New finite strain elastoplastic equations for accurately and explicitly simulating pseudoelastic-to-plastic transition effects of shape memory alloys

A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.

Shape-induced phase transition of vortex domain structures in ferroelectric nanodots and their controllability by electrical and mechanical loads

Shape-induced phase transition of vortex domain structures （VDSs） in BaTiO3 （BT） nanodots under open circuit boundary condition have been investigated using an effective Hamiltonian method. Our calculation indicates the tetragonal VDS missing in cubic BT nanodots can be induced by varying the shape of a nanodot from cube to platelet. Interestingly, a novel VDS is found in BT nanoplatelets in our simulations. Further investigation shows that it is a result of compromise between the ground state and the symmetry of the shape of the nanodot. Furthermore, based on the novel VDS, routes of controlling VDSs governed by homogeneous electric field and uniform stress are discussed. In particular, our results show the possibility of designing multi-states devices based on a single VDS. ~ 2017 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.

TRANSITIONS AND MODRPHOLOGY OF MAIN-CHAIN LIQUID CRYSTALLINE POLYMERS WITH X-SHAPED MESOGENS

The transitions and morphology of a series of main-chain liquid crystalline polymer with X-shaped mesogens were studied by means of DSC,SALS and polarizing microscopy techniques. Aneven-odd effect was observed for samples with different size of the substituents on the mesogenends. The isotropization process was similar to that of main-chain polymers with rod-likemesogens. No crystallization was detected for specimens cooling down from their isotropic meltstate. However two of the samples may crystallize in cooling process directly from the liquidcrystalline state.

Combined stress waves with phase transition in thin-walled tubes

The incremental constitutive relation and governing equations with combined stresses for phase transition wave propagation in a thin-walled tube are established based on the phase transition criterion considering both the hydrostatic pressure and the deviatoric stress. It is found that the centers of the initial and subsequent phase transition ellipses are shifted along the sigma-axis in the sigma tau-plane due to the tension-compression asymmetry induced by the hydrostatic pressure. The wave solution offers the 'fast' and 'slow' phase transition waves under combined longitudinal and torsional stresses in the phase transition region. The results show some new stress paths and wave structures in a thin-walled tube with phase transition, differing from those of conventional elastic-plastic materials.

A NOVEL SECOND-ORDER TRANSITION IN ORGANIC HYBRIDS CONSISTING OF POLYMERS AND SMALL MOLECULES

A novel transition appeared above thc glass transition temperature of chlorinated polyethylene (CPE) for binaryblends of CPE and additives such as organic small molecules or oligomers. This transition was assigned to the dissociation ofintermolecular hydrogen bonds between the polymer ard additive within the edditive rich phase. Of particular interest is thata novel pyramid crystal was observed in the annealed CPE/hindered phenol blends. Another intriguing observation is thatthese polymer/small molecule blends organized by intermolecular hydrogen bonding have several potential properties, suchas shape-memorization, self-restoration, self-adhesiveness and super damping.

Coherent control of non-resonant two-photon transition in molecular system

In this paper, we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system （Perylene dissolved in chloroform solution） by shaping the femtosecond pulses with simple phase patterns （cosinusoidal and π phase step-function shape）. The control efficiency of the two-photon transition probability is correlated with both the laser field and the molecular absorption bandwidth. Our results demonstrate that, the two-photon transition probability in a molecular system can be reduced but not completely eliminated by manipulating the laser field, and the control efficiency is minimal when the molecular absorption bandwidth is larger than twice the laser spectral bandwidth.

Quantum coherent control of two-photon transitions by square phase-modulation

A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.

