SiCp/6061Al合金复合材料的单轴循环变形行为及其时间相关特性

对T6热处理后的6061Al合金与SiCp／6061Al合金复合材料（14％，21％SiCp）的室温单轴循环变形行为进行了实验研觅讨论了基体合金和其复合材料在不同加载条件下的循环软／硬化行为和棘轮变形特征．实验研究表明：复合材料在宏观层次上体现出与基体相类似的应变循环特性和棘轮变形规律，即复合材料在非对称应力循环下也将产生一定的棘轮变形，并随应力幅值和平均应力的增加而增加；颗粒的引入使复合材料抵抗棘轮变形的能力增强，棘轮变形随颗粒含量升高而下降；复合材料的棘轮行为具有明显的时间相关特性，棘轮应变值依赖于应力率和峰值保持时间．研究得到了一些有助于复合材料循环变形行为本构描述的结论．     

45碳钢低周疲劳与应力循环棘轮失效的实验研究

对调质处理的45碳素结构钢进行了应变循环低周疲劳实验以及应力控制棘轮失效实验．对于前者进行了带平均应变和不带平均应变的实验，以研究平均应变对低周疲劳特性的影响；对于后者研究了平均应力和应力幅值对棘轮失效的影响．应变循环实验表明：平均应变对循环饱和行为以及低周疲劳循环失效圈数并没有明显的影响，但对材料的循环初期循环塑性行为有影响．棘轮失效实验结果表明：当应力幅值较大而平均应力较小时，材料的棘轮失效主要归于较大塑性应变幅值引起的低周疲劳破坏；当平均应力较大而应力幅值相对较小时，材料的棘轮失效主要归于较大的棘轮应变引起的材料韧性破坏，其失效准则可以用最大单调极限应变来表征．     

304不锈钢非比例循环棘轮行为的实验研究

在室温下对３０４不锈钢在非比例循环加载下的棘轮行为进行了实验研究。在圆形、菱形和直线形状的非比例双轴循环加载路径下,研究不同轴向平均应力、等效应力幅值大小及基历史下材料的棘轮行为特征,为了比较,还进行了单轴加载下该材料的循环棘轮行为实验,实验表明,３０４不锈钢的室温非比例循环棘轮行为明显地依赖于加载路径的形状;与单轴循环棘轮行为一样,非比例循环棘轮行为也明显地依赖于轴向平均应力和等效应幅值的大小及     

室温下20钢高周次单轴棘轮行为的实验研究

通过对20钢的单轴应变控制循环和应力控制循环实验研究, 揭示了20钢在室温下的循环变形特性, 讨论了材料的循环软/硬化特性和材料的屈服平台以及平均应力、应力幅值和应力比对材料高周次棘轮行为的影响. 研究表明: 20钢表现出弱的、与应变幅值相关的循环硬化特性; 其棘轮行为依赖于平均应力、应力幅值和应力比的大小, 在高应力水平时的高周次循环后期, 棘轮变形会出现<再次增长的现象; 材料的屈服平台对棘轮行为有明显的影响, 在对20钢的棘轮行为进行本构描述时需要加以合理考虑.     

304不锈钢的高温单轴应变循环与棘轮行为

对３０４不锈钢分别进行了高温单轴奕变控制和应力控制下的系统循环试验,揭示和分析了循环应变幅值,应变幅值历史以及温度历史对循环特性的影响以及应力幅值,平均应力及其历史对循环蠕变（棘轮效应）的影响,研究表明,无论单轴应变循环特性还是非对称单侧应力下的棘轮效应不但依赖于当前温度和加载状态,而且依赖于其加载历史,得到３０４不锈钢高温单轴循环行为的一些有意义的结果。     

