Question

What is the difference between Thermoplastics and Thermoset polymers?

A)Thermoplastics can be moulded to shape, thermoset cannot.

B)Thermoplastics have covalent bonds that can be broken and reformed, thermoset does

not.

c. Thermoplastics have entangled polymerics units that can be untangled at elevated

temperature, thermoset does not.
d. Thermoset plastics are more flexible then thermoplastics.

Q )What is/are the benefit(s) of short fibre reinforcements?

A)Increased stiffness only.

B)Increased strength and increased Toughness.

C) Increased Toughness and increased flexibility.

D) None of the above.

What is apparent density?

a)Density as measured via suspension in water.

b)Density of materials without any pores.

c)Density of material calculated with the inclusion of ONLY open pores.

e)Density of materials calculated with the inclusion of ONLY close pores.

Q Plane strain fracture toughness is a fundamental material property which:

a) is valid when specimen thickness is much greater than crack dimensions.

b) increases with increasing strain rate and decreasing temperature.

c)usually increases with strengthening.

d)is not dependent on microstructure

Q)Nickel superalloys are selected for high-temperature gas turbine blades because of:

a)High modulus.

b)High creep strength.

c)High maximum working temperature.

d) b and c.

Q. The most important mechanical properties of metals include stiffness, strength, ductilityand toughness. Which of the following statements is true:

a. Both strength and stiffness are strongly dependent on microstructure and processing.

b. Strength is a measure of resistance to elastic deformation whereas toughness is a measure of resistance to fracture.

c. Ductility is a measure of the ability of a material to plastically deform.d. Increasing strength generally increases toughness.

Answer 1

Thermoplastics:
Highly recyclable
Aesthetically-superior finishes
Remolding/reshaping capabilities Chemical resistance
High-impact resistance
Rubbery or Hard and crystalline surface options
Eco-friendly manufacturing

Thermosets:
More resistant to high temperatures than thermoplastics
Thick to thin wall capabilities
Excellent aesthetics
Higher dimensional stability
Highly flexible design
Highly Cost-effective

Option 'd' is the answer.

The addition of fibres, either short or continuous,increases ductility or makes them quasi-ductile with significant improvement in tensile strength, tensile strain, toughness and energy absorption
capacities

Option 'B' is the answer.

Apparent solid volume is the combined volume of compact solid material and the closed pores, but excludes the volume of open pores.

The apparent solid density, often abbreviated as apparent density, is the ratio of the mass of a material to its apparent solid volume.

Option 'e' is the answer.

We know that the material away from the free surfaces of a relatively thick component is not free to deform laterally as it is constrained by the surrounding material. The stress state under such conditions tends to be triaxial and as a result there is zero strain perpendicular to the plane of the two stress axes and the direction of crack propagation when a material is loaded in tension. This condition is called “plane-strain” and is seen in thick plates. Under plane-strain conditions, materials behave essentially elastically until the fracture stress is reached and then rapid fracture occurs. Since little or no plastic deformation is noted, this mode fracture is termed brittle fracture.

Increase in plane-strain sensitivity occurs as the strength increases.

Option 'c' is the answer.

A superalloy is a metallic alloy which can be used at high temperatures, often in excess of 0.7 of the absolute melting temperature. Creep and oxidation resistance are the prime design criteria which demand super alloys. They can be based on iron, cobalt or nickel, the latter being best suited for aero-engine applications. Ni based superalloys have emerged as the material of choice for these applications most of the time.

Option 'd' is the answer.

Ductility is the ability of the material to plastically deform and adapt while being stressed with a tensile load which intensively makes it resistant to compressive load as well.The latter property is called 'malleability' which allows the material to be flattened by hammering or rolling.

Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force. The complementary concept of which is flexibility or pliability.That is, the more flexible an object is, the less stiff it is.

Strength is the capacity of an object or substance to withstand great force or pressure.Different strengths range from elasticity to plasticity.

Toughness is the ability of a material to absorb energy and plastically deform without fracturing. Numerically,it is the strain energy stored by body upto fracture.

Option 'c' is the answer.

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