Piezo Based Testing Facilities to Discover New Areas in Material Characterisation 2014-28-0032
The fatigue life approach is the main topic of structural durability. Improved methods for the numerical fatigue analysis should be based on experimental results. In some fields of material testing progress in research are very hard to achieve. Especially the regime of amplitudes below the knee point of the SN-curve with a huge number of load cycles to failure is one of these challenges with respect to fatigue tests. With standard testing devices, 108 to 1010 cycles cannot be achieved in a reasonable time span because of their low and limited testing frequencies or their inflexible control systems concerning variable amplitude loading.
For this reason, a new piezo based testing facility has been developed by Fraunhofer LBF which is capable to master this challenge. Built up with a high performance piezo actuator and a specially designed high frequency load frame this testing facility enables test frequencies up to 1.000Hz and locking forces of 10kN. The control technique realises variable load amplitudes as well as variable frequencies to test materials under realistic load sequences.
Another field of cyclic material behaviour characterisation, which is very hard to investigate, is the research of the local material behaviour. Properties of gradient-affected materials such as materials after forming processes or welding seams are only investigated globally, whereas the knowledge of the local material behaviour of the individual material layers can be much more interesting and it helps to understand the cyclic component behaviour under service conditions. Standard testing devices cannot ensure a feasible research of these important material parameters due to the low accuracy of their actuator and measurement components.
Again for this area piezo based testing facilities enable new prospects in material characterisation. For example pure weldment, extracted from the laser welding seam of steel sheets with thickness of 3mm can be tested with micro specimens to get the local material behaviour in order to refine material models for the numerical design process. Therefore, amplitudes of about 1μm and forces in the region of 1N can be realised with the piezo based testing facility. Hence, it is also applicable to micro component testing in an excellent way.