagrange-Euler） kinematic description is introduced into the control equation system. The ALE description method is used to track free surface. Accurate formulations for calculating the normal vector on the free surface are presented. The discrete numerical equations by finite element method are developed by Galerkin weighted residual method. The boundary condition about free-surface tension is represented in the form of weak integration that can be computed by a differential geometry method derived in the present paper. The effect of contact angle is incorporated in the numerical algorithm. Furthermore, the numerical computations are performed and the comparison between computational and analytical results validated the effectiveness of the method. The results of this paper provide a fundamental understandings of the dynamics of liquid free surfaces, in which the surface tension and contact angle boundary conditions are taken into account. Finally, numerical simulation of largescale amplitude sloshing of liquid in a cylindrical container is performed and a numerical analysis of the effect of an annular ring-shaped rigid damping baffle on liquid sloshing oscillations in a cylindrical tank is also carried out.

Stability and reliability of pit slopes in surface mining combined with underground mining in Tonglushan mine

Slope stability is of critical importance in the process of surface-underground mining combination. The influence of underground mining on pit slope stability was mainly discussed, and the self-stabilization of underground stopes was also studied. The random finite element method was used to analyze the probability of the rock mass stability degree of both pit slopes and underground stopes. Meanwhile, 3D elasto-plastic finite element method was used to research into the stress, strain and rock mass failure resulting from mining. The results of numerical simulation indicate that the mining of the underground test stope has certain influence on the stability of the pit slope, but the influence is not great. The safety factor of pit slope is decreased by 0.06, and the failure probability of the pit slope is increased by 1.84%. In addition, the strata yielding zone exists around the underground test stope. The results basically conform to the information coming from the field monitoring.

Influence of Punch Shape on the Fracture Surface Quality of Hydropiercing Holes

Three different punches are designed for the hydropiercing experiments and finite element simulations are conducted by finite element program ABAQUS-3D to investigate the influence of punch shape on the fracture surface quality of hydropiercing holes. The results show the fracture burrs are not obvious punched by all the three punches. The collapse punched by the round punch is a little larger than the others. The fracture surface quality punched by the round punch is good with larger smooth zone and the interface between smooth zone and tear zone is even with large gradient. The size of the smooth zone is larger and the interface between smooth zone and tear zone is uneven with large gradient punched by the flat punch. The size of the smooth zone is smaller and the size of the tear zone increases from the first fractured to the last fractured punched by the inclined punch.

Research on Surface Roughness of Supersonic Vibration Auxiliary Side Milling for Titanium Alloy

The processed surface contour shape is extracted with the finite element simulation software.The difference value of contour shape change is used as the parameters of balancing surface roughness to construct finite element model of supersonic vibration milling in cutting stability domain.The surface roughness trial scheme is designed in the orthogonal test design method to analyze the surface roughness test result in the response surface methodology.The surface roughness prediction model is established and optimized.Finally,the surface roughness finite element simulation prediction model is verified by experiments.The research results show that,compared with the experiment results,the error range of the finite element simulation model is 27.5%–30.9%,and the error range of the empirical model obtained by the response surface method is between 4.4%and 12.3%.So,the model in this paper is accurate and will provide the theoretical basis for the optimization study of the auxiliary milling process of supersonic vibration.

Effect of Polymer Network Morphology on the Performance of Polymer Dispersed Liquid Crystal (PDLC) Composite Films

The effects of the morphologies of liquid crystal (LC) droplets left in polymer network on the performance of polymer dispersed liquid crystal composite films were investigated.By adjusting the relative content range of the crosslinking and diluents,the morphologies of polymer network can be changed.Therefore,the properties of PDLC composite films with imparity polymer morphologies were obtained by experiments and the finite element simulation.Results of the experimental and finite element simulation showed that the electro-optical properties of PDLC composite films were inversely proportional to the domain size of the polymer network and the mechanical properties were proportional to the domain size of the polymer network.

