Finite element simulation of ball spinning of NiTi shape memory alloy tube based on variable temperature field

As a new attempt,ball spinning was used to manufacture the nickel-titanium shape memory alloy（NiTi SMA） tube at elevated temperature.The NiTi bar with a nominal composition of Ni50.9Ti49.1（mole fraction,%） was solution treated and was used as the original tube blank for ball spinning.Based on the variable temperature field and the constitutive equation,rigid-viscoplastic finite element method（FEM） was applied in order to simulate the ball spinning of NiTi SMA tube.The temperature field,the stress field,the strain field and the load prediction were obtained by means of FEM.FEM results reveal that there is a temperature increase of about 160 ℃ in the principal deformation zone of the spun part.It can be found from the stress fields and the strain fields that the outer wall of NiTi SMA tube is easier to meet the plastic yield criterion than the inner wall,and the plastic deformation zone is caused to be in a three-dimensional compressive stress state.The radial strain and the tangential strain are characterized by the compressive strain,while the axial strain belongs to the tensile strain.The variation of spinning loads with the progression of the ball is of great importance in predicting the stable flow of the spun part.

Three dimensional finite element analysis of anatomic distal radius Nitinol memory connector treating distal radius fracture

Objective: To study the memory biomechanical character of anatomic distal radius Nitinol memory connector (DRMC) in treating distal radius fracture. Methods: Establishing three dimensional model and finite element analysis, we calculated the stress in and around the fracture faces when distal radius fracture was fixated with DRMC. Results: Axial holding stress produced by holding part of DRMC on distal radius was 14.66 MPa. The maximum stress of holding part was 40-70 MPa, the minimum stress was 3-7 MPa,and the stress of compression part was 20-40 MPa. Conclusion: The distribution of stress produced by DRMC around the fracture line is reasonable, and axial holding stress can help stabilize fracture during earlier period. The existence of longitudal compression and memory effect can transfer fixated disused section into developed section and enhance fracture healing.

Prediction of grain scale plasticity of NiTi shape memory alloy based on crystal plasticity finite element method

Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.

Simulation of isothermal precision extrusion of NiTi shape memory alloy pipe coupling by combining finite element method with cellular automaton

In order to present the microstructures of dynamic recrystallization(DRX) in different deformation zones of hot extruded NiTi shape memory alloy(SMA) pipe coupling,a simulation approach combining finite element method(FEM) with cellular automaton(CA) was developed and the relationship between the macroscopic field variables and the microscopic internal variables was established.The results show that there exists a great distinction among the microstructures in different zones of pipe coupling because deformation histories of these regions are diverse.Large plastic deformation may result in fine recrystallized grains,whereas the recrystallized grains may grow very substantially if there is a rigid translation during the deformation,even if the final plastic strain is very large.As a consequence,the deformation history has a significant influence on the evolution path of the DRX as well as the final microstructures of the DRX,including the morphology,the mean grain size and the recrystallization fraction.

Finite Element Method on Shape Memory Alloy Structure and Its Applications

It is significant to numerically investigate thermo-mechanical behaviors of shape memory alloy(SMA)structures undergoing large and uneven deformation for they are used in many engineering fields to meet special requirements To solve the problems of convergence in the numerical simulation on thermo-mechanical behaviors of SMA structures by universal finite element software.This work suppose a finite element method to simulate the super-elasticity and shape memory effect in the SMA structure undergoing large and uneven deformation.Two scalars,named by phase-transition modulus and equivalent stiffness,are defined to make it easy to establish and implement the finite element method for a SMA structure.An incremental constitutive equation is developed to formulate the relationship of stress,strain and temperature in a SMA material based on phase-transition modulus and equivalent stiffness.A phase-transition modulus equation is derived to describe the relationship of phase-transition modulus,stress and temperature in a SMA material during the processes of martensitic phase transition and martensitic inverse phase transition.A finite element equation is established to express the incremental relationship of nodal displacement,external force and temperature change in a finite element discrete structure of SMA.The incremental constitutive equation,phase-transition modulus equation and finite element equation compose the supposed finite element method which simulate the thermo-mechanical behaviors of a SMA structure.Two SMA structures,which undergo large and uneven deformation,are numerically simulated by the supposed finite element method.Results of numerical simulation show that the supposed finite element method can effectively simulate the super-elasticity and shape memory effect of a SMA structure undergoing large and uneven deformation,and is suitable to act as an effective computational tool for the wide applications based on the SMA materials.

