Research Programs
Effects of Processing Residual Stresses on Fatigue Crack Growth Behavior of Structural Materials
Research Team
Christopher Lammi
Diana Lados
Introduction
Fatigue crack growth behavior of various types of alloys is significantly affected by the presence of residual stresses induced by manufacturing processes - bulk/macro residual stresses. Presence of residual stress can create inconsistencies in data collection and interpretation, and therefore, significant errors in structural design. There is a qualitative understanding of the effects of residual stress on fatigue behavior, but the effects are not comprehensively quantified and/or compensated for. Moreover, crack growth mechanisms in residual stress fields are complex and yet to be elucidated for many classes of materials. This project addresses, from several perspectives, the relevance and effects of bulk/macro residual stresses on fatigue crack propagation behavior of common transportation materials, and provides methods for residual-stress-unbiased design.
Objectives
- Understand the effects of residual stress on long fatigue crack growth data and assess the relevance to small crack growth;
- Determine microstructural crack growth mechanisms in fields with and without residual stress;
- Create computationally (using ANSYS/ABAQUS) and produce experimentally various residual stress patterns replicating different processing conditions;
- Validate the Restoring Force Model for residual stress correction - developed by Lados, Apelian, and Donald - on significantly different classes of alloys/microstructures and/or optimize/adjust the methodology as necessary;
- Recommend methodologies to account for residual stresses and to produce consistent and high quality residual-stress-free property data to be used in design for high-performance and reliability.
Methodology
Samples from various families of commonly used transportation materials will be fatigue crack growth tested and analyzed in high and low residual stress conditions. These conditions will be used to develop/validate a residual stress corrective method developed to provide base-line residual stress free data for design. As changes in processing conditions often alter both residual stress and microstructure, a geometrical/numerical solution that only changes residual stresses will also be assessed. Creating residual stresses both geometrically/numerically and through processing allows partitioning and quantification of residual stress and microstructural effects. This approach will provide tools to quantify residual stress effects and compensate for these effects in structural design.
Expected Outcomes / Deliverables
- A fundamental understanding of residual stress effects on long fatigue crack growth data and their relevance to small crack growth;
- Fundamentals of microstructural crack growth mechanisms in fields with and without residual stress;
- An original computational technique using ANSYS/ABAQUS able to geometrically create various residual stress patterns replicating different processing conditions;
- A residual stress corrective methodology applicable to significantly different classes of alloys/microstructures that can be used to produce consistent and high quality "residual stress free" property data for high-performance and reliability design of structural components;
- Vehicles - strategies and tools - for design in the presence of super-imposed residual stress effects such as those created by quenching or other processes.
Last modified: Aug 19, 2008, 14:56 EDT