6061-T6铝合金单轴时间相关循环变形行为

对6061-T6铝合金进行系统的单轴应变循环和应力循环实验，揭示该材料在室温和高温下的循环变形行为，讨论环境温度、加载速率、峰，谷值保持对其应变循环特性及棘轮行为的影响。结果表明，6061-T6铝合金表现出弱的循环软化特性，其棘轮行为不仅依赖于平均应力和应力幅值的大小，还依赖于加载历史。尽管该合金的单拉行为对应变率的变化不敏感，但其循环变形行为却体现出明显的时间相关特性，即；应变循环下，在峰／谷值有保持时的响应应力幅值明显小于没有保持时的值，且随着保持时间的增加，响应应力幅值将进一步减小；应力循环下，在峰值有保持时产生的棘轮应变比没有保持时的值大，且随着峰值保持时间的增加及应力率的降低，棘轮应变明显增大。     

Cyclic Elastoplastic Performance of Aluminum 7075-T6 Under Strain- and Stress-Controlled Loading

Elastoplastic investigations of aerospace aluminum are important in the development of an understanding of the possible cyclic transient effects and their contribution to the material performance under cyclic loading. Cyclic plasticity can occur in an aerospace aluminum component or structure depending on the loading conditions and the presence of external and internal discontinuities. Therefore, it is vital that the cyclic transient effects of aerospace aluminum are recognized and understood. This study investigates experimentally the cyclic elastoplastic performance of aluminum 7075-T6 loaded in symmetric strain control, and asymmetric stress and strain control. A combination of cyclic hardening and softening was noticed from high strain amplitude symmetric strain-controlled tests and at low stress amplitude asymmetric stress-controlled tests. From asymmetric strain control results, the extent of mean stress relaxation depended on the size of the strain amplitude. Additionally, saturation of the ratcheting strain (plastic shakedown) was also found to occur during asymmetric stress control tests. The experimental results were further analyzed using published microstructure research from the past two decades to provide added explanation of the micro-mechanism contribution to the cyclic transient behavior.     

Uniaxial ratcheting and low-cycle fatigue failure behaviors of AZ91D magnesium alloy under cyclic tension deformation

Uniaxial ratcheting and low-cycle fatigue failure behaviors of hot-rolled AZ91D magnesium alloy were studied by uniaxial cyclic stress-controlling tension deformation experiments. The effects of stress amplitude, mean stress and stress rate on the uniaxial ratcheting response and fatigue life of the hot-rolled AZ91D magnesium alloy were analyzed. Results show that (1) the ratcheting strain and ratcheting strain rate of the hot-rolled AZ91D magnesium alloy both increase with the increase of stress amplitude or mean stress; (2) increasing stress rate will decrease the ratcheting strain and ratcheting strain rate of the hot-rolled AZ91D magnesium alloy; (3) the increase of stress amplitude and mean stress can both reduce the fatigue life of the hot-rolled AZ91D magnesium alloy, while the fatigue life will be prolonged with the increase of stress rate.     

EXPERMENTAL STUDY ON TRANSFORMATION RATCHETING OF SUPERELASTIC NITI ALLOY

超弹性NiTi合金在应力控制循环载荷下会产生峰值应变和谷值应变的循环 累积-相变棘轮行为. 室温实验表明, 峰值应变和谷值应变的演化规 律与加载应力水平和加载波形密切相关; 同时, 在循环加载过程中, 随着 循环周次的增加, 奥氏体名义弹性模量减小, 马氏体名义弹性模量增大, 奥 氏体向马氏体转变的名义开始应力下降, 耗散能降低, 并在一定的循环次数 下趋于一个稳定值. 研究得到了一些有助于后续建立超弹性循环本构模型 的结论.     

SS304不锈钢高温非比例多轴加载下时相关循环变形行为的实验研究

在973 K下,对SS304不锈钢多轴循环加载下的时相关应变循环特性和时相关棘轮行为进行了实验研究.揭示了材料在不同加载路径、不同加载速率以及不同保持时间下的循环软/硬化特性和棘轮变形行为.结果表明：在高温下,材料的循环软/硬化和棘轮变形均体现出明显的时相关效应,即其循环变形行为不仅强烈依赖于加载速率,而且还明显依赖于保持时间;另外,材料的变形行为在高温下也具有强烈的加载路径依赖性.研究得到了一些有助于后续建立时相关本构模型的结论.     

