RADIOSS Material Laws
AIM:
- To compare the results of the different material laws i.e. Law2, Law27 and Law36.
OBJECTIVES OF THE PROJECT:
- To assign different material laws on the given component.
- To prepare case wise scenario and compare the results.
- To compare the total no of cycles, energy error, mass error and simulation time of all the cases.
- To notice the analysis animation of different cases and compare whether the elements are being cracked or eliminated.
- To conclude based on the results which case would represent the on-field scenario.
PROCEDURE:
- Go to FILE > IMPORT > SOLVER DECK > FAILURE_JOHNSON_0000.RAD > IMPORT.
- CASE 1: Law2_EPSmax_failure
- Go to the property card and change the property of 5Nip to the recommended properties as follows-
Ishell = 24: QEPH 4 nodes shells are best combination of cost and accuracy.
Ismstr = 2: Full Geometric nonlinearities with possible small strain formulation.
Ish3n = 2: Stranded 3 noded shell (CO) with modification for large rotation.
N = 5: Number of integration points set to 5 for accuracy bending.
Ithick = 1: Thickness change is taken into account for accuracy.
Iplas = 1: Iterative plasticity for good accuracy.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- In this case, the Law2 material card is used which represent the elasto-plastic material using the Johnson-Cook material model.
- This model expresses material stress as a function of strain, strain rate and temperature.
- In the material card, we have an option called EPS_max which is nothing but plastic strain at failure. Failure of element happens when 1 integration point reaches EPS_max.
- This means the shell element is deleted once it reaches the maximum plastic strain defined in the model. Thus, initially the formation of crack is even and then we can see the elements being deleted. Also the Ixfem value is zero, meaning deleted.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- The Kinetic energy shows a little variation near about 4ms, the internal energy is high and hence the total energy is same as the internal energy.
- The total energy shows little variation from 4 ms as the kinetic energy varies slightly.
- CASE2: Law2_EPSmax_crack
- Open Failure_JOHNSON_1 card under failures card.
- Change Ifail_sh = 1, Dadv = 1 and Ixfem = 1.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- We can observe the elements are getting cracked at initial stage. The cracking of elements is due to the Ixfem value set to 1. Ixfem =1 : failure element cracked.
- Ifail_sh =1: Shell element is deleted or craked when D = for one integration point or layer.
- Dadv = 1: max accumulation damage value D, used for crack initiation. (Criteria for crack advancement.)
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- We can see that the internal energy is more than 30000 kgmm2/ms2 which is greater than the case 1.
- This is due to the elemens being deleted and the energy is stored as internal energy.
- CASE 3: Law2_epsmax_nofail
- Go to Failure_JOHNSON_1 and Delete the Failure_JOHNSON_1 card using right-click.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- In this model there is no failure model, hence the material Law2 is obeyed.
- Here, the EPSmax value is followed for element failure.
- Epsmax: Failure plastic strain. Failure of element happens when 1 integration point reaches EPS_max.
- This means the shell element is deleted once it reaches the maximum plastic strain defined in the model. Thus, initially the formation of crack is even and then we can see the elements being deleted. Also the Ixfem value is zero, meaning deleted.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- We can observe the internal energy and the total energy curve follow same line until 4ms where the kinetic energy shows slight variation.
- CASE 4: Law2
- Go to the MATERIAL CARD > EPS_P_MAX = 0.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- Here the elements are being stretched like an elastic material.
- This is because the strain enters the plastic stage but as there is no eps_max value(set to zero), the Radioss will take the Default value 103 which means that the material is not going to fail under plastic strain.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- As compared to the case 3 energy curve we can see that case 4 energy curve shows more internal energy increasing at the end. There is no variation in the kinetic energy because the material does not fail plastic strain.
- CASE 5: Law1 ELASTIC
- Go to the MATERIAL CARD > CARD IMAGE = M1 ELAST > Rho_initial = 0.0028, E = 71000 and Nu = 0.33.
- This will change the material properties from M2_PLAS_JOHNS_ZERIL to M1_ELAST.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- In this case, the plate component is defined as elastic material, hence the component will be in the elastic zone and will not enter the plastic deformation. Thus, there is no crack or element failure and maximum stress is developed at the contact between both the components.
