Mechanical Engineering Exam: Mechanics of Materials and Engineering, Exams of Materials science

Download Mechanical Engineering Exam: Mechanics of Materials and Engineering and more Exams Materials science in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Mechanical Engineering - Award (NFQ Level 7) Autumn 2006 Mechanics of Materials & Engineering (Time: 3 Hours) Instructions Answer FIVE questions. All Question carry equal marks. Attempt THREE questions from Section A and TWO questions from Section B. Graph papers & Log books to be provided. Examiners: Mr. S. F. O’Leary Dr. G. Kelly Mr. J. Connolly Mr. R. Simpson Section A Q1. (a) “Fatigue tests on specimens having a variety of sizes, but made of the same material, display a reduction in strength as specimen size increases”. Discuss the underlying reasons for this phenomenon and describe how this reduction in fatigue life is accounted for in design. (7 marks) (b) A polished rotating steel shaft, 200 mm long and 6 mm in diameter, is simply supported at the ends and carries a lateral load at mid-span. The shaft is also subjected to a steady axial tensile load of 8 kN along the shaft centreline. The ultimate strength of the steel is 900 MN/m2, its endurance limit is 500 MN/m2, and the strength reduction factor for reliability is 0.76. If the shaft is to turn 100,000 revolutions in the service life of the machine, determine the magnitude of the lateral load that the shaft can carry safely. (13 marks) 2 Q2. (a) Describe the simplifying assumptions of thin cylinder theory which may not be applied to thick cylinder theory. Hence, determine the limitations within which it is safe to utilise thin cylinder theory to design pressure vessels. (7 marks) (b) An external pressure of 10 MN/m2 is applied to a thick cylinder of internal diameter 160 mm and external diameter 320 mm. If the maximum hoop stress permitted on the inside wall of the cylinder is limited to 30 MN/m2, what maximum internal pressure can be applied, assuming the cylinder has closed ends? Calculate the change in outside diameter, when this pressure is applied. Given Material Properties: Modulus of Elasticity = 207 GN/m2 (13 marks) Poisson’s Ratio = 0.29 Q3. A polymer rotor disc, which is part of a turbine assembly, has a uniform thickness of 60 mm. The disc has an outer diameter of 500 mm and a central hole of 120 mm diameter. If there are 100 blades each of mass 0.12 kg pitched evenly around the periphery of the disc at an effective radius of 265 mm, determine the maximum allowable rotational speed, when the fracture stress for the polymer is 110 N/mm2 and a factor of safety of 2 is required. Given Polymer Material Properties: Poisson’s Ration = 0.38 Density = 900 kg/m3 (20 marks)