Phase transition characteristics of the Ni_(46)Mn_(35)Ga_(19) single crystal

The phase transition characteristics of the prepared Ni46Mn35Ga19 single crystal have been systematically investigated by measuring resistance,strain,heat flow,and ac magnetic susceptibility.The experimental results indicate that both magnetic transition and martensitic transformation occurred simultaneously and the corresponding transition temperature was about 356 K.Meanwhile,the prepared single crystal also exhibited spontaneous and magnetic-field-enhanced two-way thermal shape memory effect with the strains up to-0.89% and-1.90% with and without a magnetic field of 1.6 T,respectively.The possible mechanism of the large spontaneous and magnetic enhanced deformation were analyzed based on the phase transition characteristics of Ni46Mn35Ga19 single crystal and the preferential orientation of martensitic variants.

Transition to adulthood: A critical role for exercise in building overall well-being

A growing number of multidisciplinary studies have reported the beneficial effects of physical activities towards the development of overall well-being and the reduction of chronic illnesses. Physical inactivity is a serious worldwide problem and is considered the key lifestyle factor that negatively influences health and function of individuals. Here we propose that growth kinetics of body and mind and associated disproportionate physical activity may have considerable effects on the increased physical and mental illnesses and premature death rates currently observed in mid to late adulthood people. Children and young adults, being in exponential growth phase and self-motivated to engage in physical activity, possess more cognition, resilience, and mind-body-emotion-spirit integration. In contrast, as our body transitions into adulthood, there is a decline in the growth of body and mind. Furthermore, in this period, adults experience the increased stressors of career and financial demands, time pressure, and family responsibilities. The decline in growth combined with prolonged stress appears to result in reduced cognition, resilience, and mind-body-emotion-spirit integration, leading to sedentary and other faulty lifestyles, which could further lead to a predisposition to maladaptive behaviours and various chronic diseases at a later stage. In agreement with this, currently more than two thirds of the adult population across the world are physically inactive and are failing to perform the daily recommended guidelines of moderate to vigorous exercise. As negative changes and faulty lifestyles begin to occur during and after adulthood transition, creating awareness in people between 29 to 35 years of age about mindful exercise should be considered a national priority. This would allow adults to achieve overall well-being, and increased productivity and life expectancy, reducing health care-associated economic burden placed on the nation.

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T_(0). However, the T_(0) of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T_(0). In Ti_(50)Au_(50-x)Cr_(x) alloys, the strain glass appears at x = 25, and exhibits a T_(0) of 251 K, while in Ti_(50)Pt_(50-y)Fey alloys, the strain glass takes place at y = 30, and shows a T_(0) of 272 K. Both of them are comparable with the highest T_(0) value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T_(0) of the strain glass is limited. This work may help to design new strain glass systems with higher T_(0) above ambient temperature.

The Trackless Tram: Is It the Transit and City Shaping Catalyst We Have Been Waiting for?

Recent innovations in transport technology are now providing mobility that is cheaper, autonomous, electric, and with improved ride quality. While much of the world’s attention has been on how this can be applied to cars, there have been rapid adoption of these and other technologies in High Speed Rail and Metro Rail systems that run between and across cities. This paper shows how such innovations have now been applied to create the next generation of urban transit system called a Trackless Tram. Trackless Trams are effectively the same as traditional light rail except they run on rubber tyres avoiding disruption from construction for Light Rail, but they retain the electric propulsion (with batteries) and have high ride quality due to rail-type bogies, stabilization technologies and precision tracking from the autonomous optical guidance systems—with infrastructure costs reduced to as low as one tenth of a Light Rail system. As with Light Rail, a Trackless Tram System provides a rapid transit option that can harness the fixed route assurance necessary to unlock new land value appreciation that can be leveraged to contribute to construction and running costs whilst creating urban regeneration. The paper considers the niche for Trackless Trams in cities along with its potential for city shaping through the creation of urban re-development along corridors. The paper suggests that the adoption of Trackless Tram Systems is likely to grow rapidly as a genuine alternative to car and bus systems, supplementing and extending the niche occupied by Light Rail Transit (LRT). This appears to be feasible in any medium-sized or larger city, especially in emerging and developing economies, and case studies are outlined for Perth and Thimpu to illustrate its potential.

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.