基于相变材料的混凝土吊罐温控数值模拟研究

为保证混凝土吊罐在垂直运输时其内部混凝土的温度,采用相变石蜡作为吊罐温控措施,通过Fluent软件探究了不同季节和不同相变石蜡厚度下混凝土温度变化情况。结果表明:在不同季节,采用相变石蜡作为吊罐温控措施,可有效控制其内部混凝土温度的波动;在冬季环境中,当相变石蜡厚度小于40 mm时,混凝土内外温度差减小有限,消峰填谷效果不理想;在夏季环境中,随着相变石蜡厚度的增加,混凝土表面最大温度的降低程度呈现先增大后减小的趋势,当相变石蜡厚度为20 mm时,混凝土表面温度达到最低。

基于响应面法的轻质尾翼均匀挤压成形数值模拟及模具结构优化

针对轻质镁合金尾翼正挤压成形金属流动不均匀和力学性能各向异性大的问题,提出一种可调控金属均匀流动的金属蓄料池模具结构。基于Deform-3D有限元模拟分析,采用Box-Behnken响应曲面法以金属蓄料池结构参数:深度h、池壁距尾翼芯部型腔长度D 1、池壁距翼片型腔长度D 2和池壁与翼片型腔之间夹角α为变量,建立出模口金属流速均方差和成形载荷与金属蓄料池结构参数之间的响应关系。响应曲面分析结果表明:最佳的金属蓄料池结构参数为h=7 mm,D 1=13 mm,D 2=6 mm,α=11°。采用优化后的模具结构参数进行模拟验证和物理试验,金属流动不均匀和力学性能各向异性均得到改善,并成功试制出形状尺寸和力学性能指标满足要求的尾翼形零件。

功率循环试验中结温条件对IGBT器件失效模式的影响

为了探究功率循环试验中结温条件对绝缘栅双极型晶体管(IGBT)器件失效模式的影响及其失效机理,以理论分析为出发点,通过大量功率循环试验进行对比验证,基于瞬态热阻抗曲线建立了准确的三维有限元模型,并仿真分析了相关失效机理。仿真及试验结果表明,键合线失效只受结温波动的影响;焊料老化受结温波动和最大结温的影响。增加结温波动会增加键合线、焊料所受应力,而提高最大结温会影响焊料的材料特性,加速其蠕变过程。研究成果解决了解析寿命模型难以表征失效机理的问题,并为失效模式的分离提供新的研究思路。

水位升降和降雨联合作用的岸坡流固耦合及失稳机理分析:以贵州平塘六硐南岸滑坡为例

为探讨涉水滑坡受水位升降及降雨作用变形机制及稳定性影响,以贵州平塘六硐南岸滑坡为研究对象,通过野外调查及现场监测,分析滑坡灾害产生的地质背景和变形特征。基于非饱和渗流理论和极限平衡分析,运用有限元软件Geo-studio,计算滑坡在673~685 m水位波动和降雨作用不同工况组合下的稳定系数,得到渗流场、应力场和位移场的变化规律,探明滑坡变形迹象及破坏机制。结果表明:该滑坡累计位移曲线呈现“阶跃状”特征,变形与河流水位变化、强降雨在时间上存在对应关系;雨强增大会降低滑坡稳定性,雨停滞后一定时间稳定性恢复;水位上升和下降,分别会使坡体稳定性增加和降低,且升降速率越大,稳定性变化程度越明显;水位下降和降雨联合作用为最不利工况,正是因为2020年7—9月坡体历经2次最不利工况,导致滑坡复活并且变形加剧。研究成果可为山区河岸滑坡防灾减灾提供一定参考。

翘曲板材三维重构及智能化压平的建模研究

为提高板材压平质量和效率,实现智能化压平,本文采用结构光相机获取翘曲板材点云数据,进行点云分割、点云去噪和点云精简等预处理,利用最小二乘法拟合重构了翘曲板材的三维曲面.采用微分几何的曲面理论计算得到板材的翘曲曲率,提出基于三维曲面特征的翘曲板材垫铁支点和压下点的优化方法,根据三点弯曲矫平理论得到了压力下和压下位移.翘曲板材三维轮廓的重构方法和翘曲曲率计算模型确定了垫铁位置和压下位置点优化原则,为翘曲板材智能化压平提供了理论模型.理论和实验的结果显示,重构的三维曲面与实际结果吻合,基于重构三维曲面数据计算的压平力与实测结果偏差大约为2.21%,初始平直度17.2 mm·m^(-1),压平矫直后减小为3.28 mm·m^(-1),结果准确,方法可行.

