Investigator: RNDr. Karel Milička, DrSc.
Number of Project: GA106/03/1353
Agency: Czech Science Foundation
Duration: 01. 01. 2003 - 31. 12. 2005

Critical locations of power facilities operating at elevated temperatures are welds of low-alloy steel parts (in CR above all steel type 15 128). These welds are, as a rule, initiation places of cracks at long-term exposure. That is why extensive and systematic investigations are aimed to long-term reliability and safety of welds. At present, there is no general model or theory explaining properties and behaviour of welds and their dependence on technology, used weld metal, etc. Any application of advanced methods of the description of phenomenon, especially the Finite Element Method, requires a sufficiently detailed mapping of heat resistant properties and of corresponding constitutive equations over the whole area of weld.
Formulation of these maps of local mechanical properties requires an application of tests on very small specimens. Preliminary punch tests on thin disk specimens demonstrated that the test represents an apt tool for obtaining local creep properties especially at temperatures close to operational temperatures. Taking into account the fact, that results of these types of tests correspond to the results of analogical tests on massive specimens, the technique of punch tests should provide sufficient information about necessary constitutive equations. Solution of the project supposes not only an analysis of such possibility of the application of the technique, but also investigations of variances of constitutive equations during exposures of welds of different duration in conditions which simulate operating conditions.

K. Milička, F. Dobeš:
The high-temperature characterisation of welded joints using small-punch testing.
Material & Technology 38: 9-12, 2004

K. Milička, F. Dobeš:
Relation between uniaxial and equi-biaxial creep and creep fracture behaviour in P91 steel.
Materials Science Forum 482: 407-417, 2005

Milička K., Dobeš F.
Small punch testing of P91 steel
International Journal of Pressure Vessels and Piping 83: 625-634, 2006