True/ false, small explanation if possible please Hardness is defined by the res

Question

True/ false, small explanation if possible please

Hardness is defined by the resistance of the material to indentation. Bcc metals are usually ductile than fcc metals because of more slip systems exist in the former than in the latter. Work hardening is defined by heavy deformation to create high density of dislocations The very useful properties, e.g., strength and toughness, of metallic alloys, such as Fe-C, Al-Cu and Ti-Al systems, are achieved by precipitation of second phases with high elastic moduli. Larger the internal cracks in a material, higher the stress intensity factor, and tougher the material.

Explanation / Answer

VI) True

Hardness is defined as resistance against deformation.Measuring the resistance of different materials to permanent indentation is the hardness of the materials.The hardness testers such as Shore Hardness Tester and Durometers are used mainly to measure the hardness in polymers, rubbers, and elastomers.

VII) False

To undestand the concept of ductility behaviour first we have to understand two terms i.e Slip Plane and Slip direction.slip is the movement of dislocation in the atomic level.This phenomena favors the plane which has the highest planar density and the direction which has highest linear density of the atom. Together the slip plane and slip direction are known as slip system.Now lets come to the arrangewment of atoms in FCC and BCC.FCC is a closed pack unit,hence the atoms per unit cubic cell is higher in comparison with BCC.If you look carefully you will find only 1 predominant family of plane in FCC which is {111} along with only 1 family of directions which is <110> and hence has a total amount of 12 slip system.Whereas in case of BCC which is not a closed pack system, does not has a predominant atomic density.Therefore total 3 family of planes acts as the slip planes and neither of them is a dominant and hence has a total of 48 slip system .
Now when it comes to ductility ,we need to deform the material and as a result of which the dislocation present inside them will also travel,but as mentioned earlier slip is the movement of dislocation and in FCC the atoms are closed pack and has a predominant slip system and hence the slip can travel easily inside it and the material can be deformed easily as a result it will be more ductile while incase of BCC the dislocation cannot travel with such an ease.And hence we can conclude that the FCC structure has more ductility than BCC.

VIII) True

work hardening is defined by heavy deformation to create high density of dislications.Work hardening is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion.Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened.

IX) True

Strength and toughness of metallic alloys such as Fe-c , Al-Cu and Ti-Al systems are achieved by precipitaion of second phases with high elastic moduli

X)False

Strain should be be higher for tougher material .It should be plastic material and deformation should be plastic

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