Effect of residual stress on the fracture of ferritic steels

为了准确地研究残余应力对断裂的影响，首先要在构件中产生预期的应力，同时适当地控制应力的强度，这是研究的主要难点。为了开发一种调整残余应力的方法，CEA-LISN设计了一种热处理工艺，可以通过仔细调整热处理来调整材料中产生的残余应力。该项目的目的是帮助设计，随后验证和优化热处理工艺。有限元模拟和实验技术的结合，如深孔钻孔和中子/x射线衍射将被使用。作为第一步，CEA设计的热处理工艺将在Bristol进行模拟。Abaqus和Code_Aster都将在项目开始时被考虑，然后在6个月内最终决定使用哪个软件。所研究的材料是一种结构复杂的Framatome RPV压力容器钢。对铁素体-马氏体RPV钢的热处理进行全面的文献综述，以确定关键的影响参数（例如，在热处理过程中是否存在相变）。在等待CEA提供材料和热处理工艺的最终设计时，布里斯托尔的学生将使用模型材料和已知的热处理来辅助学习有限元模拟和残余应力测量。一旦项目的有限元模拟得到开发和验证，优化过程就可以应用于它，通过改变热处理来微调目标残余应力。

To accurately study the Residual Stress (RS) effect on fracture, the first step is to be able to create the expected Stress in the component while properly controlling of the intensity of the stress, which is the main difficulty. In order to develop a methodology to tune residual stress CEA-LISN has devised a heat treatment process which can adjust the residual stress induced in the material through careful adjustment of the heat treatment. The objective of this project is to help design and subsequently validate and optimise the heat treatment process. A combination of finite element simulation and experimental techniques such as deep hole drilling and neutron/x-ray diffraction will be used. As the first step, the heat treatment process designed by CEA will be simulated at Bristol. Both Abaqus and Code_Aster will be considered in the start of the project before a final decision is made within 6 months on which software to be used. The material of interest is a Framatome RPV pressure vessel steel with complex microstructure. A thorough literature review on the thermal treatment of ferritic-martensitic RPV steels will be carried out to identify the key influencing parameters (e.g. is there a phase transformation during the heat treatment). While awaiting material and the final design of the heat treatment process from CEA, the student at Bristol will be using a model material and a known heat treatment to assist with learning finite element simulation and residual stress measurement. Once the finite element simulation of the project is developed and validated, optimisation processes can be applied to it to fine tune the target residual stress through change in the heat treatment.