L06: Mechanical Properties Of Dental And Biomaterials Flashcards
What is mechanical testing?
The measurement of the response of a material (loading/stress failure) to a challenge experienced in service (deformation/strain)
What can mechanical testing characterise a material by?
Strength, stiffness, brittleness, hardness, permanent deformation, resilience, toughness
How have teeth evolved to withstand forces of mastication?
Enamel has a high modulus/stiffness so able to withstand high loads, with high wear resistance
Denture-enamel junction; sigmoidal dental tubules with a gradient - stiffness of corona, decreases towards the root. Mechanically optimised to withstand load.
What is the formula for stress?
Force/area
Stress is the force per cross-sectional area acting on the material. Load divided by area.
What is strain?
Strain is change in dimension caused by the force. (change in the material from load)
Describe a stress-strain curve for a brittle material, e.g., a dental ceramic.
Linear straight line graph
In response to a load, the material will deform slightly. Initially there is proportionality, direct proportional relationship between strain and stress (Hooke’s law). Might be a small amount of large amount of deformation per applied stress.
What is strength, stiffness and stability?
Strength = when and how it breaks
Stiffness = how much deformation under load
Stability = how and when it will return to its original form
Compare material A and B
Page 25 graphs and explanations
How is stiffness of a material defined?
Stress/strain (the ratio). Modulus of elasticity. Gradient of the linear portion of the stress-strain plot.
What is the proportional limit?
The maximum stress that still maintains proportionality is the proportional limit. It is a small region before the material breaks where there is minute amount of deformation that will still return to how it was.
What is elastic behaviour?
The material will return to its original dimensions (zero strain) when strain is removed.
If applying a non-critical load that precedes the elastic limit, when releasing the load, it will return to its original dimension.
What is the elastic limit?
The elastic limit is the point where a specific strain is reached at which permanent deformation occurs.
Is elastic limit EL bigger than proportional limit PL?
Usually they are equal, but if there is a difference, EL will always be larger.
What happens if we exceed the point of the elastic limit in a brittle material?
It will fail catastrophically (shatter/break)
What is plastic deformation?
A point in the stress/strain curve where load has exceeded the elastic limit and there is permanent deformation. When load is released beyond the elastic limit but before breaking point, it won’t return to its original dimension.
