Properties of fluids and solids Flashcards
State what is resisted by solids, liquids and gas
solids: resist compression, shear and tension
liquids: resist compression and tension
gas: resist compression
What is compression
inward force is applied to the material
What is tension
outward force is applied to the material
How do we classify solids
- composition
- simple: made of 1 material
- compound: made of 2 material - directional dependence
- ansiotropy: mechanical properties are directionally dependent
- isotropy: mechanical properties are not directionally dependent
What is tensile, pliant and rigid
tensile: capable of being stretched
pliant: capable of being bent
rigid: can’t be forced out of shape
What is a Hookean material
displacement is directly proportional to the applied load ( ie. force/ dx)
What does a force vs displacment graph tell us
tells us the elasticity of the material, gives hooke’s constant
How do we normalize a force vs displacement graph
divide the force by cross sectional area (gives stress) and divide the change in length by total length (gives strain)
What is strength in a stress-strain curve
It is the stress recorded at failure point
What is extensibility in a stress-strain curve
It is the max. strain recorded at failure point
What is elasticity in a stress-strain curve
It is the slope measured
What is resilience in a stress-strain curve
It is the ratio of work done during contraction/ work done during extensibility
What is toughness in a stress-strain curve
It is the work done (area under the curve) till failure point
Why are biological materials expressed in a J shaped stress strain curve
materials such as collagen are extensible and so are initally elastic until they are taunt and cannot be stretched much longer ( resulting in steep increase in elasticity –becomes stiff) where there is permanent deformation
Should spider silk have high or low resilience
should have low resilience because you don’t want a lot of the energy to be conserved you don’t want the silk to conserve the energy.
Draw a graph of low resilience
stress strain area under w.d due to contraction should be a lot lower than w.d due to extension
What is shear stress
It is a force applied perpendicular to the SA
What is shear strain
the amount moved in x direction / height
What is the shear modulus
shear stress/ shear strain
What is the ideal gas law
PV =nRT
What is Boyle’s law
under constant temp PV= constant
What happens when a shear stress is applied to a fluid
fluid flows
What is the difference between a fluid and solid upon shear stress application
fluid flows, solid deforms in shape
How do we increase the velocity of a fluid being sheared
increase the shearing force
What is dynamic viscosity
shear stress/ shear strain RATE= viscosity. it is the slope of shear stress vs shear strain RATE curve
Calculate the viscosity for a fluid in a 1mm depth container where 100 Pa of shear stress is applied, where the boundary layer is flowing at 5mm/s
100/ (5mm/s /1mm) = 20 Pa s
What is a shear strain rate
It is the velocity gradient ( in terms of depth of the container) It is the change in velocity / the change in distance
Describe how Netwonian fluids relate in a shear stress and shear strain rate curve
Newtonian fluid have a constant viscosity so their slope from shear stress to shear strain rate is constant
What are the other non-Netwonian like fluids ( draw their curves on a shear stress vs shear strain rate graph)
- shear thinning fluid: as shear stress increases become less viscous
- shear thickening fluid: more shear stress fluid becomes more viscous
- Bingham plastics: After a certain shear stress is applied, object has viscosity
What is a shear thinning fluid
blood,
What is a viscoelastic material
has viscosity and elasticity
Draw the stress strain curve for elastic material
slide 24 L 7
Draw the stress strain curve for viscous material
slide 25 L 7
Draw the stress strain curve for viscoelastics materials
slide 26 L 7
What objects have stress and strain in phase
elastic material
what objects have stress and strain 90 degrees out of phase
viscous materials
Name a shear thickening fluid
synovial fluid
