8090Al—Li合金的低周疲劳行为

研究了不同热处理状态８０９０Ａｌ－Ｌｉ合金的循环疲劳与断裂行为。结果表明，相同时效状态合金的循环应力随应变幅的增加而提高，低应变幅下时效状态影响较小；随应变幅的提高，时效状态的影响增强，合金出表现出的循环硬化，软化以及低周疲劳性能与位错组态，沉淀相的尺寸，晶界ＰＦＺ的形成和断口形貌密切相关。     

GH3044的低周疲劳行为研究

研究了镍基高温合金GH3044在室温和600℃的低周疲劳行为,对循环应力-应变和应变寿命数据进行了分析,给出了GH3044合金在此温度下的疲劳参数.合金的循环应力响应行为在室温下呈现循环硬化而后软化的特征,而在600℃时呈现循环硬化的特征,原因在于循环变形过程中位错之间以及位错与析出相之间的相互作用.Coffin-Ma...     

16Mn钢非比例循环塑性的研究

对正火状态１６Ｍｎ在二维循环复杂应变路径下的流动特性和强化进行了系统的实验研究。对于特定的循环应变路径，当应变幅值较小时，材料多表现为循环弱化；随着应变幅值的增加，循环弱化的现象逐渐消失，在某些路径下甚至表现为循环强化。在非比例循环加载条件下，材料的强化与路径形状密切相关。实验表明，应变的幅值和路径方向的变化所造成的强（弱）化间存在耦合。本工作在材料对非比例加载史的记忆和Ｌｅｎｓｋｙ局部确定性假设     

Cu-Cr-Zr合金高温热变形行为

为研究Cu-Cr-Zr合金的高温热变形行为,建立Cu-Cr-Zr合金的高温本构模型,采用Gleeble-1500D热模拟实验机对该合金进行不同变形条件下的热压缩实验。实验参数为:变形量60%、应变速率0. 1~5 s-1、变形温度650~900℃。实验结果表明:变形初始阶段加工硬化大于动态软化作用,使得应力值迅速增大至峰值,之后动态软化大于加工硬化作用,使得应力值降低至一定程度再趋于平稳。通过对Cu-Cr-Zr合金应力-应变曲线的变化规律进行分析可得,低应变速率和高变形温度都会促进合金动态再结晶的程度。利用计算软件对实验数据进行计算和整理,将由线性拟合所得数值代入Arrhenius本构模型,可得Cu-Cr-Zr合金的本构模型。     

CuCrZr铜合金高温阶梯疲劳与循环塑性行为研究

对CuCrZr铜合金在300和400℃开展了阶梯疲劳试验研究,从循环应变幅、平均应变、平均应变率和能量耗散率等方面研究其循环塑性行为。研究发现,CuCrZr铜合金的循环软硬化特征以及棘轮效应受到温度与循环应力的共同作用,温度越高,越易发生循环软化现象,同时棘轮效应也更加显著。基于对CuCrZr铜合金高温拉伸断裂能与高温阶梯疲劳总耗散能的对比发现,两者均与温度相关,因此将高温拉伸断裂能作为温度补偿参数,提出了一种基于能量法的线性损伤疲劳寿命预测模型,对CuCrZr铜合金高温阶梯疲劳寿命进行预测。最后,基于断口观察分析了CuCrZr铜合金与温度相关的失效机制：在较低的温度下容易发生疲劳裂纹失效,而随着温度的升高,更易发生棘轮应变累积的韧性失效。     

高强韧Ti-3Al-5Mo-4Cr-2Zr-1Fe合金低周疲劳性能研究

通过室温下应变控制疲劳试验研究了高强韧Ti-3Al-5Mo-4Cr-2Zr-1Fe合金的低周疲劳性能。结果表明:在高应变幅值下(Δεt/2=1.0%,1.2%,1.4%,1.6%),合金的循环应力响应表现为初始循环软化,而后趋于循环稳定;在低应变幅值下(Δεt/2=0.6%,0.8%),合金的循环应力响应表现为循环饱和特征。断口形貌观察发现:应变幅值为0.6%时,疲劳裂纹源只有一处,在断口表面分布有大量细小的二次裂纹。当应变幅增加到1.6%时,组织中发现多处疲劳裂纹源,二次裂纹的数量明显减少,但长度和宽度明显增加。透射电镜结果表明:在低应变幅值下(Δεt/2=0.6%),在αp/β界面处出现大量的位错堆积,在此处易产生应力集中导致微裂纹形核。而在高应变幅值下(Δεt/2=1.6%),在αp相中有明显的变形不均匀性,在αp相内出现大量的位错缠结和位错碎片,并且在αs相中出现一些位错塞积,但在β基体中没有明显的位错堆积情况。由于长条αp相的存在,能够提升α相和β相变形的相容性,延缓疲劳裂纹形核和扩展,因此使Ti-35421合金有着优异的低周疲劳性能。     

