Al－Li－Cu－Mg－Zr（8090）合金屈服强度与变形温度和速率间的关系

研究了变形温度（７７～５２３Ｋ）和变形速率（１．７７×１０－４～１．７７×１０－２ｓ－１）对Ａｌ－Ｌｉ－Ｃｕ－Ｍｇ－Ｚｒ（８０９０）合金时效后屈服强度的影响，并观察了位错结构，欠时效和接近峰值时效试样的屈服强度，随变形温度从７７Ｋ上升到２９０Ｋ而降低，而在２９０～４５０Ｋ间则表现出正温度系数。在此区间内，位错成对运动，并切过有序相δ＇－－Ｌｉ２，在应力一应变曲线上还观察到锯齿屈服效应。在高于４５０Ｋ，屈服强度随温度升高而降低，位错呈单个运动，并逐渐形成缠结．     

FCC晶体结构多晶铜的动态本构方程参数确定

以带有同步组装技术的分离式Hopkinson压杆作为热模拟装置，采用基于MTS(Mechanical Threshold Stress)模型建立的FCC晶体结构的动态本构方程，确定了多晶铜动态本构方程参数，研究了连铸多晶铜的动态冲击特性，获得的理论应力一应变曲线与实验结果相当吻合，但不能描述485～585K间回复与再结晶温度区间的变形。     

脆塑性岩石应力脆性跌落系数的试验研究

岩石的应力一应变全过程曲线以峰值应力为界,通常分为破坏前区和破坏后区两部分.由于岩石破坏后区的力学特性对诸多岩石工程,如,地下巷道、矿柱和岩爆等具有重要的工程意义,因此,此方面的研究受到理论界和工程界的重视.岩石的破坏后区一般处于非稳定状态,其力学响应用经典的应变软化模型来模拟计算难以收敛,而可以考虑采用脆塑性模型.使用RMT-150B型岩石力学试验系统,在轴向应变率保持为常数的条件下,对雅安大理岩、贵溪红砂岩和大悟花岗岩进行了常规三轴压缩破坏试验,得到不同围压下岩石的应力一应变全过程曲线.利用试验得到的应力一应变全过程曲线,得到了各种岩石的应力脆性跌落系数与围压的关系表达式,为采用非理想脆塑性模型对大理岩介质及其中的构筑物进行数值分析提供了依据.     

复合岩石在三向受压状态下的应力—应变特性研究

本文采用一套刚性组件,在200t普通压力机上对复合岩石进行了三向受压的应力一应变全过程试验,为了比较,对复合岩石的各组成岩石也进行了三向受压的应力一应变全过程试验。通过试验研究发现,侧压效应对复合岩石的力学性态有很大的影响,复合岩石在峰值强度后,仍然具有承载能力。本文以试验数据为基础,对复合岩石在三向受压下的应力一应变全过程作了详细的讨论。     

Cu—Zn—Al合金应力诱发贝氏体相变

测定了母相状态的Ｃｕ－Ｚｎ－Ａｌ记忆合金，在恒应力作用下连续加热过程与中温等温过程的变形量。通过对温度－应变特性，时间－应变特性，组织形貌以及Ｘ光结构分析，揭示出了应力，温度及升温速度对应力诱发贝氏体相变的影响。     

砖砌体结构中梁端有效支承长度的探讨

从理论上推导出砖砌体结构中梁端有效支承长度的计算公式,还给出了考虑砖砌体受压应力一应变（σ－ε）全曲线时的梁端有效支承长度计算公式以及梁变为伸臂变截面梁时公式的运用。     

试样尺寸对粗粒土强度及变形试验影响研究

对某堆石料进行了3种（大、中、小）不同直径试样的三轴固结排水剪切试验,研究在不同试样尺寸下粗粒土的应力一应变及强度特性差异,初步探讨了试样尺寸大小对应力一应变及强度性质的影响。结果表明：不同尺寸大小的试样所测定的应力一应变关系及剪胀性相似,但量值大小有差异;对相同围压下同一种级配粗粒土,较小尺寸试样峰值强度高于较大尺寸试样的强度,随着试样尺寸的增大,增加幅度呈减小趋势;低围压下试样直径变化引起的摩擦角测定值变化较大,高围压下直径影响变小。对应l％应变的割线杨氏模量和体积模量随试样大小有一定程度的变化,其变化规律有待更多试验验证。     

