Linear Elastic - Material Science and Engineering - Exam, Exams of Material Engineering

Download Linear Elastic - Material Science and Engineering - Exam and more Exams Material Engineering in PDF only on Docsity! - 1 - CORK INSTITUTE OF TECHNOLOGY INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ Semester 2 Examinations 2008/09 Module Title: Material Science & Engineering Module Code: MECH6012 School: Mechanical & Process Engineering Programme Title: Bachelor of Engineering (Honours ) in Mechanical Engineering – Year 1 Bachelor of Engineering (Honours) in Biomedical Engineering – Year 1 Programme Code: EMECH_8_Y1 EBIOM_8-Y1 External Examiner(s): Mr. Peter Clarke, Prof. Robin Clarke Internal Examiner(s): Dr Gerard Kelly Instructions: Answer any three questions. All questions carry equal marks Note if you attempt question 3 please return the equilibrium diagram with your answer book. Duration: 2 HOURS Sitting: Semester 2 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 paper. If in doubt please contact an Invigilator. - 2 - Q1. (a) Define true stress and true strain and explain and or illustrate how they differ from engineering stress and strain. (7 marks) (b) If we are interested in characterising material behaviour in the linear elastic region, should we use engineering stress and strain or true stress and strain? Justify your answer. (6 marks) (c) A certain metal alloy will produce a true plastic strain of 0.475 when a true stress of 415 MPa is applied. How much will a specimen of this alloy elongate when a true stress of 325 MPa is applied if the original length is 300 mm? Assume a value of n = 0.25 for the strain- hardening exponent. (20 marks) Q2. a) The difference between the theoretical and measured fracture strengths of britte materials is explained by the presence of small flaws or cracks. i. In terms of these preexisting flaws or cracks briefly describe what happens when a brittle material fractures in tension (5 marks) ii. Explain why ductile materials do not fail in a brittle manner even though they will also have small flaws and cracks present. (5 marks) b) Explain what is meant by stress concentration factor Kt and illustrate its effect on an axially loaded flat plate which contains an elliptical crack orientated normal to the applied stress. Upon what factors do the maximum stress at the crack tip depend (8 marks) c) A specimen of ceramic material having an elastic modulus of 250GPa is pulled in tension with a stress of 750 MPa. Will the specimen fail if its “most severe flaw” is an internal crack that has a length of 20mm and a tip radius of curvature of 0.001mm ? Justify your answer. (15 marks)