Consider the following statements pertaining to the stability of floating bodies: 1. A floating body will be stable when the center of gravity is above the center of buoyancy. 2. The position of metacenters corresponding to different axes of rotation is generally different for the same floating object. 3. For cargo ships, the metacentric height varies with loading. Which of the above statements are correct? (a) 1, 2 and 3 (b) 1 and 2 only (c) 1 and 3 only (d) 2 and 3 only
Ans: (d) Soln: Floating body will be in stable equilibrium when the center of Buoyancy lies above the center of gravity. Metacenteric height GM = BM – BG = (I/V) – BG Hence GM varies with the axis of consideration. The Metacentric heights are different for rolling, pitching, and yachting.
Consider the following statements: For a component made of ductile material, the failure criterion will be 1. endurance limit, if the external force is fluctuating 2. fatigue, if the external force is fluctuating 3. yield stress, if the external force is static. Which of the above statements are correct? (a) 1 and 2 only (b) 1 and 3 only (c) 2 and 3 only (d) 1, 2 and 3
Ans. (b) Sol. If an external force is fluctuating then material get to fail at stress which is considerably lower than the normal stress of static load. This behavior is termed as fatigue. These are two terminology used is fatigue fracture. These are fatigue strength and fatigue life. The graph in between these tells the fatigue strength and finally define endurance limit of particular material. Under fatigue failure the ductile material will fail as like as brittle material. For ductile material under static load material start yielding at yield point beyond which material get deformed permanently and finally, fail by cup and cone fracture at UTS. the allowable stress of the material is also governed by a yield stress and in Industry beyond it material termed as fail.
Which one of the following statements is correct? (a) Iron-carbon and TTT diagrams are both equilibrium diagrams. (b) Iron-carbon and TTT diagrams are both non-equilibrium diagrams. (c) The iron-carbon diagram is an equilibrium diagram but TTT diagram is a non-equilibrium diagram. (d) Iron-carbon diagram is a non-equilibrium diagram but TTT diagram is an equilibrium diagram
Ans: (c) Soln: Iron-carbon diagram is an equilibrium phase diagram but does not show time as a variable and hence the effects of different cooling rates on steel do not reveal. Moreover, equilibrium conditions are not maintained in heat treatment. Although, the iron-carbon equilibrium diagram reveals the phases and corresponding microstructure under equilibrium conditions but several useful properties of steel can be obtained under non-equilibrium conditions e.g. variable rates of cooling as produced during quenching and better transformation of austenite into pearlite and martensite