Group 2 - Mechanical Properties of Materials.pptx
- 1. Mechanical Properties of Materials Material Science and Engineering (A413)
- 2. Table of Contents 01 Stress and Strain 02 Torsion 03 Elastic Properties of Materials 04 Tensile Properties 05 Relationship of Engineering and True Stress and Strain 06 Hardness
- 3. Stress and Strain ● Stress - Force or load per unit area of cross-section over which the force or load is acting.
- 4. Stress and Strain ● Strain - Elongation change in dimension per unit length.
- 6. Engineering Stress Force (N) Cross- sectional Area (m2 ) Stress 1 Pascal (Pa) = (N/m2 )
- 7. Engineering Strain Change in Length Original Length Strain
- 8. Universal Testing Machine Tool used to determine tensile stress and strain
- 9. Universal Testing Machine (UTM) • Also known tensile machine/tester or pull tester. • A unidirectional force is applied to a specimen in the tensile test by means of the moveable crosshead. • The cross-head movement can be performed using screws or a hydraulic mechanism.
- 10. Shear Stress • Force tending to cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. Force (N) Cross- sectional Area (m2 ) Shear Stress 1 Pascal (Pa) = (N/m2 )
- 11. Shear Strain • Deformation of a material that occurs when parallel internal surfaces slide past each other due to shear stress. Shear Strain Change in Length Original Length o l l tan Shear Angle
- 12. Torsion • Torsion refers to the twisting of a structural member when it is loaded by couples that produce rotation about the longitudinal axis. • Torsional forces produce a rotational motion about the longitudinal axis of one end of the member relative to the other. • Torque stress or shear stress, is the internal force that resists a shaft or rod from twisting when a torque is applied. • Angular deformation in torsion is the angular distortion of an object caused by a twisting torque applied along the object's longitudinal axis.
- 13. Hooke’s Law • Discovered by the English scientist Robert Hooke in 1660. • For relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load. • It gives the relationship between the force applied to an unstretched spring and the amount the spring is stretched.
- 14. Hooke’s Law Stress Pascal (Pa) Elastic Modulus/Young’s Modulus 1 Pascal (Pa) = (N/m2 ) Strai n
- 15. Young’s Modulus (Modulus of Elasticity) • It is a fundamental property of materials that describes their stiffness or resistance to deformation under stress. • Measure of Stiffness: The higher the value, the stiffer the material. • Temperature Dependence: It is affected by temperature, generally decreases as temperature increases. • Applications: Engineering, Construction, and Aerospace.
- 16. Elastic Deformation • It is the temporary change in shape of a material when a force is applied, with the material returning to its original shape upon the removal of the force. • Anisotropy: Some materials exhibit different elastic deformation properties depending on the direction of the applied force. • Elastomers and shape memory metals such as nitinol exhibit large elastic deformation ranges as does rubber. Elasticity is nonlinear. Metals and ceramics show linear elasticity.
- 17. Elastic Deformation • The elastic range ends when the material reaches its yield strength. • Elastic Limit: It only occurs up to a certain limit. Beyond this point, the material will undergo permanent deformation (plastic deformation).
- 18. Tangent or Secant Modulus • The tangent modulus represents the instantaneous stiffness of a material at a specific point on the stress-strain curve. • The secant modulus represents the average stiffness of a material over a range of strain.
- 19. Shear Modulus • Shear modulus is the ratio of shear stress (force per unit area) to shear strain (displacement at the edge). • Also known as the modulus of rigidity. • Applications: Structural Design and Manufacturing
- 20. Shear Modulus Shear Modulus 1 Pascal (Pa) = (N/m2 ) Shear Stress 1 Pascal (Pa) = (N/m2 ) Shear Strain G
- 21. Elastic Properties of Materials The ability of objects to regain their original shape and size after deforming force is removed. Poisson’s Ratio - measures the deformation in material in a direction perpendicular to the direction of the applied force. Transverse Strain Axial Strain Poisson’s Ratio
- 22. Poisson’s Ratio
- 23. Plastic Deformation • It is a permanent change in the shape of a solid material that occurs when the material is subjected to a sustained force that exceeds its yield strength. • Object in plastic deformation range will first have undergone elastic deformation which is reversible so the object will partly return to its original shape.
- 24. Plastic Deformation • Soft thermoplastic materials have rather large plastic deformation range as do ductile metals such as copper, silver, and gold. • Hard thermosetting plastics, rubber and ceramics have minimal plastic deformation ranges.
- 25. Tensile Properties • Yielding - the stress level at which plastic deformation begins. • Proportional Limit - For metals that experience this gradual elastic-plastic transition, the point of yielding may be determined as the initial departure from linearity of the stress-strain curve
- 26. Tensile Properties • Yield strength - The stress corresponds to the intersection of this line and the stress-strain curve as it bends over in the plastic region. • Tensile strength - The maximum stress a material can withstand before it fractures or breaks.
- 28. Ductility • It is a measure of the degree of plastic deformation that has been sustained at fracture. • A material that experiences very little or no plastic deformation upon fracture is termed brittle.
- 29. Toughness Properties • It is a measure of the ability of a material to absorb energy up to fracture. • It is the area under the σ e curve up to the point of fracture. • For a material to be tough, it must display both strength and ductility.
- 30. True Stress Instantaneous Cross- sectional Area (m2 ) Force (N) True Stress 1 Pascal (Pa) = (N/m2 )
- 31. True Strain Original Length Final Length True Strain
- 32. True Stress-Strain Curve • For some metals and alloys the region of the true stress-strain curve from the onset of plastic deformation to the point at which necking begins may be approximated by:
- 33. True Stress-Strain Curve • In this expression, K and n are constants and will depend on the condition of the material. • The parameter n is often termed the strain hardening exponent and has a value less than unity. • By plotting the log of stress-strain curve, you will get the values for K and n.
- 34. True Stress-Strain Curve • Measure of a material's resistance to localized plastic deformation. • Quantitative hardness techniques have been developed in which a small indenter is forced into the surface of a material to be tested. • The depth or size of the resulting indentation is measured, which in turn is related to a hardness number. • The softer the material, the larger and deeper is the indentation, and the lower the hardness index number.