Three-Dimensional Simulations of RESET Operation in Phase-Change Random Access Memory with Blade-Type Like Phase Change Layer by Finite Element Modeling

An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67mA to 0.32mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.

Improving the data retention of phase change memory by using a doping element in selected Ge_2Sb_2Te_5

The crystallization characteristics of a ubiquitous T-shaped phase change memory(PCM) cell, under SET current pulse and very small disturb current pulse, have been investigated by finite element modelling. As analyzed in this paper, the crystallization region under SET current pulse presents first on the corner of the bottom electron contact(BEC) and then promptly forms a filament shunting down the amorphous phase to achieve the low-resistance state, whereas the tiny disturb current pulse accelerates crystallization at the axis of symmetry in the phase change material. According to the different crystallization paths, a new structure of phase change material layer is proposed to improve the data retention for PCM without impeding SET operation.This structure only requires one or two additional process steps to dope nitrogen element in the center region of phase change material layer to increase the crystallization temperature in this confined region. The electrical-thermal characteristics of PCM cells with incremental doped radius have been analyzed and the best performance is presented when the doped radius is equal to the radius of the BEC.

基于金属磁记忆的弯曲工字钢梁的力-磁效应

目前,基于金属磁记忆检测技术的受力状态表征及损伤评估应用广泛,但在受弯构件的检测中,弯曲长度及荷载作用位置对检测结果的影响尚不明确。为研究受弯构件的力-磁效应,本工作基于四点弯曲工字钢梁的磁记忆检测,采用考虑初始平面外弯曲和应力与磁化作用角度的力-磁耦合方法,通过COMSOL多物理场仿真软件进行了数值模拟研究,并结合有效场理论分析了钢梁弯曲长度对磁信号的影响,提出了表征损伤及荷载作用位置的磁特征参数。结果表明:检测线磁信号峰-峰值S在钢梁接近屈服状态时显著增大,并在钢梁处于承载能力极限状态时达到最大值;腹板检测线磁信号峰-峰值S_(w)在钢梁屈服和达到最大承载能力时分别随有效段长度的增加呈线性减小和以二次函数的规律减小,而下翼缘检测线磁信号峰-峰值S_(f)在钢梁屈服和达到最大承载能力时均随有效段长度的增加以二次函数的规律减小;根据磁特征参数S_(w)和S_(f)定义了磁损伤指数D和荷载作用系数S_(r),当钢梁所受外加荷载超过其最大承载能力的80%时,可根据D>0.5的特征对钢梁不安全的受力状态进行预警;荷载作用系数S_(r)与钢梁的剪跨比λ近似线性相关,可以表征荷载的作用位置。

Equal channel angular extrusion of NiTi shape memory alloy tube

As a new attempt, equal channel angular extrusion （ECAE） of nickel-titanium shape memory alloy （NiTi SMA） tube was investigated by means of process experiment, finite element method （FEM） and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.

集体记忆视角下的工业设施元素价值利用与设计

目的构建集体记忆视角下工业设施元素利用与设计方法,探索基于集体记忆的工业设施保护再利用设计路径,阐释文化遗产价值,完成文化遗产的记忆元素识别提取,将记忆元素植入到工业设施的再利用中,营造工业文化遗产过去生活场景,最终重塑工业集体文化记忆。方法通过调查分析相关基础资料,形成对文化遗产的记忆认知,进行记忆元素的提取转化,将记忆元素与工业设施的情景联系结合,从物质性与非物质性记忆元素两个角度对工业设施保护再利用进行设计研究。结果通过集体记忆视角构建了工业设施元素利用与设计方法,建立了地方归属感和文化认同感,完成了工业文化遗产的价值凸显、凝聚传承,实现了集体记忆的重塑和延续。结论工业设施保护再利用研究是以集体记忆重塑为目的,用集体记忆引导工业设施再利用设计,完成记忆元素对工业设施的设计植入,达成文化遗产的形态重构、功能植入,优化厂区布局,焕发厂区活力,最终构建地方认同、完成记忆重塑,为工业设施保护再利用研究提供研究视角。

