MACHINE DESIGN AND MATERIAL SCIENCE

1. Springs for vehicles: In vehicle suspension, it is desirable to minimize the cost as well as the mass of all components. Leaf spring suspensions for a vehicle are constrained to have a specific length l and stiffness S. In addition, due to the repeated loading, leaf spring should not fail due to fatigue loading. The geometry of the leaf spring is shown in Figure E. 7.7 (9) of the Ashby book on page 611 (571 of 3rd Edition). a. Identify the function, constraints, objective and free variables for the leaf spring design b. Derive the material indices for minimizing cost and mass of material for the identified constraints c. Explore the trade-off between cost and mass of the leaf spring using the plot of the two indices for minimizing cost and mass of the leaf spring. Restrict the material for plot to metallic and composite materials as they are commonly used for springs. d. Formulate a penalty function that combines the cost and mass of the leaf spring using an exchange constant. e. Use the penalty function to identify candidate materials for two different cases: exchange constant =0.1 (conventional vehicles minimum cost is important than mass) and exchange constant = 100 (Performance vehicles: minimizing mass is more important than cost) 2. A parallel plate clutch geometry is shown in Figure a. State the two assumptions required in determining the frictional torque applied by parallel plate clutches for a given lining material b. Explain the physical basis for validity of the two assumptions? c. In the figure, inside diameter is equal to 50 mm and outside diameter is equal to 100 mm. Use one of the assumptions you stated in part (a) to determine the maximum frictional torque and actuation force required for one of following friction lining materials Material Friction Coefficient Maximum temperature Maximum allowable pressure Leather Molded Asbestos Sintered metal 0.3 0.35 0.25 100 째C 250 째C 500 째C 200 kPa 700 kPa 1000 kPa d.