Issue 48

V. Giannella et alii, Frattura ed Integrità Strutturale, 48 (2019) 639-647; DOI: 10.3221/IGF-ESIS.48.61 645       , , , 1 1 ,  x  , , , , n i i i I i II i III i i i n i i i i da K R K K K dN da K R dN           (8) Figure 7 : MTS kink angle theory used for the FEM analyses. R ESULTS BEM and FEM analyses were performed to simulate the loading conditions of Test I. For Test I, the static load was set to 24 kN and the cyclic load was set to ±8 kN (Tab. 1). Experimental and numerical crack propagation paths are compared in Fig. 8. For such numerical analysis, neither initial notch shape (approximated by a sharp crack) nor contacts on the crack faces were considered; such simplifications allowed to decrease the runtimes with a negligible impact on the results since the combination of static and cyclic loads led to completely open crack faces during the entire fatigue cycle. The agreement between crack-growth directions and crack-growth rates was very sound among FEM, DBEM and experimental results. In summary, for this case it is possible to assess that: • the calculation of the equivalent K-factor in combination with a classical crack propagation law calibrated by Mode- I test data yields a correct crack propagation prediction; • the procedures for the calculation of the propagation angle seems to be correct. (a) (b) (c) Figure 8 : Results for Test I: (a) crack-growth rates; (b) FEM and (c) DBEM crack-growth directions; experimental crack-growth direction shown in Fig. 3. Test II was simulated with the DBEM code. No FEM analyses were performed with FRANC3D for this test since the MTS and Max Shear Stress (MSS) criteria implemented in the code were not able to satisfactorily capture the crack-growth direction. The code implements also more advanced crack-growth criteria but no dedicated material data were available for their calibration. D