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LS DYNA – Material_Modelling_From_RawData By Enos Leslie Mechanical Engineer 18th January 2022 Question: 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…
Leslie Enos
updated on 19 Jan 2022
LS DYNA – Material_Modelling_From_RawData
By Enos Leslie
Mechanical Engineer
18th January 2022
Question:
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.
OBJECTIVE
My objective for this project is to derive the data points of a graphite iron casting material and create a material model on the solver deck by verification method.
PROCEDURE
The data is extracted from the picture above using a data digitizer. The x-axis and yaxis scale is defined on the picture.
A curve is plotted with effective plastic strain vs stress. A value of 0.145 Gpa was determined using the 0.2% offset from the curve.
Elastic Modulus = 144.100 Gpa
Elastic Yield Stress =0.145 Gpa
The elastic part of the curve is removed because the linear part of the curve can be defined using the Young Modulus and Yield Strength.
IMPORT
A 2d dogbone specimen is imported to be used for the simulation and creation of the material model.
MATERIAL
Firstly, a material card is created . Linear plasticity MAT 024 is used for the phone with unit system of (g/mm/ms). . The details of the material can be seen in the image below.
CURVE INPUT
The effective strain and stress data points are incoporated into the material card by using *Define_Curve .
SECTION
BOUNDARY CONDITION
CONTROL CARDS
Control_Implicit_Solution
A linear solution is selcted as can be seen in the picture below
Control_Implicit_General
This card activates and controls the analysis. The parameters specified is seen below
Control_Implicit_Auto
This card is used for time step adjustment.
DATABASE
CONTROL TERMINATION
This keyword controls the end time of the simulation. DT is specified to 1ms.
POST-PROCESSING
Effective Strain
The maximum strain developed from the tensile test was 6.24xE-06
A cross plot of stress and effective plastic strain is plotted as shown below and the data is extracted into excel.
VERIFICATION
In order to verify the credibility of the simulation data with the physical tensile test material, the curve from the simulation is compared to that of the original curve to check if the resultant stress/strain plot is equal or deviates from its original. Below is the plot which shows all plot for the verification. The original plot with curve fit is seen in orange while the simulation data is grey color. The simulation data from the image is very close generally to the original data. At the yield point, there is some error in the simulation data. The curve become perfectly matched after the stress value of 0.22Gpa
CONCLUSION
This simulation objective has been achieved as a close to accurate material card (MAT_24 piecewise linear elasticity) has been verified for the graphite iron tensile test through verification of both physical and simulation results. There were some errors developed which could be due to the uncouthness of the data points and also difficulty in the determination of correct yield and modulus values in LS-DYNA.The results can be improved by creating a more matching curve fit and ensure even gradual increase of data points . Also more data points should be used.
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