1. School of Applied Mathematical and Physical Sciences, Dept. of Mechanics-Lab. of Testing and Materials, National Technical University of Athens, 5, Heroes of Polytechnion Avenue, Theocaris Bld., Zografou Campus, GR-157 73, Athens, Greece.
2. School of Applied Mathematical and Physical Sciences, Dept. of Mechanics-Lab. of Testing and Materials, National Technical University of Athens, 5, Heroes of Polytechnion Avenue, Theocaris Bld., Zografou Campus, GR-157 73, Athens, Greece