BIOM_Mechanical Properties Flashcards
define mechanical properties
properties that relate to the ability to withstand external forces.
why do we measure mechanical properties
for obtaining fundamental properties.
what are the 2 classifications of mechanical properties. elaborate and define.
1) Bulk/ Surface
Bulk: whole mass (strength, rigidity etc)
Surface: harness (indentation) and wear (abrasion)
2) sub-class of bulk properties (fundamental & applied properties).
fundamental: obtain from applying steadily increasing load (stress/strain).
applied: specific conditions in service (impact, fatigue, viscoelasticity)
name fundamental properties
Stress and strain
define stress
force per unit area - pascals
what are the 2 types of stress
fundamental or combined
what are the fundamental types of stress
tension, compression, shear
define tension
force perpendicular to resisting area
define compression
force perpendicular to resisting area; opposite of tension
define shear
force parallel to resisting area
what are the combined types of stress
torsion and flexure/bending
what characteristics of a surface cause increased or concentrated stress to occur
where there are notches, grooves, cracks, or surface irregularities
ceramics and glasses are sensitive to what
surface roughness
define strain
change in shape with respect to initial length (l/l = dimensionless)
what are the types of strain
elastic and plastic
what is the difference between elastic and plastic
elastic is recoverable and plastic is permanent
when taking an impression when should the material be elastic and when should the material be plastic
plastic on insertion (permanent deformation) and elastic on removal (recoverable deformation - recover from the forces of removal so that you don’t destroy your impression when you take it out of the mouth)
true or false: fundamental properties of a material that are derives from the stress-strain curve do not depend on the size of the material tested
TRUE
modulus of elasticity
slope of initial linear portion = modulus of elasticity (aka Young’s modulus) - this is where the material follows Hook’s law
rigid vs. flexible
high or low modulus
rigid = high flexible = low modulus
what is the only pure elastic fundamental property
the modulus of elasticity
what is the the elastic limit
the amount of stress which changes a material from elastic strain to plastic strain
how is ductility measured & how is malleability measured
by % of elongation (wire/sheet)
high % elongation = ductile
low % elongation = brittle
Ultimate tensile strength (UTS)
amount of stress at which the material breaks
what is the last point on the stress-strain curve
ultimate tensile strength
what is the term to describe the maximum stress that the material undergoes during stress-strain test?
maximum strength (or just simply ‘strength’)
what is the amount of energy that a material can absorb without permanently deforming
resilience
how/where on a stress-strain graph is resilience represented?
area under the ELASTIC PORTION of the curve
what is the total amount of energy that a material can absorb until after which it will fracture
toughness
how/where on a stress-strain graph is toughness represented?
total area under the curve of the stress-strain graph
true or false: you can not relate one certain fundamental property of an individual material to another different fundamental property of the same material
true - you need the individual values of each fundamental property
name 5 applied properties
impact, fatigue strength, hardness, abrasion, viscoelasticity
how is impact measured
by measuring the amount of energy that the material absorbs during an impact test.
impact is a measure of….
brittleness
what applied property is defined as repeated low forces that eventually fracture a material
fatigue strength
what is the quantitative definition of fatigue
repetitions per cycle of load until fracture
if a material is cyclically loaded with stress values lower than the ____________ , than the material will never break
fatigue limit (or endurance limit)
what is the method used to test the tensile strength of brittle material by applying tensile stresses at right angles to the direction of the applied force
diametral tensile test
what term relates to the ability of a material to resist indentations and have a resistance to be scratch
hardness
which 2 properties correspond to the plastic region of the material
Ultimate compressive strength (or ultimate tensile strength) AND maximum strength (strength).
loss of anatomic form from the surface of something
abrasion - which results in the wear of a material
what is the most difficult property to reliably measure
wear bc depends so much on conditions in service
the key concept of viscoelasticity is that it depends on _______
time
slow deformation with time under constant stress
creep
when a material is constantly deformed but may show drop in stress with time is:
stress relaxation
