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FRACTOGRAPHIC ANALYSES OF FATIGUE CRACK GROWTH IN D16T ALLOY SUBJECTED TO BIAXIAL CYCLIC LOADS AT VARIOUS R ‐RATIOS
Author(s) -
Shanyavsky A. A.,
Orlov E. F.,
Koronov M. Z.
Publication year - 1995
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.1995.tb00853.x
Subject(s) - striation , materials science , paris' law , growth rate , tension (geology) , crack closure , composite material , alloy , stress intensity factor , stress (linguistics) , compression (physics) , fractography , metallurgy , fracture mechanics , mathematics , geometry , linguistics , philosophy
Fractographic peculiarities of fatigue crack development are studied in cruciform specimens of D16T aluminium alloy under biaxial tension and tension‐compression. In the range of the biaxial load ratios λ from ‐ 1 to +1.5, and in the range of R ‐ratios 0.05 to 0.8, fatigue striation formation took place over a crack growth rate near to 4×10 −8 m/cycle. The striation spacing and the crack growth rate decrease as the ratios λ and R increase. The ratio between the increment of crack growth, da/dN , and the striation spacing, δ, is approximately 1:1 when da/dN is greater than 4×10‐ −8 m/cycle. The relationship between the number of cycles from the beginning of a test up to the growth rate of 2.14×10 −7 m/cycle ( N d ), and the crack growth period, Np , from when the crack initiates up to the instant when that growth rate is reached, was determined for different λ and R‐ratios. The value of N d increases as the stress ratio, λ, is increased. Cycle loading parameters must be taken into account in order to describe the crack growth period when using a unified method involving an equivalent stress intensity factor K e , = K 1 , F (λ, R s ). The values of F (λ, R ) for the growth rate ( F(λ, R) s ) and for the striation spacing ( F(λ, R s ) were determined and compared. The fatigue crack growth period, N t p , applicable to the stage of fatigue striation formation, (predicted by using both of the F (λ, R ) values) is correlated with the experimental data and the error is of the order of 15%.