Chapter 6 Flashcards
brittleness
tendency to fracture when even a small load is applied
ductility
how much a material can deform without sustaining internal damage
creep
deformation of a material at elevated temperatures
elasticity
ability of a material to return to its original shape after some deformation
plasticity
ability of a material to remain deformed after an external force is removed
fatigue
weakening of a material due to repeated cyclic load
hardness
ability of a material to resist permanent (plastic) change in shape
resilience
ability to absorb energy and resist impact load
stiffness
ability of a material to resist additional deformation when loading continues
toughness
ability of a material to resist fracture
tensile test
stretches a sample of a material in a specific form with a decreased diameter in the middle for 2in
engineering stress
stress = F/A(o)
F = force
A(o) = original cross-sectional area
engineering strain
strain = (l(i) - l(o)) / l(o)
l(o) = original length
l(i) = instantaneous length
shear
type of deformation that results in stress and strain = apply force in opposite directions to top and bottom of an object parallel to the surface
shear strain
strain = alpha + beta
alpha = angle between ground and bottom surface
beta = angle between z-axis and side of material
shear stress
stress = F/A(o)
torsion
occurs when twisting a material
when is poissons ratio applied? (v)
for elastically behaving materials - elongation in z-direction is proportional to force acting in the z-direction - causing contraction of the material in x and y directions
what strain can most materials handle elastically
0.005 or 0.05%
what happens above a strain of 0.005?
atomic bonds permanently deform creating permanent deformation
what is the suggested value for yield stress?
0.002 or 0.02%
yielding
point of transition from elastic to plastic deformation
stress at yielding
yield stress
how to find yield stress from graph
find initial slope (m) then draw a line with that slope starting at 0.002 or 0.005 on x-axis and find intersection
ultimate tensile strength
material begins to fail, voids form and create cracks.
at ultimate tensile strength: as ______ decreases, the amount of load needed to continue deformation decreases
area
how to compare ductility on stress strain graph
higher strain value at fracture means more ductile
how do we numerically represent ductility
percent elongation or percent area reduction
how to compare resilience on stress strain graph
area under the curve before yield strain
find Ur
how to compare toughness on stress strain graph
area under the curve before fracture
rockwell scale
machine applies a load onto a material then determines the hardness subject to:
- indenter type
- load
- dwell duration
brinell hardness test
steel ball forced into a material then the indentation diameter is measured
convert to mpa or psi using equation for HB
Vickers microhardness test
diamond indenter used and then distance between opposite corners of the diamond indent is used to get the hardness
strain hardening
for some materials, deformation after yield becomes difficult
equation with n = strain hardening exponent
fatigue definition with stress/strain
cracks develop in a material below the yield strength as damage accumulates over time and may not be visible
fatigue limit
any stress below fatigue limit means the material has an unlimited life
fatigue strength
stress after 10^7 cycles
fatigue life
number of cycles to reach fatigue failure at a given load
creep definition 2
deformation of a material over a long period with a static load
3 stages of creep
primary, secondary, tertiary
primary creep
initial deformation (lnx)
secondary creep
steady state (predictable) deformation mx+b
tertiary creep
deformation up to failure e^x
