NiTi形状记忆合金基本驱动特性

研究了预应变ＮｉＴｉ形状记忆合金的基本驱动特性，结果表明，加热和冷却过程回复力存在滞后行为；卸载过程中应力与应变具有与加热、冷却过程相关的非线性关系；卸尖力随卸载应变速率增加而降低，此外研究了预应变ＮｉＴｉ合金丝产生回复力后对外应力的响应行为。     

淬火温度对冷拉态Fe-18Mn-5Si-8Cr-4Ni形状记忆合金回复应力的影响

研究了淬火温度对Ｆｅ － １８ Ｍｎ － ５Ｓｉ － ８Ｃｒ － ４Ｎｉ 记忆合金回复应力的影响。结果表明：合金经变形后加热时产生的最大回复应力σｈ 和加热后冷却到室温时的回复应力σｃ 都随淬火温度的升高而增加,在６５０ ℃达到最大值;随后随淬火温度的进一步升高而快速下降,但是σｃ 下降的程度要比σｈ 大得多;当淬火温度高于８５０ ℃后,淬火温度的进一步升高对它们几乎没有影响;任一淬火温度下,加热后冷却到室温时的回复应力 σｃ都远大于加热时产生的最大回复应力σｈ。     

时效温度对Fe-Mn-Si-Cr-Ni-C记忆合金回复应力的影响

研究了时效温度对Ｆｅ－１４Ｍｎ－５Ｓｉ－８Ｃｒ－４Ｎｉ－０．２Ｃ记忆合金回复应力的影响。结果表明：合金经变形后加热时产生的最大回复应力σｈ随时效温度的升高而增加,在１０２３Ｋ达到最大值,比固溶态增加了７５％;随后σｈ将随时效工的进一步升高迅速下降。但是当时效温度高于１１２３Ｋ后,时效温度的进一步升高对σｈ几乎没有影响。时效后合金加热时产生的最大回复应力都大于固溶态时的回复应力。时效温度对合金加热后     

Fe-18Mn-5Si-8Cr-5Ni-0.1N形状记忆合金组织和性能的研究

研究了Fe-18Mn-5Si8Cr-5Ni-0.1N形状记忆合金的形状记忆效应、回复应力、耐蚀性能.结果表明,在Fe-18Mn-5Si-8Cr-5Ni合金中加入0.1%的氮,对合金的形状记忆效应不利,但当预变形量小于4.5%时,降低幅度较小,在14%～18%左右.在变形量小于4.5%时,含氮合金加热时的回复应力高于未加氮的合金的回复应力;当变形量大于4.5%时,含氮合金的回复应力低于未加氮的合金的回复应力,两种合金的加热时最大回复应力的最大值相近(90 MPa左右).又由于氮具有强烈的固溶强化作用,大大强化了基体,使得合金在冷却过程中因回复应力导致的塑性变形量和二次相变量减小,从而导致合金冷却到室温的回复应力显著提高,当预变形量为6%时,含氮合金的室温回复应力最大,比未加氮的合金的最大室温回复应力高约21%.同时,氮的加入有利于提高合金的耐蚀性能.     

部分循环对FeMnSi基合金形状记忆效应的研究

用Ｘ射线衍射及热膨胀法研究了预应变量为３％的两种ＦｅＭｎＳｉ形状记忆合金在室温—４５０℃区间加热时形状恢复量及ε－马氏体量随温度的变化，结果表明ε马氏体在晶体中处于不同的能量状态，４５０℃加热后仍有部分应力诱发ε马氏体没有转变，这是该系列合金形状不能完全恢复的原因之一；同时发现，预应变后，合金中贮存弹性内应力，使得在Ａｓ～Ａｆ之间同一温度区间膨胀、收缩系数不同。     

TiNi形状记忆合金在电流激励下的驱动性能研究

通过试验对电流激励下的TiNi形状记忆合金丝的约束回复应力和温度的关系进行了初步研究.主要考虑了电流的施加方法、恒定电流的大小、热循环的次数以及最大预拉应变对约束回复应力的影响.试验结果表明,台阶式施加电流和始终恒定电流的方法相比,加热速率较小,达到同一目标温度的响应时间较长,从而达到所要求的回复应力所需要时间较长.回复应力随着温度的升高而增大,最终达到最大回复应力.最大预拉应变相同时,在较大恒定电流激励下回复应力比率较大.采用相同恒定电流激励时,较大的最大预拉应变的TiNi丝会产生更大回复应力.随着恒定电流的增加TiNi丝回复应力的热循环稳定性变得稍差.即便如此,在较大恒定电流激励下其回复应力仍然拥有很好的热循环稳定性,能够满足土木工程损伤应急修复的需要.     

