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Re: Ballistic Impact
by Nick Dutton
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I removed Deformation Plasticity and created a contact surface. I am getting the following errors:
INCREMENT 1 STARTS. ATTEMPT NUMBER 3, TIME INCREMENT 6.250E-02
***WARNING: THERE ARE 2 UNCONNECTED REGIONS IN THE MODEL.
CONTACT PAIR (ASSEMBLY_PROJECTILE-1_PROJ_END,ASSEMBLY_ANVIL-1_SURF-1) NODE
PROJECTILE-1.34 IS OVERCLOSED BY 16.8125 WHICH IS TOO SEVERE.
***WARNING: THE STRAIN INCREMENT HAS EXCEEDED FIFTY TIMES THE STRAIN TO CAUSE
FIRST YIELD AT 74 POINTS
***WARNING: THE STRAIN INCREMENT IS SO LARGE THAT THE PROGRAM WILL NOT ATTEMPT
THE PLASTICITY CALCULATION AT 74 POINTS
***NOTE: MATERIAL CALCULATIONS FAILED TO CONVERGE OR WERE NOT ATTEMPTED AT ONE
OR MORE POINTS. CONVERGENCE IS JUDGED UNLIKELY.
***NOTE: SEVERE CONTACT OVERCLOSURES EXIST. CONVERGENCE IS JUDGED UNLIKELY.
***WARNING: CONVERGENCE JUDGED UNLIKELY. INCREMENT WILL BE ATTEMPTED AGAIN
WITH A TIME INCREMENT OF 1.56250E-02
Can anyone give me some guidance?
Thanks!
--- In Abaqus@..., "Nick Dutton" <greenlran@...> wrote:
>
>
> 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
>
INCREMENT 1 STARTS. ATTEMPT NUMBER 3, TIME INCREMENT 6.250E-02
***WARNING: THERE ARE 2 UNCONNECTED REGIONS IN THE MODEL.
CONTACT PAIR (ASSEMBLY_PROJECTILE-1_PROJ_END,ASSEMBLY_ANVIL-1_SURF-1) NODE
PROJECTILE-1.34 IS OVERCLOSED BY 16.8125 WHICH IS TOO SEVERE.
***WARNING: THE STRAIN INCREMENT HAS EXCEEDED FIFTY TIMES THE STRAIN TO CAUSE
FIRST YIELD AT 74 POINTS
***WARNING: THE STRAIN INCREMENT IS SO LARGE THAT THE PROGRAM WILL NOT ATTEMPT
THE PLASTICITY CALCULATION AT 74 POINTS
***NOTE: MATERIAL CALCULATIONS FAILED TO CONVERGE OR WERE NOT ATTEMPTED AT ONE
OR MORE POINTS. CONVERGENCE IS JUDGED UNLIKELY.
***NOTE: SEVERE CONTACT OVERCLOSURES EXIST. CONVERGENCE IS JUDGED UNLIKELY.
***WARNING: CONVERGENCE JUDGED UNLIKELY. INCREMENT WILL BE ATTEMPTED AGAIN
WITH A TIME INCREMENT OF 1.56250E-02
Can anyone give me some guidance?
Thanks!
--- In Abaqus@..., "Nick Dutton" <greenlran@...> wrote:
>
>
> 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
>
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