- 1. Dr. Ehab Hegazy Properties of materials
- 2. Crystal Structure • properties of materials (especially mechanical) are determined by the arrangement of the atoms. This arrangement is called the material’s crystal structure.
- 3. Atomic structure Relates to the number of protons and neutrons in the nucleus of an atom, as well as the number and probability distributions of the electrons. Crystal structure arrangement of atoms in the crystalline solid material.
- 4. Atoms can be arranged either in a Regular, periodic array (i.e., long-range order) or completely Disordered (amorphous) short range order.
- 5. What is the Unit Cell? unit cell is the smallest group of atoms which can generate the entire crystal by translation. Definition: the length of each unit cell axis is called a lattice parameter.
- 8. Metallic crystals Why metals are densely packed 1. -Typically, only one element is present, so all atomic radii are the same. 2. Metallic bonding is not directional. 3. Nearest neighbor distances(IAD) tend to be small in order to lower bond energy
- 10. • APF for a simple cubic structure = 0.52
- 11. BODY CENTERED CUBIC STRUCTURE (BCC)
- 12. FACE CENTERED CUBIC STRUCTURE (FCC)
- 13. FCC
- 14. 3 Common Unit Cells with Cubic Symmetry Simple Cubic Body Centered Cubic Face Centered Cubic (SC) (BCC) (FCC) 1- CUBIC CRYSTAL SYSTEMS
- 17. Compression of tablet Compression of tablet is reduction in the volume of the powder owing to application of the forces .
- 18. Elasticity of soft gelatin capsules Application of compression force Testing the elasticity of soft gels typically serves as an indicator whether the product can be "released-to-pack" - providing a reliable and repeatable measure to prevent failure during packaging.
- 20. Stress Stress = Force/Area Compressive, tensile, and shear. Unit Newton /meter2
- 21. Types of Stress tensile stress occurs when equal and opposite forces are directed away from each other. A compressive stress occurs when equal and opposite forces are directed toward each other. Shear stress F W Tension F W Compression
- 22. STRAIN Strain is the change in length per unit length that a material undergoes when a force is applied to it. dL/L No unit Change of length /original length
- 23. Types of Strain Elastic strain Is strain that totally disappears once the external load that caused it is removed. Plastic strain is strain that permanently remains once the external load that caused it is removed.
- 24. Example 1 (Cont.) A 10 m steel wire stretches 3.08 mm due to the 200 N load. What is the longitudinal strain? L DL Given: L = 10 m; DL = 3.08 mm Longitudinal Strain 3.08 x 10-4 0.00308 m 10 m L Srain L D
- 25. Elastic Moduli The elastic modulus of a material characterize the degree of its resistance to a given type of a deforming force. Stress is defined as the force applied per unit area (N/m2). Strain Stress modulusElastic N/m2 N/m2 …… The strain indicates some fractional change in a dimension or volume.
- 26. Elastic Moduli 1- Young modulus 2- Bulk modulus 3- Shear modulus
- 27. Young's Modulus Figure A force applied normal to the end face of a rod causes a change in length. DL L0 A FnFn Fn Fn A Fn stressTensile 0 Strain L LD 0 LL AF E / / ;modulussYoung' n D
- 28. 2 - 28 Stress-Strain Test
- 29. 2 - 29 Stress-Strain Diagram: Ductile Materials
- 30. 2 - 30 Stress-Strain Diagram: Brittle Materials
- 31. The stress-strain relationship for a metal. 108 Stress (N/m2) Strain Proportional point Yield point Break point Plastic range
- 32. Physics
- 33. Loading of long bones
- 34. Forces on vertebral column
- 35. Stress strain curve human bone
- 36. Shear Modulus The shear force is applied tangentially to the surface. A shearing force Ft causes the body to deform as shown. Dx A Ft h fixed A Ft stressShear h xD strainShear hx AF G / / modulusShear t D
- 37. Bulk Modulus The bulk modulus of a solid or a fluid indicates its resistance to a change in volume. A F P VV P B / strainVolume stressVolume modulusBulk D D The bulk modulus is negative because of decrease in V.
- 39. TYPES OF PURE FORCES Compressive: a force that results in a decrease in length along the direction of the force Tensile: a force that results in an increase in length along the direction of the force Shear: a force that causes a sliding displacement of one side of a structure relative to another side
- 40. PROPORTIONAL LIMIT can be defined as the limit of proportionality of stress to strain is represented on the stress-strain diagram as the point where the plotting converts from a straight line to a curve. Below the proportional limit, stress is proportional to strain
- 41. 41 1. Initial 2. Small load 3. Unload Elastic means reversible. Elastic Deformation
- 42. 42 1. Initial 2. Small load 3. Unload Plastic means permanent. Plastic Deformation (Metals)
- 44. DUCTILITY Ductility is the ability of a material to undergo permanent tensile deformation without fracture or rupture
- 45. MALLEABILITY Malleability is the ability of a material to undergo permanent compressive deformation without fracture .
