Challenge

Material Modeling from Raw Data in LS-Dyna

BBalaji Naga Sai Abhishikt Challa16 Nov 2021

LS-DYNA

Objective: To model material data in LS-Dyna.

Procedure:

The provided stress-strain curve image is imported into the data digitizer.

Fig 1: Stress-strain curve image is opened in the data digitizer to extract the curve points.

From the data digitizer, the points from the 1st curve are exported into excel.

Fig 2: The stress and strain points are extracted from the image and exported in excel.

The XY coordinates are saved in a suitable format for the LS-Dyna so that the file can be directly uploaded while the curve is defined.
Open the given dog-bone specimen in LS-Prepost.

Fig 3: Dog-bone specimen.

The initial keyword file contains the mesh information within it.

Fig 4: Initial keyword file.

To completely define the keyword file, additional cards must be added to simulate the tensile test.
The auto-created part is appropriately named for further identification.

Fig 5: Part is appropriately named for later identification.

A SHELL section card is defined with ELFORM=16 and a thickness of 2mm.

Fig 6: Shell section is defined with an ELFORM of 16.

Hourglass card is defined to control the hourglass formation in the shell elements.

Fig 7: Hourglass is defined with Flanagan-Belytschko viscous form.

Mat024 PIECEWISE_LINEAR_PLASTICITY card is defined with the following properties.

Density: 7.106e-06.

Young's Modulus: 144.10001.

Poisson's Ratio: 0.3000000.

yield stress: 0.1419000.

Fig 8: Mat024 card is defined.

The curve taken earlier is now loaded into the curve card.

Fig 9: Stress-strain curve is loaded.

Fig 10: The curve is fed from the yield point.

The displacement curve is also defined.

Fig 11: Displacement curve is defined up to the end of the simulation time.

To emulate the tensile test for the specimen, a Single-point constraint is created with x translational and all rotational DOF fixed.

Fig 12: Left end of the specimen is fixed in x and all rotational directions.

Additionally, y-translation is fixed on the mid node of the two ends of the specimen.

Fig 13: Mid nodes of the two sides are locked in y translational direction.

A node-set is created with all the nodes from the right end of the specimen to provide displacement in the positive x-direction.

Fig 14: A node-set is created to define the displacement.

Prescribed_motion_set is defined with the created node-set, and a DOF of 1 and VAD of 2 are chosen.

Fig 15: Displacement is defined to the other end of the specimen.

To solve this particular simulation implicit solver is chosen. To define the implicit solver, specific implicit keywords must be included.
IMPLICIT_AUTO, IMPLICIT_GENERAL, IMPLICIT_SOLUTION, and IMPLICIT_SOLVER keywords must be added from the control deck.

Fig 16: Implicit_auto card is defined.

Fig 17: Implicit_general card is defined.

Fig 18: Implicit_solution card is defined.

Fig 19: Implicit_solver card is defined.

The ASCII_option keyword from the DATABASE deck is used for the output requests, and the GLSTAT option is checked.

Fig 20: Output requests are defined.

The BINARY_D3PLOT keyword from the DATABASE deck is used for the plots, and a DT of 0.05 is entered.

Fig 21: Plots at time intervals are defined.

Finally, the TERMINATION keyword from the CONTROL deck is used to define the end time of the simulation.

Fig 22: End time for the simulation is defined.

With all these keywords included, the deck is fully defined and is now ready to solve.

Fig 23: Fully defined deck.

Open the Start LS-Dyna analysis, browse the keyword file, and hit run to run this keyword file.

Fig 24: LS-Dyna analysis browser.

Fig 25: Successful completion of solving.

Open new LS-PRE POST from the launch manager and open the LS-DYNA Binary plot (choose the D3PLOT file created) from the file menu.
The model will be loaded the same as before, but we can access only the post-processing options from the right ribbon menu.