Assignment 4-RADIOSS Material Laws Challenge

OBJECTIVE:

To setup 7 different cases in Hypermesh by changing the material cards or their associated values and compare the results obtained on running the simulation.

 

PROCEDURE:

CASE 1:

1) Open HyperWorks and select the user profile as RADIOSS.

                                                           

 

2) Import the given starter file(FAILURE_JOHNSON_0000.rad) into HyperWorks using the ‘Import Solver Deck’ Tool.

                                                 

On importing, the model can be viewed in the graphics window. On enabling ‘Shaded Elements and Mesh Lines’ the model can be viewed as shown in the image below.

                 

 

3) The property card is checked to ensure that the recommended values are provided.

                                                   

 

4) For Case 1 the model has to be run as it is, hence, no changes are made to the material card and the failure card.

            

 

5) Now the file is run in RADIOSS solver.

Save the file as ‘Law2_epsmax_failure’.

Analysis > Radioss > click ’save as’ to save the file to the required directory >export options: ‘all’ > run options: ‘analysis’ > run number: ‘1’ > options: ‘-nt 4’(number of threads set to 4, for faster simulation) > Radioss

          

On completion of the simulation, a pop-up window opens showing the run summary.

                                

 

6) After the simulation is completed, the required values such as ‘Energy error percentage’ and ‘Mass error’ can be viewed by opening the engine output file (file ending with 0001.out) using Notepad.

                            

Obtained values,

                                       

The energy error obtained is 0.8% which is within the acceptable range of -15% to 5%. Also, the mass error is 0%. Hence the result is acceptable.

 

7) To visualize the simulation results as an animation, HyperView is used. For this, the animation file(file ending with .h3d) is loaded in Hyperview.

     

The plate initially undergoes deformation and then the elements are deleted once the strain energy in the element reaches 15% of the total plastic strain. This happens because we have set the value of Eps_p_max to 0.15. 

 

8) To plot the Energy Vs Time graph, HyperGraph is opened.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

(X Type: Time > Y type: Global Variables > Y Request: Internal Energy, Kinetic Energy, Contact Energy, Hourglass Energy, and Total Energy > Y Component: MAG > Apply)

                         

From the above graph, we can see that the internal energy is increasing with respect to time up to 4 ms and after that, it remains nearly constant as the plate ruptures. The maximum value of Total Energy was observed to be nearly 30943 J. The Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body, there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact. The Hourglass Energy is zero throughout as QEPH element formulation was used. The Total Energy also increases with time as it is the sum of all energies. 

 

CASE 2:

1) In Case 2, under the Johnson-Cook failure model(/FAIL/JOHNSON) change the following values, Ifail_sh=1, Dadv=1, Ixfem=1.

By changing the Ixfem value to 1 we will get a more accurate simulation as the elements will undergo cracking before element deletion takes place.

Dadv is the criterion for crack advancement. It is only active if Ixfem=1.

                                               

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law2_epsmax_crack’.

On completion of the simulation, a pop-up window opens showing the run summary.

                          

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ are viewed by opening the engine output file (0001.out).

                       

                                     

Here the Energy error percentage is 4.1% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

     

 

As the Ixfem value was set to 1, the elements will undergo cracking first instead of direct element deletion as seen in Case 1.

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

                       

From the above graph, we can see that the internal energy is increasing with respect to time upto a point of time and after that it remains nearly constant as the plate ruptures. Also, the max energy value(30944 J) is more than case 1(27376 J) as less energy got dissipated due to less number of elements getting deleted as we have set the Ixfem value to 1, due to which the elements will undergo cracking first instead of direct element deletion as seen in Case 1.

Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact.

Hourglass Energy is zero throughout as QEPH element formulation was used.

Total Energy also increases with time as it is the sum of all energies. 

 

CASE 3:

1) In Case 3, the Johnson-Cook failure model(/FAIL/JOHNSON) is deleted.

When the Johnson-Cook failure model is used along with the Johnson-Cook material model, it provides the user more control of the failure.

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law2_epsmax_nofail’.

On completion of the simulation, a pop-up window opens showing the run summary.

                                  

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ is viewed by opening the engine output file (0001.out).

                

                                        

Here the Energy error percentage is 0.8% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

       

In this case, the failure card has been deleted and since the EPS_p_max value is set to 0.15 the elements are deleted once the strain energy in the element reaches 15% of the total plastic strain.

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

 

              

The internal energy is increasing with respect to time up to 4 ms and after that, it remains nearly constant as the plate ruptures. The maximum value of Total Energy was observed to be nearly 27525 J.

Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body, there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact. The Hourglass Energy is zero throughout as QEPH element formulation was used. The Total Energy increases with time as it is the sum of all energies.

 

CASE 4:

1) In Case 4, the ‘EPS_p_max’ value is deleted.

‘EPS_p_max’ is the maximum plastic strain for element deletion for any loading (tension, compression or shear).

                                     

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law2’.

On completion of the simulation, a pop-up window opens showing the run summary.

                        

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ is viewed by opening the engine output file (0001.out).

