Week - 9 Material Modeling from Raw Data

Objective:

Use the diagram of the true stress-strain curve of graphite iron casting. Two curves are there for different material structures. Students need to pick any one of them and use the data to create either a MAT_024 or MAT_018 material model and then validate it.

Procedure:

1. Using digitizer, extract the data from the Stress(ksi) & strain% graph (2) to an excel file.

2. From this data plot a graph in excel and use trendline (polynomial of order 3) to find the curve fit equation and R².

3. Using the curve fit equation find the Stress with Strain (converted from %), Also Convert the stress into N/mm²

4. Calculate True Strain, Effective plastic Strain & Effective stress using the following formulas.

True strain = ln (1+engineering strain)

True Stress = Effective Stress

Effective plastic Strain = True strain – True Stress/E

E = 20.9E06 psi = 144100.4273 N/mm²

5. Import the given Dogbone_specimen.k in LS DYNA Pre-Post

6. Define Curve in keyword manager using the Effective Stress and strain.

7. Define curve for displacement in keyword manager

8. Create a Material card assigning the values of casting iron and assign the curve defined.

9. Create Section Shell for the specimen assigning thickness of 2mm and ELFORM=16.

10. Edit the Part, assigning the material and section shell created.

11. Assign Boundary Conditions:
    a) Constrain all the nodes of one end of the dog bone specimen in all directions except translational Y direction
    
    b) Constrain the mid nodes of both ends of the dog bone specimen in Y translation to restrict the slip during simulation.

12. Assign Displacement for the specimen onset of nodes on another side with the curve defined.

13. Add the following control cards
    a) Control Implicit General – IMFLAG =1, DT0 = 0.005, IMFORM = 2.

b) Control Implicit Auto – IAUTO=1, ITEOPT =60, ITEWIN=5, DTMIN=0, DTMAX=0.
c) Control Implicit Solver – LSOLVR=6.

d)Control Termination – ENDTIM=1.

14. Add the following Database Cards
a) BINARY_D3PLOT with DT=0.01
b) DATABASE_EXTINCT_BINARY with STRFLG=1

c)DATABASE_ASCII with ELOUT, GLSTAT, MATSUM

15. Save the Keyword file as in the new folder and run the keyword files in LS – Run.

16. Open LS – PrePost, Import the D3 plot file created during the simulation.

17. In the Fringe Component option, Select Von-mises stress for the contour plot and save the von-mises animation videos.

Effective Stress Plot

Effective Strain plot

Stress vs Strain Plot

Conclusion:

The graph we obtained from the simulation is almost identical to the graph given.

Learning Outcome:

Performing Tensile test based on the material curve given.