Research Programs
Fatigue Crack Growth Mechanisms of Long and Small Cracks in Structural Materials
Research Team
Anastasios Gavras
Diana Lados
Introduction
Fatigue initiation and fatigue crack propagation characteristics of metallic materials are important considerations in structural applications relevant to the transportation sector including automotive, aerospace, marine, and defense industries. However, and despite the extensive research efforts dedicated to this topic, a common - fundamental and mechanistic - approach/understanding of the dynamic behavior of various classes of alloys and microstructures used in fatigue critical applications is still lacking. Thus, providing a systematic approach/understanding of fatigue crack initiation and propagation mechanisms in various classes of structural materials and transferring this knowledge to design are the focal points of this research.
Objectives
- Understand the fundamentals of small and long crack propagation mechanisms through various materials/microstructures;
- Validate the robustness of closure corrective techniques and their ability to match the differences between long and physically small cracks in various materials;
- Understand microstructurally small crack growth behavior and seek methods to adjust closure correction (Fracture Mechanics based) techniques to incorporate microstructural elements (Materials Science based);
- Understand the effects of novel processing techniques (cold spray, friction stir processing) on fatigue crack growth data and crack growth mechanisms;
- Evaluate the applicability of closure correction techniques to extremely fine-grained microstructures;
- Recommend methodologies to implement the findings/knowledge in design for high-performance and reliability.
Methodology
Samples from various classes of materials will be fatigue crack growth tested and analyzed in no/low residual stress conditions - attention is thus concentrated on microstructural effects on fatigue crack growth behavior. Relevant Microstructural Characteristic Dimensions (MCDs) will be determined for each material and varied on two levels to create microstructural differences necessary to assess small and long fatigue crack growth mechanisms in these families of alloys across a range of practical microstructural scales. For selected materials, a third "very small scale" microstructural condition with be produced using cold spray techniques and/or friction stir processing; these processes will create "fine-to-nano grained microstructures" building a bridge between micro-to-nano scale materials and providing a knowledge base for repair techniques for "in-use" or "ready-to-retire" transportation vehicle components.
Expected Outcomes / Deliverables
- A fundamental understanding of the small and long crack propagation mechanisms through various materials/microstructures;
- A robust closure corrective technique able to match the differences between long and physically small cracks in various materials;
- Fundamentals of microstructurally small crack growth behavior and methods to adjust closure correction (Fracture Mechanics based) techniques to incorporate microstructural elements (Materials Science based);
- An assessment of the effects of novel processing techniques (cold spray, friction stir processing) on fatigue crack growth data and crack growth mechanisms;
- An evaluation criterion for the applicability of closure correction techniques to extremely fine-grained microstructures;
- Methodologies to implement the findings/knowledge in design for high-performance and reliability for common use in all transportation industries and beyond.
Last modified: May 28, 2008, 10:48 EDT