Viscoelastic and Elastic Properties of dental materials dashpot and spring hardness

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description of maxwell and voigt models

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Viscoelastic and Elastic Properties of dental materials dashpot and spring hardness

  1. 1. Dr Mumtaz ul Islam 11/3/2013 1
  2. 2. • • • Resistance of a material to wear Resistance to penetration by an hard object Value of hardness is usually expressed in numbers 11/3/2013 2
  3. 3. • • • • • • • Vickers, Knoop, Brinell and Rockwell Shore ,Mohs’and barcol Vickers and Knoop both involve the use of diamond pyramid indentors Vickers hardness, the diamond pyramid has a square base Knoop hardness, one axis of the diamond pyramid is much larger than the other Brinell hardness test involves the use of a steel ball indentor Rockwell direct measurement of the depth of penetration of a conical diamond indentor 11/3/2013 3
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  5. 5. • • • • • • • Measurement of degree of permanent deformation Initially stress is very high Strain produced Elastic limit of the materials reaches Yield strength of the material is actually the indicator of hardness If any elastic deformation occurs it is of no use Hardness is the ability to resist scratching 11/3/2013 5
  6. 6. • • • • The yield stress is the value of stress beyond which the material becomes permanently distorted Elastic property the ability of a material to undergo elastic recovery When a material undergoes full elastic recovery immediately after removal of an applied load it is elastic If a degree of permanent deformation remains or recovery is slow the material is said to be viscoelastic 11/3/2013 6
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  16. 16. • • • • Mix model is used in dentistry It explains well the behavior of elastic impression materials Such materials show an instantaneous increase in strain due to the spring (A) followed by a gradual increase in strain as the dashpot (B) and spring/dashpot (C/D)system open On removal of the load the spring (A) recovers instantaneously followed by gradual recovery of the spring/dashpot (C/D). Some permanent distortion remains as a consequence of the dashpot (B) 11/3/2013 16
  17. 17. • • • Creep involves a gradual increase in strain under the influence of a constant applied load similar to that which takes place in the Maxwell model Creep implies a relatively small deformation produced by a relatively large stress over a long period of time Flow implies a greater deformation produced more rapidly with a smaller applied stress 11/3/2013 17
  18. 18.  Rheology is the study of the flow or deformation of materials 11/3/2013 18

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