基于统计断裂理论的混凝土本构关系的研究

以圆盘裂纹模型模拟混凝土内部的缺陷，基于统计断裂理论推导出了多轴应力下混凝土的损伤统计模型，并根据应变等价假说，建立了包含损伤的混凝土的基本本构关系。研究结果表明：混凝土中裂纹面之间的摩擦系数不同，混凝土的应力一应变曲线就不同，摩擦系数越大，混凝土的强度就越高；围压越大，混凝土的强度就越大。随着应力、应变的增大，损伤也随之增大，应力一应变关系也由线性变化为非线性；当混凝土的其他材性参数相同时，Weibull模量m越大，混凝土的强度就越小。这些均与当前研究成果相吻合。     

金属—陶瓷梯度材料动态温度响应变特性分析模型研究

以ＺｒＯ２／Ｔｉ－６Ａｌ－４Ｖ金属－陶瓷梯度材料为例，研究了梯度材料在承受热冲击载荷作用的动态温度响应分析模型问题，研究的重点是分析材料的热导率和热容随温度变化的特性（即变特性特性）对动态温度响应的影响。分析结果表明，当梯度材料承受热冲击载作用时，变物性特性对材料的动态温度响应和材料隔热性能预测的影响十分明显，在对梯度材料的隔热性能进行了优化设计时，必须采用动态变物性温度响应分析模型和理论进行分析     

应变速率对天津海积软土力学性能的影响

采用WF应力路径三轴仪,对天津滨海海积软土进行了不同围压、不同应变速率的三轴固结不排水剪切试验（CU）,分析了不同应变速率对海积软土试样的应力一应变关系、有效应力及试样破坏形态的影响．结果表明：CU试验应力一应变关系呈硬化特征,剪应力峰值随着应变速率的增大而增大,而孔压变化值则随着应变速率的增大而逐渐减小;不同应变速率的有效应力路径在相同固结压力下基本一致,因而正常固结黏土的有效应力路径具有唯一性;同时,应变速率对总应力强度有所影响,总应力的内摩擦角随着应变速率的增大而增大．     

骨料类型对混凝土棱柱体高温后力学性能影响研究

对不同骨料类型的混凝土棱柱体经历不同温度、不同冷却方式后的力学性能进行研究.试验结果表明,棱柱体的峰值应力下降速度和峰值应变增长幅度均随温度的升高而变大;相同条件下高温喷水冷却后混凝土棱柱体的峰值应力下降速度和峰值应变增长幅度均大于高温自然冷却后的试验值;高温喷水冷却后硅质骨料混凝土棱柱体的峰值应力下降速度和应变增长速度分别为钙质骨料混凝土的1.08倍和1.58倍.这些研究成果为进一步研究混凝土结构的抗高温性能及其损伤评估提供了一定的参考.     

高应力下接触面抗剪特性影响因素分析

通过在DRS 1型微机高压直残剪试验系统上所进行的建筑砂、标准砂、粉土和粘土与砼、金属光滑、金属粗糙界面的正交直接剪切试验研究表明 :高应力作用下土体与刚度较大的界面的剪切应力 剪切位移曲线呈现出应变硬化的特征 ,与低应力作用下土与不同结构剪切特性存在明显的区别 .根据试验数据的方差分析和直观分析结果 :对于残余强度 ,法向应力的大小是第一影响因素 ,其次是土体的性质 ,第三是界面的基底性质 ,剪切速率的影响最小 ;对于剪切应力 -剪切位移曲线起始切线斜率 ,法向应力的大小、土体的性质是主要影响因素 ,第三是界面的基底性质 ,剪切速率的影响最小 .总的来看 ,影响高应力下接触面抗剪特性的主要影响因素是法向应力的大小 ,土体的性质是其次 ,剪切速率和基底性质的影响可以不予考虑 .     

Effect of strain hardening and strain softening on welding distortion and residual stress of A7N01-T4 aluminum alloy by simulation analysis

The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress,plastic strain and welding distortion of A7N01-T4 aluminum alloy was studied by finite simulation method.The simulation results show that the weld seam undergoes strain hardening in the temperature range of 180-250 ℃,however,it exhibits strain softening at temperature above 250 ℃ during welding heating and cooling process.As a result,the strain hardening and strain softening effec...     

