BENG 112A, Winter Quarter, 2008

Homework Assignment 5

Due: Tuesday March 4th at the beginning of class

► Since many students are confused about creating stress/strain curves from Continuity, a tutorial for how to do so is posted below:

Tutorial for producing stress/strain curves from Continuity

► In addition, an example Excel spreadsheet to illustrate how to produce a stress/strain curves from the online isotropic tutorial is below:

Example Excel spreadsheet for Isotropic Tutorial example

1. Install the latest release of Continuity 6.3 from http://www.continuity.ucsd.edu/Continuity/Download on a Windows PC, Linux PC or Intel Macintosh (Mac and Linux users will need to follow instructions online for command line installation in the Release Notes). Note that a new release is pending on February 21st so wait for that one if it is not available when you first check.

  1. Review the simple Biomechanics tutorial at http://www.continuity.ucsd.edu/Continuity/Documentation/Tutorials/PassiveCubeRefined until you can successfully reproduce the output described. The example describes the simple homogeneous deformation of a finite elastic cube.

  2. For a range of loads, run three or more variations of this problem to generate stress and strain solutions and vary one or more of the following properties of the problem:
    • The size or shape of the tissue block you are modeling
    • One or more of the material parameters
    • The orientation of the fibers used to define transversely isotropic properties
    • The boundary conditions, e.g. consider including a simple shearing deformation
    • The homogeneity of the material parameters, e.g. change the properties between different elements

Submit a report summarizing the numerical experiments you performed, plotting the stress-strain results you obtained and commenting on whether and why the results were as expected or not.

► In general, a thorough report should include the following:

  • A description of your load range
  • A detailed description of the properties you varied for each of your three variations. Simply listing the parameters you changed in Continuity is not enough. Be sure to explain how the material/problem is physically changing when you vary these parameters.
  • An image of your deformed material. The image should be properly rotated/zoomed to show the deformation in the best way possible
    • The easiest way to do this is to take a screen shot. To do this, hit the PRINT SCREEN button on the keyboard. This will copy whatever is displayed on your screen at the moment. I suggest opening paint or some similar program, and pasting the image so that it can be cropped down to show just the material. Save your image file, and import it into Word.
  • Proper stress-strain plots from Excel. Be sure to label your axes. If you are including multiple curves on the same plot, make sure they are all visible (i.e. plotting all 9 stress/strain components on one small plot is probably not the best idea).
  • A written description of whether the results were what you expected or not. Tell us what you thought would happen when you altered the given properties, and compare this to what was actually seen. Comment on why this might be.

How to install Continuity on the ACS computers (i.e. in PFBH 161)

1) Download and install Python 2.4.4 from the following link: http://www.python.org/download/releases/2.4.4/

2) Download Continuity from the following link: http://www.continuity.ucsd.edu/Continuity/Download

3) The Continuity install file will attempt to install Python itself. Allow it to do so, and when it comes up with an error message, choose to proceed with the installation anyways.

4) Change the install directory for Continuity to C:\Continuity\

5) Install with the default settings

6) You will have to repeat these steps if you log off of the machine