5. Explain briefly five of the following: a) % elongation increases as gage leng

Question

5. Explain briefly five of the following: a) % elongation increases as gage length decreases b) fracture strength tensile strength on a true stress-strain curve c) coarse grained metals are more creep resistant than fine grained metals d) single phase brass alloys (Cu-Zn) are stronger than copper e) alloy steels are more readily strengthened than plain carbon steels f) the marten site start temperature decreases as carbon content increases g) ceramic materials are generally brittle h) BaTiO3 has a high dielectric constant i) polymers expand much faster than metals when heated

Explanation / Answer

a) % elongation =maximum elongation of gage length/original gage length, so if original gage length is decreased the former increases.

c)Creep is deformation of material under constant stress with time. Fine grained metals have high tensiLe strength, but low ductility. but the reverse is true in case of coarse grained metals. But this occurs at higher temperatures, as the hardenability of coarse grained metals increases and hence better forging properties.

d) in carbon steel the high level of carbon its ductility is reduced also the melting point is decreased.So alloy steel is easily strengthened by heat treatment, due to higher tensile strength and high ductility.

h) Ceramics materials have minute cracks,omnipresent flaws or interior cracks/ pores, and grain corners, which are cannot be eliminated. These cracks acts as stress raisers, such that depending on the orientation and geometry of such crack any , applied stress may be amplified at the point of the crack. When the applied stress exceeds the value of this critical stress at any such internal crack ,the interatomic bonds break and the material fractures. So ceramics are brittle.

i)Linear coefficient of thermal expansion of polymers are comparatively higher than metals.so any amount of heat they absorb from the surrounding is mostly used in increasing interatomic distance or expansion thereof, rather than increasing the temperature of the polymer.

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