Title page for ETD etd-120909-132833

Document Type thesis

Author Name Lammi, Christopher James

URN etd-120909-132833

Title The Effects of Processing Residual Stresses on the Fatigue Crack Growth Behavior of Structural Materials

Degree MS

Department Mechanical Engineering

Advisors
Diana Lados, Advisor
Diran Apelian, Committee Member
Richard Sisson, Committee Member
Mark Richman, Graduate Committee Rep
Gretar Tryggvason, Department Head

Keywords
fracture
fatigue
residual stress

Date of Presentation/Defense 2009-11-24

Availability unrestricted

Abstract
Residual stresses are a common and often undesired result of material processing, introduced through non-linear deformation and/or phase transformation of material under mechanical or thermo-mechanical loading. These macro stresses alter mechanical properties and the intrinsic fatigue crack growth characteristics of the material. Residual stress artifacts can introduce inconsistencies and significant errors when the true material behavior is needed for material development and optimization and for structural component design. The effects of quenching residual stresses on fatigue crack propagation behavior of various materials were investigated. In parallel, residual stresses similar in magnitude and distribution with the quenching residual stresses were generated using mechanical processes to decouple the effects of residual stresses from microstructural effects. Mechanical residual stress distributions predicted by 3D elastic-plastic finite element analysis showed good agreement with the stresses measured on fatigue crack growth testing specimens using fracture mechanics approaches. Crack propagation characteristics in fields with low and high residual stresses were studied using optical and scanning electron microscopy, and the effects of residual stress on crack path behavior were assessed. An original residual stress analytical correction to fatigue crack growth data was developed, compared to existing corrective methodologies, and validated using residual stress free data. Overall, the work provides tools to understand, control, and correct the effects of processing residual stresses on fatigue crack growth for accurate fatigue critical design and life predictions.

Files
clammi.pdf

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Document Type	thesis
Author Name	Lammi, Christopher James
URN	etd-120909-132833
Title	The Effects of Processing Residual Stresses on the Fatigue Crack Growth Behavior of Structural Materials
Degree	MS
Department	Mechanical Engineering
Advisors	Diana Lados, Advisor Diran Apelian, Committee Member Richard Sisson, Committee Member Mark Richman, Graduate Committee Rep Gretar Tryggvason, Department Head
Keywords	fracture fatigue residual stress
Date of Presentation/Defense	2009-11-24
Availability	unrestricted
Abstract Residual stresses are a common and often undesired result of material processing, introduced through non-linear deformation and/or phase transformation of material under mechanical or thermo-mechanical loading. These macro stresses alter mechanical properties and the intrinsic fatigue crack growth characteristics of the material. Residual stress artifacts can introduce inconsistencies and significant errors when the true material behavior is needed for material development and optimization and for structural component design. The effects of quenching residual stresses on fatigue crack propagation behavior of various materials were investigated. In parallel, residual stresses similar in magnitude and distribution with the quenching residual stresses were generated using mechanical processes to decouple the effects of residual stresses from microstructural effects. Mechanical residual stress distributions predicted by 3D elastic-plastic finite element analysis showed good agreement with the stresses measured on fatigue crack growth testing specimens using fracture mechanics approaches. Crack propagation characteristics in fields with low and high residual stresses were studied using optical and scanning electron microscopy, and the effects of residual stress on crack path behavior were assessed. An original residual stress analytical correction to fatigue crack growth data was developed, compared to existing corrective methodologies, and validated using residual stress free data. Overall, the work provides tools to understand, control, and correct the effects of processing residual stresses on fatigue crack growth for accurate fatigue critical design and life predictions.
Files	clammi.pdf