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.
Similar content being viewed by others
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
Dowling, N.E., “Fatigue at Notches and the Local Strain and Fracture Mechanics Approaches,” ASTM STP 677, 247–261 (1979).
Socie, D.F., Morrow, J. andChen, W.C., “A Procedure for Estimating the Total Fatigue Life of Notched and Cracked Members,”Eng. Fract. Mech.,11,851–859 (1979).
Sato, T., Shimada, H. andFuruya, Y., “Relation between Local-strain and Fatigue Cyclic Number of Crack Initiation from Notch-root under Low Cycle Fatigue” (in Japanese),Trans. Jap. SME,51 (466),A,1534–1540 (1985).
Shimada, H. andFuruya, Y., “Local Crack-tip Strain Concept for Fatigue Crack Initiation and Propagation,”Trans. ASME, Eng. Mat. Tech.,109 (4),101–106 (1987).
Sato, T. andShimada, H., “Evaluation of Fatigue Crack Initiation Life from a Notch,”Int. J. Fract.,10 (4),243–247 (1988).
Shimamoto, A., Takahashi, S. andYokota, A., “Fundamental Study on Rupture by Low-cycle Fatigue of Polymers Applying the Fine-grid Method,”Experimental Mechanics,31 (1),65–69 (1991).
Shimamoto, A., Yokota, A. andTakahashi, S., “Analysis on the Crack Initiation and Strain in the Vicinity of Notch Root under the Low Cycle by Fine Grid Method” (in Japanese),J. Jap. NDI,37 (9A),849–850 (1988).
Shimamoto, A., Umezaki, E. andTakahashi, S., “A Fundamental Study on Rupture by Low-cycle Fatigue of Polymers Employing the Finegrid Method” (in Japanese),J. Jap. NDI,38 (12),1101–1106 (1989).
Kikukawa, M., “Damage Accumulation in Fatigue Process” (in Japanese), Preprint of 15th Symp. on Material Strength and Fracture, 71–78 (1970).
Sato, T., Shimada, H., Kimura, K. andIguchi, H., “Local Strain Behavior at the Notch-root and the Crack-tip on Corrosion Fatigue” (in Japanese),J. Jap. NDI,39 (8),654–659 (1990).
Furuya, Y. andShimada, H., “Propagation of Small Fatigue Crack Initiated from Notch-root,”Eng. Fract. Mech.,19 (1),41–48 (1984).
Srawley, J.E., Fracture,4,ed. I.V. Liebowitz, Academic Press, 64 (1969).
Hudak, S.J., “Small Crack Behavior and the Prediction of Fatigue Life,”Trans. ASME, Eng. Mat. Tech.,103 (1),26–35 (1981).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
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
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02319665