EM-Unit-V-Mechanical properties
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This document defines and provides examples of various mechanical properties of materials including elasticity, plasticity, ductility, malleability, brittleness, hardness, toughness, stiffness, resilience, creep, and strength. It also discusses deformation of metals through elastic deformation, plastic deformation, slip and twinning. Finally, it covers different types of material failure including brittle fracture, ductile fracture, fatigue fracture and creep fracture as well as theories related to these failures.
EM-Unit-V-Mechanical properties
- 1. UNIT -V - TESTING OF MECHANICAL PROPERTIES
- 2. ELASTICITY • The ability of the material to regain its original shape after releasing the load • EXAMPLE: STEEL AND RUBBER
- 3. Plasticity • The ability of the material not to regain its original shape after releasing the load • EXAMPLE: CLAY
- 4. Ductility • The ability of the material to drawn into wire EXAMPLE: Gold, platinum, silver
- 5. Malleability • The ability of the material to drawn in to sheets. • EXAMPLE: gold
- 6. Brittleness • The ability of the material fracture without deformation EXAMPLE: Cast iron and glass
- 7. Hardness • The ability of the material to resist abrasion, indentation , machining and scratching. • EXAMPLE: DIAMOND, QUARTZ AND GLASS
- 8. Toughness • The ability of the material to absorb energy and plastically deform without fracturing. • EXAMPLE: MILD STEEL
- 9. Stiffness • The ability of a material to resist deformation against bending or loading • The ratio of stress to the strain below elastic limit.
- 10. Resilience • The ability of the material to store energy and resist shocks or impacts. • Proof resilience The maximum energy which can be stored in a body up to the elastic limit is called proof resilience. *The proof resilience per unit volume is called modulus of resilience
- 11. Creep • A slow and permanent deformation in a material under a steady load at constant temperature. • EXAMPLE: the property is considered in turbines and IC engines.
- 12. Strength • The ability of the material to withstand or support an external force or load without rupture. • Elastic strength : It’s the value of load corresponding to transition from elastic to plastic range. • Plastic strength : It’s the value of the load corresponding to plastic range and rupture.
- 13. FATIGUE • It deforms under the fluctuating or repeated loads
- 15. Machinability • The ability of the material to allow and undergo various machining operations.
- 16. Castability • The ability of the material to cast into different shape and size.
- 17. Weldability • The ability of the material to accept the joining of two similar or dissimilar materials during welding.
- 18. Formability or Workability • The ability of the material to accept and undergo the changes in shape and sizes.
- 20. FACTORS • Grain size • Heat treatment • Atmospheric exposure • Low and high temperature.
- 21. Hooks law • The stress is directly proportional to strain with in the elastic limit
- 23. DEFORMATION OF METALS • When force is applied on the metal piece, then size and shape will be altered. • Any changes in shape and size of metal is called deformation of metal. TYPES OF METAL DEFORMATION: 1. ELASTIC DEFORMATION 2. PLASTIC DEFORMATION
- 24. Elastic deformation • It’s a deformation of a body which remains even after removing the external load from the body. • The plastic deformation may occur under the tensile, compressive or torsional stresses. Plastic deformation It is the deformation of the body which completely disappears as soon as the external load is removed.
- 27. Modes • There are two modes of plastic deformation • Slip • twinning
- 28. Slip • Sliding of blocks 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
- 32. Mechanism of slip • When Shear stress applied exceeds the critical value slip occur.
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- 34. TWINNING • The second important 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.
- 35. . • twinning differs from slip in that every plane of atoms suffers some movement, and the crystallographic orientations of many unit cells are altered.
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- 38. Fracture .
- 39. 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.
- 40. Types of fracture • Brittle fracture • Ductile fracture • Fatigue fracture • Creep fracture
- 41. Brittle fracture • Fracture occur with out deformation in metal • Mostly amorphous material like glasses having this kind of fractures. (crystalline material having deformation before brittle) • Brittle fracture increased with decreasing temperature and increasing strain rate.
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- 44. Griffith theory • There is a difference between material strength to theoretical value of the ideal material. This is due to fine cracks in the material. The stresses applied on the material is concentrated more on crack portions and lead it to fracture. • i.e when the stress at the tips of a crack exceeds the theoretical stress value, the crack expands and fracture occurs.
- 45. Mechanism of brittle mechanism
- 46. . • Now the tensile stress is applied at the both sides of the material. • So the stress is maximum at the tip of the crack
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- 49. DUCTILE FRACTURE
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- 52. . • Formation of fine cavities Formation of central crack
- 53. . • Crack propagates perpendicular to the axis of the specimen • Fracture occurred at the end
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- 56. FATIGUE FAILURE • Failure occur due to repeated or fluctuating load This occur in components subjected to cyclic loading such as motor shaft, bolts, springs, gear teeth , automobile parts, suspension bridges etc ….
- 57. Mechanism in fatigue failure. • Due to crack , slip in metal the stress concentrated high in that places. • Due to cyclic loading the micro crack propagates and lead to failure (fracture) • In ductile material fatigue failure occur suddenly • High temperature increase the mobility of atoms, facilitating slip and hence the fatigue failure
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- 59. CREEP • It’s a slow and permanent deformation in metal under steady load at constant temperature. • Some materials such as zinc, lead and tin are having more creep at room temperature.
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- 61. Factors affecting creep • Grain size • Thermal stability of the micro- structure • Chemical reactions
- 62. Mechanism of creep fracture • (a)Dislocation climb at high temperature, atomic movements permit the dislocation.
- 63. (b) Vacancy diffusion • Due to applied stress a vacant places (dislocations) takes place and it lead to fracture.
- 64. ( c ) grain boundary sliding • At low temperature creep fracture takes place due to sliding of grain boundaries.
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