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21 Cards in this Set
- Front
- Back
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Forces |
Uniaxial (along a single axis)
Biaxial (along 2 perpendicular axes)
Triaxial (Equally in all directions - hydrostatic) |
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Uniaxial Forces |
Tensile
Compressive
Shear |
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Equations |
Stress = Force/ Cross sectional area
Strain = Change in length/ original length
Young's modulus = stress/ strain (Is a measure of stiffness)
Compliance = 1/ Young's modulus (measure of softness) |
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Definitions I |
Limit of proportionality Limit of linear region Elastic limit The point beyond which permanent deformation occurs Yield point The point above which strain will increase without further increase in stress Ultimate tensile stress The breaking stress |
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Definitions II |
Ductility The amount of plastic strain Elastic strain Reversible Plastic strain Irreversible Resilience Energy absorbed without permanent deformation (area under elastic part of the curve) Toughness The total energy absorbed up to fracture (total area under the curve) |
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Stress-Strain Curves |
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Poisson's Ratio/ μ |
Poisson's ratio = lateral strain/ axial strain (Typical values 0.2 - 0.4) |
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Other Moduli |
Shear modulus = shear stress/ shear strain
Bulk modulus = hydrostatic pressure/ volume change |
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Direct Tensile Measurements |
Tensile strength = breaking force/ cross sectional area
Used for: Metals, some rigid polymers and rubbery polymers |
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Compressive Measurements |
Compressive strength = 4P/ Cross sectional area
Used for: Ceramics, Hard polymers eg. Dental cements and filling materials |
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Diametral |
Compressed across the diameter
Used for: brittle materials (not ductile) |
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Static Strengths |
Tensile strength Compressive strength Diametral strength Torsional strength Flexural strength Shear strength |
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Hardness |
Depth or area of indentation under constant load |
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Brinell Hardness |
Ball indicator used for indentation
Used for: Metals |
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Rockwell Hardness |
Range of materials depending on indenter |
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Knoop Hardness Vickers Hardness |
Used mainly for ceramics, composites and hard plastics |
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Shore (durometer) Hardness |
Used for polymers and elastomers and rubbers |
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International Rubber Hardness Degrees |
Depth of penetration under dead load measurement |
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Fracture toughness |
An important property of brittle materials
Is the resistance to failure from a fracture starting from a pre-existing crack
At a critical stress value, the crack will propagate spontaneously |
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Tear Strength/ Resistance |
The force needed to initiate or continue tearing
Tear energy is the energy per unit surface area of the newly torn surface
Used for: Elastomers, eg. impression materials |
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Impact Test |
The resistance to fracture under rapid loading
Measured as energy absorbed at fracture
Empirical test
Used for: Denture based acrylic |
