GH4169合金高温力学行为本构建模及参数识别

针对涡轮盘用GH4169合金开展了高温下单调拉伸、对称循环及非对称循环的实验工作,结果表明,该材料具有比较明显的循环软化和平均应力松弛特性.采用带Ohno/Wang修正的Chaboche粘塑性理论本构方程,对其表现出的复杂力学现象进行本构建模,介绍了Levenberg-Marquadt非线性优化算法,结合材料实验数据并通过该算法识别了本构方程参数,将本构方程通过用户子程序嵌入到有限元软件ABAQUS中,对GH4169合金的上述实验现象进行了数值模拟,计算曲线与实验曲线取得了较好的一致性.     

高聚物粘弹性力学模型计算中容易被忽视的一个基本问题

在应用粘弹性力学模型模拟线形高聚物应力松弛现象时,不能忽视一个基本问题:在维持总形变不变的情况下,总应力是在逐渐衰减的,即应力不是恒定值。本文对高聚物力学松弛及粘弹性的本质进行了讨论。     

The Effect of Plastic Prestrain on Mechanical Characteristics of Grade 45 Steel and D16T Alloy under Static and Cyclic Loading

The paper covers an experimental study of the laws that govern the variation of yield limit and stress-relaxation limit as a function of stress amplitude and plastic strain in Grade 45 steel and D16T alloy under the conditions of preliminary static and cyclic tension including strain aging. The mechanical characteristics of these materials are shown to grow with increasing plastic strain irrespective of the loading type but decrease with increasing stress amplitude. It has been found that as a certain level of plastic strain is achieved the stress-relaxation levels in the materials become the same irrespective of the type of pre-loading. __________ Translated from Problemy Prochnosti, No. 4, pp. 33 – 45, July – August, 2005.     

0Cr20Ni12Mn5Mo2NbN钢循环应力应变本构关系

针对奥氏体0Cr20Ni12Mn5Mo2Nb N钢开展了系列应变幅的循环加载试验,分析了其循环应力应变特性,结果表明,循环全过程中真应力和真应变呈指数关系,基于该指数关系提出了描述循环应力应变关系的本构模型:σ=σ0+α·exp(β·ε)。     

面向货物装卸需求的越库仓门分配和货车排序

在货物种类多、批量少的越库调度系统中,货物的装卸顺序要求对于优化仓门分配和货车排序问题起着重要作用。针对这种情况,以最小化越库操作完工时间为目标,建立越库调度模型。分别基于优化仓门分配和货车排序问题,设计惯性权重非线性改变和增加交叉操作的改进粒子群算法进行迭代寻优。最后通过不同规模的数值实验,将改进粒子群算法与标准粒子群算法和遗传算法进行对比分析,实验结果表明改进粒子群算法在求解精度上比标准粒子群算法和遗传算法有明显优势,在求解时间上优于遗传算法,略逊色于标准粒子群算法。     

Ratcheting response of nylon fiber reinforced natural rubber/styrene butadiene rubber composites under uniaxial stress cycles: Experimental studies

The present study intends to study the ratcheting response of nylon fiber reinforced natural rubber (NR)‐styrene butadiene rubber (SBR) composite samples under asymmetric stress cycles. Uniaxial tests conducted on composite samples have shown how influential the weight fraction of short nylon fibers on the stress‐strain curves/loops under monotonic and cyclic loads is. NR/SBR composite samples with various fiber contents of 0, 10, 20, 30, and 40 per hundred rubber (phr) were tested under asymmetric stress cycles. In these tests, stress‐strain hysteresis loops were progressively shifted over stress cycles resulting in progressive plastic strain accumulation. Over stress cycles, ratcheting strain progressed within the first few cycles with a relatively high rate, and as the number of cycles increased, this rate decayed resulting in a plateau in strain accumulation (shakedown). The ratcheting strain rate and magnitude resulting in shakedown were highly affected by the nylon fiber content. The experimental observations showed that this plateau (shakedown) occurred after a number of cycles in NR/SBR composite samples where the widths of hysteresis loops stayed unchanged. Samples with no fiber and that with 10 phr fiber content possessed high ratcheting rates leading samples to failure after a few stress cycles. Fracture surfaces in these samples were further analyzed through SEM investigation.     

