SMA短纤维增强复合材料在热载下的相变特性

在形状记忆合金（ＳＭＡ）复合材料研究中,相变特性的研究是一个主要的工作。基于Ｅｓｈｅｌｂｙ的等效要模型和Ｍｏｒｉ和Ｔａｎａｋａ的场平均法,考虑到ＳＭＡ材料的强物理非线性,发展了增量型的等效夹杂模型（ＩｎｃｒｅｍｅｎｔａＩＥｑｕｉｖａｌｅｎｔＩｎｃｌｕｓｉｏｎ Ｍｏｄｅｌ）。考虑在某一温度循环条件下讨论开关记忆合金短纤维增强的铝基复合材料在热载下的相变行为。特别研究了ＳＭＡ短纤维复合材料在变温过程     

SMA短纤维复合材料的热胀系数和相变应变系数

基于Eshelby的等效夹杂模型、Mori和Tanaka的场平均法,考虑到形状记忆合金（SMA）的强物理非线性,发展了增量型的等效夹杂模型（Incremental Equivalent Inclusion Model)。讨论了SMA短纤维增强的铝基复合材料的热胀系数和相变应变系数。特别研究了SMA短纤维复合材料纤维几何尺寸和体积分数等参数对SMA复合材料的热胀系数和相变应变系数的影响。这些工作对于指导材料设计和了解SMA复合材料热机械特性是非常有意义的。     

智能复合材料的热力学特性

由形状记忆合金丝或颗粒增强的智能复合材料具有特殊的力学性能，本文从理论上预测了智能复合材料的热力学特性。利用Ｅｓｈｅｌｂｙ的等效夹杂原理与Ｍｏｒｉ－Ｔａｎａｋａ的平均场理论导出了本构列式和相变条件，揭示了形状记忆合金在弹性介质约束下的相变机理与过程。     

Initial value problem for high dimensional dynamic systems

ＩＮＩＴＩＡＬＶＡＬＵＥＰＲＯＢＬＥＭＦＯＲＨＩＧＨＤＩＭＥＮＳＩＯＮＡＬＤＹＮＡＭＩＣＳＹＳＴＥＭＳＺｈｕＣｈａｎｇ－ｊｉａｎｇ（朱长江）（Ｉｎｓｔ．ｏｆＭａｔｈ．Ｓｃｉｓ．,ＡｃａｄｅｍｉａＳｉｎｉｃａ,Ｗｕｈａｎ４３００７１）（Ｒｅｃｅｉｖｅｄ...     

NEWTONIAN MECHANICS ON KAHLER MANIFOLD

ＮＥＷＴＯＮＩＡＮＭＥＣＨＡＮＩＣＳＯＮＫＡＨＬＥＲＭＡＮＩＦＯＬＤＺｈａｎｇＲｏｎｇｙｅ（张荣业）（Ｉｎｓｔｉｔｕｔｅｏｆ＇Ｍａｔｈｅｍａｔｉｃｓ．ＡｃａｄｅｍｉａＳｉｎｉｃａ．Ｂｅｉｊｉｎｇ１０００８０．Ｐ．Ｒ．Ｃｈｉｎａ）Ａｂｓｔｒａｃｔ：Ｉｎ...     

An Exact Solution on the Stress Analysis of Fillet Welds

ＡＮＥＸＡＣＴＳＯＬＵＴＩＯＮＯＮＴＨＥＳＴＲＥＳＳＡＮＡＬＹＳＩＳＯＦＦＩＬＩＥＴＷＥＬＤＳＸｕｅＤａｗｅｉ（薛大为）（ＲｅｃｅｉｖｅｄＭａｒｃｈ１．１９９５）ＡｂｓｔｒａｃｔＡｎｅｘａｃｔｓｏｌｕｔｉｏｎｏｎｔｈｅｓｔｒｅｓｓｄｉｓｔｒｉｂｕｔｉ...     

On completeness for a 3-D linear theory of composite laminate

ＯＮＣＯＭＰＬＥＴＥＮＥＳＳＦＯＲＡ３－ＤＬＩＮＥＡＲＴＨＥＯＲＹＯＦＣＯＭＰＯＳＩＴＥＬＡＭＩＮＡＴＥＪｉａｎｇＹｏｕ－ｌｉａｎｇ（蒋友谅）（ＤｅｐａｒｔｍｅｎｔｏｆＡｐｐｌｉｅｄＭｅｃｈａｎｉｅｓ．ＰｅｋｉｎｇＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｌ...     

THE EXAMINATION OF TURBULENCE MODELING WITH LES DATABASE

ＴＨＥＥＸＡＭＩＮＡＴＩＯＮＯＦＴＵＲＢＵＬＥＮＣＥＭＯＤＥＬＩＮＧＷＩＴＨＬＥＳＤＡＴＡＢＡＳＥＳｕＭｉｎｇ－ｄｅ（苏铭德）（ＱｉｎｇｈｕａＵｎｉｖｅｒｓｉｔｙ，Ｂｅｉｊｉｎｇ）Ｒ．Ｆｒｉｅｄｒｉｃｈ（ＬｅｈｒｓｉｒｈｌｆｕｒＦｌｕｉｄｓｍｅｃｈａ...     

