Definitions
What is Young's Modulus?
(Elastic Modulus) Stress and strain linearly related in elastic region.
The energy absorbed before fracture is known as the...
Modulus of Toughness (total area under a stress-strain curve).
What do the following equations represent?
a. Force/InitialArea
b. (L(final)-L(initial))/Linitial
c. change in stress/change in strain
a. Engineering Stress
b. Engineering Strain
c. Elastic (Young's) Modulus
a high number of crystal imperfections centered around a line is known as a...
Dislocation.
Hardness testing is a quick and easy way to estimate the ______ of a material.
Strength.
What is the difference between elastic deformation and plastic deformation (two points each)?
Elastic Deformation: temporary deformation, stretching of atomic bonds.
Plastic Deformation: permanent deformation, break/remake of atomic bonds.
(DOUBLE !!) What is a material's Modulus of Resilience and where is it located on a stress-strain curve?
a. Energy absorbed by a loaded (stressed) material before yielding.
b. Area under the elastic part of the curve (use area of a triangle).
Calculate the engineering stress (MPa) on a magnesium bar with initial dimensions: diameter = 12 mm, length = 30.000 mm, if it were subjected to a load of 1500 kg.
130 MPa
(Photo 1) (DOUBLE!!) What kind of deformations are shown in the photos?
a. Edge dislocation (edge dislocation line moves parallel to applied stress)
b. Screw dislocation (edge dislocation line movies perpendicular to applied stress)
Plastic deformation of a single crystal usually occurs more easily when...
There is a dislocation slip across a plane with high atomic density.
What is the hardness of a metal?
A metal with a higher modulus of toughness is more resistant to...
Fracturing.
(Photo 4) a. What is the greatest tensile load (force in N) that can be placed on 2cm x 2cm stainless steel bar at 871oC before it fractures?
b. How long will a 2 meter bar of the stainless steel at 260oC be plastically elongated (final length) before breaking?
c. What is the Young’s (elastic) modulus for stainless steel at 538oC?
a. 27200 N
b. 2.0066 m
c. 175 GPa
(Photo 6) Atomic lattice deformed which forms a mirror imagine of lattice next to it is known as...
Twinning.
Cold working a metal will cause what to happen to the hardness, ductility and dislocation density?
a. hardness will increase.
b. ductility will decrease.
c. dislocation density will increase.
What is Ultimate Tensile Strength (UTS)?
Maximum strength reached on engineering stress strain curve (peak).
(Photo 2) (DOUBLE!!) Which curve is...
a. the strongest?
b. the stiffest?
c. the most ductile?
d. the most brittle?
a. B is the strongest
b. C is the stiffest
c. E is the most ductile
d. D is the most brittle
(Photo 5) What is the strain on the elongated bar?
e = 0.0113
(Photo 7) Plastic deformation of a single crystal that results in step markings on surface is known as...
Slip Bands (occurs within slip planes)
(DOUBLE!!) What are slip systems composed of and what is the relationship between slip systems and ductility?
Slip Plane - slip occurs in densely/closely packed planes.
Slip Direction - direction of slip, direction with highest linear density.
More slip systems ---> more ductile.
Less slip systems ---> more brittle.
(DOUBLE!!!) What is Cold Deformation and Cold Work (w/ formulas)?
a. Cold Deformation strengthens metals, forms new dislocations, hinders movement of atoms (Difficult to move through "forest of dislocations").
b. Cold Work is the permanent deformation of metals and alloys below crystallization temperature.
[(A0-Af)/A0]*100% if given diameter/length and width.
[(T0-Tf)/T0]*100% if given thickness.
Modulus of elasticity?
Tensile strength?
Yield strength?
a. 3.5 x 10^4 MPa
b. 240 MPa
c. 180 MPa
A metal with an FCC crystal structure is oriented so that a stress is applied in the [001] direction. When stress is applied, slip will occur on the (101) plane in the [111] direction. Calculate the magnitude of the applied stress required to produce a resolved shear stress of 2.20 MPa.
What happens to bonds when:
a. A dislocation slip is located?
b. No dislocation slip is located?
a. Break all bonds at once (high stress required to permanently deform).
b. Break "one" bond at a time (lower stress required to permanently deform).
Is true stress greater than, less than, or equal to the engineering stress? Why?
True stress is greater than engineering stress because true stress uses the instantaneous cross-sectional area and while engineering stress uses the initial cross-sectional area.