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Modelling primitives for Plane strain

Submitted by amitshah3333 on
modeliing sphere
cube
cylinder for 2D plain strain

Hi All,

I am very new to FEM process and ANSYS as well. 

I am trying to do a plane strain problem (2D) in ANSYS. 

My problem is  I dont know how to model primitives like sphere, cube, cylinder etc for 2D plane strain problem.

Like say can i model circle of 20mm radius for modeling sphere of 20mm radius???

Or can i model square of 50mm length for cube of 50mm.

May sound very dumb, but this is my geniune problem 

 

Thankyou for your time and help (in advance) 

 

 

Amit  

Akumar

By definition, plane stress/strain analysis is reduction of 3D problem into 2D planner analysis.

Plane Stress: the out of plane stresses are zero or negligible for in plane loading.

Plane strain: out of plane strains are zero

Therefore, before treating a problem as plane stress/strain, one needs to look not only on loading but also on boundary condition. Since the out of plane quatities (stresses or strains) are zero, thickness appear just as a multiplier to the stiffness matrix.

Example: 50x50x50 cube subjected to forces in xy plane.

  1. If the boundary condtions are such that cube can change length in z-direction, then the problem equivalent to plane stress condition.
  2. If boundary conditions prevent out of plane motion (i.e. if cube will not change its dimension in z-direction) then it's a plane strain condtiion.

Similarly, for sphere you can utilize axisymmetric analysis (if you're sure that the loading/boundary conditions will not trigger unsymmetric deformations). Here you model just a cross sectional segment about axis of revolution. and the problem is again 2D (cylinderical axes system).

Remember, these are all simplification of a 3D problem where certain criterias are satisfied in order to treat it in 2D. You can always verify these. 

FYI: you can refer to "Concepts and Applications of Finite Element Analysis" by Cook, Witt, Malus and Plesha. Not much mathematics, but lots of useful and practical informations.

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Thu, 08/30/2012 - 15:33 Permalink