Physically-based modelling of inelastic deformation of martensitic steels at high temperature

 
Speaker: Professor Noel O'Dowd
Affiliation: School of Engineering
             Bernal Institute/ University of Limerick, Ireland
Date:June 6th,2017 Time:10:00-12:00 Location:A509


Abstract: 
Martensitic steel is widely used in pipe and boiler components of conventional power plant due to its excellent high temperature characteristics. The objective of this work is to investigate the micro-mechanisms of deformation and fracture in a modified 9Cr-1Mo steel (P91).  Martensitic steels have complex, hierarchical microstructures and deformation at the macroscale is influenced by interactions between blocks, packets and prior austenite grain (PAG) boundaries in the material during plastic deformation. Electron backscatter diffraction (EBSD) and scanning electron microscope (SEM) are employed to characterise the steel, identifying block/packet/PAG boundaries and their relative orientations. The microstructural deformation of P91 has been examined experimentally at 500 oC using a combination of mechanical testing, electron backscatter diffraction (EBSD), and finite element analysis (FEA). The measured experimental microstructural deformation in the vicinity of a sharp notch has been compared with the predictions from a microstructural model using a representative volume element (RVE) approach, incorporating a crystal plasticity material model. A non-linear, strain gradient crystal plasticity model is used to simulate the mechanical response of the material. Two different approaches to represent the microstructure of P91 are discussed. One using a directly measured microstructure from an EBSD scan and an alternative approach using a modified Voronoi tessellation (VT) approach. The orientation relationship between the PAG, packet and block for P91 steel is found to have the Kurdjumow-Sachs (K-S) relationship. This orientation information is incorporated explicitly to represent the material microstructure within a representative volume element (RVE) in a finite-element analysis. The modified VT model is a substitute for the EBSD model at the block level. The simulation results reveal size dependence of block/packet boundaries on the overall plastic deformation and show the importance of the correct representation of the material microstructure to predict mechanical behaviour. The implications of using microscale models in the prediction of global failure and structural integrity of components is also considered.


 
Biography:
Professor Noel O'Dowd is Chair of Mechanical Engineering at the University of Limerick. Noel received his degree in Mechanical Engineering from NUI Galway and went onto compete a PhD in Solid Mechanics from Brown University, USA. After completing his PhD, he took up a research fellowship with the Graduate Aeronautical Laboratories at the California Institute of Technology. Professor O'Dowd then joined the academic staff at Imperial College London for thirteen years before joining the University of Limerick in 2006. He was Vice-Chair of the American Society of Pressure Vessels committee on Materials and Fabrication for four years and is a Visiting Professor at Imperial College London. Professor O'Dowd's research is in the area of computational mechanics and fracture mechanics of engineering materials. He has published over a hundred and thirty research articles in these and related areas.

信息来源: 理学院 发布人:周璇浏览量:2248发布日期:2017-06-05

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