                     

                              

Here the Energy error percentage is 1.1% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

           

 

Since the EPS_p_max value was set to zero, we can see from the animaton that the elements are not getting deleted. 

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

 

                   

The internal energy is increasing with respect to time and has a higher maximum value as the elements are not getting deleted because of which there is less energy dissipation as compared to the previous cases. The maximum value of Total Energy was observed to be nearly 38728 J. Kinetic Energy of the rupture plate elements is almost zero as there is no movement of the plate. The Hourglass Energy is zero throughout as QEPH element formulation was used. The Total Energy also increases with time as it is the sum of all energies.

 

CASE 5:

1) In Case 5, the material model is changed to Law 1 (Linear Elastic) and the values of density, E, and Nu are set to the recommended values.

Law 1 represents a linear relationship between stress and strain. This law is used to model purely elastic materials.

                                               

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law1’.

On completion of the simulation, a pop-up window opens showing the run summary.

                           

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ is viewed by opening the engine output file (0001.out).

                       

                                    

Here the Energy error percentage is 1.3% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

 

Since Law 1 was used the plate acts as a Linear Elastic material and the deformation takes place within the elastic region only. Hence, it does not undergo any rupture or element deletion.

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

 

                 

From the above graph, we can see that the internal energy and the total energy is increasing exponentialy with respect to time. Due to the elastic behaviour, as the strain increases high stresses are developed in the plate, as a result the internal energy and total energy values are observed to be very high. 

The maximum value of Total Energy was observed to be nearly 865645 J. The Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body, there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact. The Hourglass Energy is zero throughout as QEPH element formulation was used.

 

CASE 6:

1) In Case 6, the given starter file(Law27_0000.rad) having material model Law 27(Elasto-Plastic Material with Brittle Failure) is imported into HyperWorks.

Law 27 combines an isotropic Elasto-plastic Johnson-Cook Material model with an orthotropic brittle failure model. This law is applicable for shells. It is useful for modeling brittle failure of Aluminium, glass, etc.

                 

The property card is also edited and the recommended values are given.

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law27’.

On completion of the simulation, a pop-up window opens showing the run summary.

                             

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ is viewed by opening the engine output file (0001.out).

                

                                

Here the Energy error percentage is 0.8% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

 

       

The elements can be seen undergoing brittle failure. As the value of 'EPS_f' is set to 0.151 the elements will undergo deletion when the percentage of tensile strain exceeds this value. 

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

               

From the above graph, we can see that the internal energy is increasing with respect to time up to a point of time and after that, it remains nearly constant as the plate ruptures. The maximum value of Total Energy was observed to be nearly 29581 J. Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body, there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact. The Hourglass Energy is zero throughout as QEPH element formulation was used. The Total Energy also increases with time as it is the sum of all energies.

 

CASE 7:

1) In Case 7, the material model is changed to Law 36 (Elastic Plastic Piecewise Linear Material).

For this model, user-defined functions for the work hardening portion of the stress-strain curve can be provided.

The Elastic Portion of the stress-strain curve can be defined by Young’s Modulus and Poisson’s Ratio.

 

The lab data is inputted as a curve which acts as the user-defined function.

(Create>curve>new>name the curve>input the data>update)

             

After creating the curve, it is defined in the material card by changing 'N_funct' to 1 and selecting the newly created curve under the 'fct_ID' option. Also, Fscale and Eps_dot values are set to 1.

                                       

 

2) Now the file is run in RADIOSS solver.

Save the file as ‘Law36’.

On completion of the simulation, a pop-up window opens showing the run summary.

                     

 

3) After the simulation is completed, the values such as ‘Energy error percentage’ and ‘Mass error’ is viewed by opening the engine output file (0001.out).

                

                           

Here the Energy error percentage is -1.4% and the mass error is 0% both of which are within the acceptable range. Hence the result is acceptable.

 

4) The simulation results is visualized as an animation using HyperView.

        

 In this case, the material was modeled using user-defined functions obtained from lab data. The EPS_p_max value was set to 0.16, therefore the elements are deleted once the strain energy in the element reaches 16% of the total plastic strain.

 

5) The Energy Vs Time graph is plotted.

Under ‘data file’, the Time History File ( file ending with T01) is loaded.

           

From the above graph, we can see that the internal energy is increasing with respect to time up to a point of time and after that, it remains nearly constant as the plate ruptures. The maximum value of Total Energy was observed to be nearly 43366 J. Kinetic Energy of the rupture plate elements is zero initially as there is no movement of the plate. But, after the impact of the rigid body, there is a slight variation in the kinetic energy due to some movement of the plate elements caused due to the rigid body impact. The Hourglass Energy is zero throughout as QEPH element formulation was used. The Total Energy also increases with time as it is the sum of all energies.

 

COMPARISON:

           

CONCLUSION:

On comparing the different cases we see how the stresses vary and how the element deletion or cracking takes place depending on the type of Material Model used and also depending on the values given to various parameters under these material models.

For Law 36 (Elastic Plastic Piecewise Linear Material) we can provide the lab data curves obtained on testing the material in the lab as user-defined functions for the work hardening portion of the stress-strain curve. Hence, case 6 will represent the on-field scenario the best.