Download to read offline
Uploaded byAravind Ra
UNIT- V (MECHANICAL PROPERTIES AND DEFORMATION MECHANISMS)
The property of Palstic deformation makes the metal suitable for various forming processes such as rolling , forging, pressing, drawing, spinning, extrusion and stamping
UNIT- V (MECHANICAL PROPERTIES AND DEFORMATION MECHANISMS)
- 1.
- 2. Plastic deformation • It’sa deformation of a body which remains even after removing the external load from the body. • In crystalline material deformation occur at a temperature lower than 0.4Tm Tm – melting point temp. of a material • The plastic deformation may occur under the tensile, compressive or torsional stresses.
- 3. . • The propertyof Palstic deformation makes the metal suitable for various forming processes such as rolling , forging, pressing, drawing, spinning, extrusion and stamping
- 4.
- 5. MECHANISM OF PLASTICDEFORMATION • Plastic deformation is defined as a process in which the object due to applied force changes its size or shape in a way that is not reversible. • Plastic deformation is seen in many objects, including:
- 6. Slip • Sliding ofblocks of the crystal over one another along definite crystallographic planes called slip planes • i.e --- displacement of one part of the crystal relative to another along a particular plane and direction The combination of slip plane and slip direction is called slip system
- 7. Mechanism of slip •When Shear stress applied exceeds the critical value slip occur.
- 8. TWINNING • The secondimportant mechanism in the metal deformation. • Here the atoms in the part of a crystal subjected to stress, rearrange themselves so that one part of the crystal become the mirror to the other.
- 9.
- 10.
- 11. Fracture - definition •Fracture is the mechanical failure of the material which will produce the separation or fragmentation of a solid into 2 or more parts under the action of stress. Brittle fracture Ductile fracture Fatigue fracture Creep fracture
- 12. Brittle fracture • Itsa fracture which takes place by the rapid propagation of crack with a negligible deformation. • Mostly amorphous material like glasses having this kind of fractures.
- 13.
- 14. . • Now thetensile stress is applied at the both sides of the material. • So the stress is maximum at the tip of the crack
- 16. . Griffith’s theory isapplicable only for brittle fracture
- 17. . The fracture whichtakes place by a slow propagation of crack with appreciable plastic deformation. DUCTILE FRACTURE
- 18.
- 19.
- 21. FATIGUE FRACTURE • Failureoccur due to repeated or fluctuating load
- 22.
- 23.
- 24.
- 25.
- 26.
- 27. CREEP • It’s aslow and permanent deformation in metal under steady load at constant temperature.
- 28.
- 29. Factors affecting creep •Grain size • Thermal stability of the micro- structure • Chemical reactions • Prior strain (cold working or work hardening)
- 30. Mechanism of creepfracture (a) Dislocation climb (b) Vacancy diffusion
- 31. ( c )grain boundary sliding
- 32.
- 33. Mechanical tests ofmetals Destructive tests
- 34. Classification of mechanicaltests • Destructive test • Non – Destructive test
- 35. Tensile test destructive test– ductile material
- 36.
- 37.
- 39.
- 40.
- 41.
- 42.
- 43.
- 44.
- 46.
- 47. Pure Shear force •A pure shear force applied top and bottom parallel to its faces
- 48. . Shear stress, Where, F= Shear force applied A = Area of shear Shear strain: The shear strain is defined as the tangent of the strain angle θ. Shear strain, γ = tan θ
- 49. Limitations of sheartest • Need attachment with UTM machine . • Material at last gets bend • So we will get the bending stress also, not the pure shear type. • Very difficult in processing
- 50. Torsion test • Rotationalforce given to material about longitudinal axis. • This torsional forces produce a rotational motion about the longitudinal axis of one end of the member relative to the other end.
- 52. HARDNESS TEST Brinell Hardness VickersHardness Rockwell Hardness Types of Hardness Test
- 53. Brinell hardness test Standardloads range between 500 kg and 3000 kg in 500 kg increments. During a test, the load is maintained constant for 10 to 15 seconds.
- 55.
- 56. Vickers hardness test Highaccuracy than brinell due to square based diamond pyramid indenter The Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds.
- 57.
- 58. . Where P = Appliedload in kg, θ = Angle between the opposite faces of diamond = 136°, D = Mean diagonal length in mm.
- 59. Advantages • The diagonalsof the square indentation can be measured more accurately than the diameters of the circles. • This method is suitable for hard materials as well as for soft materials. • The Vickers indenter is capable of giving geometrically similar impression with different loads. Thus, the hardness number is independent of the load applied.
- 60.
- 61. Rockwell hardness test Industriesused due to its high accuracy, simplicity and rapidity In this test , the dial gives the direct reading of hardness; no need of measuring indentation diameter or diagonal length using the microscope
- 62.
- 63. Advantages • Simple • Readingtaken directly • Time consuming process • Suitable for mass production • We can measure any range of value with various indenters. • Metallic and also plastics used limitations Its not accurate than vickers test
- 64. IMPACT TEST- TO STUDYTHE BEHAVIOUR OF THE MATERIAL UNDER SUDDEN LOAD IZOD TEST CHARPY TEST
- 65.
- 66.
- 67.
- 68.
- 69.