部分循环对FeMnSi基合金形状记忆效应的研究

用Ｘ射线衍射及热膨胀法研究了预应变量为３％的两种ＦｅＭｎＳｉ形状记忆合金在室温－４５００℃区间加热时形状恢复量ε－马氏体量随温度的变化，结果表明ε－马氏体在晶体中处于不同的能量状态，４５０℃加热后仍有部分应力诱发ε马氏体没有转变，这是该系列合金形状不能完全恢复的原因之一；     

影响Fe-Mn-Si-Cr-Ni形状记忆合金相变点的因素

研究了变形量和回复退火温度对Fe-14Mn-5Si-8Cr-4Ni形状记忆合金相变点的影响。结果表明：当回复退火温度为673K时，Af点和Ms点都随变形量的增加而显著增加，As点增加较缓慢；303K加热前和加热后合金电阻率之差△ρ也随变形量的增加而增加，可回复变形量随变形量的变化与△ρ的变化是一致的。Fe-Mn-Si-Cr-Ni形状记忆合金的形状回复来源于应力诱发γ→ε马氏体转变及其逆转变；当变形量为10%时，Ms点随回复退火温度的增加而显著下降。     

Ti－17合金的热压缩变形行为研究

通过热模拟压缩试验，测试了Ｔｉ－１７合金在温度Ｔ＝８０５～９４５℃，应变速率ε＝１０（－３）～８０ｓ（－１）、变形程度ε＝５０％范围内的真应力－应变曲线，研究了不同温度、不同应变速率下的流动应力及组织变化规律。发现，在（α＋β）两相区降低温度或提高应变速率，流动应力σ变化较大，动态再结晶易于进行；在β区通常只发生动态回复，流动应力σ随温度和应变速率变化较小，高温、低应变时发生连续再结晶。试验还用Ｚｅｎｅｒ－Ｈｏｌｌｏｍｏｎ因子确定了该台金发生连续再结晶的临界因子Ｚｃ的数值，ｌｏｇＺＣ＝４１．２。     

预应变对Ni-50.4Ti合金记忆应变和回复力的影响

研究了预应变对经过不同热处理的Ｎｉ－５０．４Ｔｉ（原子分数,％）合金记忆应变和回复力的影响,分析了回复力产生的过程。预应变大约为８．５％时试样具有最大的记忆应变和回复力。热处理提高了母相的屈服强度从而使材料的记忆应变和回复力提高。     

Temperature and Time Dependence on Recovery Stress Relaxation in Nickel Titanium Wire during Isothermal Holding at High Temperatures

In this study, the influence of kinematically constrained thermal cycling (heating, isothermal holding and cooling) on the recovery stress in annealed nickel titanium wire was investigated. A 4% pre‐strained nickel titanium wire was heated to temperatures (150, 200, 250 and 300 °C) much higher than the austenite finish temperature. It was observed that the maximum recovery stress obtained at different conditions decreases significantly after the first thermal cycle and reduces gradually with further increasing the number of thermal cycles. It was also seen that the recovery stress increases with time during isothermal holding at 150 °C. During isothermal holding at other temperatures, the recovery stress shows an exponential decrease, and the decrease rate of the recovery stress depends on the isothermal holding temperature. The higher isothermal holding temperature is the more the recovery stress decreases. The decrease rate reduces with increasing the number of thermal cycles.     