一种基于混合硬化本构模型的汽轮机轮盘榫槽疲劳寿命预测方法

针对汽轮机转子轮盘的受力特点,以非对称载荷下材料的瞬态应力应变响应为基础,在内变量理论框架下,建立起某型汽轮机轮盘材料的率无关循环塑性本构模型;并结合局部应力应变法,进一步建立了基于混合硬化本构模型(N-5L1)描述平均应力松弛行为的汽轮机轮盘榫槽疲劳寿命预测方法。通过与实验结果相比较,表明混合硬化本构模型能够较好地模拟脉动加载下转子轮盘材料的循环应力应变响应及平均应力松弛行为,由此建立的寿命预测方法可对轮盘榫槽进行较为准确的疲劳寿命预测(与试验寿命误差总体落在1.5倍分散带以内),明显优于基于平均应力松弛经验公式的疲劳寿命预测值。     

Modeling of Constitutive Behavior for Epon 828/T-403 at High Strain Rates

Experimental results on the uniaxial compressive stress-strainbehavior of Epon 828/T-403 over a strain rate range from 1.1 × 10^–4 to 5.2 × 10³ s^–1were simulated using a viscoelastic viscoplastic constitutive modeldeveloped by Hasan and Boyce (1995). An optimal combination of materialparameters for the constitutive model was determined by curve-fittingthe experimental results. A comparison between the modeling andexperimental results shows that this model, with proper parameters, iscapable of capturing the strain-rate effects, as well as the typicalpolymeric compressive stress-strain behavior, of Epon 828/T-403, whichincludes the stages of linearly elastic, nonlinearly elastic, yield-like(peak) behavior, strain softening, and nearly perfect flow. For all thestress-strain behavior modeled over seven decades of strain rate span,the maximum error between modeling and experimental results is less than25%. The temperature increase induced by the dissipated plasticwork is also computed and found to be between 3 and8°C at these strain rates.     

The rate-dependent behaviour of ± 55 ° filament-wound glass-fibre/epoxy tubes under biaxial loading

This paper presents the results of an experimental investigation into the behaviour of glass-fibre-reinforced epoxy tubes subjected to monotonic biaxial loading. Commercially available tubes with a filament winding pattern of ± 55 ° were tested in a biaxial testing machine with various ratios of axial stress to hoop stress. In addition, the tubes were tested at three rates of monotonic loading. The resulting stress/strain curves were analyzed and biaxial failure envelopes in terms of stress and strain were constructed demonstrating the complexity of the behaviour of the tubes. It is shown that the rate and ratio of biaxial loading affect the monotonic failure strength, damage accumulation and the mode of failure. In addition, these results are discussed based on macro and micro observations of damage and failure modes.     

The Non-Linear Viscoelastic Response of Polycarbonate in Torsion: An Investigation of Time-Temperature and Time-Strain Superposition

Data are presented from torsional stress relaxationexperiments on a commercial polycarbonate. Tests were performedon samples over a range of torsional strains from 0.0025 to 0.08and at temperatures from 30 to 110°C at a fixed aging time of64,800 s (18 h). Following the scaling approach of Penn andKearsley [Trans. Soc. Rheol. 20 (1976)] we were able todetermine the stress relaxation response at shear strains to0.07. Then the individual data sets at each strain andtemperature could be described using a stretched exponential formrelaxation function. Over the range of temperatures studied thedata at each strain were superimposed using conventional time-temperature superposition. For strains up to the yield strainthe data at each temperature could also be superimposed to form amaster curve following the principle of time-strainsuperposition. Interestingly, the master curves found from time-strain superposition at each temperature did not have the sameform. Similarly, the master curves found from time-temperaturesuperposition at each strain did not have the same form.     

Greatly Improved Conductivity of Double‐Chain Polymer Network Binder for High Sulfur Loading Lithium–Sulfur Batteries with a Low Electrolyte/Sulfur Ratio

Binders have been considered to play a key role in realizing high‐energy‐density lithium–sulfur batteries. However, the accompanying problems of limited conductivity and inferior affinity of soluble polysulfide intermediates bring down their comprehensive performance for practical applications. Herein, the synthesis of a novel double‐chain polymer network (DCP) binder by polymerizing 4,4′‐biphenyldisulfonic acid connected pyrrole monomer onto viscous sodium carboxymethyl cellulose matrix, yielding a primary crystal structure is reported. Consequently, the resulted binder enables superior rate performance from 0.2 C (1326.9 mAh g^?1) to 4 C (701.4 mAh g^?1). Moreover, a high sulfur loading of 9.8 mg cm^?2 and a low electrolyte/sulfur ratio (5:1, µL mg^?1) are achieved, exhibiting a high area capacity of 9.2 mAh cm^?2. In situ X‐ray diffraction analysis is conducted to monitor the structural modifications of the cathode, confirming the occurrence of sulfur reduction/recrystallization during charge–discharge process. In addition, in situ UV–vis measurements demonstrate that DCP binder impedes the polysulfide migration, thereby giving rise to high capacity retention for 400 cycles.