超弹性NiTi合金率相关相变图案演化模拟

基于超弹性NiTi合金薄板在不同温度下的拉伸实验结果,采用三段线性弹塑性本构模型,通过热物理常数等效法考虑相变潜热对温升的影响,利用有限元软件ABAQUS对相变图案演化进行模拟,揭示相变图案演化的率相关性机理。模拟结果表明:超弹性NiTi合金在拉伸过程中发生应力诱发马氏体相变,宏观表现为局部相变带的萌生、扩展与合并;由于相变潜热的释放,相变带的萌生伴随着局部温升,温升的峰值与加载应变率密切相关;局部相变带与加载方向成一定夹角,角度为50°~65°;随着加载速率增加,试样从等温向绝热状态转变,相变应力与局部温升随之增加,相变更容易在低温区域萌生,导致相变带数量不断增加;模拟的超弹性NiTi合金在不同应变率下的相变图案及温度场演化与实验结果吻合较好,为阐明该合金的相变局部化演变过程提供了参考。     

基于共振测量和有限元仿真的材料常数识别

利用共振测量和有限元仿真计算，在一个以材料弹性常数为控制变量的非线性优化过程中，极小化测量与计算了圆柱形试件的固有频率，从而间接地识别出各向异性合金材料的弹性常数，给出铁基合金PM2000在室温以及镍基单晶合金CMSX6，CMSX4，SSR99和MC2和20－1200℃温区弹性常数的识别结果。     

NiTi合金(B2,B19’和R相)键合特征与弹性性质的第一性原理研究

运用第一性原理方法计算NiTi合金三种相结构(B2、B19’和R相)的电荷密度、态密度、Mulliken布居、弹性常数,在此基础上探究NiTi合金的键合特征、弹性性质及其内在联系。计算结果表明NiTi合金主要成键类型是金属键,其次还包括共价键和离子键。离子键主要由Ti原子向Ni原子转移少量电荷形成,共价键主要由Ni-3d和Ti-3d的轨道杂化形成,此外B19’和R相中Ni-Ni原子间存在电子云重叠也具有共价键特征。弹性性质计算表明三种相结构的NiTi合金均为延性材料,并具有不同程度的弹性各向异性特征。延性强弱顺序依次为B2RB19’,弹性各向异性程度的强弱顺序为B19’B2R。材料的延脆性和弹性各向异性主要与合金中共价键、金属键的特征和强度有关。金属键具有无方向性特征,金属键越强材料的延性性能会越强;共价键具有方向性特征,共价键越强,同时金属键越弱,则材料的弹性各向异性的程度会越高。本研究揭示了NiTi合金在B2→R→B19’马氏体相变过程中键合特征和弹性性质的变化情况,对NiTi合金器械的设计和应用具有重要的参考意义。     

新型稀土磁致伸缩材料Tb0.27Dy0.73Fe1.95的各向异性参数研究

全面测量了《110》轴向取向的Tb0.27Dy0.73Fe1.95(商品名为TDT-110)超磁致伸缩材料的各向异性常数.利用超声波穿透法测量在零磁场下的各向异性弹性常数Cij,用振动样品磁强计测量了该材料的各向异性磁导率μ11和μ33,用磁致伸缩测量仪测量了该材料的各向异性微分磁致伸缩应变常数d.     

纤维增强复合材料动态性能参数的识别方法

构造了一种纤维增强复合材料等效动态性能本构模型。根据经典层板理论分别推导出了显含弹性常数和显含阻尼系数的纤维增强复合材料层板的刚度矩阵和等效阻尼矩阵。利用模态试验方法, 得出了弹性常数、等效阻尼系数与层板振动模态之间的显式关系。通过识别本构方程中的等效阻尼系数, 可以方便地推导出任意铺层数和任意铺层角度下层板的等效阻尼矩阵。算例分析表明, 利用此方法识别出的弹性常数和等效阻尼能够满足工程精度要求。      

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

聚氨酯弹性体隔板夹层结构的等效参数计算

针对聚氨酯弹性体的隔板夹层结构,阐述了多种不同的等效参数计算方法,并对等效参数进行计算。首先讨论和计算了不考虑结构剪切变形时的整体结构等效参数计算方法,将整体夹层结构等效为正交各向异性薄板,给出了考虑夹芯抗弯刚度的整体刚度系数表达式。其次,在考虑夹层结构夹芯存在剪切变形的情况下,推导了由分隔隔板和聚氨酯弹性体组成的夹芯胞元的等效弹性常数;最后,使用基于应变能密度等效分析的有限元方法对夹芯胞元等效弹性常数进行计算,并与理论分析结果进行对比,二者误差在10%以内。     

