1. Clausthal University of Technology Institute of Tribology and Energy Conversion Machinery, , Leibnizstraße 32, Clausthal-Zellerfeld 38678 , Germany ;
2. Ain Shams University , 11517 Cairo , Egypt
3. Clausthal University of Technology Institute of Tribology and Energy Conversion Machinery, , Leibnizstraße 32, Clausthal-Zellerfeld 38678 , Germany