【作者】 吴琳琳；

【导师】 郑津洋； 刘鹏飞； 徐平；

【作者基本信息】 浙江大学 ， 化工过程机械， 2014， 博士

【摘要】 深冷容器是用于液化天然气等深冷液化气体储运的极端承压设备,在能源、化工航空航天等领域已得到了广泛应用。奥氏体不锈钢是一种综合力学性能优良的材料,其韧塑性和低温性能尤为突出,被广泛用于深冷容器制造。为了实现国家倡导的“低碳”、“绿色”等发展理念,迫切需要通过提高许用应力、采用应变强化技术和采用分析设计等轻量化途径来减轻容器重量、降低重容比和制造运行能耗。在这一前提下,开展奥氏体不锈钢容器在室温和深冷环境下的强度研究,揭示奥氏体不锈钢深冷容器在不同工况下的强度裕度,对于促进深冷容器的轻量化设计,实现安全与经济并重、安全与资源节约并重具有重要意义。短时过量静载荷导致的韧性破坏是压力容器最基本的强度失效原因之一,是本文关注的对象。此前容器强度研究多集中于室温下简单结构容器的塑性垮塌失效,较少考虑三轴度效应对材料延性的削弱及其引起的复杂结构容器局部失效,也较少涉及深冷环境对容器强度的影响。为了分析深冷容器在不同工况下的强度,保证深冷容器的本质安全,本文在国家高技术研究发展计划(863计划)重点项目(项目编号2009AA044801)和教育部博士点基金(项目编号20090101120161)的支持下,以室温和-196℃深冷环境为例,在考虑三轴度效应的材料断裂应变、容器强度预测及弹塑性分析设计方法等方面进行研究,主要完成的工作如下：(1)开展奥氏体不锈钢光滑圆棒和缺口圆棒在室温和深冷环境下的拉伸试验。运用考虑微观损伤的Gurson-Tvergaard-Needleman (GTN)模型,建立拉伸试验全过程的参数化仿真模型,分析三轴度效应和深冷环境对材料断裂应变的影响,得出室温和深冷环境下材料断裂应变随三轴度变化的拟合关系。结果表明,随着三轴度的增大,材料断裂应变减小；深冷环境下材料的屈服强度和抗拉强度有大幅提高,断面收缩率和断裂应变有一定下降。(2)建立一种考虑三轴度效应的奥氏体不锈钢深冷容器强度预测方法。经室温水压爆破试验验证,本方法可以较好的预测容器强度。采用本方法探讨深冷环境对容器强度的影响,结果表明深冷环境对材料的强化作用会导致容器的塑性垮塌压力大幅提高,但深冷环境对材料的延性有一定削弱,导致容器的局部失效压力提高幅度有限；建议在深冷容器中尽量避免在高应力应变区设置高局部三轴度的结构附件,以降低局部失效风险,充分利用材料低温强化对容器强度的增益作用。(3)基于所建立的容器强度预测方法,参考国外先进技术标准,提出一种奥氏体不锈钢深冷容器弹塑性分析设计方法,并探讨其中材料本构模型和局部失效判据的设置。归纳奥氏体不锈钢深冷容器的常用轻量化途径,分析其在不同设计方法和不同工况下的强度裕度。结果表明,采用弹塑性分析设计和应变强化工艺等轻量化方法时,容器在常温和深冷环境下仍具有一定强度裕度。更多还原

【Abstract】 Cryogenic pressure vessels, which are used as normal storage and transportation equipments for cryogenic liquefied gases, are widely used as extreme pressure equipments in the fields of energy, chemical machinery, aerospace engineering and so on. With excellent cryogenic mechanical properties, austenitic stainless steel is now widely used in the manufacturing of cryogenic pressure vessels.To achieve national development concept of "low carbon" and "green", vessels thickness, weight, and energy consumption should be reduced through adopting light weight technologies such as increasing allowable stress, cold stretching technology, and design by analysis. In this context, researches on strength of austenitic stainless steel vessels at room temperature and cryogenic temperature, which reveal the strength margin of cryogenic vessels under different working conditions, have great significance in improving the design method of cryogenic vessels and realizing the balance between security and economy.Ductile rupture due to excessive short term static load is one of the most essential strength failure modes, which is also the focus of this dissertation. Previous research focused on plastic collapse load of simple pressure vessel at room temperature. However, few research has been introduced on triaxiality and its influence on material ductility, which could cause local failure of vessel with complex structure. Vessel strength under cryogenic environment is not fully investigated. Supported by the National High Technology Research and Development Program (863Program Project No.2009AA044801) and the Research Fund for the Doctoral Program from Ministry of Education of China (Project No.20090101120161), this dissertation focused on strength of austenitic stainless steel cryogenic vessels, and investigated the effect of triaxiality on fracture strain, strength prediction of cryogenic vessels and design method by elastic-plastic analysis. The main work is listed below.(1) Tensile tests of smooth specimen and notched specimen from austenitic stainless steel were carried out at room temperature and cryogenic temperature. Based on damage mechanics, the parameterized simulation model of the whole process of tensile test was established applying Gurson-Tvergaard-Needleman (GTN) model to predict the influence of notch sizes on the material ductile rupture failure, and analyze triaxiality effect and fracture strain at room temperature and cryogenic temperature. The results showed that high triaxiality and cryogenic temperature would decrease fracture strain.(2) Based on plastic collapse and local failure modes, strength prediction method of pressure vessels was established and proved by burst test at room temperature. This method was used in strength prediction of vessels under cryogenic environment. The result showed that plastic collapse load increased obviously under cryogenic environment, but high triaxiality of complex structure might cause local failure and the strength increase of complex cryogenic vessel might be limited.(3) Based on the strength prediction method established in this paper and advanced foreign standards, a design method by elastic-plastic analysis was introduced considering plastic collapse and local failure. The true stress-strain curve parameter and local strain limit were discussed for Chinese austenitic stainless steel and cryogenic vessels. Different light weight design methods were compared and strength margin of cryogenic vessels under room temperature and cryogenic temperature were analyzed. The results showed that vessels still had enough strength margin after using light weight design.更多还原