1. What is Mechanical Properties ?
Mechanical properties describe how a material behaves under applied forces (loads). These properties are crucial for design, manufacturing, and material selection in engineering applications.
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Table of Contents
2. Stress–Strain Behavior
Key Terms:
- Stress (σ) = Force / Area
- Strain (ε) = Change in length / Original length
Regions of Curve:
- Elastic Region
- Material returns to original shape
- Follows Hooke’s Law
- Yield Point
- Plastic deformation (permanent deformation starts)
- Plastic Region
- Permanent deformation occurs
- Ultimate Tensile Strength (UTS)
- Maximum stress material can withstand
- Fracture Point
- Failure of material
3. Elastic Properties
Elasticity
- Ability to regain original shape after removal of load
Hooke’s Law
- Stress ∝ Strain (within elastic limit)
Modulus of Elasticity (Young’s Modulus)
- Measure of stiffness
- Higher value → stiffer material
4. Plastic Properties
Plasticity
- Ability to undergo permanent deformation without breaking
Yield Strength
- Stress at which plastic deformation begins
5. Strength of Materials
Types of Strength:
- Tensile Strength → resistance to pulling
- Compressive Strength → resistance to crushing
- Shear Strength → resistance to sliding failure
6. Ductility and Malleability
🔸 Ductility
- Ability to be drawn into wires
- Measured by % elongation
🔸 Malleability
- Ability to be hammered into sheets
👉 Example:
- Gold → highly ductile and malleable
🔹 7. Hardness
- Resistance to indentation, scratching, wear
🔸 Common Tests:
- Brinell Hardness Test
- Rockwell Hardness Test
- Vickers Hardness Test
8. Toughness
- Ability to absorb energy before fracture
- Represented by area under stress-strain curve
🔹 9. Brittleness
- Material fractures without significant deformation
👉 Example: Glass, ceramics
🔹 10. Resilience
- Ability to absorb energy in elastic region
- Measured by modulus of resilience
🔹 11. Creep
- Time-dependent deformation under constant load at high temperature
📌 Stages:
- Primary creep
- Secondary (steady-state) creep
- Tertiary creep (failure stage)
🔹 12. Fatigue
- Failure due to repeated cyclic loading
- Occurs below yield strength
📊 S–N Curve:
- Shows relation between stress and number of cycles
🔹 13. Important Relationships
| Property | Description |
|---|---|
| Strength | Resistance to failure |
| Elasticity | Return to original shape |
| Plasticity | Permanent deformation |
| Ductility | Ability to stretch |
| Toughness | Energy absorption |
| Hardness | Resistance to wear |
| Brittleness | Sudden fracture |
14. Engineering Significance
- Design of machine components
- Material selection for structures
- Failure analysis
- Safety and reliability
Example:
- Bridges → high strength & toughness
- Springs → high elasticity
- Cutting tools → high hardness