Some new fixed point theorems in probabilistic metric spaces

ＳＯＭＥＮＥＷＦＩＸＥＤＰＯＩＮＴＴＨＥＯＲＥＭＳＩＮＰＲＯＢＡＢＩＬＩＳＴＩＣＭＥＴＲＩＣＳＰＡＣＥＳｚｈｕＣｈｕａｎ－ｘｉ（朱传喜）（ＭａｔｈｅｍａｔｉｅｓＤｉｖｉｓｉｏｎ,Ｎａｎｃｈａｎｇ．Ｕｎｉｖｅｒｓｉｔｙ,Ｎａｎｃｈａｎｇ）（Ｒｅｃｅｉｖ...     

Analysis of complex stress intensities for cracked laminates

ＡＮＡＬＹＳＩＳＯＦＣＯＭＰＬＥＸＳＴＲＥＳＳＩＮＴＥＮＳＩＴＩＥＳＦＯＲＣＲＡＣＫＥＤＬＡＭＩＮＡＴＥＳＨｕＨｕｒａｎｇ（胡互让）;ＷｕＣｈｅｎｇｐｉｎｇ（吴承平）（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌ．ＡｅｒｏｓｐａｃｅａｎｄＭａｎｕｆａ...     

Micro-mechanical behaviors of SMA composite materials under hygro-thermo-elastic strain fields

An analytical procedure to evaluate the behavior of shape memory alloy (SMA) composite under hygrothermal environment is presented. The SMA wires are considered as inclusions embedded in a homogeneous matrix medium of the composite. The inhomogeneity associated with the phase transformation and thermal strains in the SMA wire as well as the hygrothermal strain in the matrix is homogenized using Eshelby’s equivalent inclusion method. In the present work, a similar approach adopted for SMA composites by Marfia and Sacco [Marfia, S., Sacco, E., 2005. Micromechanics and homogenisation of SMA-wire-reinforced materials. J. Appl. Mech. 72 (2), 259–268.] is considered in order to validate the response of SMA composite subjected to thermo-elastic strain field. However, in the present approach, certain modifications and new derivations for the inelastic strain tensors is carried out. First, the constitutive laws for the SMA wire and matrix are expressed in terms of the average strain in the composite. The evolutionary equations used to characterize the pseudoelastic (PE) behavior of the SMA wire are redefined in terms of the eigen strains (phase transformation and thermal strains) occurring in the SMA wire, which are then expressed in terms of the average strain in the composite. Further, the SMA composite constitutive law under coupled hygro-thermo-elastic strain fields is proposed. The generic homogenized hygric and thermal inelastic composite tensors required for the proposed hygro-thermo-elastic constitutive law are derived. Finally, the SMA composite lamina is characterized using Eshelby’s equivalent inclusion method. Using the proposed modifications and derivations, the analytical results are validated for the case of thermo-elastic strain fields and the procedure is then extended to evaluate the SMA composite behavior under hygro-thermo-elastic strain fields. The results include the effect of thermo-elastic and hygro-thermo-elastic strains on the transformation stresses and the nature of hysteresis due to hygric and thermo-elastic strains.     

Micro–macro analysis of shape memory alloy composites

The aim of the paper is to develop a micro–macro approach for the analysis of the mechanical behavior of composites obtained embedding long fibers of Shape Memory Alloys (SMA) into an elastic matrix. In order to determine the overall constitutive response of the SMA composites, two homogenization techniques are proposed: one is based on the self-consistent method while the other on the analysis of a periodic composite. The overall response of the SMA composites is strongly influenced by the pseudo-elastic and shape memory effects occurring in the SMA material. In particular, it is assumed that the phase transformations in the SMA are governed by the wire temperature and by the average stress tensor acting in the fiber. A possible prestrain of the fibers is taken into account in the model.Numerical applications are developed in order to analyze the thermo-mechanical behavior of the SMA composite. The results obtained by the proposed procedures are compared with the ones determined through a micromechanical analysis of a periodic composite performed using suitable finite elements.Then, in order to study the macromechanical response of structural elements made of SMA composites, a three-dimensional finite element is developed implementing at each Gauss point the overall constitutive laws of the SMA composite obtained by the proposed homogenization procedures. Some numerical applications are developed in order to assess the efficiency of the proposed micro–macro model.     

Effects of matrix inelasticity on the overall hysteretic behavior of TiNi-SMA fiber composites

The effects of the inelastic deformation of the matrix on the overall hysteretic behavior of a unidirectional titanium–nickel shape-memory alloy (TiNi-SMA) fiber composite and on the local pseudoelastic response of the embedded SMA fibers are studied under the isothermal loading and unloading condition. The multiaxial phase transformation of the SMA fibers is predicted using the phenomenological constitutive equations which can describe the two-step deformation due to the rhombohedral and martensitic transformations, and the inelastic behavior of the matrix material using the standard nonlinear viscoplastic model. The average behavior of the SMA composite is evaluated with the micromechanical method of cells. It is observed that the inelastic deformation of the matrix due to prior tension results in a compressive stress in the matrix after unloading of the SMA composite and this residual stress impedes the complete recovery of the pseudoelastic strain of the SMA fibers. This explains that a closed hysteresis behavior of the SMA composite is no longer observed in contrast with the case that an elastic behavior of matrix is assumed. The predicted local stress–strain behavior indicates that the cyclic response of matrix is crucial to the design of the hysteretic performance of the SMA composite under the repeated loading conditions.     