Low cycle fatigue behavior of zirconium–titanium–steel composite plate

The low cycle fatigue behavior of zirconium–titanium–steel composite plate under symmetrical and asymmetric stress control was studied. The effects of mean stress and stress amplitude on cyclic deformation, ratcheting effect and damage mechanism were discussed in detail. The results show that under symmetric stress control, the forward ratcheting deformation is observed. Under asymmetric stress control, the ratcheting strain increases rapidly with mean stress and stress amplitude increasing. Under high stress amplitude, the influence of mean stress is more significant. In addition, by studying the variation of strain energy density, it is found that the stress amplitude mainly promotes the fatigue damage, while the mean stress leads to the ratcheting damage. In addition, fracto- graphic observation shows that the crack initiates in the brittle metal compound at the interface, and the steel has higher resistance to crack propagation. Finally, the accuracy of life prediction model considering ratcheting effect is discussed in detail, and a high-precision life prediction model directly based on mean stress and stress amplitude is proposed.     

������ʷ��63Sn37Pb��ѧ���ܵ�Ӱ��

 在室温下通过对63Sn37Pb进行一系列棘轮实验和单轴拉伸实验，得到加载历史对材料棘轮应变累积速率以及延伸率的影响关系。拉伸棘轮试验和压缩棘轮试验表明，在相同加载条件下，没有加载历史的试件较有加载历史的试件会发生更大的棘轮变形，加载历史在很大程度上抑制棘轮变形的累积速率。此外，没有加载历史的试件断后延伸率要比有加载历史的试件大。热处理可以改善材料的延性，有效的增大材料的延伸率。     

SS304不锈钢在室温单轴循环加载下的时相关棘轮行为

对SS304不锈钢在室温单轴循环加载下的时相关棘轮行为和时相关应变循环特性进行了实验研究．讨论了材料在不同加载速率、不同保持时间和不同加载波形下的循环软／硬化行为和棘轮行为特征．结果表明：即使在室温下,SS304不锈钢也表现出明显的时相关效应;材料的循环变形行为,特别是棘轮行为明显地依赖于加载速率和保持时间以及加载波形的形状．研究得到了一些有助于时相关循环变形行为本构描述的结论．     

304不锈钢棘轮变形过程中应变诱发马氏体相变行为研究

利用OM, SEM和XRD对单轴非对称应力循环下304不锈钢棘轮变形过程中的微观组织变化进行了实验观察. 结果表明: 304不锈钢棘轮变形过程中,当棘轮应变达到一定值后会 产生应变诱发马氏体相变, 形成板条状 马氏体,并且随循环周次的增加, 形成的应变诱发 马氏体相对量逐渐增加.因马氏体相变而诱发的塑性变形对总的棘轮变形量产生一定的影响,材料的棘轮应变应由两部分组成, 即应力引起的塑性应变和相变诱发的塑性应变.     

45钢在应变循环与棘轮变形下的随动硬化演化实验研究

对调质处理的45碳钢进行了不同应变幅值的对称应变和具有平均应变控制下的屈服面半径和背应力演化分析,及具有不同平均应力的低应力、较高应力幅值控制下的屈服面半径和背应力演化分析．研究表明：屈服面半径在给定应变幅值下随循环周次的增加而变小,且随循环塑性应变幅值增大而减小,在单调加载时增大;循环背应力幅值随单调应变而减小,随循环塑性应变幅值增大而增大．     

Reliability comparison between SAC305 joint and sintered nanosilver joint at high temperatures for power electronic packaging