稀土Y元素对CuAlMn形状记忆合金晶粒细化及其力学性能的影响

CuAlMn形状记忆合金具有优良的耐热稳定性和高阻尼特性,在多种领域有着明确的目标需求,然而,晶粒粗大易导致沿晶断裂,严重弱化了合金的力学性能。为改善合金力学性能,引入了稀土Y元素,采用电弧熔炼吸铸炉制备了Cu-11.36Al-5Mn-xY(x=0~3,质量分数/%,下同)系列铸态合金,又经固溶时效对合金微观组织进行了调控和均质化。采用DSC、XRD、金相和SEM对合金的相变、物相、微观组织结构进行了表征。通过显微硬度计和万能材料试验机测试了合金的硬度和力学性能。结果表明,Y元素添加可有效细化CuAlMn合金晶粒,晶粒尺寸从数百微米下降至10μm左右,同时伴随着大量网格状含Y析出相沿晶析出,冷却过程中晶粒形核区的增多和生长受到抑制是晶粒细化的主要因素。合金硬度随Y元素添加量的增大而升高,这与合金中大量含Y硬脆相的析出有关,Y含量越高,析出相体积分数越高,此外,固溶时效态样品硬度高于铸态样品,源于固溶时效态样品析出相在整个基体内的分布和更高的析出相体积分数。合金的压缩强度和拉伸断裂强度在Y元素含量为0.1%~0.4%时得到明显提升,其强化机制可通过细晶强化、沉淀强化和固溶强化来理解。合金压缩断裂应变在Y元素含量为0.4%时达到最大,断后伸长率在Y元素含量为0.1%时达到最大,其变化趋势与晶粒细化和沉淀析出相的耦合效应有关。

形状记忆合金在辅助器具和康复设备中的应用

背景:随着科技的不断进步,新技术和新方法的引入将为形状记忆合金在辅助和康复领域的应用带来更多的可能性和新的突破。目的:通过综述形状记忆合金在辅助器具和康复设备中的应用现状,讨论它们的主要方法、技术和结果,归纳总结并提出建议,希望形状记忆合金能够不断优化,为辅助和康复设备的发展带来更多新的变革。方法:通过计算机检索万方、Pub Med和Web of Science数据库,以“形状记忆合金,应用进展,正畸,矫形,假肢,康复,特性,植入,力学性能,镍钛记忆合金,驱动”为中文检索词,以“Shape memory alloys,Application,Orthodontics,Orthopedic,Prosthetics,Rehabilitation,Properties,Implant,Drive,Progress,Prostheses”为英文检索词,最终纳入91篇文献进行综述。结果与结论:(1)形状记忆合金具有耐腐蚀性、耐磨性、生物相容性、抗疲劳性和抗扭结性等特性,相比其他传统材料(不锈钢、钛合金、钴铬合金等)具有更低的弹性模量且无生物毒性,适合作为假体长期植入体内。由于其具有形状记忆效应和优异的力学性能,遂主要作为驱动元件或作为连接设备和人体的桥梁应用于假肢、矫形器和康复设备中。(2)使用形状记忆合金驱动元件能够减轻设备质量、消除噪声、容易操作、便于携带和更好地辅助关节运动等,比起使用气动、液压和电气驱动方法的设备优势明显。(3)另外形状记忆合金在变形时能够产生恒久、稳定的应力,相比不锈钢、钛合金和铝合金矫形器具有更高的材料回收率且不用频繁更换调整,所以在矫治畸形方面更具实用价值。(4)目前形状记忆合金在矫形器中应用最多,在镫骨假体中的临床应用效果最好。而由于技术及成本等的限制,形状记忆合金在假肢和康复设备中的应用较少,且缺乏对应用效果的大样本研究。(5)虽然形状记忆合金在辅助和康复领域得到了一定的发展,但仍存在许多问题:对形状记忆合金进行精准控制很难;形状记忆合金的冷却速度慢;无法对其变形速度进行控制;缺乏对不同性状形状记忆合金的对比研究和专家共识;形状记忆合金成本高,价格贵。(6)未来应注意开发新型形状记忆合金,增加对比性研究,采用新技术、新方法(如4D打印等)解决目前存在的问题,从而研发出高性能的辅助器具和康复设备。

