Ballistic Impact

Hi All,

   I am trying to determine the nodal displacements of a cylindrical projectile after impacting a hard target in Abaqus 6.8-1.  I am thinking I will need to use a UMAT (which I have never done) for an equation I am using that better predicts stress at high strain rates than the Johnson-Cook model.  Currently I am trying to get this to run just once so I can see the output file before I start optimizing my code.

  Can someone please give me advice on the following?  What I am doing wrong, how and where do I implement the UMAT (I know C++ and Python), etc..

***
  I am modeling an axisymmetric deformable projectile, and using an axisymmetric analytical rigid wire for the impact surface.

***
  For the material, I have under "material behaviors":

Deformation Plasticity:
  I have values for young's modulus, poisson's ratio, and yield stress.  I am unsure what I need to put for exponent and the yield offset input boxes, or if I even need to define "deformation plasticity."

Plastic:
  I am currently trying to use Isotropic hardening (should I be using Johnson-Cook?).  I am uncertain as to what values need to go in the Yield Stress/Plastic Strain input boxes.  I have quasi-static compression test data for the material.  Should I be fill these input boxes with that data?  What Yield stress value corresponds to the 0 plastic strain?

  There is a suboption menu with "Rate Dependent" in which you can select Johnson-Cook hardening.  I currently do not have it selected.

Elastic:
  I have isotropic type selected and Young's modulus and Poisson's ratio in the input boxes.


***
  I defined a section for the projectile of type solid, homogeneous using the defined material and it's properties.

***
  Under Assembly I used an Independent instance type. When I created the parts, I made it so that one end of the projectile (the impact end) was at the same location as the anvil (rigid wire).

***
  I currently have 2 steps:
Initial:
  I defined a reference point on the analytical rigid wire at it's center, and put an ENCASTRE BC there. Do I need to create a contact surface?

Step-1:
  I chose dynmamic explicit with all default options.  What should I change to obtain better results?  Since the Initial step wouldn't let me define an axial velocity I did it on this step.  I chose the entire projectile part to give this velocity to.  Should I give the velocity to each node on the projectile mesh?  If so, how would I do this?

***
  For the mesh, I am currently using a Tri element shape with "Free" selected under Technique (should I select "Use mapped meshing where appropriate" under "Algorithm?").

  Under Element type I am currently using "Explicit" under "Element Library" and "Quadratic" under "Geometric Order", and all the default under "Element Controls". I also have selected "Axisymmetric Stress" for "Family".

I realize that there are a lot of questions.  Thank you so much for taking the time to read all of this.

Sincerely,
  Nick