凹槽结构强化液滴合并弹跳的数值研究

目的 为研究凹槽结构对液滴合并弹跳现象的影响,提高液滴自弹跳的速度和能量转化率。方法 通过有限元方法模拟,研究了液滴在凹槽结构上的动态行为和槽深H、槽宽W及液滴尺寸对V型槽和矩形槽上液滴的弹跳速度、无量纲速度、表面能转化率、动量和总动能的影响。结果 凹槽内与槽外液滴间的合并弹跳包含液滴接触、产生液桥、三相线收缩和液滴弹离表面4个过程;宽高比相同时,液滴弹跳速度和表面能转化率均随液滴半径先增大后减小,凹槽宽高比为1.5,液滴合并弹跳半径为0.25 mm工况下表面能转化效率最高;矩形槽与V型槽,宽高比为1.5,液滴合并弹跳半径为0.25 mm时,液滴弹跳速度与表面能转化率随半径比先增大后减小,在半径比为1时达到峰值,二者表面能转化率最大值为27.87%和30.66%。槽宽恒定时,凹槽结构强化液滴合并弹跳存在最佳凹槽宽高比和最优弹跳半径,V型槽提升液滴弹跳效率比矩形槽高约12%。结论 合并后液滴撞击V型槽侧壁的反作用力使液滴旁瓣较矩形槽更早受到侧壁面抑制而发生回流,从而提升了其能量转化效率,减少了液滴的振荡损失与黏性耗散。研究结果在设计高效的自清洁功能表面、提高冷凝表面换热效率、预防和抑制换热器表面结冰、成霜等工业领域有重要的应用意义。

车用垂直腔面发射激光器模组整板金锡共晶焊接工艺

激光雷达及飞行时间(ToF)传感器中垂直腔面发射激光器(VCSEL)模组使用的银胶固晶工艺存在银迁移及硫化问题,亟需开发一种可靠性高并可量产的整板金锡共晶焊接工艺。以单颗焊接模式下单因素实验及正交实验为基础,借助Ansys热仿真工具,探究整板焊接中基板与压头之间合适的匹配温度。单因素控制变量实验发现,固晶芯片推力随共晶温度、压头行程、共晶时间的增加先增大后减小,正交实验得到最佳工艺参数为共晶温度320℃、压头行程500μm、共晶时间4 s。采用优选工艺参数500μm、4 s、270~350℃进行整板焊接,平均固晶芯片推力为821 N,相较银胶固晶工艺提高了139%。

有限元仿真在“过程设备设计”教学中的实践与探讨

“过程设备设计”是过程装备与控制工程专业的主干核心课程,该课程具有理论复杂、交叉学科多、实践性强等特点,课堂教学难度大。随着计算机技术和数值方法的迅速发展,尝试将有限元仿真应用到“过程设备设计”的课堂理论教学和专业课程设计,旨在激发学生的课堂学习热情、培养专业技能、提高综合素质。实践表明,有限元仿真能有效深化学生对于复杂理论公式推导的理解,显著改善了课堂教学氛围,获得了较好的教学效果。

SiCp/Al复合材料在常规与超声振动辅助条件的切削过程和表面形成的有限元分析

SiCp/Al复合材料是一种典型的难加工的材料,由于其基体中颗粒增强导致常规切削中加工质量差、切削阻力高、加工损伤高,机械加工性差,常规切削已不能满足加工要求。通过切削仿真,对比分析常规与超声振动辅助切削条件下复合材料的切削过程、SiC颗粒的损伤特性、工件的表面形貌与亚表面损伤。结果表明,相比于常规切削,超声振动辅助切削可以提高复合材料的表面完整性,减少复合材料的亚表面损伤,并且能够提高工件的表面质量。