基于机器学习的汽车吸能结构耐撞性智能预测方法

汽车零部件正向设计中,为快速预测所设计的吸能结构的碰撞吸能特性,以吸能盒为研究对象,通过有限元压溃变形仿真生成数据集,训练得到一种新的可识别几何结构和记忆时序特征的预测模型。模型通过基于图的编码器进行几何结构识别,采用长短期记忆网络和图卷积神经网络处理时序数据,并输出预测结果。对比表明:吸能盒压溃形态预测结果与有限元仿真结果一致,压溃变形量的预测精度可达95.33%,最大吸能值的预测精度可达99.98%。预测模型相较于有限元计算,其计算效率分别提高了174.5倍和210.5倍,可以快速准确地预测吸能盒的碰撞性能。

基于Bi-LSTM的浅层地下双孔洞探测技术

文章探究一种基于深度学习的浅层地下孔洞探测技术,以应对地下孔洞给桩基施工安全所造成的严重威胁。基于浅层地震反射波法的原理,采用基础施工过程中的桩锤激震作为激励源,通过在探测区域地表上布置少量加速度传感器采集孔洞反射信号,并将反射信号作为深度学习的输入,以输出孔洞信息,建立一种新型的智能孔洞探测方法。结果表明,双向长短期记忆神经网络(bidirectional long short-term memory neural network,Bi-LSTM)的预测模型对于地下双孔洞的工况具有较高的识别准确率,在容许误差为2 m的情况下,孔洞位置和直径的预测准确率可达95.3%。该研究验证了基于深度学习的多孔洞探测技术的可行性,有望为施工前期土层地质状况的评估提供技术保障。

基于改进SSA-LSTM模型的双曲度板材成形回弹预测

为了准确预测双曲度板材成形回弹量,控制板材加工成形质量,利用ABAQUS有限元软件对板材成形回弹过程进行仿真,构建长短时记忆网络模型(LSTM)。针对麻雀搜索算法(SSA)容易陷入局部最优的问题,提出基于Circle混沌映射、反向学习、高斯与柯西变异扰动的改进麻雀搜索算法,优化LSTM模型的学习率、迭代次数、隐藏层神经元个数,并将模型与BP神经网络模型、LSTM模型和普通SSA-LSTM模型进行对比分析。结果表明,该模型对双曲度板材成形回弹预测达到整体最优预测效果,具有一定有效性和可行性。

变形承载一体的基于形状记忆合金片状致动器的智能复合材料结构性能分析

在形状记忆合金片上引入预应变可以制备成一个受热可回复的片状致动器,将其表面粘贴在复合材料结构表面便可以得到一个集承载和变形一体化的智能复合材料结构。本文主要聚焦于智能复合材料结构承载过程中的变形问题,通过有限元分析的方法对智能复合材料结构在承载时的受热致动变形能力和在受热致动变形之后的承载能力两个问题进行了分析研究。分析结果表明:智能复合材料结构在承载过程中仍然能够顺利变形,但是其变形过程中的胶层应力会受到载荷大小的影响,且相同载荷下受热致动过程加载时的胶层应力与加载过程中受热时的胶层应力相比会更大。