A thermomechanical model for a 1-D shape memory alloy wire with propagating instabilities

A thermomechanical boundary value problem and constitutive model are presented for a shape memory alloy (SMA) wire under uniaxial loading. The intent is to develop a one-dimensional continuum model of an SMA element that includes all the relevant thermomechanical couplings and is suitable for inclusion in finite element analyses. Thermodynamic relations are derived from phenomenological considerations consistent with recent experimental observations and are calibrated to a typical commercially available NiTi wire material. The model includes both temperature-induced and stress-induced transformations that are necessary to exhibit the shape memory effect and pseudoelastic behaviors. The model accommodates possible unstable mechanical behavior during stress-induced transformations by allowing softening transformation paths and including strain gradient effects. This should provide a tool to study propagating transformation fronts and localized latent heat transfer with the surroundings and a variety of interesting future structural applications, such as composites with embedded SMA elements.     

Thermomechanical properties of smart composites

The smart composite materials reinforced by SMA show a high performance and special deformation behavior. The thermomechanical constitutive formulas of the composites are derived by means of Eshelby's equivalent inclusion method and Mori-Tanaka's mean field concept. The interaction between the inclusion and crack and toughening mechanism are considered and the energy release rate of a crack in the smart composite is calculated. This work shows that there are the multiple mechanisms contributing to the toughening of the smart composite materials reinforced by SMA.This project is supported by the National Natural Science Foundation of China.     

A two-level micromechanical theory for a shape-memory alloy reinforced composite

A two-level micromechanical theory is developed to study the influence of the shape and volume concentration of shape-memory alloy (SMA) inclusions on the overall stress–strain behavior of a SMA-reinforced composite. The first level exists on the smaller SMA level, in which, under the action of stress, parent austenite may transform into martensite. The second level is on the larger scale consisting of the metastable SMA inclusions and an inactive polymer matrix. The evolution of martensite microstructure is evaluated from the irreversible thermodynamics, in conjunction with the micromechanics and physics of martensitic transformation. By taking martensite to exist in the form of thin plates on the micro scale and assuming SMA inclusions to be homogeneously aligned spheroids on the macro scale, the overall stress–strain behaviors of a NiTi-reinforced composite are calculated for various SMA shapes and concentrations. The results indicate that, under a tensile axial loading, martensitic transformation is easier to take place when SMA inclusions exist in the form of long fibers, but most difficult to occur when they are in the form of flat discs. In general the levels of the applied stress at which martensite transformation commences, finishes, and austenitic transformation starts, and finishes, are found to decrease with increasing aspect ratio of the SMA inclusions while the damping capacity increases with it; these properties point to the advantage of using fibrous composites for actuators or sensors under a tensile loading.     

SMA复合材料在热载条件下的残余应力分析

本文基于三相复合圆柱模型发展了增量型的分析方法,讨论在ＳＭＡ复合材料中由于ＳＭＡ材料相变以及各相材料热特性随温度变化引起的残余应力。研究基体与过渡恸介面和纤维与过渡界面间的残余应力,同时讨论由于基体相的变化对残余应力的影响。特别研究了涂层和复合材料基体间界面处的残余应力受纤维体积比、涂层厚度、纤维最大相变应以及基体中纤维取向等影响,而且讨论了计及应力对相就运动方程的影响时对ＳＭＡ复合材料相变温度和     

A 2D finite element based on a nonlocal constitutive model describing localization and propagation of phase transformation in shape memory alloy thin structures

Here, the effects of localization and propagation of martensitic phase transformation on the response of SMA thin structures subjected to thermo-mechanical loadings are investigated using nonlocal constitutive model in conjunction with finite element method. The governing equations are derived based on variational principle considering thermo-mechanical equilibrium and the spatial distribution of the nonlocal volume fraction of martensite during transformation. The nonlocal volume fraction of martensite is defined as a weighted average of the local volume fraction of martensite over a domain characterized by an internal length parameter. The local version of the thermo-mechanical behavior model derived from micromechanics considers the local volume fraction of martensite and the mean transformation strain. A 4-noded quadrilateral plane stress element with three degrees of freedom per node accounting for in-plane displacements and the nonlocal volume fraction of martensite is developed. Numerical simulations are conducted to bring out the influence of material and geometrical heterogeneities (perturbations/defects) on the localization and propagation of phase transformation in SMA thin structures. Also, a sensitivity analysis of the material response due to the localization and the other related model parameters is carried out. The detailed investigation done here clearly shows that the localization of phase transformation has significant effect on the response of shape memory alloys.