1 / 32

MECHANICAL PROPERTIES OF MATERIALS Department of Physics KL University

MECHANICAL PROPERTIES OF MATERIALS Department of Physics KL University. Objectives. Identification of elastic and plastic behaviour of materials through molecular level Behaviour of ductile and brittle materials with external load

marthal
Download Presentation

MECHANICAL PROPERTIES OF MATERIALS Department of Physics KL University

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MECHANICAL PROPERTIES OF MATERIALS Department of Physics KL University

  2. Objectives • Identification of elastic and plastic behaviour of materials through molecular level • Behaviour of ductile and brittle materials with external load • Measurement of various properties like hardness and toughness of materials

  3. Basic Terms • Stress • Strain • Types of Stress • Types of Strain • Hooke’s law • Elasticity • Plasticity • Ductility • Brittleness • Hardness • Toughness • Fatigue • Creep • Fracture

  4. ElasticityPlasticity Regainsto original shape Deforms permanently

  5. 1. Initial 2. Small load 3. Unload bonds stretch return to initial d F Elastic deformation Molecular approach Elastic means reversible

  6. 1. Initial 2. Small load 3. Unload bonds p lanes stretch still & planes sheared shear d plastic d elastic + plastic F Plastic deformation Molecular approach Plastic means permanent • Process of plastic deformation in crystals is by slip process (motion of dislocation) and in non-crystalline solids, the plastic deformation is by viscous flow mechanism.

  7. Stress: The internally developed forces per unit area of a material due to the application of external force. Its SI unit is Pascal (or) N/m2

  8. StrainFractional change in the dimensions of a material due to the application of external force. • It has no unit

  9. Types of Stress & Strain • Tensile stress – Longitudinal Strain • Compressive Stress – Volume Strain • Shear stress – Shear Strain

  10. F Tension W Tensile Stress – Longitudinal Strain Equal and opposite forces directed away from each other

  11. W F Compression Compressive StressLongitudinal strain Equal and opposite forces directed towards each other

  12. Shear Stress – Shear Strain Tangential force

  13. Hooke’s Law Within elastic limit, Stress α Strain Stress = E x Strain E - Modulus of elasticity, Unit : N/m2

  14. Differentmodulli of elasticity

  15. Modulus of elasticity of materials depends on bond strength between atoms, stronger the bond, larger will be the modulus of elasticity. • Values of the modulus of elasticity for ceramic materials are about the same as for metals; for polymers they are lower. These differences are a direct consequence of the different types of atomic bonding in the three materials types.

  16. Increase in temperature of material, decreases the modulus of elasticity.

  17. loaded unloaded Poisson’s Ratio: • If lateral strain along x- and y- directions is same • (ε x = ε y),material may be isotropic.

  18. DUCTILITY Material – thin wires – withstands plastic deformation

  19. BRITTLENESS Fractures without deformation

  20. Hardness: - withstand plastic deformation or indentation produced in the material. Creep: - time dependent deformation at constant load

  21. Strength :Ability to withstand loads Types of strength 1.Yield strength : Strength beyond which it exhibits plasticity 2. Tensile strength (or) Ultimate strength : Strength at which the material breaks or fractures

  22. Tensile Strength TS F = fracture or ultimate strength Necking acts as stress concentrator y engineering stress Typical response of a metal strain engineering strain • Maximum stress on engineering stress-strain curve. • Metals: TS occurs when noticeable necking starts. • Polymers: TS occurs when polymer chains are aligned and about to break.

  23. Toughness : Energy absorbed up to fracture. Fatigue: Failure under cyclic (or) repeated stress Fracture: Breakage of a material into separate parts under the action of stress

  24. Engineering Stress-Strain Diagram ultimate tensile strength 3 necking Strain Hardening Slope=E yield strength Fracture 5 2 Elastic region slope =Young’s (elastic) modulus yield strength Plastic region ultimate tensile strength strain hardening fracture Plastic Region Stress (F/A) Elastic Region 4 1 Strain ( ) (DL/Lo)

  25. Stress – strain curve – brittle and ductility

  26. Engineering and True Stress-Strain Engineering stress (σn )= F/A0 A0 – original area of cross section Engineering strain εn = (L-L0)/L0

  27. Engineering and True Stress-Strain Curve

  28. Hardness Tests Indentation Method • Brinell Hardness Test • Rockwell Hardness Test • Vicker Test

  29. VH = 1.854F/d2 , d = (d1+d2)/2

More Related