单轴压缩下炭质板岩的应变速率效应及声发射特性

为了探究应变速率对炭质板岩单轴力学特性和声发射特征的影响,开展了4组不同准静态应变速率（8.50×10^-6s^-1、1.70×10^-5s^-1、1.70×10^-4s^-1和3.34×10^-4s^-1）下的单轴压缩试验,并同时监测了加载过程的声发射信号。基于试验数据,总结分析了应变速率对炭质板岩应力-应变关系、能量耗散及声发射特征的影响规律,探讨了应变速率的影响机制。同时,基于加载过程中耗散能密度的演变规律,提出了将耗散能曲线平直段起点作为炭质板岩闭合应力σ_cc、平直段终点作为扩容应力σ_cd的特征应力确定方法。结果表明：在准静态应变速率范围内,炭质板岩的弹性模量和峰值强度随应变速率的增大均先增大后减小,在应变速率1.7×10^-4s^-1时达到最大值;闭合应力、起裂应力和扩容应力与峰值应力的比值基本在0.37、0.55和0.74左右,不随应变速率发生变化;应变速率对声发射信号影响显著,随应变速率增加,0~50kHz内的主频率占比逐渐增加,而100~250kHz内的主频率占比逐渐减小,炭质板岩的破坏形式逐渐由张拉破坏变为剪切破坏。     

不同应变率下冰的动态力学行为及毁伤效应分析

为了解冰材料在宽应变率范围内的动态压缩力学特性,利用准静态压缩实验装置和分离式Hopkinson压杆（SHPB）装置开展了应变率为10^-4~10³ s^-1范围内-20℃冰试件的动态压缩实验,测得了冰在该应变率范围的单轴压缩强度处于8.44~40.70 MPa之间,并进一步研究了其动态压缩强度随应变率变化的演化规律,给出了相应的数学表达式;利用修正的含高压高应变率效应的冰本构模型,通过二次开发技术将其嵌入到有限元软件LS-DYNA中,数值研究了冰弹高速撞击铝合金靶板的毁伤规律.     

海水海砂再生混凝土单轴受压应力-应变全曲线

为探究海水海砂再生混凝土（SSRAC）力学性能,设计了不同配合比下海水海砂再生混凝土棱柱体试件,并进行了单轴受压应力?应变全曲线测试。在试验加载应变率10^-5 s^-1和10^-2 s^-1下,得到了试件的破坏模式,分析了峰值应力、峰值应变和弹性模量的变化规律以及应变率、再生粗骨料（RCA）取代率和贝壳含量对上述指标的影响规律,讨论了海水海砂再生混凝土的动态增长因子（DIF）。基于电子计算机断层扫描（CT）测试得到了海水海砂再生混凝土内部的孔隙分布,对应力?应变曲线的特征指标变化趋势进行了解释。最后,在现有再生混凝土单轴受压本构模型的基础上,考虑特征指标的动态增长因子,通过修正下降段形状系数得到了预测应力?应变全曲线。     

Cu-Cr-Zr-Ce合金高温流变应力的研究

利用Gleeble-1500D热模拟试验机对Cu-Cr-Zr-Ce合金在变形温度为600~800 ℃、应变速率为0.01~5 s^-1条件下进行了热压缩试验,测定了其应力-应变曲线,并通过光学显微镜观察了其热压缩过程中的微观组织.结合两者分析了动态回复和再结晶机制.结果表明,动态再结晶是该合金软化的主要机制.     

真空热压烧结CuW30复合材料的热压缩变形特性

采用真空热压烧结法制备了CuW30复合材料,在Gleeble-1500D热模拟机上对该材料进行等温热压缩模拟试验.研究了温度为650~950 ℃、应变速率为0.01~5 s^-1、最大变形量为50%条件下的流变应力行为.结果表明：CuW30复合材料存在明显的动态再结晶特征.材料的稳态流变应力随应变速率的增大而增大,在恒应变速率条件下,合金的真应力水平随温度的升高而降低.热变形过程的流变应力可用双曲正弦本构关系来描述.在给定的变形条件下,计算的热变形激活能为231.150 kJ/mol.根据试验分析,合金的热加工宜在850~950 ℃范围内进行,应变速率为0.01~0.1 s^-1.     

6111铝合金热变形流变行为及本构模型

试验材料为厚2 mm的6111铝合金,利用ZWIKE100KN高温材料试验机对该材料在350~550℃,0.1~10 s^-1应变速率下进行热拉伸试验.结果表明：受位错密度的影响,6111铝合金的流变应力随温度的升高而降低,随应变速率的增大而增大;可以分为应变硬化和饱和稳态流变两个阶段.基于Voce饱和外推模型（H-S模型）构建以温度、应变、应变速率为变量因素的6111铝合金流变应力本构模型,通过回归拟合试验数据求解模型中的参数.试验数据与计算该模型得到的预测曲线吻合较好,验证了该模型的可行性.     

