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WORK HARDENING

WORK HARDENING. Work hardening , also known as strain hardening or cold working , is the strengthening of a metal by plastic deformation. Course Name: Mechanical Behaviour of Materials Level(UG). Authors: R. Mridhula/Amol Subhedar

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WORK HARDENING

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  1. WORK HARDENING Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. Course Name: Mechanical Behaviour of Materials Level(UG) Authors: R. Mridhula/Amol Subhedar Guide: Prof. P. Pant

  2. Learning Objectives After interacting with this Learning Object, the learner will be able to: • Explain how work hardening occurs and leads to strengthening. • Quantify the strengthening effect of work hardening mechanism.

  3. Definitions of the components/Keywords: 1 Dislocation : is a crystallographic defect, or irregularity, within a crystal structure. Slip is the process by which plastic deformation is produced by dislocation motion Burger’s Vector(b) : Represents the magnitude and direction of the lattice distortion caused by dislocation in a crystal lattice Work Hardening : Strengthening of a metal by plastic deformation 2 3 4 5

  4. Master Layout 1: Formation of dislocations 1 Step 1: Plot of ∆Xo versus ∆T Step 1: Nearly dislocation free sample 2 ∆X0 : Supersaturation prior to precipitation ∆T : undercooling Sample 3 Dislocation 4 5

  5. Step 1

  6. Master Layout 1: Formation of dislocations 1 Step 1: Plot of ∆Xo versus ∆T Step 2: Elastic deformation of sample due to applied stress Dislocation 2 Stress Stress 3 4 Sample 5

  7. Step 2

  8. Master Layout 1: Formation of dislocations 1 Step 1: Plot of ∆Xo versus ∆T Step 3: Sample work hardens Dislocation 2 Stress Stress 3 4 Sample 5

  9. Step 3

  10. Master Layout 2: Quantification of Work Hardening Step 1: Stress dependence on dislocation density = Strength of the material due to factors other than dislocations = Correction factor (typically 1) = Magnitude of Burger’s vector = Dislocation density = Shear Modulus

  11. Step 1

  12. Questions • Number of dislocations formed during elastic deformation is higher than that of plastic deformation. True or False? • As the work hardening formula implies, is it possible to achieve arbitrary high value of hardening for given material? • Which of the following equation is correct? • A • N • D • Work hardening equation applies to following regions on stress strain curve. • Elastic region only • Plastic region only • Both of the above regions

  13. Answers • False. • Dislocation density in a material cannot increase infinitely. So there is a limit on how much strengthening can be achieved by strain hardening. • a • Both of the above regions. However in elastic region number of dislocations are negligibly small, and strength is governed by stretching of bonds.

  14. Links for further reading Reference websites: • http://en.wikipedia.org/wiki/Work_hardening Books: 1.G. Dieter, Mechanical Metallurgy, Third Edition(1986), McGraw Hill Book Company. 2. W. Callister, Materials Science and Engineering - An Introduction, Seventh Edition(2007), John Wiley & Sons, Inc. Research papers:

  15. Summary Number of dislocations increase with applied stress Interaction of dislocations among each other resist further Plastic deformation

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