Fatigue Creep in Nuclear Structures

This course will provide an introduction to creep analysis and creep fatigue damage as well as a look at the design codes and assessment methods available. Examples and case studies will be used to consolidate the knowledge gained by the attendees and gauge their understanding.



Intro to creep and Mechanisms of creep

To introduce creep and creep relaxation behaviour of material at elevated temperatures. Mathematical model of creep will be introduced, and simple secondary creep model will be presented in detail. Stress, time and temperature effects on creep behaviour will be discussed. Larson-Miller Relation for creep rupture will be presented as well. Finally this session will be concluded by demonstrating analytical examples of both creep of an uniform bar loaded by a constant force and stress relaxation of an uniform bar with a fixed displacement load.


Creep analysis – Case Study (1)

To present both analytical and numerical creep analysis case studies. The analytical creep analyses discussed include 1) Creep Analysis of a Beam subjected to Pure Bending Moment; 2) Stress Relaxation (Creep) in a Bolt. The numerical creep analysis case study is for a practical creep analysis of an engine inner casing by using FE analysis.


Creep analysis – Case Study (2)

To present both analytical and numerical creep analysis case studies. The analytical creep analysis case study includes 1) Time delay contact switch with creep mechanism; 2) Creep analysis of a two bar structure; 3) Creep analysis of a three bar structure. The numerical creep analysis case study introduces a practical bolt relaxation analysis for a steam turbine outer casing.


Intro to fatigue and assessment methods

To introduce fatigue and fatigue assessment methods of material or component subjected cyclic or repeated loads. General characteristics of fatigue will be discussed in detail. Both high cycle fatigue and low cycle fatigue assessment methods will be introduced, and the topics cover the S-N curve, different fatigue design parameters, Goodman Diagram, Endurance Limits, Improving fatigue life, Stabilized Cyclic Hysteresis Loop, Coffin and Manson Law, Low Cycle Fatigue Data, Neuber's Rule for Fatigue Analysis and Cumulative Damage Rule, etc.


Intro to creep fatigue damage

To introduce creep fatigue mechanism and its damage assessment for components subjected to cyclic loads and high temperature creep condition. The topics covered in the session include creep-cyclic plasticity interaction, elastic follow-up, creep enhanced plasticity, cyclically enhanced creep, creep ratchetting and creep fatigue interaction.


Creep and Creep/Fatigue relevant design codes

To introduce creep and creep/fatigue relevant design codes including ASME Boiler & Pressure Vessel Code and R5 Assessment Procedure for the High Temperature Response of Structures.


Assessment and treatment of creep fatigue

To introduce assessment and treatment of creep fatigue damage of nuclear components. The introduced assessment methods include rule-based methods, novel direct methods and detailed step-by-step analysis method.