真空热压烧结Cu-Al2O3热变形行为研究

采用真空热压烧结法制备Cu-Al₂O₃复合材料,并在Gleeble-1500D热模拟机上对其进行高温压缩试验.阐述了内氧化原理,分析了真空热压烧结制备的铜基复合材料的微观组织和材料性能,研究了在变形温度为650~950℃,变形速率为0.01~5 s^-1,最大真应变为0.7时的流变应力行为.结果表明：变形温度和变形速率对流变应力的影响较大,随着变形温度的升高和应变速率的减小,峰值应力逐渐减小.采用双曲线正弦模型建立了材料高温变形时的流变应力本构方程,确定热变形激活能为220.7 kJ/mol.     

钢管RPC抗多次冲击动态力学性能研究

采用φ75 mm分离式霍普金森压杆试验装置对16个钢管活性粉末混凝土试件进行了不同应变率下的多次冲击压缩试验,得到了动态应力-应变曲线和破坏形态.试验结果表明：当应变率小于80 s^-1时,钢管RPC在多次冲击下仍能保持较稳定的力学性能;当应变率大于106 s^-1时,钢管RPC在多次冲击下发生塑性变形,表现出良好的延性,核心RPC开裂.多次冲击作用下,钢管RPC仍保持较高的强度、较好的延性和完整性,是一种抗冲击性能良好的防护工程材料.     

TC6钛合金4种典型组织的动态力学行为研究

 采用分离式霍普金森压杆技术,研究了4种典型组织TC6钛合金试样在高应变率加载条件(10³ s^-1)下的动态力学行为,并分析了原始组织对动态力学行为的影响.结果表明:在高应变率加载条件下,4种典型组织TC6钛合金的流变应力显示了相同的变化规律:变形初期,应变较小时,流变应力随应变增加快速增加;随后流变应力出现振荡,应力达到峰值后,流变应力随应变的增大而逐渐减小,呈现稳态流变;最后流变应力快速下降;在10³ s^-1数量级的高应变率加载条件下,随着应变率的增加,4种组织的流变应力均呈上升趋势;4种组织TC6钛合金都是应变率敏感材料,但4种组织的应变率效应不同;63#网蓝组织显示了较高的应变率敏感性,64#固溶时效组织则表现出较低的应变率敏感性,61#等轴组织和62#双态组织应变率敏感性相当.     

3种观赏性石斛的光合特性比较研究

为探明3种观赏性石斛属Dendrobium Sw.植物在光合生理方面的差异,为其栽培及规模化种植提供理论依据。本研究以3种观赏性石斛(叠鞘石斛D.denneanum Kerr.、流苏石斛D.fimbriatum Hook.和束花石斛D.chrysanthum Wall.ex Lindl.)为材料,测定其叶片的光响应曲线、CO₂响应曲线及叶绿素相对含量(SPAD值),探究其光合特性。结果表明,叠鞘石斛、流苏石斛和束花石斛3种石斛属植物的光补偿点(LCP)分别为2.15 μmol·m^-2·s^-1、3.74 μmol·m^-2·s^-1、1.79 μmol·m^-2·s^-1,光饱和点(LSP)分别为995.09 μmol·m^-2·s^-1、679.44 μmol·m^-2·s^-1、712.28 μmol·m^-2·s^-1,LCP均低于5 μmol·m^-2·s^-1,LSP均低于1 000 μmol·m^-2·s^-1,属于典型的阴生植物,具有较强的耐阴性;3种石斛的最大净光合速率(P_max)分别为3.54 μmol·m^-2·s^-1、3.86 μmol·m^-2·s^-1、4.03 μmol·m^-2·s^-1,表观量子效率(AQY)分别为0.042,0.044和0.051,束花石斛的P_max和AQY最大,光合作用能力较强。3种石斛的CO₂响应曲线中,最大净光合速率(A_max)大小依次为叠鞘石斛(11.99 μmol·m^-2·s^-1)、流苏石斛(10.87 μmol·m^-2·s^-1)、束花石斛(4.75 μmol·m^-2·s^-1),叠鞘石斛利用CO₂进行光合作用的能力最强;3种石斛的CO₂饱和点(CSP)无显著性差异,在CO₂浓度不大于2 000 μmol·mol^-1时均未到达饱和点;CO₂补偿点(CCP)具有显著性差异,CCP分别为100.12 μmol·m^-2·s^-1、158.02 μmol·m^-2·s^-1、134.44 μmol·m^-2·s^-1,其中叠鞘石斛的CCP最低,对低浓度CO₂的利用能力最强。3种石斛叶片的SPAD值分别为51.09,56.93和58.06,其高低与其净光合速率的大小有一定程度的相关性。在3种石斛中,束花石斛的光合作用能力最强,对弱光的利用能力较强;流苏石斛对弱光的利用能力较弱,光照适应范围狭窄;叠鞘石斛对强光的利用能力较强,光合作用适应范围较广。此外,3种石斛均具有较强的耐阴性,对CO₂的耐受性也较强,在种植时应提供适当的遮阴和增加CO₂浓度来提高石斛的光合作用能力。     

