Experimental Study on Tribological Behavior of Polyurethane Threads and PET Threads

Polyurethane threads and PET threads were selected to fabricate synthetic gecko setae for future wall-climbing robots.Tribological behavior of polyurethane threads and PET threads sliding against themselves, under condition of dry friction,was investigated and compared on a test rig for adhesion and friction.Under different normal forces,the upper specimen on a U-shaped clamp moved relatively to the lower specimen on a stationary frame at an angle of 45 degrees.The sensor of two dimensions simultaneously transmitted electric information of normal forces and friction into computer for calculating averaged friction coefficient.It was found that friction coefficient of polyurethane threads was 4.22 while normal forces varied from 0.5 mN to 2 mN,which was 14 times larger than PET threads whose friction coefficient was 0.29 while the normal forces ranged between 0.2 mN and 1 mN.It is the high surface energy that contributed to larger friction coefficient of polyurethane threads.Experimental results provide theoretical fundamental and slection basis for bio-mimic design of the feet of gecko robots.