Ratcheting behavior of sintered nanosilver joints was examined by cyclic shearing tests at different temperatures. Fatigue lives of sintered nanosilver joints were compared with those of soldered SAC305 joints. An improved non-contact displacement detecting system combining infrared heating was developed to measure the deformation of the joints. Effects of temperature, mean stress, and stress amplitude on the ratcheting behavior of both kinds of the joints were analyzed. Shear strength of the sintered nanosilver joints is larger than that of the soldered SAC305 ones. The ratcheting displacement and its rate in both kinds of the joints increase with increase in temperature, mean stress, and stress amplitude. The fatigue life of sintered nanosilver joint is much longer than that of soldered SAC305 one under the same loading conditions. It is concluded that sintered nonosilver joint has demonstrated a longer fatigue life and better response to shearing and cyclic loading than SAC305 joint, especially at high temperatures. An improved temperature-dependent modified Goodman model is proposed and is proved to be able to accurately predict the fatigue life of the sintered nanosilver joints and the soldered SAC305 joints by introducing the temperature-dependent fatigue strength exponent and the fatigue strength coefficient.     

紫铜的非比例循环塑性变形行为实验研究

对紫铜在非比例循环加载下的循环行为进行了实验研究,开展了圆形和菱形应变路径的双轴非比例循环加载试验,并进行了４种具有平均应力排比例循环路径的循环棘轮试验,实验研究表明,紫铜的塑性应变率方向和塑性模量的演化强烈地依赖于应变路径形状和等效应等幅值;紫铜的非比例循环棘轮行为也明显依赖于加载路径形状、幅值,平均庆力及其历史。     

Ratcheting Behavior of a Non-conventional Stainless Steel and Associated Microstructural Variations

Ratcheting fatigue behavior of a non-conventional stainless steel X12CrMnNiN17-7-5 has been investigated with varying combinations of mean stress (σ_m) and stress amplitude (σ_a) at room temperature using a servo-hydraulic universal testing machine. X-ray diffraction profile analysis has been carried out for assessing possible martensitic phase transformation in the steel subjected to ratcheting deformation. The results indicate that ratcheting strain as well as volume fraction of martensite increases with increasing σ_m and/or σ_a; the phenomenon of strain accumulation is considered to be governed by the associated mechanics of cyclic loading, increased plastic damage as well as martensitic transformation. A correlation between strain produced by ratcheting deformation and martensitic transformation has been established.     

High Load Ratio Fatigue Strength and Mean Stress Evolution of Quenched and Tempered 42CrMo4 Steel

The fatigue strength at a high number of cycles with initial elastic–plastic behavior was experimentally investigated on quenched and tempered 42CrMo4 steel. Fatigue tests on unnotched specimens were performed both under load and strain controls, by imposing various levels of amplitude and with several high load ratios. Different ratcheting and relaxation trends, with significant effects on fatigue, are observed and discussed, and then reported in the Haigh diagram, highlighting a clear correlation with the Smith–Watson–Topper model. High load ratio tests were also conducted on notched specimens with C (blunt) and V (sharp) geometries. A Chaboche model with three parameter couples was proposed by fitting plain specimen cyclic and relaxation tests, and then finite element analyses were performed to simulate the notched specimen test results. A significant stress relaxation at the notch root became clearly evident by reporting the numerical results in the Haigh diagram, thus explaining the low mean stress sensitivity of the notched specimens.     

非比例载荷下Al-7Si-0.3Mg合金的循环特性及微观机理

在等效应变幅为0.22%时, 研究了Al--7Si--0.3Mg铸造铝合金在比例、圆形、正方形、菱形、矩形与椭圆形路径下的循环变形行为, 并用TEM观察了疲劳失效试样的位错结构. 结果表明: 在多轴加载条件下, 材料均表现出循环硬化现象, 循环硬化的速率和程度对加载路径有依赖性; 非比例载荷下材料的疲劳寿命远小于比例加载时的寿命, 且非比例加载下的疲劳寿命对各种非比例加载路径有依赖性, 其中圆形路径下疲劳寿命最短; 位错在不同的加载路径下形成不同的组态结构, 位错与强化相、枝晶界及位错间的交互作用是铸造铝合金发生循环硬化的主要原因.