考虑应变硬化的水电站压力钢管 整体安全评估

本文提出了考虑材料应变硬化的水电站压力钢管整体安全评估方法,该法引入以整体安全系数为评估指标的承载力极限状态方程,依据ASME压力容器管道与规范中考虑应变硬化的钢材本构模型,采用弹塑性分析求解考虑应变硬化后的结构极限承载力和结构整体安全系数,参照国内外压力钢管设计规范拟定了结构整体安全系数限值,形成了可成套应用的结构整体安全评估方法。研究表明,该法可为压力钢管承载力安全评估提供新途径,并可用于优化压力钢管结构设计方案。     

骨料级配对应变硬化水泥基材料力学性能的影响

水泥基复合材料的高脆性是诱发结构开裂、腐蚀甚至失去承载能力的主要原因.PVA纤维增强水泥基复合材料（SHCC）的应变硬化特性和多微缝开裂特征可显著改善此类材料的性能.通过三点受弯和直拉试验对比了骨料颗粒级配合理与否对SHCC材料力学性能的影响.结果表明：适宜的颗粒级配可以显著改善SHCC的应变硬化特性,骨料的最大粒径可以由ECC材料常用的110μm放大到1.25 mm,便于此类材料在实际工程中的推广应用.     

Theoretical calculation of the strain-hardening exponent and the strength coefficient of metallic materials

The purpose of the present article is to theoretically calculate the strain-hardening exponent and the strength coefficient of metallic materials. For this purpose, two equations are used. The first one correlates the strain-hardening exponent and the strength coefficient with the yield stress-strain behavior, while the other one correlates the fracture strength and the fracture ductility. From these two equations, the expressions of both the strain-hardening exponent and the strength coefficient are deduced. Theoretical results from the deduced expressions are then compared with test data. Through the comparison of equations and data, if adequate test data are lacking, the deduced expressions can be used to theoretically calculate the strain-hardening exponent and the strength coefficient for metallic materials. The characteristics of the theoretical approach are simple and easy to use. In addition, the theoretical results can be further applied to examine the correctness of the test data.     

X80管线钢真实应力屈强比的测定及对管线安全性的影响

试验测算出X80、X65、X60、X46、Q235等五种材料的名义应力屈强比σs/σb和真实应力屈强比Ss/Sb及硬化指数n.比较发现,Ss/Sb值较σs/σb值小约13%,表明X80等高强度、高屈强比材料在屈服后真实塑性变形裕度仍较大;管线钢n对σs/σb的变化也并不敏感.由此认为,屈强比对管线结构安全性的影响并非如通常认为的那么严重.     

城市固体废弃物应变硬化机制与强度参数确定方法

 通过对常规三轴仪进行改装,开展最大竖向应变达50%的城市固体废弃物(MSW)三轴剪切试验。试验表明：大应变条件下MSW试样发生破坏且其破坏应变随填埋深度增大而减小。通过组分分离得到MSW的基本相和加筋相,并对其分别进行三轴固结排水剪切(CD)试验,发现其应力–应变曲线均呈应变硬化型。在此基础上,对基本相进行筛分,并结合不同粒径粒组的微观结构阐述基本相中有机纤维体的存在形式及其加筋作用机制。进一步对各粒组进行CD试验,发现除粒径小于0.075 mm的粒组外其余粒组的应力–应变关系均表现为应变硬化。通过基本相灼烧前后的CD试验比较,发现有机纤维体在应变达到一定程度后才开始发挥加筋作用,且剪切过程中伴随着纤维体断裂以及纤维体与颗粒间滑移。最后,基于MSW的三轴剪切试验结果,分别对三轴固结不排水剪切(CU)试验和CD试验抗剪强度参数的确定方法进行探讨。     

Enhanced mechanical properties of dual-phase steel by repetitive intercritical annealing

The effect of repetitive intercritical annealing on the mechanical properties and work-hardening response of a typical C–Mn dual-phase (DP) steel was studied by consideration of different pre-intercritical annealing microstructures and martensite volume fractions. It was revealed that the DP steels produced from the initial martensitic microstructure have much better mechanical properties compared with those originated from the ferritic–pearlitic banded microstructure. The repetitive intercritical annealing of the initial martensitic microstructure was effective for the enhancement of strength–ductility balance, where at a comparable ductility; a twofold increase in the tensile strength was obtained. Finally, these results were discussed based on the Crussard–Jaoul work-hardening rate analysis.     

Features of local inelasticity distribution in D16T aluminum alloy under static tensile conditions

We have assessed the characteristic of local inelasticity distribution, which controls the evolution of microstructural processes in a loaded surface layer of D16T structural aluminum alloy specimen in view of the strain-hardening stages and deformation mechanism changeover. The deformation stages for static tensile conditions are correlated with the characteristic of local inelasticity distribution, in order to determine the relationship between the deformation mechanism changeover and local inelasticity kinetics for the transition point from strain-hardening to strain-softening of the alloy under study. Translated from Problemy Prochnosti, No. 4, pp. 141–148, July–August, 2009.     

Effect of Scandium Additions on the Tensile Properties of Cast Al-6Mg alloys

Effect of aging on the mechanical properties of Al-6Mg alloy doped with varying concentration of scandium ranging from 0.2 to 0.6 wt.% is analyzed. As-cast samples were aged isochronally for 60 min at different temperatures ranging from 100 to 500 °C. Evaluation of mechanical properties of the aged Al-6Mg (Sc) alloys was done by employing an Instron testing machine. Various strain rate of testing were used to find out the values of strain-rate sensitivity of the experimental alloys. The influence of scandium is much pronounced on yield strength than on the tensile strength. Alloys with higher scandium content have shown higher yield strength and the values of strain-rate sensitivity ‘m’ at peak-aged condition have been found to be comparatively high at higher scandium concentration. The fracture of the experimental alloys occurs through microvoid coalescence.     

Comparison of formability of steel strips, which are used for deep drawing of stampings

The paper concerns evaluation and comparison of formability of steel strips, which are used in Czech Republic for production of intricate deep stampings. The properties of sheet-metal which have the principal influence upon the success of deep drawing or strech-forming are described. Two methods used for determination of strain-hardening exponent are compared. It is concluded, that the method according to SN 42 0436 is suitable for approximation of stress-strain curve of given sheet-metal only from point of view of functional values. The values of strain-hardening exponent, calculated by the method using maximum uniform elongation, are more strongly correlated with pure stretchability than are the values of it, calculated by the method according to SN 42 0436.     

Micromechanical Modeling of Strain-Hardening Behavior in Dual-Phase Steels

A mathematical model is developed to consider the impact of microstructural parameters, including the volume fraction and the average particle size of martensite, on the flow stress and strain-hardening behavior of dual-phase microstructure. In this regard, the micromechanical approach is applied for partitioning the stress and strain in ferrite and martensite. Martensite carbon content and geometrically necessary dislocations, generated from austenite-to-martensite transformation, and strain accommodation at the ferrite–martensite interface, are involved to modify the partitioned stress of martensite and ferrite, respectively. Having partitioned stress in each phase, the global stress is estimated as the function of steel chemical composition, ferrite grain size, martensite particle size, aspect ratio, and volume fraction. To evaluate the applicability of the proposed model, four dual-phase steels containing 12, 25, 34, and 48% volume fractions of martensite are prepared from the intermediate quenching process, and then after the strain-hardening stages are investigated. Comparing the experimental result and model output reveals that the presented model shows good predictive capabilities to identify strain-hardening stages and estimate the inverse of the strain-hardening exponent.