Actuation Mechanism of Two-step Reverse Transformation Behavior in TiNi Alloys Deformed at Parent Phase

1　IntroductionTiNishapememoryalloys (SMAs)arethepromisingfunctionalmaterialstobeusedasimportantactuatorsinmicromachinesandintelligentmachinesduetotheirlargeoutputstrainorstress[1,2 ] .ItiswellknownthattheSMAsdeformedatmartensiticphasehaveacapableofgeneratingforceormotionwithanenergyinputbyheating .Theac tuationcharacteristicoftheSMAsiscloselyrelatedtotheirdeformationformationandtemperature (thestateoftheSMAs) .Inotherwords ,theactuationcharacteristicoftheSMAsisdependentontheirreversema…     

Experimental and theoretical study on thermal and moisture characteristics of new-type bamboo structure wall

Thermal and moisture characteristics of the bamboo structure wall were tested in natural climate and three representative variation processes of heat and moisture: heating from solar radiation in summer at normal temperature and humidity, heating from solar radiation in summer at normal temperature and high humidity after rain, humidifying from brash in summer at high temperature and normal humidity. The results show that, in summer, the largest temperature difference between external and internal surface of the 28 mm-thick bamboo plywood wall is 11.73 °C (at 15:40) and the largest strain difference is 136 μm/m (at 18:50), both in ambient and indoor conditioned environment. In heating process, lengthways of the wall surface are in contracting strain while transverse ways are in expanding strain at initial stage and in contracting strain during later period. When the high temperature wall is humidified by rain, the surface temperature drops, moisture content increases and the expanding strain is presented on the surface during the whole process. Temperature and moisture content are two important factors which affect thermal and moisture stress (TMS) of the bamboo structure wall. The TMS is not only related to temperature and moisture content, but also greatly affected by temperature gradient, moisture content gradient and rates of changing.     

一种热成型钢热压缩流变行为的本构方程

根据热冲压工艺的时间—温度特征,采用Gleeble-3500热模拟试验机,在温度为773~1 173 K、应变速率为0.01~0.50 s-1条件下,对1种热成型钢进行热压缩实验,求解井上胜郎模型参数,获得相应的应力应变曲线。实验结果表明:变形温度和应变速率对该热成型钢力学性能有很大的影响,温度升高流变应力减小,应变速率增大流变应力增大。由计算所得井上胜郎模型参数得到模型的预测值与实验结果吻合较好,修正模型之后,得到的预测值更接近实验值。     

Hot deformation behavior of Super304H austenitic heat resistant steel

The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s~(-1) using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The results show that the flow stress of Super304H steel decreases with the decrease of strain rate and the increase of deformation temperature;the hot deformation activation energy of the steel is 485 kJ/mol.The hot deformation equation and the relationship between the peak stress and the deforma...     

Simulation of microwave's heating effect on coal seam permeability enhancement

As hydraulic fracturing was forbidden in some countries due to possible negative environmental impacts and enhanced coalbed methane(ECBM) was restricted by in-situ conditions, microwave heating was proposed to enhance coalbed permeability. One of the mechanisms of improving coal permeability with microwave irradiation is that thermal expansion caused by microwave heating. To study the influence of microwave's heating effect of coal samples, the simulations were conducted using a coupled electromagnetic, thermal and mechanical model in this paper. The temperature, Von-Mises stress and strain distribution of coal sample are recorded every 10 s. The permeability distribution is also obtained based on the relationship between strain and permeability from articles. It was found that volume average temperature, stress, strain and permeability increase almost linearly with time. The average permeability increased from 1.65×10~(-16) m~2 to 3.63×10~(-16)m~2 under 2.45 GHz and 500W microwave radiation after 300s. The significant increase proved microwave to be effective in coal seam permeability enhancement.     

Effects of Compression Parameters on Deformation Behaviors of Semi-Solid ZA27 Alloys

1　IntroductionZinc -basedalloyscontaining 8% - 2 7%alumi num ,1 % - 3 %copperandamarginalqualityofmagne siumhavebeenobservedtobepotentialmaterials,whichcouldbeeffectivelyandeconomicallysubstitutedinplaceofbronzes,aluminumalloys,castironsandsteelsforava rietyofengineeringapplications[1,2 ].Inspiteofanumberofmerits,suchasgoodcastability,mechanicalpropertiesandexcellentwearresistance,thealloyssufferfromporos ity,especiallyforZA2 7alloy,duetoitswiderangeofso lidificationtemperature[2 ].Inrecenty…     

热处理对4Cr5MoSiVl钢热疲劳裂纹扩展驱动力的影响

利用自制的高频感应加热、吹风冷却式试验机,对4Cr5MoSiVl钢缺口板状试样进行了Coffin型热疲劳试验。记录了热循环次数、热疲劳裂纹长度、试样中热应力变化之间的关系。分析了热循环过程中试样中应力的变化及热处理的影响。结果表明:热疲劳裂纹扩展驱动力为循环下限温度时的拉应力,驱动力的产生起源于循环上限温度时的压缩塑性应变,主要受钢的组织循环稳定性和钢的高温屈服强度所控制。4Cr5MoSiV1钢淬火后,经较高温度回火,使组织较为稳定时,可以得到较低的热疲劳裂纹扩展驱动力,从而具有较低的裂纹扩展速度。