Nonlinear finite elements/Homework 7

Problem 1: Index NotationEdit

  • Determine whether the following expressions are valid in index notation. If valid, identify the free indices and the dummy indices.
 
  • Show the following
 
  • The elasticity tensor is given by
 

where   are Lame constants,   is the second order identity tensor, and   is the fourth-order symmetric identity tensor.The two identity tensors are defined as

 

The stress-strain relation is

 

Show that the stress-strain relation can be written in index notation as

 

Write the stress-strain relations in expanded form.

Problem 2: Rotating Vectors and TensorsEdit

Let ( ) be an orthonormal basis.Let   be a second order tensor and   be a vector with components

 
  • Write out   and   in matrix notation.
  • Find the components of the vector   in the basis ( ).
  • Find the components of the vector   in

the basis ( ).

  • Find the components of the tensor   in the orthonormal basis.
  • Rotate the basis clockwise by 30 degrees around the   direction. Find the components of  ,  ,  , and   in the rotated basis.

Problem 3: More BeamsEdit

Use ANSYS to solve the following problems.We want to see how the beam element BEAM188 that ANSYS provides behaves. If you use some other tool choose the equivalent element.

Beam188 is based on Timoshenko beam theory. The element uses linear shape functions for all degrees of freedom.The beam element refers to the following papers:

  • Simo, J.C. and Vu-Quoc, L., 1986, "A three-dimensional finite strain rod model. Part II: Computational Aspects," Computer Methods in Applied Mechanics and Engineering, 58, pp. 79-116.
  • Ibrahimbegovic, A., 1995, "On finite element implementation of geometrically nonlinear Reissner's beam theory: Three-dimensional curved beam elements," Computer Methods in Applied Mechanics and Engineering, 122, pp. 11-26.

Part A:Edit

Consider a beam of length   = 100 in., cross-section 1 in.   1 in., and subjected to a uniformly distributed transverse load   lbf/in. Model one half of the beam using symmetry considerations.

Hinged-Hinged BeamEdit

The boundary conditions are

 

Compute a plot for this case using Beam188 elements. What do you observe?

Clamped-Clamped BeamEdit

The boundary conditions are

 

Compute a plot for this case using Beam188 elements. Comment on your plot.

You will have the save your results at the end of each load step to get the data you need.

Part B:Edit

For this problem you will try to reproduce some of the results given in Simo and Vu Quoc (1986) and Ibrahimgbegovic (1995) using Beam188 elements.

  1. Simulate the unrolling of a cantilever beam from Section 4.1.1 of Ibrahimbegovic (1995) and compare your results with the results shown in the paper.
  2. Simulate the clamped-hinged deep circular arch from Example 7.3 of Simo and Vu Quoc (1986) and compare you results with the results shown in the paper.
  3. Simulate the buckling of a hinged right-angle frame under both fixed and follower loads from Example 7.4 of Simo and Vu Quoc (1986) and compare your results with those shown in the paper.