304不锈钢高温多轴非比例循环棘轮行为的粘塑性本构描述

对304不锈钢600℃下的非比例循环棘轮行为进行了系统的实验研究，在统一粘塑性循环本构模型的框架下对其进行本构描述，模型中，通过随动硬化背应力演化和各向同性变形阻力演化，对304不锈钢在非对称应力循环下的循环附加硬化流动特性进行模拟，在等温条件下，在各向同性变形阻力演化方程中引入温度项来考虑温度效应，在随动硬化应力演化方程中引入动态恢复项的衰减系数，反映材料在特定温度范围（500－600℃）下入最大应变幅值衰减记忆函数∧（q)和最大各向同性变形阻力衰减记忆系数ω反映加载历史对循环棘轮行为的影响，将模型应用于304不锈钢高温多轴循环棘轮行为及其对加载历史依赖性的描述中，预言结果与实验结果吻合较好。     

碳纤维增强PEEK树脂基复合材料的单轴时相关循环特性实验研究

通过对碳纤维/PEEK复合材料(纤维体积分数30%)的单调拉伸、 应力控制循环、 应变控制循环实验, 对该材料的应力、 应变循环特性以及棘轮行为的率相关、 时相关特性进行了系统的研究。研究表明: 与PEEK树脂基体材料相比, 加入碳纤维使材料的抗蠕变性能有所提高。在应变控制循环实验中, 响应应力幅值与应变加载速率和应变加载幅值密切相关; 在应力松弛效应的影响下, 响应应力幅值随着应变峰值保持时间的增加而减小。室温下, 碳纤维/PEEK复合材料在非对称应力循环中产生明显的棘轮应变, 并且对加载应力幅值和平均应力具有明显的依赖性, 此外, 当在较低的加载速率和具有一定峰值保持时间情况下, 棘轮应变显著增强。      

McDowell模型改进及1070钢棘轮效应的预测

利用McDowell 模型对1070 钢比例和非比例循环加载条件下的棘轮效应进行了预测,通过对McDowell模型的修正,为McDowell 模型中的单轴参数Ai引入了与塑性应变累积相关的演化方程,改进后的McDowell 模型能精确的预测具有拉压平均应力的单轴棘轮效应,具有平均应力的拉扭比例加载,常轴向应力的扭转循环,非比例循环载荷以及多重步骤加载条件下单轴平均应力变化的棘轮效应,改进的模型对较大循环数的棘轮效应也能给予较好的描述。     

单轴应力循环作用下AZ91D镁合金的棘轮行为

对AZ91D镁合金进行了室温单轴应力控制下的循环实验,研究幅值应力σ_p、平均应力σ_m及峰值应力σ_a、应力比及加载历史对AZ91D镁合金棘轮行为的影响.结果表明:棘轮应变率随σ_a和σ_m的提高而增大;σ_p和应力比对棘轮行为产生很大的影响;先前高平均应力、幅值应力水平的循环历史很大程度上抑制后续低应力水平时的棘轮行为;先前低应力水平对后续的棘轮行为也会产生影响;AZ91D镁合金的ε_r与σ_p并不一一对应,给出了ε_r与σ_m和σ_a的关系式.     

多种循环加载制度下Q235材料性能试验

对Q235钢进行了变应力载荷幅值及不同预变形和载荷保持时间等条件下的循环加载试验,并分析了其力学响应和材料性能。研究结果表明：Q235钢在应力控制的循环加载过程中表现出明显的循环软化特性和棘轮效应,棘轮应变的大小主要取决于载荷水平;当循环载荷逐级增大时,前期的变形会导致后期的棘轮应变增大;而当循环载荷逐级减小时,后期的棘轮应变值取决于最大载荷时的棘轮应变,且棘轮应变率接近于零;当预变形的响应应力峰值小于后期控制应力峰值时,预变形对材料的棘轮效应具有抑制作用,且预变形量越大,抑制效果越明显;载荷保持时间延长会使材料的棘轮应变增大,棘轮应变率增大,从而加速材料失效。     

Electronic Speckle‐Pattern Interferometry Measurements of Structural Ratcheting Strain

