Chapter 6 - Mechanical Properties of Metals Flashcards
ASTM
American Society for Testing and Materials
ways that loads are applied (3)
- tension
- compression
- shear/torsional
tension tests
a specimen is deformed, usually to fracture, with a gradually increasing tensile load that is applied along the long axis of a specimen, standard diameter is 0.505”, recorded as load or force vs elongation
engineering stress
σ = F/Ao, measured MPa or psi
1 MPa
10^6 N/m^2
engineering strain
ϵ = (li-lo)/lo = ∆l/lo, unitless
compression tests
force is compression and the specimen contracts along the direction of the stress, negative stress and strain, used when a materials behavior under large and permanent strains is desired or when the material is brittle in tension
shear stress
τ = F/Ao
plastic deformation
nonrecoverable deformation, corresponds to the breaking of bonds with original atom neighbors and then re-forming bonds with new neighbors
yielding
when plastic deformation occurs
proportional limit
(P) the location on the graph where the stress-strain curve departs from linearity
yield strength
(σy) the stress corresponding the intersect of a line offset by 0.002 from the original curve and the stress-strain curve, measure of a metals resistance to plastic deformation
fracture point
(F) point of fracture
tensile strength
(TS) the stress at the maximum on the engineering stress-strain curve, maximum stress that can be sustained by a structure in tension
necking
occurs at TS, when the subsequent deformation begins to be at one point
ductility
measure of the degree of plastic deformation that has been sustained at fracture, indicates to a designer the degree to which a structure will deform plastically before fracture, specifies the degree of allowable deformation during fabrication operations, generally increases with temperature
brittle
a metal that experiences very little or no plastic deformation upon fracture
resilience
(Ur) the capacity of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered, computed by finding the area under the engineering stress-strain curve taken to yielding
resilient materials
those having high yield strength and low moduli of elasticity, used in spring applications
toughness (2)
the area under the σ-ϵ curve up until the point of fracture
- fracture toughness: indicative of a material’s resistance to fracture when a crack is present
- notch toughness: the ability to absorb energy and plastically deform before fracturing
true stress
σ = F/Ai
true strain
ϵ = ln[(li/lo]
strain-hardening exponent
(n) constant used in predicting where necking may begin
