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Question 1

Substances with high thermal diffusivity

Answer 1

rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly.

Question 2

Thermal conductivity is desirable in

Answer 2

cooling fins, cutting tools, and die-casting molds to extract heat. In contrast, materials with low thermal conductivity are used in furnace linings, insulation, coffee cups, and handles for pots and pans

Question 3

To reduce thermal stresses

Answer 3

a combination of high thermal conductivity and low thermal expansion is desirable.

Question 4

superconductive metal

Answer 4

electrical resistance that equals to exactly zero.
➢ The issue with these metals is that they are superconductive only at very low temperatures, which creates difficulty in use.

Question 5

Piezoelectric materials

Answer 5

generate an electric field when a mechanical stress is
applied on it.

Question 6

Some metals are more resistant to corrosion than others. Why?

Answer 6

Passivation: Formation of a protective oxide layer such as Al2O3, TiO2, Cr2O3 .
➢ Galvanization (coating of steel or iron with zinc to form zinc oxide) is a common process for corrosion resistance.
➢ Tin coating is applied for inside of cans (for food storage).
➢ Stainless steel (has many alloying elements especially chromium and nickel).

Question 7

Yield Strength

Answer 7

The stress (F/A) required to produce a very slight yet specified amount of plastic deformation.

Question 8

Ultimate (Tensile) Strength:

Answer 8

Maximum stress a material can withstand while being pulled before breaking.

Question 9

Compressive Strength

Answer 9

Maximum stress a material can withstand while being pushed before breaking. CAN BE VERY DIFFERENT from TENSILE STRENGTH!

Question 10

Hardness:

Answer 10

Resistance to permanent indentation.

Question 11

Ductility:

Answer 11

The extent of plastic deformation that the material undergoes
before fracture.
Brittle materials (such as ceramics and glass) can have only a few percent total elongation or less (and usually, without a significant necking), whereas the ductile materials can have much more than a few percent total elongation.

Question 12

Toughness:

Answer 12

Amount of energy absorbed by a material before it fractures.

• The area under the stress–strain curve up to fracture is known as the material’s toughness.

Question 13

Stiffness:

Answer 13

is the rigidity of an object — the extent to which it resists deformation in response to an applied force.

Question 14

The tension test is the most common test for determining the following mechanical properties of the part’s material:

Answer 14

o modulus of elasticity, E o strength
▪ yield stress, Y
▪ ultimate strength, UTS (also known as UTS or maximum stress)
o whether it is ductile or brittle o toughness
o resilience
o range of elastic deformation (where Hooke’s Law is applicable) and plastic def.

Question 14

Modulus of Elasticity, E

Answer 14

The higher the E value, the higher the load required to stretch the specimen to the same extent, and thus the stiffer is the material.

Question 15

Compression

Answer 15

During the compression test, if the bottom and top surface of the specimen is hold with friction (which is the usual case), then as the specimen is compressed, the cross-sectional area bulges (increases) toward the center (away from the top and bottom). This is called barreling.

Question 16

Torsion-testing equipment consists of:

Answer 16

1. A twisting head, with a chuck for gripping the specimen and for applying the twisting moment to the specimen.
2. A weight head, which grips the other end of the specimen and measures the twisting moment of torque.

Question 17

Bending Methods

Answer 17

Bending is a commonly used test method for brittle materials such as ceramics and carbides.

Question 18

Hardness-Testing

Answer 18

Hardness is defined as the resistance to permanent indentation. It gives an
indication of the strength of a material and of its resistance to scratching and to wear.

Question 19

Fatigue Failure

Answer 19

Cyclic or periodic loads causes cracks to grow with every stress cycle. These cracks propagate through the material until a critical crack length is reached and the material fractures. This phenomenon is called fatigue failure and it is responsible for the majority of failures in mechanical components.

Question 20

Fatigue strength can be improved by:

Answer 20

Case hardening (Chapter 4)
– Fine surface finish which reduces the effects of surface
imperfections
– Inducing compressive residual stresses on surfaces
– Materials which do not have many inclusions, voids or impurities

Question 21

Creep

Answer 21

Creep is the permanent elongation of a component under a static load
maintained for a period of time. It generally occurs at elevated temperatures (relative to Tm). The mechanism of creep is generally grain boundary sliding.

Question 22

Impact

Answer 22

Impact tests measure the effects of dynamic loading on a material. Impact toughness is the amount of energy that a material can absorb from a sudden impact.