闭孔泡沫铝压缩力学性能的实验和三维有限元模拟

基于X射线电子计算机断层扫描技术,建立了反映闭孔泡沫铝真实结构的三维有限元模型.对闭孔泡沫铝准静态和动态压缩力学性能进行了实验和数值模拟,分析了闭孔泡沫铝的变形特性及力学性能,验证了模型的可靠性.结果表明,准静态压缩下,试件主要沿加载轴45°方向产生塑性变形.压缩速率为低速时,其变形模式与准静态相同.闭孔泡沫铝试件截面上结构薄弱处首先出现应力集中,材料达到塑性屈服.在高速压缩下,试件加载端首先达到塑性屈服.比较闭孔泡沫铝不同应变率下的屈服强度,动态压缩下的屈服强度远高于准静态压缩下的.应变率280~700 s-1下,其屈服强度变化不明显,应变率继续升高至2 000 s-1,屈服强度略微提高.      

超纯Cr17铁素体不锈钢热变形过程的动态回复行为

采用热力模拟试验机进行单道次压缩试验,旨在揭示超纯Cr17铁素体不锈钢在热变形过程中的动态回复行为.在变形速率为1 s-1,最大真应变为0.8的条件下研究了900~1 150℃范围内的热变形行为及组织演化规律.结果表明,单道次压缩得到的应力-应变曲线均呈动态回复型.变形温度越高,动态回复越快.当变形温度较低时,微观组织演化以晶界拱出和变形晶粒的形成为主要特征;当变形温度较高时,微观组织演化以大量亚晶界和亚晶的形成为主要特征.     

Mechanical behavior of a near α titanium alloy under dynamic compression: Characterization and modeling

Dynamic compression tests under strain rates from 870 s^?1 to 2100 s^?1 were conducted for a near α Ti–8Al–1Mo–1V titanium alloy with equiaxed microstructure. Compression behavior, adiabatic shearing and band microstructure were investigated via characterization and calculation. The results demonstrate that all dynamic constitutive curves exhibited obvious stress fluctuation phenomenon with double increase-decrease changing stages at the primary stage of compression. The dislocation multiplication theory can be used to explain this phenomenon. After the stress fluctuation period, work hardening coexisted with the thermal softening, resulting in the slow hardening tendency in constitutive curves. J-C model was utilized to quantify the dynamic constitutive curves. The deviations between the predicted and experimental curves under high strain rates may be attributed to the over-consideration of thermal softening effect in J-C model. Adiabatic shearing band (ASB) began to form under the strain rate of 2100 s^?1. A total shearing strain of 8.1 within ASB achieved in 8.9 μs, corresponding to a local strain rate of about 9.1 × 10⁵ s^?1 and is over 430 times of the macro strain rate. Post annealing was conducted on ASB before EBSD characterization. Due to the static recrystallization during annealing, the α phase within ASB generally presented as ultra-fine grains less than 1 μm in diameter.     

不同应变速率热变形双相不锈钢的取向特征

在MMS-200热模拟实验机上,对S32750超级双相不锈钢在1 000℃,应变速率为0.01～10 s-1的条件下进行了高温压缩实验,利用电子背散射衍射(EBSD)技术对其晶体取向和晶界特征进行了分析.研究结果表明:在低应变速率时,铁素体晶粒出现〈111〉∥压缩轴织构;在高应变速率时,〈001〉织构又明显增加.铁素体晶粒随着应变速率的增加变得细小,而小角度晶界数量增加;在应变速率为10 s-1时,形变后奥氏体晶粒得到了〈110〉织构.应变速率的增加使奥氏体晶粒变大,小角度晶界数量增加.奥氏体相在小应变速率条件下变形可以获得更多的Σ3孪晶界.     

