The section will cover the behaviour of materials by introducing the stress-strain curve. The concepts of elastic and plastic deformation will be covered. This will then lead to a discussion of the micro-structure of materials and a physical explanation of what is happening to a polycrystalline material as it is loaded to failure.

1. Section 4 Behaviour of Materials The section will cover the behaviour of materials by introducing the stress-strain curve. The concepts of elastic and plastic deformation will be covered. This will then lead to a discussion of the micro-structure of materials and a physical explanation of what is happening to a polycrystalline material as it is loaded to failure. © Loughborough University 2010. This work is licensed under a Creative Commons Attribution 2.0 Licence .

7. Elastic-Plastic Stress-Strain Curves Low / Medium Carbon Steels Aluminium Alloys and Alloy Steels  ult = Ultimate Strength  YU = Upper yield point  YL = Lower yield point  pr = Proof stress   0.1% 0.2% 0.1%  pr 0.2%  pr  ult Limit of Proportionality    YU  YL  ult E Strain Hardening Necking

12. True Stress-Strain Curve   Onset of necking True Stress-Strain Curve Corrected for complex stress state in the neck region Engineering Stress-Strain Curve A true P x P x P x P x A

19. Edge Dislocations Stress Stress Stress Stress Stress Stress Slip plane Burgess vector, b

23. Strain Hardening (cont.) (a) Edge dislocations arranged side-by-side (b) Opposing Edge dislocations Tension region Slip plane Compression region Slip plane

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