Experimental verification of three-dimensional mixed-mode crack propagation analysis

In the Aerospace field, the phenomenon of fatigue is one of the biggest challenges which have to be considered during the design phase. Material flaws, pre-cracks and crack initiations due to cyclic loading may lead to crack propagation in aircraft components. For aero-engine parts, because of high temperatures and time-dependent loads, this occurrence induces often a catastrophic failure. During the product development, a Damage Tolerant Design must be made, within an accurate prediction of the phenomenon. Because of the intricate geometries and loadings, the result is frequently a mixed-mode crack propagation and advanced tools for its estimation are required. Cracktracer3D is an MTU software able to study the mixed-mode cyclic crack propagation, based on the calculation of the Stress Intensity Factor from the FEM stress field analysis. In some cases, the complexity of the model, the impact of several parameters and computational limitations, create numerical results which may be imprecise and different from the experimental ones. Under the assumption of crack nucleation, the subsequent crack propagation must be investigated. The thesis aims to analyse the most complex scenario, namely, the mixed-mode crack propagation. An in-depth study of the experiments is conducted to comprehend the crack behaviour and related non-idealities. Through several tests, the predicted results are compared and examined to verify the validity of Cracktracer3D. A deep understanding of the theory behind the software is essential to achieve the best code-settings. Two main categories of specimens are studied: Single Edge Cracked Four-Point Bending Specimen with slanted crack and Single Edge Cracked Specimen with traction-torsion sinusoidal loads in different phases. The findings are precisely compared and arising discrepancies are used as a starting point for a different and enhanced crack propagation approach. This new method has been implemented in a Fortran subroutine of Cracktracer3D, aiming to match the experimental mixed-mode crack propagation results.