Micro-hardness of surface layer of irradiated Polybutene Terephthalate (PBT) David Manas, Miroslav Manas, Martin Ovsik, Michal Stanek, Lenka Chvatalova, Pavel Stoklasek and Lenka Hylova MATEC Web Conf., 76 (2016) 02018 Published online: 21 October 2016 DOI: 10.1051/matecconf/20167602018