Zr41.25Ti13.75Ni10Cu12.5Be22.5块状非晶合金的低周疲劳行为

研究了室温完全反向应力控制条件下块状非晶合金Zr41.25Til3．75Nil0Cul2．5Be22．5的低周疲劳行为，结果表明，完全非晶和合晶态相非晶合金均表现为循环稳定直至断裂．完全非晶合金的寿命远高于合晶态相非晶合金．通过试样断裂表面及外表面SEM观察，解释了应变稳定循环产生的机制．两种非晶合金的疲劳断口均可观察到裂纹的萌生、扩展及过载断裂区．合晶态相非晶中的晶态相没有起到阻碍裂纹扩展的作用，而是作为裂纹萌生点或疏松．     

一种定向凝固镍基高温合金的高温低周疲劳行为

本文研究了一种定向凝固镍基高温合金的高温低周疲劳行为。结合对合金微观变形结构的观察,分析了温度、应变保持时间对合金低周疲劳性能的影响。结果表明,温度对合金的变形有着明显影响,在760℃以下合金呈现循环硬化,而在850℃和980℃时则表现为循环软化,这是由于合金在不同温度范围内具有不同的微观变形机制。在应变峰值、应变谷值以及同时在应变峰值和谷值分别引入保持时间后,合金的高温低周疲劳寿命均有一定程度的降低。     

AZ91镁合金的应变疲劳行为研究

研究了铸态和挤压态AZ91镁合金的室温应变疲劳行为。结果表明，铸态镁合金表现为循环应变硬化，而挤压态镁合金可呈现循环应变硬化、软化或循环稳定。与此同时，对两种状态的AZ91镁合金的应变寿命行为和循环应力-应变行为进行了分析测试，确定了相应的室温应变疲劳参数。此外，利用扫描电子显微镜观察分析了铸态和挤压态AZ91镁合金的疲劳裂纹萌生和扩展行为。     

Simulation of welding of 2A12-T4 aluminum alloy by different yield stress models

To investigate the effects of strain hardening, strain softening and dynamic balance behaviors of 2A12-T4 aluminum alloy on the welding residual plastic strain and residual stresses, the true stress-true strain curves at different temperature of certain material were used in the FEM modeling process. The simulation results show that little influence on the welding residual plastic strain and residual stresses was found as the strain hardening, strain softening and dynamic balance worked together.     

FeWMoCo时效硬化合金的表面冶金工艺（Ⅰ）

利用双层辉光离子渗金属技术可在工业纯铁表面形成铁、钨、钼、钴时效合金。研究了形成这种合金的表面冶金工艺和渗层组织状态、渗层成分分布以及渗金属工艺参数改变对渗层厚度及渗层成分分布的影响。结果表明， 表层Ｗ， Ｍｏ ， Ｃｏ 含量可达到高Ｃｏ 时效合金Ｗ１１ Ｍｏ７Ｃｏ２３ 的水平， Ｃｏ 含量为１８ ％ ～３０ ％ ， Ｗ 含量为７ ％ ～１７ ％ ， Ｍｏ 含量为５ ％ ～９ ％ 。     

Cyclic deformation and phase transformation of 6Mo superaustenitic stainless steel

A fatigue behavior analysis was performed on superaustenitic stainless steel UNS S31254 (Avesta Sheffield 254 SMO), which contains about 6wt.% molybdenum, to examine the cyclic hardening/softening trend, hysteresis loops, the degree of hardening, and fatigue life during cyclic straining in the total strain amplitude range from 0.2 to 1.5%. Independent of strain rate, hardening occurs first, followed by softening. The degree of hardening is dependent on the magnitude of strain amplitude. The cyclic stress-strain curve shows material softening. The lower slope of the degree of hardening versus the strain amplitude curve at a high strain rate is attributed to the fast development of dislocation structures and quick saturation. The ε martensite formation, either in band or sheath form, depending on the strain rate, leads to secondary hardening at the high strain amplitude of 1.5%.     