钢横梁SMA蜂窝结构加劲肋面外疲劳性能研究

针对某公路钢桁架桥工字型横梁腹板加劲肋下方出现纵向开裂问题,基于形状记忆合金(SMA)、蜂窝结构和波折腹板特性给出6种加劲肋方案:(1)横梁为原桥直腹板工字钢形状,有腹板间隙;(2)栓接钢板加固;(3)加劲肋为蜂窝结构,横梁为工字钢直板形状;(4)加劲肋为蜂窝结构,腹板为正弦波纹形状;(5)加劲肋为蜂窝结构,腹板为折线形状;(6)加劲肋下部抵住下翼缘板,不焊接。通过三维有限元数值模拟对不同加劲肋结构形式、有无SMA的蜂窝结构加劲肋腹板面外变形、疲劳应力幅和扭转角进行了比较研究。结果表明:腹板间隙处出现较大应力集中与变形扭转;栓接钢板加固、蜂窝结构加劲肋直腹板的抗面外变形疲劳效应效果显著,应力幅与位移都减少80%以上,蜂窝结构加劲肋直腹板相比于栓接钢板加固在提升抗扭转效应基础上钢材用量节约74.07%;蜂窝结构加劲肋折线腹板形式和加劲肋抵住下翼缘板方案不能有效加强抗扭刚度;使用SMA材料更有利于减少面外变形疲劳效应,最大应力幅减少可达77.86%,最大横向位移减少达到33.33%。综上所述,蜂窝结构加劲肋以更少的成本来增强横梁腹板抗面外变形与抗扭刚度。

球墨铸铁管道磁记忆应力检测的数值模拟及验证研究

目的针对当前磁记忆应力检测方法研究较少的问题,建立适用于球墨铸铁管道的磁记忆应力检测方法,并进行合理验证。方法采用解析计算和有限元仿真模拟2种方法,建立球墨铸铁管道磁记忆应力检测模型,研究应力值和传感器提离值对球墨铸铁管道磁记忆信号的影响,并通过搭建球墨铸铁管道磁记忆应力检测实验平台进行模型验证。结果轴向峰值和径向零点位置不随应力变化发生偏移,信号强度随应力值增加呈线性变化。球墨铸铁管道磁记忆信号随着提离值的增加呈指数衰减,在2.5~4 mm内,提离值的衰减近似呈线性,信号波动较小,适用于信号采集。结论2种方法的结果较为吻合,球墨铸铁管道磁记忆应力检测实验平台的结果与数学仿真计算具有很好的一致性,这些模拟和实验结果均验证了基于解析计算和有限元建立的2种磁记忆应力检测模型的数值合理性。

面向SOT-MRAM的磁屏蔽仿真设计与优化

磁随机存储器由于其高读写速度、接近无限次的读写次数和低功耗等优异特性受到越来越多的关注。磁随机存储器采用磁场方向来操作存储位,外部磁场很容易对磁结产生干扰导致读写错误的发生。因此采用磁屏蔽封装结构来减小外部磁场对存储器的影响具有重要意义。本文针对第四代自旋轨道矩磁随机存储器的磁屏蔽优化设计进行研究,根据自旋轨道矩磁随机存储器的面内磁场敏感特性,采用平行式磁屏蔽封装形式,建立了磁屏蔽有限元模型,分析了磁屏蔽结构因素(间距,面积和厚度)和磁饱和现象对磁屏蔽效果的影响,为磁存储器磁屏蔽设计提供了新思路。

联合CNN与LSTM神经网络的斜拉索损伤识别方法

索结构中,拉索响应与损伤之间处于高度非线性状态,常规数学模型对拉索损伤识别普遍存在精度欠佳问题。针对该问题创建了七丝钢绞线的拉索有限元模型,提出基于组合指标的CNN&LSTM神经网络损伤识别方法。借助该拉索有限元模型模拟4类损伤工况,分类提取响应。对比分析总能量变化率、频率、能量比偏差与能量比方差等不同指标对损伤程度的表征,建立能量与频率相结合的组合损伤指标。对比分析联合CNN&LSTM神经网络面对各损伤指标,以及传统中单独的卷积神经网络(CNN)与长短记忆法(LSTM)针对组合损伤指标的识别结果。研究发现,基于组合指标的联合CNN&LSTM深度学习网络的拉索损伤识别准确率最高,达到96.67%,高于CNN的86.63%及LSTM的82.15%,表明CNN&LSTM在斜拉索损伤识别应用中具有较大潜力。