The Stress - Strain Relationship for Solids
Mohr’s circle for plane strain state
Figure 24 is the Mohr’s circle for plane strain state. The method to construct the circle is similar to that construct Mohr’s circle for plane stress state.
Principal Strains and the directions
Figure
25
Same as principal stresses, principal strains ε1, ε2 (shown in Figure 25) are the strains that occur on an inclined planes where shear strains = 0. From the Mohr’s circle for plain strain, we can get [7]:
The direction of ε1, ε2 are shown in Figure 24, too. The angle can be calculated by:
Maximum shear strain and the directions
Figure
26
The maximum shear strain is [7]:
The angle between the plane that maximum shear strain occurs and reference plane is:
Stress-strain relationship
With plane stress assumption, for isotropic material, in elastic region, the stress-strain relationship should be [5]:
Note:
Tri-axial stress state elastic analysis
In general, at a point, 3 normal stresses may act on faces of the cube, as well as, 6 components of shear stress (Figure 27). For the 6 shear stresses, only 3 of them are independent, because:
Figure
27
The stain components are shown in Figure 27, too.
The stress on an inclined plane
To simplify the case, choose a set of reference coordinates (Figure 28) coincident to the principle stresses, and then the stresses σn and τn in any inclined plane with normal direction (l, m, and n) can be calculated by following equtions [9]:
p
Figure
28
Mohr’s circle
Figure 29 is the Mohr’s circle for general tri-axial stress state. The 3 equtions shown above that calculate the stresses on an inclined plane express 3 circles. The 3 circles intersect in point D, which should be located within the 3 reference circles. The value of coordinates of D is the stresses of the inclined plane.
D
τn
σn
Figure
29
Stress-strain relationship
In general tri-axial stress state, for isotropic material and in elastic region, if taking into account thermal effect, the stress-strain relationship should be [10]:
Reference:
[1] http://zone.ni.com/devzone/cda/ph/p/id/250#toc3
[2] http://www.jwave.vt.edu/crcd/farkas/lectures/mechprop/tsld001.htm
[3] Class notes from Dr. J. H. Burge
[5] http://www4.eas.asu.edu/concrete/elasticity2_95/sld001.htm
[6] http://www.egr.msu.edu/classes/me423/aloos/lecture_notes/lecture_4.pdf
[7] http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/calc_principal_strain.cfm
[8] Mechanics of material (Hongwen Liu)
[9] http://www.shodor.org/~jingersoll/weave4/tutorial/tutorial.html
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