GRAIN SHAPE EFFECT IN SUPERPLASTIC DEFORMATION

The method controlling grain shape in TMT processing and the effect of grain shape on char- acteristic parameters in superplastic deformation were discussed.The accommodation velocity of grahl boundary sliding,which is the dominant mechanism in superplastic deformation,and the contribution of each mechanism to the total strain,as influenced by grain shape,were ana- lyzed.Grain shape has been shown to be an essential structural factor for superplasticity.Then an analysis was made about the effect of grain shape on the region transition strain rate so that a new concept,critical aspect for superplasticity,was worked out.These predictions were compared with the measured results in an Al-Zn-Mg alloy.

Shape Coexistence and Band Termination in Doubly Magic Nucleus ^40Ca

Shape coexistence and band structure near yrast line of the Z ＝ N doubly magic nucleus 40Ca have been investigated by the configuration-dependent cranked Nilsson-Strutinsky approach. The observed normal deformed and superdeformed bands are explained and the terminating states are confirmed by the calculations. The transition quadrupole moment Qt of the calculated superdeformed band is in good agreement with the observed one at high spin. There is shape coexistence within the same configuration. Possible normal deformed and superdeformed bands with rotation around the intermediate axis in several interesting configurations of40Ca are discussed. Possible favored superdeformed band terminations in 38Ca and 38Ar are predicted. The experimental results in 38Ar are discussed simply.

Fe对Ni-Mn-Ga合金微丝形状记忆效应的影响

以Ni-Mn-Ga合金微丝为基础分析Fe元素掺杂前后对合金微丝的形状记忆效应的变化。用真空磁控钨极电弧熔炼炉制备Ni-Mn-Ga-Fe合金,并用高真空精密熔体抽拉设备将母合金制备成微丝。采用EDS能谱分析仪、DSC差示扫描量热分析仪、XRD、DMA动态机械分析仪,研究Fe元素掺杂Ni-Mn-Ga合金微丝后的物相、马氏体相变行为、微丝的形状记忆效应。结果表明,Ni-Mn-Ga-Fe合金微丝显示的是四方结构马氏体相和面心立方结构奥氏体相的混合相,对微丝采用步进式阶梯有序化热处理,有序化热处理能有效降低微丝内部缺陷,释放内应力,细化微丝内部晶粒,收缩晶格体积,马氏体孪晶界面更加平直,孪晶面更易移动,微丝的伸长率提高。在258 K下对制备态Ni-Mn-Ga-Fe合金微丝进行单程形状记忆的测试,拉伸到350 MPa后卸载到0 MPa,随后将微丝升温到奥氏体态后,应变恢复率为78.75%,而在289K对有序化热处理态Ni-Mn-Ga-Fe合金微丝进行单程形状记忆测试,应变恢复率达到100%。在126 MPa和240 MPa下分别对有序化热处理态三元Ni-Mn-Ga合金微丝和Ni-Mn-Ga-Fe合金微丝进行恒应力拉伸,两种微丝双程形状恢复能力均接近100%,但Ni-Mn-Ga-Fe合金微丝在发生形变时的弹性应变储能略高于Ni-Mn-Ga合金微丝。Fe的加入使得到的合金微丝的力学性能高于传统三元形状记忆合金微丝;制备态下和热处理态的Ni-Mn-Ga-Fe合金微丝的马氏体相变温度较Ni-Mn-Ga合金微丝分别提高6.0 K和11.5 K,热滞分别降低6.7 K和1.5 K。

A study on the effects of the transit parking time on traffic flow based on cellular automata theory

This paper mainly deals with the effects of transit stops on vehicle speeds and conversion lane numbers in a mixed traffic lane. Based on thorough research of traffic flow and cellular automata theory, it calibrates the cellular length and the running speed. Also, a cellular automata model for mixed traffic flow on a two-lane system under a periodic boundary condition is presented herewith, which also takes into consideration the harbour-shaped transit stop as well. By means of computer simulation, the article also studies the effects of bus parking time on the traffic volume, the transit speed and the fast lane speed at the same time. The results demonstrate that, with the increase of the bus parking time, the traffic volume of the transit stop and the transit speed decrease while the fast lane speed increases. This result could help calculate the transit delay correctly and make arrangements for transit routes reasonably and scientifically.

