13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- crack tip it has been shown that the stress intensity factor during a fatigue loading has to be corrected by the factor Ktemp. This thermal effect on the stress intensity factor varies slowly with time and can be considered as constant during one cycle. Consequently the temperature has no effect on the stress intensity factor range K but it has an effect on both the maximum, Kmax, and minimum, Kmin, values of the stress intensity factor: Kmax=Ktemp+Kcyc,max (11) Kmin=Ktemp+Kcyc,min (12) However, Ktemp can affect crack closure by changing the load ratio (equation 13) and because of the compressive nature of the thermal stresses around the crack tip: min ,max ,min ,max max cyc cyc cyc temp cyc temp min K K K K K K K K K R (13) In the two problem geometries presented in this paper, the results on the thermal correction of the stress intensity factor are very closed. For a stress intensity factor range of 20MPa mand a stress ratio of 0.1 the thermal correction is about -0.521MPa m for an infinite plate with a semi-infinite through crack and -0.316MPa mfor a finite plate with a central through crack with considering thermal losses due to convection. In conclusion the geometry of the specimen and the thermal boundary conditions have a very small effect on the results. For test on mild steel at a loading frequency of 100Hz, the values of Ktemp remain very small and a new stress ratio of 0.087 (compared to 0.1, the initial stress ratio) can be calculated. However, since the dissipated energy rate per unit length of the crack front is proportional to both the loading frequency and to K4/ y 4 this effect should be more important for ductile metals (low yield stress) loaded under high stress intensity range. Revisiting the frequency effect on the fatigue crack growth could be also interesting by taking this thermal correction consideration. References [1] W.S. Farren, G.I. Taylor, The heat developed during plastic extension of metals. Proc Roy Soc A (1925)107 422–51. [2] G.I. Taylor, H. Quinney, The latent energy remaining in a metal after cold working. Proc Roy Soc A, (1934) 143 307–26. [3] P.C. Paris, Fatigue - the fracture mechanics approach, Fatigue an interdisciplinary approach, Syracuse University Press, 1964. [4] J.R. Rice, The mechanics of crack tip deformation and extension by fatigue, Fatigue crack propagation, ASTM, Special Technical Publication 415, Philadelphia, 1967. pp. 247–311. [5] H.S. Carslaw, J.C. Jaeger, Conduction of heat in solids, Oxford, Clarendon Press, 1947. [6] N. Ranc, T. Palin-Luc, P.C. Paris, Thermal effect of plastic dissipation at the crack tip on the stress intensity factor under cyclic loading, Engineering Fracture Mechanics 78 (2011) 961–972
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