Damage in fatigue: A new outlook
Conference
·
OSTI ID:136781
- Univ. of Sheffield (United Kingdom). Faculty of Engineering
This paper concentrates on the difficulties produced by linear elastic fracture mechanics (LEFM) and how recent research has removed many of these difficulties thereby permitting the design engineer to have a much improved basis for solving complex problems of engineering plant subjected to cyclic loading. This paper intends to show that: (1) In polycrystalline materials the period of initiation is in reality, zero and fatigue lifetime is entirely composed of crack propagation. (2) The fatigue limit of a metal, component or structure is related to whether or not a crack can propagate. (3) Elastic Fracture Mechanics is only a beginning in the science of, and application of, fracture mechanics. (4) Fatigue Damage is current crack length and the rate of damage accumulation is the rate of crack growth. (5) Only two basic forms of crack extension occur when any combination of the three loading mode mechanisms (Modes 1, 2, and 3) are applied, namely Stage 1 (shear crack growth) and Stage 2 (tensile crack growth). (6) Three fundamentally different fatigue crack growth thresholds exist. (7) The fatigue resistance of a metal is predominantly concerned with a crack changing its crack-growth direction, ie from Stage 1 to Stage 2, or vice versa. (8) Notches fall into two clearly defined categories; sharp notches where failure is related to the mechanical threshold condition, and shallow notches where failure is related to the material threshold condition. (9) Complex three-dimensional cyclic stress systems should be evaluated with respect to the possible Stage 1 and Stage 2 crack growth planes. (10) Barriers to fatigue crack growth can have origins in the microstructure (eg: grain boundaries) and in the mechanical state (eg: other crack systems). (11) The removal of a fatigue limit by a corrosive environment can be evaluated by the interface conditions between the Elastic-Plastic Fracture Mechanics (EPFM) and Microstructural Fracture Mechanics (MFM) regimes.
- OSTI ID:
- 136781
- Report Number(s):
- CONF-950740--; ISBN 0-7918-1344-4
- Country of Publication:
- United States
- Language:
- English
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