R32在家用空调器中的应用研究

对比R32与R410A的基本物性和热力循环性能,并在同一台家用定频热泵空调器上进行性能测试。相对于R410A,在给定工况下,R32的理论循环制冷量最大可提高15％,能效比最大提高6％,容积制冷量和容积制热量增加7％～8．9％。性能测试结果表明,R32系统的制冷剂充注量比R410A系统的减少24％,额定制冷能力和能效比比R410A系统分别提高8％和3．3％,额定制热能力和性能系数也高于R410A系统。理论热力循环分析及性能测试结果均表明,R32制冷性能相对R410A有较大幅度的提高,制热性能比R410A略高或相当,但R32系统的排气温度较高,比R410A系统高出11．5～25．7℃,恶劣工况下排气温度甚至能达到114．9℃。     

Mg处理X100管线钢的焊接CCT曲线及其组织

采用焊接热模拟技术和显微组织分析等方法,对Mg处理X100管线钢在连续冷却转变下的显微组织的变化规律进行了研究。通过对Mg处理X100管线钢CCT曲线的建立和显微组织分析结果表明:对比焊接CCT模拟工艺和常规950℃保温的CCT工艺,前者AC1、AC3相变点要分别高于后者25℃,奥氏体晶粒显著大于后者,冷却相变点要低于后者50～80℃。在焊接热模拟工艺下,当冷却速度在0.1～3℃/s之间时,组织以准多边形铁素体(QF)和粒状贝氏体为主;在3～30℃/s的冷却速度范围,主体组织为粒状贝氏体(GB)和针状铁素体(BF);当冷却速度为30～50℃/s,组织以贝氏体铁素体(BF)为主;大于50℃/s的冷却速度,将形成马氏体(M)组织。     

Temperature and stress fields evolution during spark plasma sintering processes

Numerical modelling of Spark Plasma Sintering (SPS) processes is essential to evaluate temperature and stress distributions that can result in sample inhomogeneities. Most of the available literature, however, produced analysis in static conditions. In this work, we focused our attention on the time evolution of current density, temperature and stress distribution during a SPS process using a new approach that includes a PID control in the algorithm, allowing a realistic simulation of experiments performed using a temperature controller. Controlled temperature experiments have been simulated and discussed, with special interest focused on the time evolution of the process. The results showed that stress gradients inside the samples (~40%) are much greater than the temperature gradients (~2%), suggesting that heterogeneities in the microstructure can also be caused by the stress gradient. During the evolution of the process, a peak in stresses is experienced by the alumina sample at the beginning of the cooling stage, caused by differences in contraction between the sample and the die. It has been proved that, using a controlled cooling stage, these peaks in the stresses can be easily eliminated.     

低温风洞电动推杆热防护结构设计及传热分析

为解决低温风洞中电动推杆的热防护问题,设计了使其能够在低温风洞高温工况(323 K)和低温工况(110 K)下正常工作的热防护结构。采用数值模拟方法校核了热防护结构强度及刚度,分析了电机发热功率,冷却气体流量和加热片加热功率等因素对推杆元件温度的影响。结果表明:低温风洞内压力达到极值0.35 MPa时,由厚度5 mm,材料S30408不锈钢制成的圆筒形热防护结构最大变形量为0.397 mm,最大应力为160.62 MPa;冷却气体流量大于等于0.005 kg/s时,高温和低温工况下电机最高温度均不大于418 K的允许工作温度;当加热功率达到500 W时,缸杆端部各考察截面温度均高于263 K;在高温工况和加热功率为500 W的低温工况下,冷却气体流量为0.005 5kg/s时,缸体、缸杆均能维持在263—313 K的工作温度,且高温工况最大温升与温差分别为3.62、2.81 K,低温工况最大温降与温差分别为4.94、6.82 K,满足温度稳定性与均匀性要求。     

Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

Acoustic emission activity was measured in the glass transition range of dental porcelain during firing. Transient and residual stresses in porcelain during cooling from a temperature higher than porcelain sag point and during re-heating of the tempered porcelain were calculated by computer simulation using a viscoelastic stress analysis. The detected acoustic emission event was discussed with the relative rules of the simulated transient stresses. High acoustic emission activity was detected at the temperature where the internal stress faded away for heating and build up for cooling. The low-level acoustic emission pulses were only detected in the following conditions: (1) in the temperature range where porcelain behaved like an elastic solid; (2) at temperatures higher than the deformation point of porcelain; (3) with a re-heating process of the porcelain without tempered stress. From these results, it was concluded that elastic energy is released related to transient stress in porcelain during viscoelastic deformation and can be detected by the acoustic emission method. The acoustic emission method is considered to be helpful in non-destructive testing in order to understand transient stress due to viscoelastic deformation of glassy materials in heat treatment.     

