properties of materials Flashcards
What properties need to be considered?
Unmixed compounds ~storage conditions, shelf life During mixing ~heat generation, setting time, viscosity Set material ~strength, toughness, solubility
Why are mechanical properties important?
Indicates how material will respond to applied forces
Ensures it can function in mouth- occlusal forces and changes in temp
Material usually has minimum value it must achieve ISO standards eg. Mean flexural strength>300MPa
What are some mechanical properties?
Stress and strain ~elastic limit, plastic flow, Young’s elastic modulus, fracture strength, yield stress, Ultimate tensile strength, ductility, resilience, fracture toughness Fatigue Hardness Abrasion resistance (wear)
What types of loading are there?
Tension- pulling Compression- squashing Shear- rubbing over Torsional- twisting Bending- combination stress, tension and compression
What is stress?
The force per unit cross-sectional area that is acting on a material
(Mega) pascals, MPa
Stress=force/original cross area
What is strain?
Fractional change in the dimensions caused by force
Strain=change in length/original length
What is resilience?
The amount of energy a material can absorb without undergoing any plastic deformation
What is toughness?
The amount of energy a material can absorb to the point of fracture
What is ductility?
The amount of plastic strain at fracture
What is elastic modulus?
A measurement of the stiffness, (mega or gigs) pascals, MPa or GPa
What is fatigue?
Loads are too small to cause catastrophic failure
Accumulated stress can cause crack propagation leading to failure
Fatigue life, limit, strength
What is hardness?
Ability to withstand surface indentation by a compressive force
How is hardness measured?
Indentation techniques
~Knoop, Vickers, Brinell or Roackwell
~Directly proportional to size of indentation
~Hardness number, large for soft, small for hard
Scratch test
~hardness indicates resistance to wear
What are some chemical and physical properties?
Elasticity, viscosity and viscoelasticity ~working and setting times Durability and degradation ~solubility, corrosion and erosion Thermal properties ~conductivity, diffusivity, expansion and exothermic Adhesion Colour and aesthetics Biological properties
What is elasticity?
Strain when stretched and instantaneously return to original state once stress is removed
