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Mechanical Properties

Mechanical Properties. Stress-strain Diagram: Fundamentals. Stress and strain:definitions. Stress = Load/Cross-sectional area. Strain = Displacement/Reference length. Types of loading. Tension Test:engineering properties. Engineering stress= load/initial cross-sectional area=P/A 0.

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Mechanical Properties

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  1. Mechanical Properties Stress-strain Diagram: Fundamentals

  2. Stress and strain:definitions Stress = Load/Cross-sectional area Strain = Displacement/Reference length

  3. Types of loading

  4. Tension Test:engineering properties Engineering stress= load/initial cross-sectional area=P/A0 Engineering strain= displacement/initial length=d/l0

  5. Elastic Deformation in metals Obeys Hooke’s law for metals s= E e Linear Slope = elastic modulus, E

  6. Fundamental concept of elastic deformation Model to explain elasticity

  7. Elastic deformation Eng. stress Slope = Elastic modulus, E Area under curve = resilience Eng. strain

  8. Poisson’s ratio:another elastic property Specimen elongates in the longitudinal direction but contracts laterally Note: There is no lateral stress only lateral deformation due to an elastic property of the material called Poisson’s ratio, n n = - lateral strain/longitudinal strain

  9. Yield point (continuous)non-ferrous alloys Yield strength sy Proportionality limit Eng. stress Offset is 0.2% of the gage length 0.2% offset Eng. strain

  10. Yield Point (discontinuous)steels Upper yield point Lower yield point Eng. stress Eng. strain

  11. Types of yielding

  12. Plastic Deformation Ultimate tensile strength or tensile strength Fracture stress x Eng. stress Area under the curve TOUGHNESS % elongation to fracture Eng. strain

  13. Increase in stress for every deformation increment Some notes Strain/work hardening Real curve x Ideally plastic curve Eng. stress Eng. strain

  14. What happens to the specimen during the tension test?

  15. What is the mechanism of fracture? Necking At max. load Change in stress state from uniaxial to triaxial Microvoid formation Void coalescence FRACTURE Microcrack formation Crack propagation

  16. Process of fracture

  17. Some ending notes • True stress= Load/ Instantaneous cross-sectional area s = P/Ai • True strain = displacement/instantaneous length e = ln (l/l0) Plastic portion of true stress-strain curve described by s = K en (Hollomon/Power law) K =strength coefficient n = work hardening coefficient

  18. True stress-strain diagram

  19. Effect of temperature

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