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Experimental and numerical investigation of creep crack growth

: Hollstein, T.; Kienzler, R.

Institute of Metals, London:
3rd International Conference on the Creep and Fracture of Engineering Materials and Structures '87
London: Pineridge Press, 1987
pp.563-576 : Abb.,Tab.,Lit.
International Conference on the Creep and Fracture of Engineering Materials and Structures <3, 1987, Swansea>
Conference Paper
Fraunhofer IWM ()

Experimental and numerical results are presented for the high-temperature alloy Ni Cr 22 Co 12 Mo (Inconel 617) at the constant temperature of 900 degrees C. Side grooved compact specimens and centre notched tension specimens were tested under constant applied forces. The crack opening displacements were measured at the load line and the creep crack growth rates a were determined using the direct current potential drop technique. From these data the parameter of creep fracture mechanics, the C-integral, was calculated by an approximative formula. The correlation between a (covering several orders of magnitude) and C can be described within a scatterband by a power law independent of size and geometry of the specimens and the loading condition. Values of C were calculated numerically from the line integral that is path-independent only in the long-time range. In the course of the finite element calculation it turns out that the crack tip modelling - elastic or elastic-plastic - is of mi nor influence on C, whereas values of C depend strongly on the material constants describing the creep law. It was checked that approximative formulae lead to quite accurate results. Plane stress and plane strain calculations deliver upper and lower bounds, respectively, of the more realistic three dimensional numerical simulation. The agreement between numerically and experimentally determined C data is rather satisfactory in the secondary creep regime.