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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2009/
Module Title: Mechanical Materials (2D)
Module Code: MECH
School: School of Mechanical & Process Engineering
Programme Title: Bachelor of Engineering (Honours) in Mechanical Engineering Bachelor of Engineering (Honours) in Biomedical Engineering Programme Code: EMECH_8_Y EBIOM_8_Y
External Examiner(s): Prof. Robin Clarke, Mr. John J. Hayes Internal Examiner(s):Mr. W. Corr
Instructions: Answer any three questions
Duration: 2 Hours
Sitting: Winter 2009
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1. (a) Justify the key simplifying assumption which distinguishes thin-from thick-walled pressure vessel theory. (3 marks)
(b) A steel cylindrical boiler has an internal diameter of 1.0m, a length 2.0m and walls of thickness 25mm. In a hydraulic test the boiler is filled with water at atmospheric pressure. What further volume of water needs to be pumped into the boiler to test it at a gauge pressure of 10 MPa? The steel has a modulus of elasticity of 200 Gpa and a Poisson’s ration of 0.3. The water has a bulk modulus of 2 GPa. (8 marks)
(c) The test is monitored using two strain gauges, one longitudinal and on hoop-orientated. What strains will these gauges read? (6 marks)
(d) Why might such a vessel be hydrotested before gas testing? (3 marks)
Q3. (a) Define the terms modulus of resilience and modulus of toughness for a material and describe: (2 marks) (i) the optimum choice of material for a spring application (3 marks) (ii) the improvement of resilience in long bolts. (3 marks)
(b) In pile-driving operations, show that the maximum dynamic stress induced in the pile can be written σd = 2 x HammerPotentialEnergyxYoungPile ' sVolumeModulus (5 marks)
(c) Piles of identical geometry are to be selected from the aluminium tensile test results of Fig. 3.1 or the structural steel results of Fig. 3.2. Calculate the approximate moduli of resilience and toughness for each pile type and recommend a choice of material from a pile driving perspective. (7 marks)
Q4. (a) For a built-in beam which subsides a distance δ before loading, show that a “prestressing moment” of magnitude
M =±^6 LEI 2 δ
is introduced at the supports. (5 marks) (b) For the beam shown in Figure Q4, (i) Calculate the force and moment reaction Vω , Mω at the wall. (4 marks) (ii) Calculate the slope at the tip. (5 marks) (iii) Show that the deflection at the right hand end of the beam can be written
EI y L^4 1944
= −^163 ω (6 marks)
Where the standard notation applies. Hint: Singularity functions probably provide the most direct route to solution.
