False.

Ionic bonding is directional

False.

Secondary bonding is called secondary bonding because it does not involve the transfer of electrons.

False.

For BCC, its closest-packed directions are <111>.

False.

FCC has 4 effective atoms per unit cell.

False.

For BCC, it is <110>.

False.

BCC is 0.68, FCC is 0.74.

False.

FCC has the highest in a cubic structure.

False.

There are 7.

False.

Polymers in solid state (Plastics) interact each others via secondary bonding. Although individual molecules are connected with covalent bonds, the lower observed melting temperature in plastics is the consequence of secondary bonding rather than the primary bondings.

False.

Although the area and number of atoms in (110) plan for BCC and FCC are the same, but based on the hard sphere model the ratio of radius of atom and lattice parameter, (R/a), is not the same for BCC as compare to FCC. Thus the planar density are not the same.

False.

Although there are 2 unknown lattice parameters for Hexagonal crystal system, but as mentioned in the class, for HCP the ratio of c/a is fixed. So, only 1 lattice parameter is needed to solve its crystal properties.

False.

Some single crystals have anisotropic properties, this is not desired in the common practice when using metallic materials

False.

Atoms in the crystal lattice can vibrate and the magnitude of vibration depends on the temperature. So defects such as
vacancy, self‐interstitial, substitutional impurity, interstitial impurity, can and will move. Line defects such as dislocation can also move upon temperature and mechanical loading.

False.

Other factors such as crystallographic structures, valency and electronegativity also need to be considered.

False.

Atoms are much too small to be observed using optical microscope. X‐diffraction is the most common method used to reveal the crystal structure as well as poly‐crystal or single crystal.

False.

Within a grain, we have a single crystal. So the crystal structure, crystal orientation and chemical composition are all the same.

Vacancy density increases linearly with respect to temperature.

False.

The symbol “┴” means that the extra plane is above the dislocation line. Likewise the symbol “T” means the extra plane is
below the dislocation line.

True.

Grain boundaries can prevent further movement of dislocation, so contain more dislocations

True.

BCC has 4 non‐parallel closest‐pack direction, 6 for FCC and 3 for SC

True.

APF for BCC is smaller than FCC, so larger atoms can fit into the interstitial site.

False.

There is no volume change between the strain at yield strength and the strain at the ultimate strength. In this range
atomic spacing is not changed.

True.

All these planes have the same area in a cubic system.

False.

Strength of a material is associated to its ultimate strength, while stiffness is associated to the initial modulus.

False.

There are materials (rubber) that are non‐linear elastic.

False.

The Burgers vector of a screw dislocation is parallel to its dislocation line

True.

False.

The yield point is associated to the beginning of plastic deformation. So, upon removal of load, the sample will have 0.2% of plastic strain.

False.

Necking begin after the ultimate strength is reached

False.

The grain boundaries is more chemical active, so it is more reactive to the etching solution and become as observed in the optical microscope.

False.

All above quantities have units of Pascal (Pa) or pound per square inch (psi)

False.

Strain is dimensionless, it has no units.

False.

Plastic deformation in metals is slip along the closest‐packed direction, so no volume change take place

False.

Both plastic and elastic deformation in metals does not alter the crystal structure. For plastic deformation, slip occurs, while in elastic deformation, very small displacement take place and it is not enough to alter crystal structure.

False.

Yielding is the onset of plastic deformation.

True.

True stress is load over the instantaneous cross sectional area, while engineering stress is the load over the initial cross sectional area. During tensile displacement, as the length increases the cross sectional area decreases, thus true stress is always large than engineering stress.

False.

True strain is the incremental displacement over the instantaneous length, while engineering strain is the incremental displacement over the initial length. At a given tensile load, as the instantaneous length is greater than the initial length, so thus true strain is always less than engineering strain.

False.

Area of both curves is the same, as it is just the toughness of the material

True.

Unit for stress is MPa and strain is dimensionless, so unit for the area under the stress‐strain curve is the unit of stress times the unit of strain.

True.

All these quantities are based on areas in the stress‐strain curve, thus they all have the same unit.

False.

“Cup‐and‐cone” fracture surface is a typical pattern for ductile failure

False.

Crystalline ceramics is transgranular brittle failure, due to the lack of intergranular motions in ionic materials.

False.

True.

High‐strength metals do not slip, thus no clear brittle‐to‐ductile transition

False.

Most of metallic samples used are polycrystalline, there are only handful of applications that requires single crystal. Moreover the grain boundary enhances the strength in metals.

False.

Yield strength is the onsite of plastic deformation. In plastic deformation, dislocation density is increased providing additional strengthening. However, for elastic deformation materials recovers its original dimensions upon unloading, hence no defects were generated in the deformation process.

False.

True.

Steel is a ferrous metal, so the fatigue limit (or endurance limit) is associated to infinite number of repeating cycles. If the question has to do with Aluminum, copper or brass (which are nonferrous metals, we will be using the 107 repeating cycles for the fatigue limit design.

True.

Although secondary creep rate depends on the applied load and temperature, but the activation energy is only
associated with temperature.

False.

In a typical creep curve there are three regions: primary creep, secondary creep and tertiary creep. The creep rate
decreases with time in the primary creep region, creep rate remains constant with in the secondary creep region (which is called steady‐state creep), while the creep rate increases with time at the late stage of creep which one calls tertiary creep.

True.

Some students seem to think the area under the stress‐strain curve must be Megapascal (MPa). This is wrong in concept. The unit for the stress is force over area, while strain is dimensionless. Therefore the unit for the area of stress‐strain curve is the unit of stress times the unit of strain, which is force over area. So it can be newton per meter square which is also called pascal, it can also be pound per inch square which is called psi. I can also used any unit of force per any unit of length square.

True.

In fatigue failure one always has crack initiation, crack propagation and rapid failure. So the surface will contain different features (smooth and rough) depending on the growth.