THE STRESS STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

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Solid Mechanics of Stress and Strain

The Stress - Strain Relationship for Solids


< coordinates to the strains with respect to {x',y',z'} (Figure 23) is performed via the equations [7]:



THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521



Mohr’s circle for plane strain state


Figure 24

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521



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


THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


Figure 25

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


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 STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


The direction of ε1, ε2 are shown in Figure 24, too. The angle can be calculated by:

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


Maximum shear strain and the directions


Figure 26

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


The maximum shear strain is [7]:


THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


The angle between the plane that maximum shear strain occurs and reference plane is:

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


Stress-strain relationship

With plane stress assumption, for isotropic material, in elastic region, the stress-strain relationship should be [5]:


THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


Note: THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


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:

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521 THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

Figure 27

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521 THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521


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]:

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521






p





Figure 28







THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521



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

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

τn


THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521

σn

Figure 29

THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521



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]:



THE STRESS  STRAIN RELATIONSHIP FOR SOLIDS OPTI 521






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

[4] Class notes from Dr. Stone’s OPTI 222 class

[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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