STUDY OF THE EQUILIBRIUM HCP CRYSTAL SHAPE BY THE ISING MODEL

The Isin g model is used to investigate (0001), (10^-10), (10^-11) interfaces, etc. , for the hcp lattice. The system studied here have the nearest-neighbor (NN) and next-nearest-neighbor (NNN) pair interactions. The interface energy, interface phase transition at zero temperature and roughening temperature are used to analyse the properties of these interfaces. As a special case of the hcp crystals, we give the equilibrium shape of the He crystal at T=OK.

城轨桥梁梁端扣件静力特性数值与试验研究

为研究城市轨道交通中简支梁桥梁端扣件的静力特性,现场实测并采集轨道交通高架线上U形梁梁端双层弹性扣件的应力应变数据,对实测扣件的受力变化规律进行分析;在此基础上,分别建立2D和3D有限元模型(考虑双层弹性扣件的非线性刚度,保守地不考虑轮载偏心及横向力的影响),分析了扣件力随梁端转角和错位的变化情况,并研究了悬臂长度和扣件刚度等参数的影响。结果表明:扣件力随梁端转角和梁端错位线性变化;悬臂越长,扣件刚度越大,则扣件受力越大;扣件最大上拔力接近初始扣压力,其长期反复作用且数值较大,致使扣件螺栓松动,甚至弹条掉落。

空间索面异型轨道专用悬索桥设计及关键技术

以重庆市郊铁路跳磴至江津线跨江轨道专用桥为工程背景,结合建设条件和技术标准,从总体布置、结构设计两方面介绍该桥推荐方案——主跨610 m外张型空间索面异型悬索桥。针对该桥约束体系、结构刚度、高窄主梁抗风性能、钢梁疲劳性能等关键技术开展研究:根据梁端纵向位移、跨中缆梁位移差等优选纵向高性能阻尼器参数和人字形柔性中央扣索数量;采用空间索面主缆、主跨梁顶设压重混凝土板、变高度钢箱梁、边跨混凝土-钢箱底板结合梁等多种措施综合提高结构刚度,并通过车桥耦合动力分析和轨道几何形位分析评估结构刚度合理性;结合风洞试验确定主梁气动外形优化措施;在设计钢箱梁顶底板板肋、明确钢梁疲劳检算部位及容许应力幅值基础上,开展钢箱梁疲劳检算。

功能梯度形状记忆合金纳米梁力学性能研究

功能梯度形状记忆合金(Functionally Graded Shape Memory Alloys,FG⁃SMA)兼具功能梯度材料和形状记忆合金的双重特性,故在航空航天、生物医疗、微机电系统(Micro Electro Mechanical System,MEMS)中得到了广泛的应用。当微结构尺度达到纳米尺度,表面效应对微结构力学性能的影响是十分显著的。为了探究表面效应对功能梯度形状记忆合金纳米梁力学性能的影响规律,基于梁弯曲理论及Gurtin⁃Murdoch表面弹性理论,考虑拉压不对称、温度对FG⁃SMA纳米梁的影响,建立了考虑表面效应的FG⁃SMA纳米梁相变力学模型。分析了梯度指数、载荷、温度及拉压不对称系数对FG⁃SMA纳米梁力学性能的影响规律。研究表明,弯矩、梯度指数对截面响应影响显著,而温度和拉压不对称系数对其影响较小;忽略表面效应的影响会低估FG⁃SMA纳米梁的抗弯性;在弯矩达到一定程度后,表面效应对FG⁃SMA纳米梁中性轴偏移趋势影响不大。研究结果对FG⁃SMA纳米梁在微机电领域的设计及应用提供了一定的基础与依据。