THE EFFECTS OF FREQUENCY AND R-RATIO ON FATIGUE CRACK GROWTH BEHAVIOUR IN Al-Li-Cu-Mg ALLOY (8090) PLATE

Autor: R. M. J. Kemp, P. J. Gregson, R. N. Wilson
Rok vydání: 1992
Předmět:
Zdroj: Fatigue & Fracture of Engineering Materials and Structures. 15:291-308
ISSN: 1460-2695
8756-758X
DOI: 10.1111/j.1460-2695.1992.tb01271.x
Popis: — The effects of frequency and R-ratio on the fatigue crack growth rate of the Al-Li-Cu-Mg alloy 8090 have been assessed in air. Compact tension test pieces (B= 25 mm) were tested at constant Pmax using a triangular waveform (CA) and the crack length was monitored by a four-wire pulsed potential drop technique. Crack closure measurements were made during the test by a front face compliance technique. The crack growth rate was found to be dominated by the high level of crack closure and the fatigue fracture morphology. Two fracture types were identified; a highly deviated “shear” fracture mode which was in competition with a macroscopically flat “tensile” fracture mode. The tensile fracture mode was predominant at low test frequency, high R-ratio and short crack lengths whereas the shear mode was predominant at high frequency, low R-ratio and long crack lengths. The transition from tensile to shear mode was primarily controlled by the effective stress intensity factor range, ΔKeff. The effect of loading variables on the transition was explained in terms of the diffusion distance of hydrogen relative to the effective cyclic plastic zone diameter. Test piece thickness had a secondary effect on the transition and this was explained in terms of gas transport considerations.
Databáze: OpenAIRE
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