Question Four (25 points) (a) Write T between the brackets in front of each stat
ID: 2250349 • Letter: Q
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Question Four (25 points) (a) Write T between the brackets in front of each statement if the statement is true, and F ir the statement is false. 1. For a material to fail under Fatigue loading, the stress should exceed the 2. Fatigue failure is sudden but gives obvious warnings before it happens. 3. Fatigue failures are similar in 4. The first stage of fatigue failure is the initiation of micro crack(s) at place(s) of high stress appearance to static brittle factures. concentrations 5. The S-N graph never does become horizontal for nonferrous metals and alloys, and hence these materials do not have an endurance limit. ( (b) The principal stresses from question three should be as follows Assuming the loading can be considered as a static loading, specify a suitable shaft material from Table A-20 (attached) in order to provide a safety factor of 2. Use MSS theory.Explanation / Answer
Fatigue failure occurs when structures are subjected to fluctuating and dynamic stresses, due to which failure of the material could occur at a stress level which is much lower than the static strength of the material. Fatigue occur after a lengthy period of repeated cycle of stresses/strains. It occurs very sudden without warning. This type of failure is brittle in nature of even ductile material in the sense that it has very little or no plastic deformation along with the failure. The failure process occurs by initialization and development of cracks and the fracture surface is perpendicular to the direction of the stress application.
Most nonferrous materials do not have a fatigue limit in the SN curve, at greater cycles(N) it continues its downward trend. Regardless of the magnitude of the stress fatigue will occur ultimately. Generally fatigue strength is defined at some specified number of cycles (Eg 10^7) at which failure will occur.
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