Projects can only be established as ACE endeavours if they meet the mission’s criteria. Because these projects are associated with considerable commitment in terms of resources and duration, strict strategic and competitive criteria apply. ACE projects compete for the same resources as research projects in the scientific departments within the Materials Mechanics division. There must therefore be sufficient common interest in an ACE project as well as high added value and scientific standards. ACE projects are classified in two categories.
Exploratory projects aim at assessing creative approaches with relatively high risk. The duration of these projects is initially limited to one to two years. By the expiration of the exploratory project, an evaluation will determine whether it is to be terminated or to be continued as a reference project.
Reference projects have a duration of three to five years and involve substantial resources. They demonstrate our scientific and technological capabilities to a considerable degree combined with the demand for significant international visibility. When the ACE research platform initially went into operation, two reference projects were established: LISA and CraMaSS.
- Reference Project LISA
- Reference Project CraMaSS
- Nano scaled hierarchical microstructure of dental enamel
Reference Project LISA
Prior basic research projects with EMBRAER have shown that it is, in principle, possible to produce aircraft fuselage structures with friction stir welding (FSW) instead of conventional riveted joints. Both configurations of skin-stringer as well as skin-skin in butt-joints are possible in the same manner, resulting in a substantial reduction in weight. Further development and up-scaling of suitable process technologies are necessary for implementing this new concept in aerospace engineering. Furthermore, optimization of the damage tolerance behaviour is an important aspect in increasing the structure's lifespan. Different areas of expertise drawn from the Materials Mechanics division are required to address these issues. The participation of EMBRAER, our partner from the industrial sector, adds to this expertise.
The objectives of the LISA reference project are the development of an FSW process technology (hardware and procedures) for producing skin-stringer joints, modifying residual stress of the base material in the skin area by means of laser technology, analysing sub-component damage tolerance behaviour and validating existing numerical models to describe and predict the crack growth behaviour of sub-components. The demonstrator component developed and produced in the context of the reference project is to be compared with a conventionally riveted aircraft structure in regards to weight and efficiency.
Reference Project CraMaSS
The objective of the cooperative project undertaken by both research platforms at the Helmholtz-Zentrum Geesthacht, ACE and MagIC, is to develop and test the performance of a new crash component made of magnesium. Magnesium is currently available as wrought alloys with considerable strength in the form of sheets or extruded profiles and is significantly lighter in weight than aluminium. However, based on its hexagonal crystal structure, magnesium’s ductility is reduced and exhibits a tension-compression asymmetry due to twinning, which has a detrimental effect on its deformation behaviour.
Profiles consisting of two alloys (AZ31, ZE10) are produced and tested by means of laser or solid state joining (Bobbin Tool FSW) for the reference project. In addition, extruded profiles are produced as reference samples from the Extrusion Research and Development Center in Berlin. Tension and compression tests on simple basic material samples serve to calibrate the constitutive equations for the structure simulation of the crash behaviour. The deformation behaviour predictions conducted independent of the crash experiments are compared with measurement data with regard to force-displacement behaviour and energy uptake as well as with the deformation patterns of the different versions.
The results provide, for the first time, information on the potential and the limitations of magnesium crash components made of magnesium sheets and also provide important details for further developing magnesium alloys for such components.
Reference Project: Nano scaled hierarchical microstructure of dental enamel
Bovine dental enamel exhibits a complicated fibrous hierarchical microstructure with particular mechanical properties on each size scale. The primary aim of this project is to establish a computational model for each hierarchy level in order to simulate the mechanical properties of the dental enamel in its entirety. The modeling work helps understanding the benefits of the material’s hierarchy. The long term goal is to optimize the design of artificial hierarchical material systems.
Several tasks are to be conducted for this aim:
- Development of a computational model that can describe the mechanical characteristics of a hierarchical material
- Numerical modeling and prediction of mechanical properties of dental enamel at various hierarchy levels
- Investigation of how different hierarchies of dental enamel affect and interact each other
- Understanding the relationship between hierarchical arrangement and mechanical properties
- Optimization and improvement of the mechanical properties of the macroscopic material by adopting hierarchical structure design