A Journal of Applied Mechanics & Mathematics, #49
A Bad Example
Most of us are inclined to trust an established textbook. We assume (1) the author knows what he is talking about, (2) the book has been carefully vetted by several editors and reviewers, and finally (3) the fact that it is well established in the market means that thousands of other readers have tacitly endorsed it as well. While these assumptions are usually true, they are no guarantee, and they
Governor sensitivity is the ratio of
A. range of speed to the mean speed
B. maximum speed to the minimum speed
C. mean speed to the range of speed
D. effort of governor to the range of speed
E. governor lift to the range of speed
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(a) Describe the steps usually considered in the process of material selection.
(b) How material selection is done using decision theory.
Ans. (a) Like any other aspect of engineering design, material selection is also equally important aspect. Material of part depends on the requirements of the part, number of parts needed, and manufacturing process to be adopted to make the part. The material selection primarily depends upon its properties and several other factors like availa
Temperature has pronounced effect on the properties of zinc and zinc alloys. The creep resistance, in particular, decreases rapidly with increasing temperature. Ductility and general fabricating characteristics increase with temperature. Drawing and forming operation should never be attempted below 20°С. More severe operations can be performed readily at temperatures above 50°C. Zinc alloys become somewhat brittle below 0°C, depending on the particular composition, but recover their normal prope
Season cracking is spontaneous cracking which occurs on exposure to atmospheric corrosion in brass objects with high residual tensile stresses at the surface. It occurs with high-zinc brasses but rarely with 15 per cent zinc or below. Alloys susceptible to spontaneous season cracking will crack when exposed to corrosive conditions under high service stress, even if they are free from internal strains. Season cracking can be prevented by avoiding the production of internal microstresses or by rem
State, with reasons, suitable material for the manufacture of each of the following, giving the approximate composition :
(a) a brass for deep pressed containers; (b) a brass for small machined bolts ; (c) a bronze for the impeller of a sea-water pump.
(a) The suitable brass for deep pressed containers is the admiralty brass containing copper and zinc in the proportion of 7 to 3, with 1% of tin.
The addition of tin to the basic cartridge brass (70% copper, 30% zinc), gives
(a) What is the main difference between a brass and a bronze ?
(b) State the composition, and two common uses of a bronze commonly used in engineering.
(c) What is the general effect of adding a small proportion of (1) phosphorus, (ii) lead, to a bronze ?
(a) A brass is an alloy of copper and zinc, the major constituent being copper. A bronze is an alloy of copper and tin, the major constituent being copper.
(6) A bronze commonly used in engineering and commonly known
(a) Which two elements are alloyed to form a brass ?
(b) What are the differences (i) in composition, (ii) in uses, of an 'alpha' and an 'alpha-beta' brass ?
(a) A brass is essentially an alloy having major constituents as copper and zinc. Minor proportions of elements such as lead and tin may be included to promote special properties.
(b) An alpha brass is an alloy in which zinc does not exceed by 38%. This brass is ductile and, therefore, used for cold-rolled sheets, wire
What do you understand by a free-cutting steel? What elements are usually added to make a steel free cutting, and how they make the steel free. cutting?
A free-cutting steel is one in which an element like lead or sulphur is deliberately added to promote rapid machining
When sulphur is added to steel, it forms a brittle constituent with manganese, known as manganese sulphide, which being brittle, allows chip cracks to propagate and breaks chips into easily handled lengths.
(i) Permalloy, (ii) Invar, (iii) Elinvar, (iv) Platinite, (v) Dumet wire. Ans. (i) Permalloy has 78.5% nickel. It has a high permeability and low hysteresis loss.
(i) Invar contains 36% nickel and has an exceedingly low coefficient of linear expansion. Since its expansion is proportional to the temperature within limits of atmospheric temperature change, it is used for secondary standards of length.
(ii) Elinvar contains 32% nickel with small percentage of Cr, W, Mn, Si and C. In addit
Music wire is a previously treated steel wire used for small helical springs. It requires no heat-treatment except a low-temperature anneal to relieve the forming strains. Such a wire is given a special heat treatment called patenting and then cold-rolled to develop a high yield strength.