Local approach to fatigue based on energy considerations
- ANPA, Rome (Italy)
The paper presents a development of a fatigue crack growth theory published by the author in 1981 based on an energy approach. In an ideally elastic material containing a crack the only mechanism through which energy can be absorbed during a virtual crack extension is that associated to the creation of new free surface. It is an in-out situation in that a crack of a given length 2a under a stress state {sigma} either becomes unstable or stays like it is. In a real elastic-plastic material the energy absorption rate R comes mainly from the energy stored ahead of the crack tip as plastic strain energy. The resistance R is no longer represented by a constant term, but becomes a rather complex function of crack length increasing the crack grows. The consequence is that there is sufficient energy in the system to drive the crack to a point where the driving force G is equal to the resistance R and the crack stops. Unloading the system and reloading it, the crack grows by fatigue indicating that the previous condition G = R is no longer satisfied. If this happens it is because the volume that yields ahead of the crack tip is not capable during the reloading to absorb energy with the same rate as before. This causes the crack to grow further to regain the loss through the yielding of new material and establishes again the equilibrium between G and R. The author has related this lack of capability to develop the same energy absorption rate in any of the following cycles to a shake-down effect that takes place in the plastic enclave. The theory and the equation explain why short cracks shall grow faster than large ones. It also explains why the fatigue crack growth rate depends on the ratio between the minimum and maximum stress and is practically the same in any material independently of the yield stress and toughness that the material may have.
- OSTI ID:
- 403232
- Report Number(s):
- CONF-960706-; ISBN 0-7918-1770-9; TRN: IM9651%%267
- Resource Relation:
- Conference: American Society of Mechanical Engineers (ASME) pressure vessels and piping conference, Montreal (Canada), 21-26 Jul 1996; Other Information: PBD: 1996; Related Information: Is Part Of Fatigue and fracture -- 1996: Volume 1. PVP-Volume 323; Mehta, H.S. [ed.] [GE Nuclear Energy, San Jose, CA (United States)]; Bhandari, S. [ed.] [Framatome, Paris (France)]; Jones, D. [ed.] [Westinghouse Bettis, Pittsburgh, PA (United States)]; Rahman, S. [ed.] [Univ. of Iowa, Iowa City, IA (United States)]; Wilkowski, G. [ed.] [Battelle, Columbus, OH (United States)]; Yoon, K.K. [ed.] [Framatome Technologies, Lynchburg, VA (United States)]; PB: 412 p.
- Country of Publication:
- United States
- Language:
- English
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