Austenitic grain size evolution and continuous cooling transformation diagrams in vanadium and titanium microalloyed steels

The evolution of the austenitic grain size in medium carbon steels microalloyed with vanadium and titanium was studied as a function of reheating temperature, heating rate, and titanium content. High resolution dilatometric techniques were used to determine the continuous cooling transformation (CCT) diagrams for two different austenitization temperatures. The microstructure and hardness were determined for different cooling rates. The results revealed a significant effect of titanium concentration on the austenitic grain growth control. The smallest grain size was found in the steel with a Ti concentration = 0.019 wt%. Low heating rates produced smaller grain sizes than high heating rates although an abnormal grain growth took place. In these steels, at temperatures above 1050 °C the influence of the reheating temperature on their hardness for cooling rates around 2 °C · s^–1 was negligible. The higher reheating temperatures caused a slight increase in their hardenability. Finally, it was found that the greater the titanium content, the greater the hardness of these steels, but only when the titanium percentages were higher than 0.020 wt%.     

微通道换热器用于家用柜机空调时整机性能的对比实验研究

微通道换热器的应用日益普遍。文章通过将微通道换热器引入3 HP柜式家用空调,并对系统性能和充注量等进行了对比研究。实验表明:当只更换室内换热器,室内微通道换热器翅片间距为1.4 mm时,系统性能达到最优:与原机相比,系统充注量降低15.9%,制冷量基本相当,制冷COP提高2.2%;制热量比原机提高3.9%,制热COP则提高了11.2%。当将室内外换热器都更换为微通道换热器后,系统的充注量降低54%,与原机相比:制冷量提高0.8%,系统COP提高5.2%;当制冷剂更换为R290时,系统最优充注量降为500 g。     

6061-T6铝合金中厚板-节点套多层多道焊数值模拟

为研究铝合金中厚板-节点套接头在多层多道焊后的残余应力和变形分布,本文基于ABAQUS软件建立了该接头三维有限元模型,采用双椭球热源、生死单元法以及顺序耦合法,对6061-T6铝合金中厚板-节点套多层多道焊进行数值模拟,并分析了接头的温度场,以及在夹具约束下的焊接残余应力及变形的分布情况。研究结果表明:数值模拟与实际接头的熔池形状吻合度较高;摆动焊接过程中温度曲线呈多峰结构;焊件的升温速率明显大于冷却速率,且冷却速率随时间逐渐减小;焊接残余应力主要集中在焊缝及夹具区域,且小于6061-T6铝合金在室温下的屈服强度;接头的最大横向残余应力为129.9 MPa,中厚板上的横向残余应力大于节点套上的横向残余应力;接头的最大纵向残余应力为132.9 MPa,沿焊接方向,焊缝处的纵向残余应力呈山峰状分布;该接头在Y轴方向上的变形最大,为1.494 mm,该接头的最终变形结果为上凸变形。     

Influence of thermoviscoelastic properties and loading conditions on the recovery performance of shape memory polymers

This work investigated the influence of material properties and loading conditions on the recovery performance of amorphous shape memory polymers using a recently developed thermoviscoelastic model. The model incorporated the time-dependent mechanisms of stress and structural relaxation and viscoplastic flow to describe the glass transition of the material from a soft viscoelastic rubber to a hard viscoplastic glass. The model captured many important features of the unconstrained strain recovery response and of the stress hysteresis observed in the constrained recovery response. A parameter study was developed that varied the model and loading parameters one-by-one to compare their effects on the start and end temperatures and recovery rate of the unconstrained recovery response and on the stress hysteresis of the constrained recovery response. The loading parameters included the cooling rate, the annealing time, and the high and low temperatures of the programming stage and the heating rate of the recovery stage. The results confirmed experimental observations that viscoelasticity is the underlying mechanism of the unconstrained recovery response. In contrast, the constrained recovery response was influenced by the interaction of many different mechanisms, including thermal expansion and structural and stress relaxation. For the loading parameters, the cooling rate of the programming stage and the heating rate of the recovery stage had the largest influence on both the constrained and unconstrained recovery response.