建筑膜材料双轴向拉伸弹性常数的估算方法

以机织物增强建筑膜材料为对象,研究了通过单轴向拉伸试验来获取双轴向拉伸弹性常数的方法。根据膜材料双轴向拉伸弹性模量的确定方法,以二维正交各向异性材料的本构关系为基础,以膜材料经纬向拉伸应力比为设定加载参数,导出了机织膜材料单轴向和双轴向拉伸弹性模量之间的关系,提出了采用单轴向拉伸弹性常数估算建筑膜材料双轴向拉伸弹性常数的方法。通过参考文献中对GF/PTFE和PVDF1202T膜材料拉伸试验的测试结果,验证研究所提出方法的适用性。结果表明,在工程实践中利用单轴向拉伸试验来获得膜材料双轴向拉伸弹性模量是可行的。     

用环形试样测定软磁材料磁各向异性的研究

采用趋近饱和定律测定了纳米晶合金环形试样有效磁各向异性常数＜K＞.为了对比测量的准确度,同时测试了传统的晶态坡莫合金环形试样的磁晶各向异性.结果表明,用环形试样可以完成对低矫顽力的软磁材料进行磁各向异性的测定.     

纳米晶软磁合金环形试样有效磁各向异性的研究

采用趋近饱和定律首次测定了纳米晶合金环形试样有效磁各向异性常数〈K〉.为了对比测量的准确度,同时测试了传统的晶态坡莫合金环形试样的磁晶各向异性.结果表明,用环形试样可以完成对低矫顽力的软磁材料进行磁各向异性的测定.     

形状记忆合金超弹性分段线性模型及其阻尼特性

建立简单有效的本构关系模型是形状记忆合金（SMA）工程应用和理论分析的一个必要条件。考虑相变过程中马氏体含量的影响,对SMA非线性本构关系进行简化,建立了SMA超弹性应力应变关系的分段线性模型。以此为基础,给出了损耗因子等特性参数计算表达式,并探讨了特性参数随应变幅值、温度等变化的规律,最后应用于一种常见的振动模型,考察了影响其隔振性能的因素。结果表明：应变幅值是影响SMA耗能能力的主要因素;并联弹簧的刚度会对SMA的作用效果产生影响。     

Vibrations of plates with superelastic shape memory alloy wires

The article illustrates an approach to the passive vibration control of thin plates utilizing prestressed superelastic shape memory alloy (SMA) wires. The SMA wires can freely slide within protective sleeves that are either embedded within the structure or bonded to its surface. The vibration control mechanism combines an effective continuous elastic foundation representing the support provided by SMA wires to the structure with the energy dissipation as a result of the hysteresis occurring in the wires. The other approach to the vibration control employs superelastic wires attached to the structure at discrete points. The mathematical formulation of the problem presented in the article can be adopted for a rigorous computational analysis. In particular, a closed form expression is obtained for the loss factor in large aspect ratio plates supported at the midspan by a system of parallel SMA wires. As follows from numerical examples presented for such plates, the proposed method offers a significant damping, far exceeding that observed in conventional engineering structures.     

形状记忆合金超弹性本构关系的神经网络模型

通过试验，研究了受过循环变形、具有稳定超弹性变形性能的形状记忆合金丝在拉伸到不同应变幅值条件下卸载的超弹性变形行为。根据试验测得的结果，提出了基于神经网络的形状记忆合金超弹性本构关系模型，并把模型计算的结果和实验数据进行了比较分析，结果表明，该模型具有很高的精度。该模型避免了已有模型在参数确定上的困难，具有一定的工程应用价值，为建立形状记忆合金本构模型提供了一个新的思路。     

基于形状记忆合金的X形板阻尼器的力学模型

根据超弹性形状记忆合金（SMA）的分段线性化本构关系,建立了X形SMA板式阻尼器的力学模型;通过MATLAB程序进行数值模拟,绘制了X形SMA板的阻尼力滞回曲线,并研究了位移幅值、温度、形状尺寸对阻尼器基本特征参数（等效割线刚度、单位循环消耗的能量、等效阻尼比）的影响。结果表明：X形SMA板式阻尼器具有“旗帜”形的滞回曲线,耗能较小,但复位能力好;随位移幅值增加,耗能力和等效阻尼比增加,等效割线刚度降低,温度的影响与此相反;阻尼器的特征参数随板高增加均呈降低趋势;增加板宽,单位循环耗能与等效割线刚度增加,而等效阻尼比不变。研究结果为X形SMA板式阻尼器的设计和工程应用提供了理论依据。     

New insights into nickel-free superelastic titanium alloys for biomedical applications