多轴载荷下ZL101铝合金的低周疲劳行为

研究不同等效应变幅下ZL101铝合金在多轴比例和非比例载荷下的低周疲劳行为,并用透射电镜观察合金的疲劳行为中的位错结构。结果表明：合金在两种加载方式下均表现为循环硬化;在非比例载荷下合金表现出附加强化,但程度不明显;合金的疲劳寿命随等效应变幅的增加而降低,合金在非比例加载下的疲劳寿命低于比例加载时的疲劳寿命。对位错结构的观察表明,随等效应变幅度的提高,合金的低周疲劳位错结构从交叉位错带转化为位错胞,合金在非比例加载下更易形成位错胞结构。     

Cu及Cu－Zn合金预变形和循环软化的滑移线形貌

观察了两种不同滑移方式的材料──纯Ｃｕ及Ｃｕ－Ｚｎ合金经预变形及循环软化后的表面滑移线形貌．发现二者预变形的双交滑移特征不同，且Ｃｕ－Ｚｎ合金的交滑移与应力—应变曲线上的动态应变时效现象相对应．Ｃｕ－Ｚｎ合金循环软化后有两种衬度的滑移带，而纯Ｃｕ则主要表现为驻留滑移带，说明两种材料疲劳应变的容纳方式不同．根据滑移带形貌解释了它们不同的软化行为．     

15MnVN钢的氢致硬化和氢致软化

研究了不同氢含量、应变速率条件下１５ＭｎＶＮ钢氢致硬化和氢致软化现象。试验证实，氢的存在首先造成氢致硬化，而当塑性变形开始后又导致氢致软化。这一作用受钢中氢偏聚控制，并受应变速率的诱导作用。氢的存在对钢的抗拉强度无明显影响。     

Low cycle fatigue life: Dependence on test mode

Fatigue hardening and softening in materials result in different lives in low cycle fatigue, depending on the test mode. The problem is discussed based on the cyclic stress-strain relation, and a suitable testing mode is suggested for the design of structural parts, which are subjected to either constant load or constant displacement fatigue.     

铝合金板材温热成形性能

在20℃～300℃的温度范围内,分别对7B04-T6和6061-T6铝合金薄板进行了单拉试验,结果表明,7B04-T6高强度铝合金的断后延伸率和拉伸极限应变在温热状态下都有显著的提高,比较适合于温热成形,而6061-T6则不太适合。另外,基于Fields&Backofen本构方程,对7B04-T6在不同温度状态下的强化规律进行了分析和探讨,结果表明,随着温度的逐渐升高,应变强化指数n值不断减小,应变率敏感系数m值则显著增大,应变率强化明显增强,这也是在温热状态下其成形性能提高的主要原因。     

Influence of Tempering Temperature on Cyclic Viscoplastic Behaviour of 55NiCrMoV7 Steel

Low cycle fatigue behaviour of a steel 55NiCrMoV7 under tour tempered conditions is reported. One special type of total swain controlled isothermal cyclic deformation tests were performed in the temperature range 20℃ to 600℃ for the steel tempered 2h at 350℃, 460℃, 560℃ and 600℃. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturatioo. At 10^-2 strain rate, σmax.Δσ／2 decrease with the test tumperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300℃ to 600℃, but the maximal softening intensity occurs at room tumpemture. The strain rate influences notably the cyclic behavioor when T≥50℃, The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.     

铸造铝合金在多轴非比例载荷下的低周疲劳行为研究

主要研究了356铸造铝合金在多轴非比例载荷下的低周疲劳性能。结果表明，合金在循环变形过程中表现为循环硬化特征，循环硬化的程度表现出对非比例加载路径的依赖性；在相同等效应变幅值下，合金的非比例加载低周疲劳寿命小于比例加载，且非比例加载低周疲劳寿命也表现出对非比例加载路径的依赖性；在多轴疲劳寿命预测模型中考虑非比例加载路径对疲劳寿命的影响可以大大提高寿命模型预测的精确度。     

Length scale-dependent deformation behavior of nanolayered Cu/Zr micropillars

The mechanical behavior of incoherent Cu/Zr multilayers was studied in uniaxial compression experiments using micropillars with individual layer thicknesses (h) ranging from 5 to 100 nm. The deformation behavior of these micropillars are size dependent, transiting from dislocation dominated symmetrical slip at large h to shear localization induced by asymmetric slip and grain boundary mediated deformation at small h. During compression studies the multilayer micropillars exhibit a transition from strain hardening to shear softening at small h, and work softening at greater h. A maximum strain hardening rate is observed at a critical h of 20 nm, which was explained in terms of a transition from dislocation interactions to cross-slip of dislocations. The mechanical strength of the micropillars is also dependent on h, which was quantitatively analyzed using the confined layer slip model. In addition, the influence of pillar diameter on the mechanical behavior is also investigated. The effect of extrinsic size on the deformation mechanisms is discussed with respect to the intrinsic size effect with variation in h.