- 46. BRITTLENESS Brittleness is the material behavior where a material undergoes fracture or rupture with little or no prior permanent deformation. Materials that are brittle usually have a very ordered atomic Structure which does not permit the easy movement of dislocations. A good example is the class of materials known as ceramics. Their ordered atomic structure does not permit easy dislocation movement, and hence, they are brittle.
- 47. Ductile fracture Plastic deformation takes place before fracture
- 48. Brittle fracture No Plastic deformation takes place before fracture
- 50. RESILIENCE Energy absorbed up to proportional limit
- 51. 51 Toughness Lower toughness: ceramics Higher toughness: metals Toughness is the ability to absorb energy up to fracture (energy per unit volume of material). A “tough” material has strength and ductility. Approximated by the area under the stress-strain curve.
- 52. FATIGUE Fatigue refers to the fact that under cyclic loading a material will undergo failure at a lower applied stress than it normally would if it were not under cyclic loading. The name "fatigue" is derived from the fact that the materials seem to tire under this type of repetitive loading.
- 53. WEAR Wear is the loss of material from one or both of two contacting surfaces because of the mechanical activity between them
- 54. Questions model 1- The ability of material to absorb energy up to proportional limit is called …….. 2- Ultimate strength and breaking strength are the same in case of ……… 3- fatigue occurs when material subjected to …….load 4- Elastic modulus represent ………of materials 5- The whole area under stress strain curve of dental material represent …. 6- No plastic deformation takes place in of ………….fracture. 7- The stress at which the material fracture is called ----------- 9- dislocations generally move more ……….. at lower temperature. 10- Malleability is the ability of a material to undergo permanent ……….. deformation without fracture 11- Brittleness is the material behavior where a material undergoes fracture or rupture with ……………. prior permanent deformation 12-…………. is the loss of material from one or both of two contacting surfaces because of the mechanical activity between them 13- area under stress strain including elastic and plastic deformation is known as …….. 14- area under stress curve up to fracture point is called …………. 15- area under stress strain curve up to proportional limit is called …………………..
- 55. Example 1. A steel wire 10 m long and 2 mm in diameter is attached to the ceiling and a 200-N weight is attached to the end. What is the applied stress? L DL A A F First find area of wire: 2 2 (0.002 m) 4 4 D A A = 3.14 x 10-6 m2 -6 2 200 N 3.14 x 10 m F Stress A Stress 6.37 x 107 Pa
- 56. Example 2. The elastic limit for steel is 2.48 x 108 Pa. What is the maximum weight that can be supported without exceeding the elastic limit? L DL A A F 8 2.48 x 10 Pa F Stress A Recall: A = 3.14 x 10-6 m2 F = (2.48 x 108 Pa) A F = (2.48 x 108 Pa)(3.14 x 10-6 m2) F = 779 N
- 57. Example 2(Cont.) The ultimate strength for steel is 4089 x 108 Pa. What is the maxi- mum weight that can be supported without breaking the wire? L DL A A F 8 4.89 x 10 Pa F Stress A Recall: A = 3.14 x 10-6 m2 F = (4.89 x 108 Pa) A F = (4.89 x 108 Pa)(3.14 x 10-6 m2) F = 1536 N
- 58. Example 3. In our previous example, the stress applied to the steel wire was 6.37 x 107 Pa and the strain was 3.08 x 10-4. Find the modulus of elasticity for steel. L DL 7 -4 6.37 x 10 Pa 3.08 x 10 Stress Modulus Strain Modulus = 207 x 109 Pa This longitudinal modulus of elasticity is called Young’s Modulus and is denoted by the symbol Y.
- 59. Example 4: Young’s modulus for brass is 8.96 x 1011Pa. A 120-N weight is attached to an 8-m length of brass wire; find the increase in length. The diameter is 1.5 mm. 8 m DL 120 NFirst find area of wire: 2 2 (0.0015 m) 4 4 D A A = 1.77 x 10-6 m2 or FL FL Y L A L AY D D
- 60. Example 4: (Continued) 8 m DL 120 N Y = 8.96 x 1011 Pa; F = 120 N; L = 8 m; A = 1.77 x 10-6 m2 F = 120 N; DL = ? or FL FL Y L A L AY D D -6 2 11 (120 N)(8.00 m) (1.77 x 10 m )(8.96 x 10 Pa) FL L AY D DL = 0.605 mmIncrease in length:
- 61. Example 7. A hydrostatic press contains 5 liters of oil. Find the decrease in volume of the oil if it is subjected to a pressure of 3000 kPa. (Assume that B = 1700 MPa.) / P PV B V V V D D 6 9 (3 x 10 Pa)(5 L) (1.70 x 10 Pa) PV V B D DV = -8.82 mL Decrease in V; milliliters (mL):
- 62. Thank you