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# Stress & Strain Properies of dental materials

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### Stress & Strain Properies of dental materials

1. 1. Properies of dental materials Dr Mumtaz ul Islam 1 10/30/2013
2. 2. Why properties  To evaluate performance of a material  Many factors were considered  Situation where a material used  Manipulation  In situ (in its original place)  In vitro  In vivo 2 10/30/2013
3. 3. Properties in different situations  Unmixed materials (shelf life)  During mixing manipulation and setting (thorough mixing, standard manipulation and setting process)  Set material (physical &chemical)  Working time: time available for mixing and manipulating a material  Setting time: the time taken by a material to attain a certain level of rigidity or elasticity 3 10/30/2013
4. 4. Physical properties  Mechanical properties  Stress  Tensile  Compressive  Fracture (flexural)  A stress resisting a compressive force is referred to as a compressive stress and that resisting a tensile force a tensile stress 4 10/30/2013
5. 5. Strain  Measure of the fractional change in length caused by an applied force  When strain becomes large, the dimensions of test specimens may change in a direction at 90º to that of the applied force  Poissons ratio  The ratio of strain occurring at 90º to the direction of the applied force to that occurring in the direction of the force 5 10/30/2013
6. 6. Stress-strain relationship 6 10/30/2013
7. 7. Stress-strain relationship  Tensile strength  Compressive strength  The value of stress which corresponds to the limit of proportionality, P, is referred to as the proportional limit  Point E is the yield stress. This corresponds to the stress beyond which strains are not fully recovered  High value of proportional limit indicates that a sample of the material is more likely to withstand applied stress without permanent deformation 7 10/30/2013
8. 8. Proof stress  This indicates the value of stress which will result in a certain degree of permanent deformation upon removal of the stress. For example, the 0.1% proof stress (commonly used for alloys) is the level of stress which would result in a 0.1% permanent deformation 8 10/30/2013
9. 9. Modulus of elasticity  Modulus of elasticity  Stress / Strain  A steep slope giving a high modulus value, indicates a rigid material  shallow slope, giving a low modulus value, indicates flexible material 9 10/30/2013
10. 10. Ductility and malleability  The value of strain recorded between points E and T indicates the degree of permanent deformation which can be imparted to a material up to the point of fracture  For a tensile test this gives an indication of ductility  For a compressive test it indicates malleability  Elongation at fracture is the property, ductile materials shows 10 10/30/2013
11. 11. Swagging machine 11 10/30/2013
12. 12. Resilience and Toughness  Resilience may be defined as the energy absorbed by a material in undergoing elastic deformation up to the elastic limit  Total amount of energy which a material can absorb up to the point of fracture  Brittleness is opposite of toughness 12 10/30/2013
13. 13. Fracture toughness and impact strength  For brittle materials fracture may occur suddenly at a stress which is apparently well below the ideal fracture stress 13 10/30/2013
14. 14. single-edge-notched specimen (SEN) 14 10/30/2013
15. 15. Impact test &impact strength  When the stress is increased very rapidly it may be termed an impact test  The important practical property obtained is the impact strength  When the presence of a small notch or crack in the surface of a material has a marked effect on impact strength the material is said to be notch sensitive 15 10/30/2013
16. 16. Charpy impact tester 16 10/30/2013
17. 17. Different stress strain graphs 17 10/30/2013
18. 18. Fatigue life and fatigue limit  Application of a cyclic stress at a given magnitude and frequency and to observe the number of cycles required for failure. The result is often referred to as the fatigue life  Applying number of stress cycles, say 10 000, and determine the value of the cyclic stress required to cause fracture within this number of cycles  The result in this case is referred to as the fatigue limit  Fatigue crack always occurs in the surface of material 18 10/30/2013
19. 19. Fatigue life and fatigue limit 19 10/30/2013
20. 20. Wear  Indenting and scratching of the surface by abrasive toothpastes or food is termed abrasive wear  Fatigue wear minimal degree of scratches due to intermittent stresses  Erosion loss of material by chemical action 20 10/30/2013
21. 21. Abrasion 21 10/30/2013
22. 22. Attrition 22 10/30/2013
23. 23. Attrition 23 10/30/2013
24. 24. Erosion 24 10/30/2013
25. 25. 25 10/30/2013