Test 2 Flashcards

A common test that determines the relationship between load and deformation - measures elastic properties, plastic properties, and failure properties!

The ratio of -lateral / axial strain under an applied stress. Describes the fact that volume is rarely constant under a load.

Describes the elastic properties. The tensile test (not accurate) and Cantilever Test are better!

Point at which permanent deformation begins.

Permanent (irreversible deformation).

Maximum stress before beginning plastic deformation.

The increase in stress to continue deformation beyond the elastic limit.

Maximum stress value a material can support.

The amount of deformation a material will tolerate before failure. Can be measured with percent elongation and percent area of reduction.

Localized deformation in a small section in gauge length beginning at the ultimate tensile strength point. Reason: deformation is usually distributed but there’s a point where the material properties become non uniform and therefore a localized area of stress happens.

Deformation before necking is linearly proportional as it varies with gauge length - direct proportionality. After necking, not proportional due to the localization of damage in the neck.

Measure of elastic energy storage. Formula: yield stress²/2E.

Measure of energy absorbed before failure. Formula: (yield stress + ultimate stress)/2 * failure strain.

Yielding (plastic deformation) does not occur uniformly over the length of the specimen. Deformation bands spread throughout the specimen competition in size.

Measures material's resistance to localized plastic deformations (dents/scratches). Hardness and tensile strength are both proportional to one another therefore hardness test can approximate the tensile strength.

The value of E depends on the change of force with respect to the interatomic radius (dF/dr) and total number of bonds. The stiffness and density of bonds in the cross-section control this.

Asymmetric or symmetric change in interatomic distance with temperature. Asymmetric means the interatomic distance changes with temp. Symmetric means interatomic distance; a new energy level is constant with increasing temp. REMEMBER alpha*T*L = thermal strain.

Stronger bonds have a lower thermal expansion coefficient and a higher melting point. They do not stretch as much because of their strength.

Intramolecular or chemical bonds, including ionic, covalent, and metallic bonds.

Intermolecular or physical bonds, including van der waals and hydrogen bonds.

Minimum volumetric unit which repeats in a crystal lattice.

Number of atoms which are in contact with one particular atom.

Fraction of unit cell volume occupied by atoms.

Having different properties in different directions.

Properties are independent of direction.

Found in metals and non-metals where metal gives up valence electron and non metal takes it (held together by charge difference) - creating non directional bonds.

Sharing of valence electrons with materials with smaller electronegativities. Forms directional bonds.

Have shared electrons between different atoms (independent molecule units). They have low melting and boiling points; weak van der waal forces between the structures and are soft and flexible.

Structures with continuous covalent bonds between atoms in a repeating pattern. They have high melting and boiling points; only covalent bonds and are extremely hard.

Found in alloys and metals where metal ions give up 1, 2, and 3 valence electrons to a “sea of shared electrons”. Non directional bonds with high electrical conductivity and ductility of most metals.

Caused by attraction. London dispersion is the permanent and weakest bonds and dipol-dipole is temporary in polar molecules.

Formed between hydrogen and fluorine, oxygen, and nitrogen creating the strongest intermolecular bond.

Solids arranged in a highly ordered microscopic structure.

Solid composed of many grains in a crystal structure.

Solids that are not organized into any definite lattice pattern.

Refers to the shape and size of crystals.

Refers to the structure features of an alloy (grain or phase structure)

Self Interstitial Atoms, Vacancies, and Impurity Atoms

Atoms squeezed into voids which are not normally occupied — can generate high stresses in the material.

Most common point defect, allows diffusion to occur and lets atoms rearrange to lower energy configurations.

Substitutional -alloy atoms replace the host atoms of the structure (same size). Interstitial - small alloy atoms fit into spaces between host atoms (smaller size)

Edge dislocations and screw dislocation

The presence of an extra half of the plane in the crystal structure - forms when materials are deformed.

A bulk of a sample goes through partial shear and is shifted by 1 or more unit cells.

These are regions of atomic disorder and higher energy which creates more chemical activity. The angle of misalignment can be found by finding the angle between the two high-density lines near the grain boundary.