Online Archiv

May 7, 2010 10:00 - 11:00

Empa, Thun, Konferenzraum L503

Speakers

Prof. T.W. Clyne, University of Cambridge (UK)

Leadership of diskussion

Dr Johann Michler, Empa

Content

Recent technical advances are expanding nanoindentation testing capabilities to encompass a wide range of temperatures and strain rates. For instance, operation within vacuum chambers, which is now starting to become recognised practice, allows testing at temperatures of up to at least about 800°C, with minimal concerns about oxidation of either specimen or (diamond) indenter tip. It also allows low temperature operation without condensation problems.  Furthermore, many indenters can be operated in impact mode, with the potential to create relatively high local strain rates within the specimen. A major area of challenge, however, concerns the extraction of material constitutive relations (stress-strain curves) from nanoindentation experiments, in both quasi-static and impact modes, using FEM modelling. The main problems lie in the relatively weak sensitivity of standard load-displacement measurements to the constitutive relations and in the various sources of discrepancy between model and experiment. Prominent among these is the occurrence of creep deformation, which is common during quasi-static indentation. These problems are compounded in the case of impact indentation by the extra degree of freedom introduced by the constitutive relation being a function of strain rate – ie by strain rate hardening effects. However, various promising directions of development are identified. These include study of residual indent shape and, for impact mode, monitoring of the indent displacement history, in order to make the comparison between model predictions and experiment more comprehensive, and convergence to a unique solution thus more efficient and robust. It is also noted that, for impact mode, a reliable methodology needs to incorporate modelling the dynamics of the complete mechanical system.

 

The language of the presentation is English.
Free entrance, guests are welcome

Vortragssprache: Englisch