Abstract: Several tensile specimens with a central hole were subjected to a cyclic loading for which the Von Mises stress was beyond the initial yield stress in the vicinity of the hole. The tensile machine was fixed together with a phase‐shifting electronic speckle‐pattern interferometry measurement bench that makes it possible to perform strain measurement along the tensile axis. The plastic strain map corresponding to the 30th cycle was obtained. For the considered measurement field, the resolution of the strain measurement is close to 10^?5. By varying the loading, it was possible to detect and observe the deformation corresponding to an early stage of the ratcheting phenomenon. The non‐ratcheting cyclic plasticity behaviour was not observed during the 30th cycle. In the Discussion section, the experimental results were interpreted using Melans’s theorem, which allowed us to determine an upper bound for the yield stress. Eventually, it is shown that the procedure followed in this work could be a way to obtain some interesting data related to the material behaviour laws.     

内压弯管在面内循环弯曲载荷作用下棘轮效应的研究

利用多轴试验机研究了内压及面内循环弯曲载荷作用下低碳钢弯管的棘轮效应。试验研究表明最大棘轮应变发生在顶线位置的环向。对于个别试件,内缘线位置也发现了环向棘轮应变,但所有试件的外缘线位置均未发现棘轮应变。内压不变时棘轮应变速率随面内循环弯曲载荷的增大而增大;面内循环弯曲载荷不变时,棘轮应变速率随内压的增大而增大。通过用户编程,采用Chen—Jiao—Kim随动强化模型,利用弹塑性有限元法对弯管进行了循环塑性分析。与试验结果相比,Chen—Jiao—Kim随动强化模型能给出较好的预测。采用C—TDF提出的等效塑性应变增量控制法确定了结构的棘轮边界。     

A plastic shakedown constitutive curve based on uniaxial ratcheting behavior of 304 stainless steel at room temperature

On the basis of the Bauschinger effect, a relationship between the elastic space defined in this study and the accumulated plastic strain is measured in uniaxial ratcheting tests of 304 stainless steel at room temperature. According to this relationship, a new model of uniaxial ratcheting is established and used to simulate uniaxial ratcheting behavior. The results of simulation agree well with the experimental results. These results demonstrate that the relationship between the elastic space and the accumulated plastic strain plays an important role in uniaxial ratcheting simulation. Furthermore, by taking into account the interaction of ratcheting and viscoplasticity, the relationships among elastic space, accumulated plastic strain and loading cases are discussed. It can be seen that, when the stress ratio R of valley stress versus peak stress is not less than zero, the accumulated plastic strain is a function of the peak stress. So, a constitutive curve is obtained to describe the stable states of plastic shakedown for 304 stainless steel material under the stress ratio R ≥ 0. It can be used to determine the accumulated plastic strain of engineering structures under cyclic loading only by an elastic–plastic analysis.     

SS304不锈钢循环变形行为温度效应的实验研究

对SS304不锈钢进行了系统的室温、高温单轴和非比例多轴应变控制循环和应力控制循环行为的实验研究。重点讨论了温度变化对材料应变循环特性和棘轮行为的影响；同时也讨论了在同一温度、不同加载形式条件下材料的应变循环特性和循环棘轮行为特征。结果表明，SS304不锈钢的循环变形行为具有明显的温度效应，并且在400～600℃范围内，材料会体现出显著的动态应变时效特性。     

合金钢的高温单轴棘轮效应实验研究1.25Cr0.5Mo

利用MTS810电液伺服试验机在300℃温度下对1.25Cr0.5Mo合金钢进行了单轴棘轮效应实验研究,探讨了温度、应力幅值、应力峰值、平均应力以及加载历史对材料棘轮效应的影响.以0.1%/s及0.2%/s两种不同的应变加载速率分别对材料进行单轴拉伸实验,结果表明1.25Cr0.5Mo合金钢在所研究的温度范围内的变形行为是率无关的;在0.4%应变幅值下进行了单轴应变循环实验,响应应力幅值随循环次数几乎没有变化,可视为循环稳定材料;单轴棘轮效应实验表明棘轮应变速率随平均应力、应力幅值及温度的升高而增大;棘轮变形依赖于加载历史,先前较大的循环应力对后继较小的循环应力下的棘轮变形起抑制作用.