Two round robins on mode I fatigue delamination propagation organized by Technical Committee 4 of the European Structural Integrity Society compared three unidirectional carbon fiber reinforced composites, one with thermoplastic (poly-ether-ether-ketone) and two with thermoset (epoxy) matrix tested at five laboratories. Different approaches for data evaluation and their effect on the in-and inter-laboratory scatter are discussed and compared. Results are very sensitive to small scatter in the load signal, and, therefore, a new route to evaluate the crack growth rate from pairs of load and displacement data is presented.

Abstract:As a generalized semi-finished product, the use of magnesium sheets requires addressing two major aspects of their processing: their microstructure and texture control, which are both essential for the forming behavior of such sheets during their forming to parts. Further, the processing of such sheets is complex, and therefore expensive, and requires simplification. In this work, magnesium alloys AZ31, ZE10, and ME21 are investigated in the form of conventionally rolled sheets, as well as in the form of extruded sheets. Their microstructural and textural development are correlated to their mechanical and forming properties. During extrusion, strong textures develop that hinder stretch-forming operations, even in rare earth-containing alloys. Chemical composition and process parameters have a significant impact on the texture development, and enable the design of sheet materials with weak textures and potentially enhanced formability.

Magnesium alloys with rare earth or Ca additions often form weak textures during rolling of magnesium sheets or extrusion of round bars. However, in the case of the extrusion of flat profiles of such alloys strong textures may develop. This is of fundamental importance because weaker textures are associated with higher ductility or formability. Variations in the activity of deformation and recrystallization mechanism play a role in the microstructure and texture development during the underlying forming procedures. In this study, magnesium alloys with Zn or Mn as the main alloying elements were modified with rare earth or Ca and extruded to flat profiles. The microstructure and texture development is compared and related to the mechanical properties. Alloying and processing aspects are discussed with a view to tailor the mechanical properties of such flat profiles.