True/False for Structures Final

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For cubic crystals, as values of the Miller indices h,k, l decreases, the distance between adjacent and parallel planes decreases

FALSE

In a FCC structure, [100] is a close-packed direction

FALSE

In general, the physical properties of single-crystals and glasses are isotropic (i.e. do not depend on the direction of measurement)

FALSE

Point-defects are also created by the application of shear stress

FALSE

Since materials with no dislocations may be very strong but cannot be plastically deformed, therefore, dislocations weaken a material and makes the elastic deformation possible

FALSE

The concentration of dislocations in a solid follows the law of thermodynamics and is given, at equilibrium, by N_d=Nexp(-Q/kt)

FALSE

The equilibrium number of vacancies for a given quantity of material depends on temperature and decreases when temperature increases

FALSE

The fact that X-ray can ionize matter is used in the standard X-ray diffraction technique

FALSE

The grain size is often determined when the properties of a single crystalline material are under consideration, and the grain size has a significant impact of strength and response to further processing

FALSE

For a ductile material, all deformation up to the ultimate tensile stress is uniform throughout the sample. However at maximum stress, a small constriction (necking )begins to form

TRUE

In materials, dislocations are created by the application of shear stress

TRUE

Materials are not as strong as predicted by theory because flaws act as stress concentrators and lead to failure at stresses lower than theoretical values

TRUE

Materials with strong chemical bonds tend to have high melting points

TRUE

Plastic deformation in a metal is accomplished by means of point defects moving within preferred slip systems

TRUE

The bonds found in solid 'noble gases' (He, Ne, Ar, Kr, Xe, Rn) originate from the synchronization of electronic clouds, which induces weak, short-scale, attractive forces between induced electric dipoles

TRUE

The impurity defects in the solid solution are either substitutional or interstitial

TRUE

The solidification of a liquid alloy of eutectic composition yields a microstructure consisting of alternating layers of the two solid phases

TRUE

A brittle material can become ductile as temperature decreases

FALSE

As the dislocations density increases in a material, it becomes softer

FALSE

Ceramics are always ionic in nature

FALSE

The kinetics of a martensitic reaction is limited by the diffusion of species

FALSE

The yield strength is the maximum value of stress on an engineering stress-strain curve

FALSE

When repeated over and over, the stacking sequence ABABAB... yields a FCC structure

FALSE

A ductile failure has extensive plastic deformation in the vicinity of the advancing crack. Crack opening proceeds relatively slowly and any further extension requires increased levels of applied stress

TRUE

A system is at equilibrium when it is in its most stable state; that is when its phase characteristics do not change over time

TRUE

A young's modulus of a material is the slope of the stress-strain curve in the elastic deformation region, and is specific to each material

TRUE

Cold-working increases the yield strength and tensile strength and decreases the ductility of a material

TRUE

Cracks propagate if the stress at their tip exceeds a critical value. The largest and the most highly stressed crack will grow first

TRUE

Positions of the diffraction peaks (d_hkl) provide geometrical information of the crystal structure, and symmetry

TRUE

The addition of impurity atoms to a metal results in the formation of a solid solution

TRUE

The atomic linear density (LD) is defined as the number of atoms per unit length whose centers lie on the direction vector for a specific crystallographic direction

TRUE

The solubility of carbon in iron depends on temperature. This is why, upon cooling from a melt, steel will produce precipitates of carbon-rich phases

TRUE

There are no perfect crystals and many material properties are improved by the presence of imperfections

TRUE

Twinning occurs at low temperatures and high rates of shear loading (shock loading) conditions, where there are few present slip systems (restricting the possibility of slip)

TRUE

Unit Cell is the smallest repetitive volume which contains the complete lattice pattern of a crystal

TRUE

When temperature is sufficiently high compared to the melting point, atoms diffuse away from the initial position in a random-walk manner

TRUE

X-rays are ionizing radiations because their photon energy is larger than the binding energy of electrons in an atom

TRUE


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