Week - 9 Material Modeling from Raw Data

AIM: -

To perform the simulation and validate the curve as shown in the figure (Raw data) with the simulation post-processing curve.

OBJECTIVE:-

• Using the given video link, extract the data from the figure, and use it for validation.

• Create a material model for the Dogbone specimen using the diagram of the true stress-strain curve (graphite iron).

• From the above condition, simulate and validate the material model by performing a tensile test on a Dogbone specimen.

PROCEDURE: -

• Data Extraction & Graph calculation

• First import the stress and strain data from the stress-strain curve by using a DigitizeIt r.

• Import the Stress-strain curve image in the data digitizer as shown below.

• Next click on the set scale it shows the set Xmin, where we want to Xmin select by using the cursor and entering the value as 0 as shown below.

• Click on ok next shows the set Xmax select X-axis maximum point and give the value 0.7.

• Next it is asking set Ymin to select the Ymin point and give the value is 0.

• Next ask the set Ymax to select the maximum point in Y-axis and give the value 60.

• It shows X-axis and Y-axis is a Red line as shown

• Next select the point capture mode and pick the points randomly along the curve path 2 as shown below.

• Next Export the data to Excel format and save the data.

• Next open the file in Excel it shows the stress and strain values as shown below.

• Here strain in percentage and stress in kilo pound-force per square inch (KSI) so convert both values as shown below.

Strain % = 10^-2

Stress 1 ksi =0.00689476 Gpa

• So, we have multiplied the values for strain = strain % ×10^-2

For stress = stress (ksi) × 0.00689476

• Next , find the effective plastic strain as shown below.

Effective Plastic Strain = True strain - (True stress / Young's Modulus)

Here,

True stress = Stress

True strain = Strain

Young's Modulus E =20.9E+06 pound-force per square inch (PSI)

change the units of Young's modulus PSI to Gpa as shown below.

20.9E+06 PSI = 144.100427424 Gpa.

• Plot the graph Effective stress vs Effective plastic strain. Here effective stress is nothing but True stress.

• Next open the keyword file in the notepad and assign the above values for the Mat_curve as shown below.

• Next save the file and open it in the LS-Pre post check the mat curve as shown below.

• Create Material & section card for part

• Next create the material 024 and section shell as shown below.

• The section property of the dogbone specimen is assigned as a shell element with 1mm thickness along with ELFORM=2 (Belytschko-Tsay)

• The material and section are assigned to their respective part ID.

• Boundary condition (SPC Set)

• Next create the Boundary Conditions as shown below.

• The nodes at the fixed end are constrained in the Z and Y direction, the X direction is not constrained because of lateral compression during the tensile test.

• The nodes in the middle are constrained in the X direction since the neutral axis passes through the middle of the specimen in the Z direction.

• Boundary condition (Prescribed Motion set)

• Create the curve for displacement as shown below.

• Assign the displacement curve to the Prescribed Motion set as shown below.

• The nodes pulling at one end are assigned with a boundary-prescribed motion in ‘-Z’ direction using VAD displacement with a load curve of -1.0 m/s.

• Control cards

• To activate implicit analysis and define associated control parameters.

• Implicit_Auto

• Implicit_General

• Implicit_Solution

• Implicit_Solver

• Termination

• Database

• Create Database cards as shown below.

• ASCII_Option

• ASCII_options give the outputs ELOUT, GLSTAT, MATSUM, NODOUT, RCFORC, SWFORC, and SPCFORCE.

• Binary D3 plot

• Extent Binary

• History shell

• Run the simulation

POST PROCESSING: -

• Result:-

• CONTOUR PLOTS OF VON MISES STRESS

• CONTOUR PLOTS FOR EFFECTIVE PLASTIC STRAIN

• Z STRAIN

• STRESS AND STRAIN

CONCLUSION: -

The stress-strain data is extracted and validated from the image using a Data digitizer by MAT_024(Piecewise linear plasticity) which captures the actual stress-strain behavior similarly.

Few variations in the simulation data lead to a lack of information data from Density and Poisson’s ratio for the raw data.

NOTE: LS-DYNA FILE is too big to upload on a website. So, I shared the google drive link to download.

Download link : https://drive.google.com/drive/folders/1GV1VzOf5bMyWLoJ6ib2TdTe5t5ohrriP?usp=sharing