Hot deformation map and its application of GH4706 alloy

The hot deformation behaviors of GH4706 alloy were investigated using compression tests in a deformation temperature range from 900℃ to 1200℃ with a strain rate range of 0.001–1 s?1. Hot processing maps were developed on the basis of the dynamic material model and compression data. A three-dimensional distribution of power dissipation parameter (η) with strain rate and temperature reveals that η decreases in sensitivity with an increase in strain rate and a decrease in temperature. Microstructure studies show that the grain size of GH4706 alloy increases when η is larger than 0.32, and the microstructure exhibits local deformation when η is smaller than 0.23. The hot processing map at the strain of 0.7 exposes a domain peak at η=0.32 for the temperature between 940℃ and 970℃ with the strain rate from 0.015 s?1 to 0.003 s?1, and these are the optimum parameters for hot working.     

3D激光沉积增材制造TC4高应变率动态力学行为及本构关系研究

通过对3D激光沉积TC4在较宽温度（298~1 073 K）和应变率范围（0.001~5 000 s^-1）内的单轴压缩试验,系统研究了该材料的塑性流动行为,分析了材料的微观组织特性及其变形断裂微观机制.结果表明材料在压缩载荷下具有明显的应变率硬化和温度软化效应.在压缩加载条件下,材料的破坏模式为绝热剪切带的萌生和拓展,而初始缺陷成为诱导剪切带形成的主要原因.3D激光沉积TC4材料屈服强度与铸造TC4接近,略低于传统锻造TC4.文中基于位错动力学热激活理论建立了可以较好描述材料在不同温度不同应变率下的塑性流动行为物理概念的本构模型.     

Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical (USC) rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s-1. The softening mechanism was dynamic recovery (DRV) at 950°C and the strain rate of 1 s-1, whereas it was dynamic recrystallization (DRX) under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ·mol-1. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate (θ)–flow stress (σ) and -?θ/?σ–σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s-1, with a power dissipation efficiency η greater than 31%.     

Hot deformation behaviors of WE71 alloy under plain strain compression at elevated temperature

Hot deformation behaviors of WE71 (Mg–7Y-1Nd-0.5Zr) alloy was investigated by plain strain compression tests conducted at temperatures ranging from 350 °C to 500 °C and strain rates varying from 0.01 s^-1 to 10 s^-1. Results show that the hot deformation of WE71 was accompanied by the precipitation of rich Zr phase with granular shape and block-shaped phase rich in element Y. When deformed at low temperature and high strain rate, the softening behavior of the alloy was synergically determined by shear bands propagation, adiabatic heating, twinning formation and dynamic recrystallization (DRX). For the conditions of high temperature and high strain rate, DRX was the major softening mechanism while the formation and annihilation of extension twinning resulted in a special flow curve characteristic at the strain of around 0.3. According to the microstructural observations, it can be concluded that the irregular flow curves of WE71 alloy during plain strain compression process are mainly ascribed to shear bands propagation, adiabatic heating, twinning formation and DRX.     

Dynamic recrystallization behavior of the Ti–48Al–2Cr–2Nb alloy during isothermal hot deformation

The hot deformation behavior of the as-cast Ti–48Al–2Cr–2Nb alloy was investigated by isothermal compression tests at deformation temperatures ranging from 1000℃ to 1200℃,and strain rates from 0.001 s~(-1)to 0.1 s~(-1).The single peak stress features common to all flow curves indicate that DRX is the dominating softening mechanism.The calculated values of the hot deformation activation energy Q and stress index n are 296.5 kJ mol~(-1)and 3.97,respectively.Based on this,the Arrhenius type constitutive equation was successfully established.The DRX critical condition model and relationship among DRX volume fractions,deformation temperatures and strain rates were obtained to optimize the process.Combined with microstructure analysis,it's concluded that 1200℃/0.01s~(-1)is the optimization parameter.Besides,both DDRX and CDRX were observed in theγphase evolution.The deformation mechanism from the inter-grain dislocation motion to the grain boundary migration and grain rotation was discussed.     

铜/石墨复合材料热变形行为研究

通过Gleeble-3500热模拟试验机对铜/石墨复合材料进行热压缩试验,研究变形温度为700～850 ℃、应变速率为0.001～1.000 s^-1时该复合材料的热变行为。通过光学显微镜研究复合材料显微组织的演变,根据实验数据构建该复合材料的本构方程和热加工图。使用Zener-Hollomon参数模型对该复合材料的流变应力进行研究。研究发现,铜/石墨复合材料的流变应力随着应变温度的升高而降低,随应变速度的增大而增大。计算得出该复合材料的热变形激活能为463.02 kJ/mol,表明材料具有良好的成形能力。通过构建的本构方程验证了最大应力的吻合性,发现计算值和试验值的误差在9.5%以内,说明该方程对复合材料的流变行为具有指导作用。热加工图表明了该复合材料的适宜加工温度为780～820 ℃,变形速率为0.050～0.100 s^-1;变形温度为830～850 ℃时,变形速率约为0.001 s^-1。