TME260 Fatigue & Fracture H16

The course covers fatigue and fracture mechanics. In particular three approaches for fatigue design of structures and components are studied: The stress based approach where the global mechanical response is elastic. Here the influence of stress raisers needs particular consideration. In the strain based approach an even more detailed analysis is adopted to account for localised yielding at stress raisers during cyclic loading. Finally, the fracture mechanics approach explicitly analyses the growth of cracks using methods of fracture mechanics. The limitations of using linear elastic fracture mechanics studying crack growth and final fracture are discussed and an introduction to non-linear fracture mechanics is given.

For all these approaches, methods to evaluate fatigue life that can be expected under various operational load conditions (including irregular load histories and multi-axial loading) are presented and motivated.

In the industry the use of codes for fatigue design is common. In this course, such approaches are demonstrated for the case of welded joints. Further, fatigue design in conjunction with FE-analysis of stresses and strains in a component is given special attention.

In addition to the main focus on metallic materials, the course also provides an overview of fatigue of materials such as composites, polymers and ceramics. In particular challenges regarding submitting such materials to fatigue loading, and available means of prediction predictions are discussed.

In this context it can be noted that especially fatigue is a phenomenon highly affected by statistical uncertainties (in load, strength, geometry etc). The course will provide an overview of this topic and also provide some insight into how these challenges are met in the industry. Related to this topic is the introduction to fatigue testing including a lab visit that is part of the course.

Finally, cases where the design has not prevented operational failures will be discussed. This includes an investigation of reasons for some failures, as well as insight into how failure investigations are carried out and how allocation of responsibilities can be made.