Abstract

Background: In the Clean Sky 2 project DIMES, the cyclic loading of a section of an A320 wing with pre-existing damage was carried out. Methods: We present a Digital Image Correlation (DIC) prototype system to monitor crack propagation in the aircraft wing. This system includes a mount for easy installation and adjustment in a confined space. Results: Strain localization and evaluation due to crack propagation was successfully observed in the Region-of-Interest (ROI) during cyclic fatigue loading. The results from the DIC prototype system were supported by conventional contact Resistance Strain Gauge (RSG) sensors acting as a far-field monitor. Conclusions: Future improvements, the combination of two DIC modules for a stereo DIC system and the potential of the DIC system for ground-based tests and Structural Health Monitoring (SHM) applications are also discussed.

Wedge indentation experiments were conducted to study the depth dependence of geometrically necessary dislocation (GND) structures in single-crystalline tungsten. Single-crystalline tungsten exhibits a pronounced indentation size effect (ISE), which can be rationalized based on GNDs. The dislocation mechanisms, however, are still under debate. Due to the plane strain condition during the wedge indentation, the dislocations in the cross sections underneath indents could be analyzed based on the Nye tensor and the lattice rotations determined using transmission Kikuchi diffraction. The dislocation structures depend on the size of the indent confirming the different hardness regimes and the bilinear ISE reported recently. For shallow indents, the dislocations are rather localized at the tip of the indent, while with increasing depth the dislocation volume expands; subgrains and distinct rays of increased dislocation density form. At larger depths, the indentation-induced deformation fields exhibit characteristics similar to the kink-type shear at a stationary crack tip. Graphical abstract