h1

TY  - THES
AU  - Schwinn, Julian
TI  - Ermüdungsrissverhalten von Tailored Welded Blanks unter Berücksichtigung der Eigenspannungen und der Geometrie eines Dickenübergangs
PB  - Rheinisch-Westfälische Technische Hochschule Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2019-01904
SP  - XIII, 131 Seiten : Illustrationen, Diagramme
PY  - 2018
N1  - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2018
AB  - Scope of past and current research and development in aviation is the reduction of the aircraft’s weight in order to reduce fuel consumption as well as to raise payload and range. A potential joining technology to replace the riveting (state of the art) of fuselage parts is friction stir welding (FSW), because riveting is expensive and raises the aircraft’s weight. FSW enables to weld high strength aluminium alloys that are used in aircraft manufacturing without drastic loss of mechanical properties. Furthermore, it is possible to produce load optimized structures by joining sheets with different thickness (Tailored Welded Blanks, TWB). In the present work, an Al-Mg-Sc alloy was investigated. Al-Mg-Sc alloys offer good corrosion and damage tolerance properties and can be processed by creep forming, which allows to produce double curvature parts.The process of FSW introduces macroscopic residual stresses, which influences the fatigue crack growth behavior significantly. Additionally, the crack arresting capability of riveted structures does not apply to welded structures due to the material’s bond. The fatigue crack growth behavior is essential for the engineering design approach of damage tolerance. Thus, the aim of the present work is to investigate and quantify the crack growth behavior of FSWed structures of the Al-Mg-Sc alloy AA5028-H116.To achieve this aim, experimental and evaluation procedures were advanced. With the help of finite element simulation with fracture mechanics analysis and 3D digital image correlation experimental dependent geometry functions were determined in order to provide stress intensity factors for the cyclic fatigue crack growth experiments on welded specimens. By this means, crack growth curves for rather large specimens could be determined with high accuracy. In order to be able to investigate residual stresses and their influence on the crack growth, the cut-compliance-method was applied. Finite element simulations were used to cover the geometrical influence of the thickness transition for the determination of the residual stresses by means of the cut-compliance-method. Crack growth behavior and residual stresses were determined for specimens with and without thickness transition with the crack growing perpendicular to the weld as well as growing along the weld.Macroscopic residual stresses and their influence on the crack growth were determined for the residual stress affected specimens. Thereby, residual stress affected crack growth curves could be corrected and thus attributed to the base material’s crack growth behavior. For this reason, a correction for the mean stress regarding the cyclic stress intensity factor was specified. It became apparent that the changes in crack growth rate were affected prevailingly by the residual stress. Major effects due to the microstructural changes inside the weld were not observed. The crack growth behavior of the highly distorted specimens with thickness transition could not be explained by solely considering the residual stress. Thus, further investigations of the crack mouth opening displacement were included.
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/755550
ER  -