Dynamic ageing and unstable behavior in plastic flow of alloys and in frictional sliding

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175404

Estrin, Y ^[1]

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1. Univ. of Western Australia, Nedlands (Australia)

Dynamic interaction between solutes and moving dislocations, referred to as dynamic strain aging DSA, is well known to give rise to a negative contribution to the strain rate sensitivity of the flow stress. Decreased SRS is a cause of a number of detrimental effects, such as reduced ductility and loss of fracture toughness, which explains a significant interest of the metallurgy community in DSA. An extreme manifestation of DSA is discontinuous yielding, or the Portevin-Le Chatelier effect, that comes about when the SRS becomes negative due to a developed dynamic strain ageing effect. It has also been found recently that a pseudo-Portevin-Le Chatelier behavior may result from a dynamic interaction of dislocations with precipitates. The gist of the cur-rent models for such dynamic systems is the recognition of the fact that the impeding action of obstacles to dislocation motion may increase with decreasing strain rate and the corresponding dwell time at the obstacles. The resulting stress vs. strain rate dependence is represented by a characteristic N-shaped curve. Unstable behavior giving rise to discontinuous yielding is associated with the descending part of this curve, while the period of the attendant relaxation oscillations can be calculated once the positions of the extreme and the shape of the ascending branches are known. An interesting parallel is found in frictional sliding where dynamic {open_quote}ageing{close_quote} of contacting asperities and the resulting increase in sliding resistance become more pronounced for lower sliding velocities. A corollary of this is a stick-slip behavior whose period can be found from the N-shaped characteristic, by analogy with the Portevin-Le Chatelier effect. One obvious application of the analysis is in the prediction of the periodicity of earthquakes associated with discontinuous frictional sliding on a crustal fault.

• OSTI ID: 175404
• Report Number(s): CONF-950686--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALLOYS
DISLOCATIONS
DUCTILITY
FLOW STRESS
FRICTION
RELAXATION
SLIP
STRAIN AGING
STRAIN RATE