The authors would like to thank Prof. J. Vlček and M. Kormunda from University of West Bohemia for the depth sensing indentation tests. The present work was supported by the Ministry of Education of the Czech Republic;
contracts J07/98:143100003;
ME301(2000);
by the Grant Agency of the Czech Republic;
contract 202/00/P037 and by the project NATO SfP 972379;