Raghuwar-Mechanical_Properts_of_DM-_Part_1.ppt
- 1. Dr. Raghuwar D Singh Associate Professor Prosthodontic Department King George’s Medical University UP, Lucknow
- 2. Dental Materials: Properties of Dental Materials – Physical, Mechanical Biocompatibility Micro structure of metal alloys Impression materials Gypsum product Dental Resins – Denture base and Restorative Resin Dental Amalgam Dental Cements Direct filling Gold Dental casting alloys Finishing and polishing materials Dental Ceramics
- 3. Mechanical Properties of DM Mechanical Properties: 1.Stress 2.Strain Mechanical Properties based on elastic deformation: 1.Stress- Strain diagram/ curve 2.Modulus of elasticity 3.Poisson’s ratio 4.Flexibility 5.Resilience
- 4. Strength Properties: 1.Proportional limit 2.Elastic limit 3.Yield strength 4.Diametral tensile strength 5.Flexural strength 6.Fatigue strength 7.Impact strength
- 5. Other Mechanical properties: 1.Toughness 2.Fracture toughness 3.Brittleness 4.Ductility and Malleablility 5.Hardness
- 6. STRESS Force per unit area; Stress= Force/Area It is normally defined in terms of mechanical stress, which is the force divided by the perpendicular cross sectional area over which the force is applied.
- 7. Stress: Internal resistance to applied external force.
- 9. Types of stresses.... Axial Compressive Stress- Tensile Stress-
- 10. ....Types of stresses Non Axial Shear – Tends to resist the sliding of one portion of a body over another. Torsion Bending
- 11. Flexural Stress: Bending forces
- 12. STRAIN Strain: change in length per unit original length when stress is applied; = Length / Original length Strain(ε)= Deformation/Original length
- 13. Elastic Strain Plastic Strain
- 14. Mechanical Propertied based on Elastic deformation 1. Stress- Strain diagram/ curve 2. Modulus of elasticity 3. Poisson’s ratio 4. Flexibility 5. Resilience
- 17. ELASTIC MODULUS Is a measure of elasticity of the material: how stiff the material is in the elastic range. Elastic modulus= Stress/Strain The slope of the curve A B Stress (Pa) Strain R e s i l i e n c e A B Stress (Pa) Strain
- 19. POISSON’S RATIO Ratio of lateral to axial strain within the elastic range. For an ideal isotropic material of constant volume the ratio is 0.5. Most material have values of 0.3.
- 20. FLEXIBILITY Ability of a material to return to its original form indicates its elasticity, but the strain taking place at elastic limit is known as flixibility. Flexibility is bending capacity. It can be defined as the strain that occurs when the material is stretched to its proportional limit.
- 21. RESILIENCE Defined as the amount of energy absorbed within a unit volume of a structure when it is stressed to its proportional limit. The property if often described as “springback potential.”
- 22. Resilience: The resistance of a material to permanent deformation. Proportional limit Elastic limit A Stress (Pa) Strain R e s i l i e n c e A Stress (Pa) Strain
- 23. STRENGTH PROPERTIES 1. Proportional limit 2. Elastic limit 3. Yield strength 4. Diametral tensile strength 5. Flexural strength 6. Fatigue strength 7. Impact strength
- 24. Strength properties: Strength is the stress that is necessary to cause fracture or a specified amount of plastic deformation.
- 25. PROPORTIONAL LIMIT It is defined as the greatest stress that a material will sustain without a deviation from the linear proportionality of stress to strain.
- 26. ELASTIC LIMIT The maximum stress that a material will withstand without permanent deformation.
- 27. YIELD STRENGTH Defined as the stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. It is the amount of stress required to produce a predetermined amount of permanent strain usually 0.1% or 0.2% which is called the Percent Offset.
- 28. For brittle materials such as composites and ceramic – Yield strength can not be measure. YS indicates a degree of permanent deformation (usually 0.2%) Continue……