To compare the different material failure property cards using Radioss

OBJECTIVE:

To study and compare the effect of different material failure property cards on the given rupture plate model. To compare the 7 cases given based on the following:

1. Total number of cycles, Energy error, mass error and simulation time

2. To notice the animation of all the 5 cases and to describe whether the elements are being deleted or cracked.

3. To plot different energies and notice the difference

4. To arrive at the on-field scenario based on the results.

5. To list down case by case scenario results and the conclusion as to why the failure happened.

PROCEDURE:

The below procedure is common for all the cases and changes are to be done as per the case.

1. Import the file FAILURE_JOHNSON_0000.rad using the radioss solver.

2. Check the material failure property card and changes are done as given in every case

3. Then go to Analysis>>Save the file name as given in the question>>Select number of cores as -nt 4>>Radioss

4. Go to Hyperview>>Load the necessary .h3d file to view the necessary simulation.

5. Get the necessary contours as given in the Hyperview window and save the simulation results contours.

6. Go to Hypergraph>>Load the necessary T01 file to get the various graphs associated with the simulation.

7. Step 1-6 is repeated for various material card changes.

CASE SETUP AND EXECUTION:

Case 1: The material failure property card is not changed and the model is run as such.

The von-mises contour obtained is shown below:

The various energy plots obtained is shown below:

Case 2: The material failure property card is changed with the given values and the model is simulated.

The von-mises contour obtained is shown below:

The various energy plots obtained is shown below:

Case 3: The material failure property card is deleted and the model is simulated.

 The von-mises contour obtained is shown below:

The various energy plots obtained is shown below:

Case 4: The failure card and the value of EPS_p_max is deleted and the model is simulated.

 The von-mises contour obtained is shown below:

The various energy plots obtained is shown below:

Case 5: The material model law is converted to Law1 elastic with same value of elasticity, Poisson's ratio and density and the model is simulated

The von-mises contour obtained is shown below:

 The various energy plots obtained is shown below:

Case 6: The material model law27 is adopted and the model is simulated

The law27 is applicable only for shell elements. This law combines an isotropic elastoplastic Johnson-Cook material model with an orthotropic brittle failure model.

The von-mises contour obtained is shown below:

 The various energy plots obtained is shown below:

Case 7: The material model law36 is adopted and the model is simulated

This model law is applicable to both shell and brick elements. This law models an isotropic elastoplastic material using user-defined function for the stress vs strain curve for different strain rates.

User Defined Curve:

The von mises contour obtained is shown in the figure below.

The energy plot obtained is shown below.

RESULTS AND COMPARISON:

Case 1 and Case 2:

Johnson cook material model represents an isotropic elastic-plastic material. Material stress is expressed as a function of strain, strain rate and temperature. 

                                 CASE 1                                                             CASE 2  

In case 1 Ixfem = 0 and Dadv = 0 whereas in case 2 it is 1 respectively. The material failure is defined by the Ixfem. The value 0 would delete the entire element without cracking whereas value 1 would crack the element and then deletes it. Stress generation in case 1 is less than case 2 due to this reason. This is shown in the simulation below.

Case 1:

Case 2:

Energy plots comparison:

                                   CASE 1                                                                   CASE 2

As shown in the above figures, the graph is smoother for case 2 since the element is cracked and deleted. As shown in the above figures the total energy curves looks similar. The hourglass energy remains zero for both the cases since QEPH element formulations are used.

Case 3 and Case 4:

 In these two cases, the failure Johson card is deleted. In case 3, the element fails when it reaches a strain of 15% plastic strain value. In case 4, that value is set to zero (eps_p_max). This is observed in the simulations given below.

Case 3:

Case 4:

As shown in the simulation above, in case 4 there is no deletion of elements as observed in case 3. This is because elements undergo infinite deformation in case 4 since eps_p_max is set to 0.

Energy plots comparison:

In the kinetic energy plot, there is a sharp spike in the value for case 3 since elements are deleted whereas in case 4 it remains fairly constant since there is no deletion of elements. Also, there is an exponential increase in internal energy for case 4 but for case 3 it is a linear increase.

Clearly the Von-Mises stress for case 3 is lesser when compared to case 4 since the elements are not deleted in the latter.

Case 5:

In this case there is no failure card and the material assigned is elastic material (Law1) M1_elastic.

The stress simulation is shown in the figure below:

Energy plots :

From the energy plots it can be shown that the material absorbs a lot of energy before deformation. The deformation is temporary and material gets back to original shape once the load is removed. The energy error observed is less compared to M2 material law. Since its a ductile material the internal energy increases thereby increasing the stress values. 

Case 6:

This law combines an isotropic elastoplastic Johnson-Cook material model with an orthotropic brittle failure model. This law is applicable only for shells. The material behaves as a elastic material till it reaches the plastic yield stress.  For higher stress values, the material behaves as a plastic material.

From the simulation it is clear that the plate fails when material reaches eps_f1 0.151.

Energy plots :

From the energy plots, it can be seen that the internal energy is increasing continously. No hourglass energy is observed since there is QEPH formulation of shell elements. 

The kinetic energy plots show small fluctuations since no element is displaced due to crack or deletion.

Case 7:

Here user defined values are given to define the stress-strain curve in the strain hardening region. The defined curve is explained in the procedure.

Energy Plots:

The stress value in this case is much higher. It can be inferred that material has absorbed more stress due to its elasto-plastic behaviour. Due to plastic nature of the material, the kinetic energy has a sharp spike. The hourglass energy remains zero due to QEPH element formulation.

Now, the results obtained for mass error and energy error for all the cases is given below:

CONCLUSION:

The following conclusions can be drawn based on the results obtained during simulation.

The selection of material is based on the application. Suitable material must be selected in accordance with the application and the following properties are validated in this challenge.

Law 1: It is applicable for perfectly elastic model used for static or quasi-static analysis. Not suitable for real time scenarios.

Law 2: It represents isotropic elasto-plastic material using Johnson-Cook material model. This model expresses strain as a function of strain, strain rate and temperature. Most cases temperature effect is neglected. Ideal for crash test analysis.

Law 27: It combines isotropic elastoplastic Johnson-Cook material model with an orthotropic brittle failure model. 

Law 36: It is suitable when user-defined values are needed to define the stress-strain curve in the strain hardening region.

Drivve link for files: https://drive.google.com/file/d/1OmAzI2fcfO-fX9qiUihK10DHNfDljG7k/view?usp=sharing