报告内容简介

During uniaxial tensile test, some metals exhibit a distinct yield point, known as upper yield point, followed by an abrupt load drop and a nearly constant load plateau known as Lüders plateau, with the stress level referred to as lower yield stress. Over the extent of Lüders plateau, the material is macroscopically characterized by inhomogeneous deformation which appears as localized plastic band which is called Lüders band. Lüders band is usually observed to initiate at the grip location, and propagate from one end or both ends to another at an angel of 50 ~ 55 °.

Most nuclear steels are subject to strain ageing effect. At lower temperature, static strain ageing (SSA) is observed in the form of Lüders plateau. While at higher temperatures within the range of dynamic strain ageing (DSA), C-Mn steels used for the secondary systems (feed water line and steam line) in nuclear industry are sensitive to DSA at in-service temperatures (around 200 °C). Lüders band significantly affects the bending behaviour of steel pipes/tubes. Bending moment plateau can be observed alongside localized curvature. For tubes with larger D/t ratio and longer Lüders strain, premature collapse was found to occur before the material proceed to hardening regime.

Strain-based design (SBD) is desired in lieu of traditional stress-based design when applied load is well beyond yield. Yield point elongation, which is commonly observed in carbon steels such as pipeline steel, has not been sufficiently understood regarding fracture assessment. Meanwhile, operating pipelines are subject to a biaxial loading condition, which is induced by additional internal pressure. However, existing design and analysis codes such as BS 7910, DNV-RP-F101, R6 do not incorporate biaxial loading in fracture assessment, resulting in underestimation of crack driving force. Thus, a detailed, systematic study on the effect of yield plateau, with and without biaxial loading, within the scope of SBD is pursued. This on-going project aims to a) develop a strain-based crack driving force estimation scheme for pipeline with flaws subject to high plastic straining; b) ssystematically investigate the effect of internal pressure on fracture behaviour of pipeline girth welds; c) uunderstand the influence of Lüders plateau on fracture behaviour of pipeline girth welds, with and without internal pressure; d) understand the real behaviour of Lüders deformation and improve the fracture assessment in presence of Lüders plateau; and e) propose assessment procedures for SBD incorporating biaxial loading and Lüders plateau. Some experimental and numerical simulation results will be discussed.

报告人简介

王彬-西安交大固体力学专业1985年毕业，88年和91年在英国曼大获机器人动力学硕士和冲击动力学博士。先后在新加坡南洋理工，澳洲帝京，英国曼大和阿伯丁大学任教。现任伦敦布鲁奈尔大学Reader in Applied Mechanics and Structural Integrity, 澳门太阳娱乐网站官网副院长。
 
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