Characteristics of Natural Fiber Composites Materials Reinforced with Aluminum and Copper Powder for The Performance of Automatic Motorcycle Clutch Pad oleh Riyadi Riyadi, Ahmad Kholil, Januar Parlaungan Siregar, Siska Titik Dwiyati, Danang Budi Pratama, Ari Setiawan, Eko Arif Syaefudin