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Fatigue crack-tip deformation, crack growth and life prediction in polycarbonate

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Abstract

Low-cycle fatigue fracture of polycarbonate is investigated. Local strain in the vicinity of the notch root and crack tip has been measured in real time by using a fine-grid method. The relationships among the local strain, crack initiation from the notch root and crack propagation of the crack tip are studied, and a method for more precise life estimation is suggested.

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Abbreviations

N c :

number of cycles for fatigue crack initiation

N ef :

number of cycles required for the breaking of the 10th element (distance=254 μm) ahead of a crack tip by the advancing crack

N 1,N 2,N 3 :

cycle numbers measured

\(\varepsilon _1 \) :

local strain at the notch root of crack-initiation process

\(\Delta \varepsilon _1 \) :

local-strain (\(\varepsilon _1 \)) range

\(\Delta \bar \varepsilon _1 \) :

mean local-strain range (\(\Delta \varepsilon _1 \)) damage accumulation value for crack initiation

\(\varepsilon _1^T \) :

local strain at one element ahead of a propagating crack tip

\(\Delta \varepsilon _1^T \) :

local-strain (\(\varepsilon _1^T \)) range

\(\Delta \bar \varepsilon _1^T \) :

mean local-strain (\(\Delta \varepsilon _1^T \)) damage accumulation value for crack propagation

\(\Delta \varepsilon _1 \) :

local-strain range (\(\Delta \varepsilon _1 \)) at one cycle number

\(\Delta \varepsilon _{N_C } \) :

local-strain range (\(\Delta \varepsilon _1 \)) at crack initiation (N C )

\(\Delta \varepsilon _N \) :

local-strain range (\(\Delta \varepsilon _1 \)) at arbitrary cycles number (N)

\(\Delta \varepsilon _{N_1 } ,\Delta \varepsilon _{N_2 } ,\Delta \varepsilon _{N_3 } \) :

local-strain ranges (\(\Delta \varepsilon _1 \)) at the notch root measured for cycle numbersN 1,N 2 andN 3, respectively

R :

stress ratio\(R = \sigma _{\min } /\sigma _{\max } \)

a :

crack length

W :

specimen width

Δδ:

nominal cyclic-stress amplitude

ΔK :

stress-intensity range

ΔK ap :

initial value of ΔK obtained regarding the notch as the initial crack

da/dN :

fatigue crack propagation rate

References

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Shimamoto, A., Umezaki, E. Fatigue crack-tip deformation, crack growth and life prediction in polycarbonate. Experimental Mechanics 35, 251–256 (1995). https://doi.org/10.1007/BF02319665

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