Mechanical Properties Of Solids Topic
Mechanical Properties of Solids
Detailed Notes from Toppers
Reference: NCERT Books for 11th and 12th Classes
1. Stress and Strain
Detailed Notes:
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Stress: Force applied per unit area.
- Tensile stress: Pulling force.
- Compressive stress: Pushing force.
- Shear stress: Force applied tangentially.
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Strain: Fractional change in dimension
- Longitudinal strain: Change in length.
- Transverse strain: Change in width.
- Shear strain: Change in angle.
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Stress-strain curve: Represents the relationship between stress and strain.
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Hooke’s law: Stress is proportional to strain within elastic limit.
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Elastic modulus: ratio of stress to strain within elastic limit.
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Young’s modulus: Elastic modulus for tensile or compressive stress.
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Poisson’s ratio: ratio of transverse strain to longitudinal strain.
2. Elasticity and Plasticity
Detailed Notes:
- Elasticity: Ability to regain original shape after deformation.
- Plasticity: Ability to retain deformation after stress removal.
- Yield strength: Stress at which material starts to deform plastically.
- Ultimate tensile strength: Maximum stress a material can withstand.
- Fracture toughness: Resistance to crack propagation.
3. Hardness and Toughness
Detailed Notes:
- Hardness: Resistance to permanent deformation.
- Toughness: Ability to absorb energy before fracture.
- Moh’s scale: Qualitative measure of hardness based on scratch resistance.
- Vickers hardness test: Measures hardness by diamond indentation.
- Brinell hardness test: Measures hardness by ball indentation.
- Rockwell hardness test: Measures hardness by depth of indentation.
- Charpy impact test: Measures toughness by energy absorbed during fracture.
- Izod impact test: Similar to Charpy test, but with different specimen.
4. Creep and Fatigue
Detailed Notes:
- Creep: Gradual deformation under sustained stress.
- Fatigue: Failure under repeated stress below ultimate strength.
- Creep curves: Plots of strain vs. time under constant stress.
- Fatigue curves: Plots of stress vs. number of cycles to failure.
- Endurance limit: Maximum stress that can be applied indefinitely without fatigue failure.
5. Fracture
Detailed Notes:
- Fracture: Separation of material into two or more pieces.
- Types of fracture:
- Ductile fracture: Gradual separation with significant plastic deformation.
- Brittle fracture: Sudden separation with little or no plastic deformation.
- Griffith theory of fracture: Explains brittle fracture based on energy release.
- Energy release rate: Energy released per unit area of crack growth.
- Fracture toughness: Resistance to crack propagation.
6. Dislocations and Defects
Detailed Notes:
- Dislocations: Linear defects in crystal structure.
- Types of dislocations:
- Edge dislocation: Extra half-plane of atoms.
- Screw dislocation: Spiral arrangement of atoms.
- Point defects: Defects involving single atoms or ions.
- Line defects: Dislocations
- Surface defects: Cracks, pores
- Volume defects: Voids, inclusions
7. Strengthening Mechanisms
Detailed Notes:
- Strengthening mechanisms: Techniques to improve mechanical properties.
- Grain size refinement: Reduces grain size to increase grain boundaries and hinder dislocation movement.
- Solid solution strengthening: Adding alloying elements to distort the crystal lattice and impede dislocation motion.
- Precipitation hardening: Formation of precipitates that act as barriers to dislocation movement.
- Strain hardening: Cold working to increase dislocation density and hinder further dislocation movement.
- Work hardening: Strengthening due to plastic deformation.