EARTH238 Lecture Notes - Lecture 6: Ellipse, Simple Shear, Body Force
30 Aug 2016
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Lecture 6
- Incremental Strain and total strain
o Red line is the material line, green line is the long axis
o Deformation will rotate these lines
▪ Material line rotates faster
▪ Aspect ratio of the ellipse and orientation changes with deformation
• Rotational deformation(strain)
▪ Long axis does not coincide with the same material line at all times
- Coaxial and non-coaxial strain
o Coaxial
▪ Long axis and short axis coincide with the same material
▪ Red line will not rotate wrt to strain ellipse
▪ All coaxial deformation is pure shear
▪ No strain in 3D → plane strain
o Simple shear is usually non-coaxial strain (all non-coaxial is not simple shear)
▪ Along the direction the two circles there is no deformation?
▪ Imagine a deck of cards → even if there is strain the length does not change
- Finite and Infiitesimal Strain
- Gneiss pics
o If elongated and then folded the line will not match up (fragmented)
o Contraction and then elongation will not show a break
Forces
- Body forces vs surface forces
If stress is oblique to a plane
o Has two components: normal and shear
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Document Summary
Lecture 6: red line is the material line, green line is the long axis, deformation will rotate these lines, material line rotates faster, aspect ratio of the ellipse and orientation changes with deformation, rotational deformation(strain) Long axis does not coincide with the same material line at all times. Imagine a deck of cards even if there is strain the length does not change. If elongated and then folded the line will not match up (fragmented: contraction and then elongation will not show a break.
