Week 3 Flashcards
What is the equation for stress?
Force/Area
What is the equation for strain?
displacement (Lf-Li)/ initial length (L)
What is the sign for tension?
+
What is the sign for compression?
-
Describe what happens during a tension or compression test.
tension test = machine moves up (pulls)
compression test = machine moves down (pushes)
What happens when the load reaches a maximum point during a tension or compression test?
it starts to plateau
After the load reaches its maximum point, what happens to the material?
nicks form
What happens end of the compression or tension test?
- material breaks off
- you’ll have two pieces of metal and a graph called a force-displacement curve
If you want to be able to compare materials what must you do to the force-displacement curve?
convert force –> stress and
displacement –> strain
Temporary deformation of a material’s shape that is self-reversing after removing the load
elastic deformation
E, ratio of stress to strain
Elastic modulus/modulus of elasticity/ Young’s modulus
What denotes material stiffness and is determined by the slope of the elastic (linear) portion of the stress-strain curve?
elastic modulus
Materials with high elastic modulus have (low/high) stiffness
high
What is an example of a material with high elastic modulus?
ceramic materials
Materials with low elastic modulus have (low/high) stiffness.
low
is the stress when it ceases to be linear
proportional limit
permanent deformation
plastic deformation
the ability of a material to be drawn or plastically deformed without fracture
ductility/plastic deformation
What is yield strength?
σY, stress corresponding to the yield point at which the material begins to deform plastically. Is the stress at which there is a specified deviation from stress-to-strain proportionality, usually 0.1%, 0.2%, or 0.5% of the permanent strain. Always slightly higher than PL.
**where plastic and elastic curves meet and follow that point and draw a parallel line to the y-axis
the maximum stress sustained before failure
ultimate tensile strength
Describe the stress-strain curve for a brittle material
ONLY ELASTIC DEFORMATION
E= elastic modulus
strain e = elastic deformation
(*): tensile strength and fracture strength are the same
no yield point because there is no plastic deformation
Describe the stress-strain curve for ductile polymers
E = elastic modulus
has a yield stress
Is the maximum strength useful? No. because you have 300% deformation, so that point in polymer materials is not used. If you want to use something to determine if the material is useful, you must use the yield strength
Compare mechanical properties (stress-strain curve) for ceramic, metal, hard tissue, and polymers.
ceramic = brittle = no plastic deformation
polymer = low stiffness = low load = lots of plastic deformation
*metals can move around the graph depending on what type of metal you’re referring to
hard tissue = bone, dentin, cementum
