Edith Cowan University School of Engineering Advanced Mechanical Design Assessed Problem 1 Polisher Shaft Design Due Date: 9:00am 15th May 2017 Assessment Submission: Hardcopy (ONLY) and a completed ECU coversheet. Submit to Engineering Office, building 23. Completed in groups of up to 2 students (max.) A hand held polisher, depicted in Figure 1, has either a sanding disk or a polishing cloth attached to the disk shaft as illustrated in the schematic below (Figure 2). The disk shaft, which rotates at 400RPM, is made of forged steel that has an ultimate tensile strength of 700MPa and yield strength of 450MPa. The worst loading condition occurs when an object is sanded or polished near the disk periphery (diameter of 250mm). The applied force between the object and the disk creates a friction torque of 15Nm during polishing and 12Nm during sanding. During these loading conditions, the coefficient of friction between the object and the disk is 0.3 during polishing and 3 during sanding. Due to the heat generated during sanding and polishing as well as from the motor, the shaft operates at a worst case of 100°C. Determine the minimum number of hours of operation until shaft fatigue failure with 99.99% reliability, if 45% of the time the polisher is sanding and 55% of the time is spent polishing. Please read the notes at the end of the assignment question sheet.Figure 1. Example polisher for illustration purposes only (note: this is a fictional problem) Figure 2. Schematic of polisher disk, shaft and bearings Note: I. Please include full working out for all the calculations on this question sheet (below) II. Also, include the Modified Goodman diagram for all necessary fatigue calculations III. Clearly indicate which charts have been used to derive coefficients or correction factors Image Source (only for example purposes): http://www.sfonlines.com/F0159070JC-9070-SKIL-POLISHER/q?pid=942&doit=order Ftangential Fnormal 250mm 75mm 3mm 20mm 12mm 22mmDr. Ferdinando Guzzomi Email: [email protected]