Issue34

S. Keck et alii, Frattura ed Integrità Strutturale, 34 (2015) 371-378; DOI: 10.3221/IGF-ESIS.34.41 375 commercial finite element program ABAQUS. The simulations are performed with ABAQUS and ADAPCRACK3D. Using the latter, the numerical simulations of the fatigue crack growth and the fracture mechanical analysis are computed. For crack propagation it is assumed that linear elastic fracture mechanics is valid [4]. For executing the numerical simulations Young’s moduli are required. Those were needed, among other things, for calculating fracture mechanical parameters. Thus, values are chosen according to the determined ones (cf. Tab. 1). Consequently, due to reasonable simulation the inhomogeneous orthotropic material is approximated as a homogeneous orthotropic continuum. Fibre direction E1 [GPa] E2 [GPa] E3 [GPa] 0° 3 20 3 45° 3 4.2 4.2 90° 3 3 20 Table 1 : Mechanical properties for numerical simulations. The fatigue crack growth rate curve for specimens with fibre direction perpendicular to the loading direction is illustrated in Fig. 7. The da / dN versus Δ K eq data are plotted on logarithmic scales. The fatigue crack growth rate curves for other directions are shown in Figs. 8 (45°) and 9 (0°). For each curve a fit of the necessary Forman/Mettu equation parameters (Tab. 2) has been carried out. This crack growth equation [5] is given by max 1 1 1 1 p th n eq FM eq q C K K da C K dN R K K                                 (2) Parameter Fibre direction 0° 45° 90° C FM 5E-04 2E-04 9E-05 γ 0 0 0 R 0.1 0.1 0.1 Δ K th 0.8 0.9 1.0 K C 4.5 9.0 9.0 n 3.5 2.0 2.5 p 5.0 3.0 2.5 q 0.50 0.25 0.25 Table 2 : Forman/Mettu equation parameters. It can be seen that near-threshold values can hardly be found due to the material and the sensitivity of the measurement system. Therefore, the threshold values can only be regarded as extrapolations. The data for the linear intervals are well-recorded, so that a fit of the parameters was possible. The slope of the fatigue crack growth rate curve for specimens with 0° fibre direction is much steeper than the other ones. The crack growth rate data for 45° specimens and 90° specimens are very similar.