Potentials and limitations in finite element based crack propagation analysis using FRANC3D
Typ
Examensarbete för masterexamen
Program
Applied mechanics (MPAME), MSc
Publicerad
2020
Författare
Haeg, Jonas
Elfving, Filip
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
About 80% to 95% of all structural failures occur due to a fatigue mechanism1. Accurate
fatigue assessment is therefore of great importance. This thesis focuses on a
finite element analysis based approach, implemented in the program FRANC3D, to
simulate crack propagation under fatigue loading. This approach is not commonly
used at GKN, where the thesis was carried out. FRANC3D offers the users many
options, the effect of which has not been previously investigated at GKN. In this
thesis, a sensitivity study of various settings in FRANC3D was performed for propagation
analyses of a semi-elliptical surface crack in a rectangular test specimen. A
group of settings were identified to be recommended and were later used for fatigue
assessment of Kb test specimens for two different load types: tensile and four-point
bending. The results were validated against handbook-type solutions, provided by
NASGRO, and towards test results. Fatigue crack growth assessment was also performed
for an embedded crack in a circular specimen—a load case not supported
within NASGRO. A statistical evaluation of the finite element based approach gave
similar results as the handbook-type solutions and matched the test results with
respect to mean fatigue life. Thus, this thesis can be considered to have validated
FRANC3D for GKN’s internal use. This opens up the opportunity for more accurate
fatigue life calculations for components with complex geometry and complex
thermal and mechanical loading histories.
Beskrivning
Ämne/nyckelord
Fatigue , crack propagation , FRANC3D , NASGRO , acture mechanics , SIF , M-integral , surface crack , embedded crack