High Cycle Fatigue Simulation using Extended Space-Time Finite Element Method Coupled with Continuum Damage Mechanics

High cycle fatigue (HCF) is a failure mechanism that dominates the design for many engineering components and structures. Surface treatments such as laser shock peening (LSP), ultrasonic nanocrystal surface modification (UNSM) and many others introduce significant residual stresses in the material, which drastically affects the fatigue life. Motivated by the need for effectively incorporating the residual stress effect in the fatigue life prediction, two approaches are developed in this thesis.In the first approach, a strain-life approach based model is implemented. Specifically, the effect of LSP induced residual stresses on fatigue life of dynamic spinal implant rods is studied. Strain-life model is applied to predict the fatigue lives of LSP treated spinal implant rods subjected to the bending fatigue loads. However, it is observed that, the traditional life prediction methods due to their empirical nature cannot effectively model residual stress relaxation. Both safe-life and damage tolerance approaches are based on limited loading conditions and specimen geometry in the test. Extrapolation of such test data to the complicated parts with multiaxial loading conditions becomes very difficult. Motivated by these limitations, a multiple temporal scale computational approach is developed to assess the fatigue life of structural components. This full-scale simulation approach is proposed in light of the challenges in employing the traditional computational method based on Finite Element Method (FEM) and semi-discrete schemes for fatigue design and analysis. Semi-discrete schemes are known to suffer from either the time-step constraints or lack of convergence due to the oscillatory nature of the fatigue loading condition. As such, simulating loading conditions with cycles on the order of hundreds of thousands and beyond is generally an impractical task for FEM. On the other hand, there is a great demand for such a computational capability as factors such as stress history and triaxiality, nonlinear coupling among the loads are known to critically influence the fatigue failure and generally not fully accounted for in the empirical design approaches that are in practice today. More specifically, an extended space-time method (XTFEM) based on the time discontinuous Galerkin formulation is proposed to account for the multiple time-scales in fatigue problems. XTFEM is coupled with the two-scale continuum damage mechanics model for evaluating fatigue damage accumulation, with a damage model governing the fatigue crack-initiation and propagation. HCF simulations are performed using the proposed methodology on a notched specimen of AISI 304L steel to predict total fatigue life under different conditions. More than 1 million loading cycles are successfully simulated to accurately predict the irreversible fatigue damage growth in the specimen. Fatigue life results are verified by comparison with those obtained using traditional safe-life approach. Based on the extensive work performed, it is concluded that the proposed formulation is robust, accurate and not restricted by the time-step for simulating the practical fatigue loading histories. Such framework is ideal for simulating the random HCF loading experienced by many engineering components during their lifetime and can serve as a robust tool for determining the residual life.

Name thesis:degree_name

PhD

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Engineering and Applied Science: Mechanical Engineering

Grantor dc:publisher

University of Cincinnati

Year dc:date

2012

Author dc:creator

• Bhamare, Sagar D.

Contributors dc:contributor

• Qian, Dong

• Mechanics
• High Cycle Fatigue
• Laser Shock Peening
• Space-Time Method
• Enrichment
• Two-Scale damage model
• Dynamic Spinal Implants

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352490187

OAI identifier oai:identifier

oai:etd.ohiolink.edu:ucin1352490187