Materials Exam 2 T/F Questions

False

The strength of ceramics is commonly lower in uniaxial compression than in uniaxial tension

False

The yield strength of metals is defined using 1% permanent strain

True

The failure strength of ceramics in compression is usually much higher than the failure strength in tension

False

The strength of pure metals is well below their ideal strength due to the presence of flaws that create stress concentrations

False

The ideal strength of pure elements is approximately 1% of their Young’s modulus

False

Thermoplastics commonly have lower strength than elastomers

The unit of slip of an edge dislocation occurs in a direction parallel to the dislocation line

False

The yield strength of a ductile metal is the stress at which necking begins

False

The tensile strength of a ductile metal is the stress at which fracture occurs

True

Necking is the formation of a local reduced cross-section in a material during a tensile test

True

The ductility of a material can be expressed as the elongation to fracture in a tensile test

False

At temperatures well below the glass transition temperature, a polymer can be cold drawn at nearly constant stress

True

At temperatures below but approaching the glass transition temperature, a thermoplastic polymer will have limited ductility

True

At temperatures close to or slightly above the glass transition temperature, a thermoplastic polymer will exhibit cold drawing

False

At temperatures well above the glass transition temperature, a thermoset polymer will exhibit viscous flow

True

At temperatures well above the glass transition temperature, a thermoplastic polymer will exhibit viscous flow

True

The total strain in a material is equal to the sum of elastic strain and the plastic strain

True

The plastic work per unit volume when a ductile material is deformed is equal to the area under the stress-strain curve

False

The yield strength of a brittle material is the stress at which fracture occurs

True

A hardness test is performed by pressing a hard indenter into the surface of a material into the surface of a material and measuring the indentation made.

False

The strength of a material is a fixed material property and cannot be manipulated

True

Defects in crystals are important because they can significantly affect the properties of materials

True

Point defects in crystals include vacancies and substitutional or interstitial impurity atoms

False

An edge dislocation is a planar defect in a crystal

False

The unit of slip of a screw dislocation occurs in a direction perpendicular to the dislocation line

False

The unit of slip of an edge dislocation occurs in a direction parallel to the dislocation line

True

The Burger’s (slip) vector of a screw dislocation is parallel to the dislocation line

True

Yield strength is the stress beyond which a ductile material becomes plastic

True

Yield properties and ductility are measured with standard tensile tests continued to failure

True

Beyond the yield point, most metals work harden, causing a rise to a maximum called the tensile strength

True

At temperatures above Tg, a thermoplastic polymer will show some plasticity

True

Plastic strain is the permanent strain resulting from deformation of a material

False

Ductility is a measure of how much elastic strain can be tolerated by a material

True

Plastic work is done in deforming a material permanently

True

Crystalline ceramics are brittle at room temperature. They have yield strengths, but these are never reached, as they fracture first

True

Uniaxial compression can result in permanent strain

True

The size of the permanent indentation in a hardness test is a measure of resistance to plastic deformation

False

Both elastic modulus and strength can be manipulated through materials processing

True

Bonds, like springs, have a stress-strain curve. The peak strength is the bond strength

False

Engineering metals have strengths much less than E/15. This is explained by the presence of grain boundaries, which are weaker than the grain interiors

True

There are two primary types of dislocations, called edge dislocations and screw dislocations

True

The ideal strength of a material is usually much higher than the measured strength

False

Point defects in crystals include vacancies, substitutional atoms, interstitial atoms, and dislocations