Extracted text: A Helical compression spring is required to exert a force of 40N when compressed to a length of 65 mm. At a length of 45 mm, the force must be 60 N. The maximum operating temperature is 85°C, and the application requires a life of 200 000 cycles. The spring is installed over a shaft with a diameter of 16 mm. Use ASTM A 228 music wire, without pre-setting condition. Both ends should be squared and ground. Determine the design shear stress and the WAHL factor. Comment on the calculated value of the spring index.