Superelastic titanium (Ti) alloys are a group of unique functional metallic materials capable of recovering a substantial amount of mechanical strain thereby offering superior resilience. Such strain recovery is significantly greater than that exhibited by conventional elasticity and has been demonstrated to be clearly beneficial and necessary for a vast range of biomedical and dental applications. For example, the age-related physiological deterioration of bones signifies the necessity of employing superelastic implants. Currently, NiTi alloy remains to be the premier choice of superelastic alloys in the broad biomedical sector. However, recently reinforced views on the toxic, carcinogenic and allergenic properties of nickel have resulted in intensified concerns. This has encouraged the design and fabrication of Ni-free superelastic Ti alloys. In addition, enabled by additive manufacturing (AM) or 3D printing, hierarchical micro-architectured lattice meta-materials can exhibit exceptional superelasticity without undergoing phase transformations, upending the conventional perception and unlocking brand-new pathways to exploiting metal superelasticity. This article discusses recent developments in Ni-free superelastic Ti alloys and the determining factors affecting their superelastic recoverable strain. The importance of implant superelasticity relative to the elastic and “superelastic” properties of human bones is examined. Also discussed are the advances in Ni-free Ti-based superelastic alloy design and superelasticity-demanding medical and dental applications. The impact of the AM-enabled micro-architectural design on the development of superelastic structures or superelastic meta-materials is deliberated. Future research priorities are suggested.     

Shape memory characteristics and superelasticity of Ti-Ni-Cu alloy ribbons with nano Ti2Ni particles

Microstructures and deformation behaviour of Ti-45Ni-5Cu and Ti-46Ni-5Cu alloy ribbons prepared by melt spinning were investigated by transmission electron microscopy, thermal cycling tests under constant load and tensile tests. Spherical Ti2Ni particles coherent with the B2 parent phase were observed in the alloy ribbons when the melt spinning temperature was higher than 1773 K. Average size of Ti2Ni particles in the ribbons obtained at 1873 K was 8 nm, which was smaller than that (10 nm) in the ribbons obtained at 1773 K. Volume fraction of Ti2Ni phase in the ribbons obtained at 1873 K was 40%, which was larger than that (20%) in the ribbons obtained at 1773 K. The stress required at temperatures of Af + 10 K for the stress-induced martensitic transformation increased from 93 MPa to 229 MPa and apparent elastic modulus of the B2 parent phase increased from 56 GPa to 250 GPa with increasing the melt spinning temperature from 1673 K to 1873 K in Ti-45Ni-5Cu alloy ribbons. The critical stress for slip deformation of the ribbons increased by coherent Ti2Ni particles, and thus residual elongation did not occur even at 160 MPa, while considerable plastic deformation occurred at 60 MPa in the ribbons without Ti2Ni particles. Almost perfect superelastic recovery was found in the ribbons with coherent Ti2Ni particles, while only partial superelastic recovery was observed in the ribbons without coherent Ti2Ni particles.     

L10-TiAl基本物性的计算与比较研究

为了从理论上进一步揭示L10型TiAl金属间化合物的本征物性,采用第一原理赝势平面波方法,计算了L10型TiAl金属间化合物的平衡晶格常数、合金结合能、形成热、弹性常数以及点缺陷形成能,并与其他计算方法和实验测试的结果进行了比较.点缺陷形成能的分析结果表明,富Ti合金易出现Ti反位缺陷,富Al合金易出现Al反位缺陷;双空位形成能的分析结果表明,Ti-Ti最近邻双空位形成能最低,表明这种Ti-Ti最近邻双空位最稳定.基于晶体总电子态密度与各原子分波态密度等电子结构信息,对上述计算结果进行了初步分析.     

Modeling the microstructural evolution of Ni-base superalloys by phase field method combined with CALPHAD and CVM

A quantitative simulation with phase field method (PFM) in a real alloy system was performed with a new strategy of modeling the microstructure evolution of Ni-base superalloys, in which, the calculation of phase diagrams (CALPHAD) method and cluster variation method (CVM) are combined with the PFM. In this strategy, the four sub-lattice model is used to evaluate the chemical free energy density while CVM to calculate some parameters, such as the lattice misfit and gradient coefficients in phase field equations. With this strategy, the microstructure evolution of a Ni–Al binary alloy at the temperature of 1000 K has been simulated; the elastic energy due to the lattice misfit and elastic inhomogeneity between γ and γ′ phases has also been taken into account. Moreover, the directional coarsening phenomenon of Ni–Al alloy has been reoccurred when the various external stress conditions are applied, which shows good agreement with Pineau’s directional coarsening map.     

A numerical study on bolted end-plate connection using shape memory alloys

Superelastic shape memory alloys (SMAs) have the ability to recover their original shape after experiencing large strains. A new beam-to-column connection incorporating long shank SMA bolts is presented in this paper. By using the unique characteristics of SMAs, the connection possesses self-centering abilities. The 3D connection model is created using the software ANSYS, and Auricchio’s model is used to simulate the superelastic behavior of the SMA bolts. With cyclic loads applied on the beam ends, the behavior of the connection is studied. The results show the semi-rigid and moderate energy dissipation characteristics of the connection. Since the moment-carrying capacity of bolt cluster controlled below the elastic flexural capacity of connecting beam, a superelastic hinge forms just at the beam-to-column interface. The inelastic interstory drift angle of the connection reaches 0.035 rad, and 94% of the total rotations are recoverable upon unloading.     

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.