Issue 35

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 35 (2016) 114-124; DOI: 10.3221/IGF-ESIS.35.14 123 C ONCLUSIONS atigue crack growth for a semi-elliptical crack with two different initial notch form in cruciform specimens and bending plate of D16 aluminum alloy is studied. Experiments and calculations made under biaxial cyclic tension- compression and bending are described. All the experimental and numerical results are shown: - for the same specimen configuration and different the crack front position as a function of cyclic tension-compression and bending loading, the following constraint parameters were analyzed, namely, the non-singular T -stress, z T -factor and the stress triaxiality parameter h in the 3D series of elastic-plastic computations; - the governing parameter of the elastic-plastic stress fields I n -factor distributions along various crack fronts was also determined from numerical calculations, this governing parameter is used as the foundation of the elastic-plastic stress intensity factor; - under cyclic bending, it can be seen that the crack propagation paths differ with diverse initial flaw forms, but under biaxial loading converge to the same configuration when the crack depth ratio is larger than about 0.5; - it is found that there is relationship between the crack growth rate on the free surface of specimen and COD for both tested cruciform specimens and bending plate; - a significant reduction of the crack growth rates is observed in the direction of the deepest point of the crack front with respect to the crack front intersection with the free surface of the bending plate; - the experimental and numerical results of the present study background provide an opportunity to explore the suggestion that crack growth rate may be represented by the plastic stress intensity factor, rather than the magnitude of the elastic SIFs alone; - it is stated that the elastic-plastic stress intensity factor, which is sensitive to the constraint effects and elastic-plastic material properties, is attractive as the self-dependent unified parameter for characterization of the material fracture resistance properties. A CKNOWLEDGMENT he authors gratefully acknowledge the financial support of the Russian Scientific Foundation under the Project 14- 19-01716. R EFERENCES [1] Newman, J.C., Raju, I.S., An empirical stress-intensity factor equation for the surface crack, Eng. Fract. Mech., 15 (1- 2) (1981) 185-192. [2] Carpinteri, A., Brighenti, R., Part-through cracks in round bars under cyclic combined axial and bending loading, Int. J. Fatigue, 18 (1) (1996) 33-39. [3] Shlyannikov, V.N., Tumanov, A.V., An inclined surface crack subject to biaxial loading, Int. J. Solids Struct., 48 (2011) 1778-1790. [4] Shlyannikov, V.N., Kislova S.Yu ., Tumanov, A.V., Inclined semi-elliptical crack for predicting crack growth direction based on apparent stress intensity factors, Theoret. Appl. Fract. Mech., 53 (2010) 185-193. [5] Shlyannikov, V.N., Tumanov, A.V., Characterization of crack tip stress fields in test specimens using mode mixity parameters, Int. J. Fract., 185 (2014) 49-76. [6] Shlyannikov, V.N., Zakharov, A.P., Multiaxial crack growth rate under variable T-stress, Eng. Fract. Mech., 123 (2014) 86–99. [7] Shlyannikov, V.N., Tumanov, A.V., Zakharov, A.P., The mixed mode crack growth rate in cruciform specimens subject to biaxial loading, Theoret. Appl. Fract. Mech., 73 (2014) 68-81. [8] ANSYS Mechanical APDL Theory Reference Release 14.5// ANSYS, Inc. Southpointe, 275 Technology Drive, CanonBurg, PA 2012. [9] Guo, W.L., Elasto-plastic three dimensional crack border field-I, Eng. Fract. Mech., 46 (1993) 93-104. F T