- Though, we can see some elements penetrating through the plate elements, because the contact definition is not proper.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- This curve shows more internal energy upto 800000 kgmm2/ms2.
- There is no kinetic energy developed.
- CASE 6: Law27
- Go to FILE > IMPORT > SOLVER DECK > LAW27_0000.RAD > IMPORT.
- Go to the property card 5Nip and change the values to the following-
Ishell = 24: QEPH 4 nodes shells are best combination of cost and accuracy.
Ismstr = 2: Full Geometric nonlinearities with possible small strain formulation.
Ish3n = 2: Stranded 3 noded shell (CO) with modification for large rotation.
N = 5: Number of integration points set to 5 for accuracy bending.
Ithick = 1: Thickness change is taken into account for accuracy.
Iplas = 1: Iterative plasticity for good accuracy.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- In this case we use Law27 i.e. isotropic elasto-plastic material law with orthotropic brittle failure model. Orthotropic materials differ along three mutually-orthogonal axes.
- Here, the material damage and failure happens only in tension.
- We can observe that some elements are failing like brittle material failure and also some elements being deleted.
- This law allows the modeling of material damage and brittle failure in two principle directions which is controlled by EPS_f1 and EPS_f2.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- This curve shows less variation in kinetic energy as it fails like brittle material failure.
- CASE 7: Law 36
- Go to FILE > IMPORT > SOLVER DECK > FAILURE_JOHNSON_0000.RAD > IMPORT.
- Go to CURVES > CREATE > RENAME > PLASTIC_TRUE_STRESS_STRAIN_CURVE and enter the following co-ordinates-
|
X |
Y |
|
0.0 |
300.0 |
|
0.000484405 |
360.13 |
|
0.00111878 |
390.56 |
|
0.0032105 |
442.82 |
|
0.00478134 |
465.98 |
- Go to MATERIALS > ALUMINIUM > CARD IMAGE = M36_PLAS_TAB.
- Now, go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
- This will run the Radioss simulation.
- Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
- Click on view Results, which will open Hyperview window.
- In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
- The Law36 material law helps in modeling isotropic elasto-plastic material using user defined functions for the work hardening portion of the stress-strain curve for different strain rates. The curve is nothing but the stress-strain curve after the yield point. The yield point is set to 0.
- The Law36 model has 4 damage and rupture parameters-
- EPS_p_max is the maximum plastic strain for element deletion for any loading like tensile, compression and shear.
- EPS_t is the beginning of the tensile damage. From this point the stress value defined in the curve is reduced by a factor. Where EPS_1 is the largest principal strain.
- EPS_m is the end of tensile damage. The stress value is null but the element is not deleted.
- EPS_f is the tensile failure strain value for element deletion.
- We observe that the elements fail at the maximum stress value and some elements are being deleted once they reach the EPS_f value. This type of failure is a real life failure as we have defined a true stress-strain curve. These curves are obtained from lab testing of the components.
- Open Hypergraph 2D and load T01 file.
- Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
- This graph shows energy lesss than 30000 kgmm2/ms2 as we have used plas_tab material.
COMPARISION TABLE:
|
CASE |
NO OF CYCLES |
ENERGY ERROR |
MASS ERROR |
SIMULATION TIME (S) |
MAX STRESS VALUE |
|
C1 |
49380 |
0.8% |
0% |
345.89 |
275 |
|
C2 |
49217 |
4.1% |
0% |
458.64 |
295.1 |
|
C3 |
49408 |
0.8% |
0% |
352.53 |
270.7 |
|
C4 |
49304 |
1.1% |
0% |
362.32 |
424.7 |
|
C5 |
47969 |
1.3% |
0% |
215.29 |
1089 |
|
C6 |
49508 |
0.8% |
0% |
231.56 |
287.5 |
|
C7 |
53130 |
1.7% |
0% |
373.08 |
596.8 |
LEARNING OUTCOMES:
- The use of different material laws and their behavior.
- The EPS_max values for every material laws and their significance.
- The solving of the constants i.e. a, b, n, d1, d2 and d3.
- To plot von-mises stress values in the simulation using Hyperview.
- To plot the energy graph in Hypergarph2D.
CONCLUSION:
- Hence, by completing this project we conclude that the material laws have been applied and compared for the best on-field results.