Assignment 4-RADIOSS Material Laws Challenge

AIM:

To run the analysis of the given model in seven cases with the given setup and analyse the results.

 

OBJECTIVE:

The objective of the assignment is to understand the different material card parameters and how they affect the simulation, the material failure, etc.

 

CASE SETUP:

 

Case	Setup
1	Case 1 analysis is carried out with Law 2 material and its default properties with recommended property cards.
2	Case 2 analysis is carried out with the same setup as above but with the failure card defined. In the failure card, the configuration is kept as JOHNSON and the Ifail_sh flag is kept to 1 (shell is deleted / cracked). The Ixfcm flag is kept to 1 which enables to view the crack propagation as the failure happens in the shells. The Dadv flag (criterion for crack advancement) is also kept to 1.
3	Case 3 analysis is carried out with the Law 2 material, without the failure card. The failure card is deleted and the other setup is kept the same.
4	Case 4 is carried out with the same Law 2 material with the Eps_p_max deleted. The Eps_p_max is the plastic failure strain. Deleting this value keeps the value at default value (10^30).
5	For case 5, we use the same setup as above but with Law 1 material. The E, rho_initial & nu values are kept the same as in the above case.
6	Case 6 analysis is done with Law 27 (Plast_BRIT) material
7	For case 7, the analysis is done with Law 36 (Plas_TAB) material with the following values for the parameters: E = 71000                                   Eps_t = 0.1 Rho_inital = 0.0027                     Eps_m = 0.11 Nu = 0.33                                    Eps_f = 0 Eps_p_max = 0.16                     Nfunc = 1 The strain & stress values are given as follows: 0                         300.0 4.84405e-4         360.13 0.00111878        390.56 0.0032105          442.82 0.00478134        465.98

PROCEDURE:

For cases 1 to 5 and case 7, the FAILURE_JOHNSON starter file is used. For case 6, the LAW 27 starter file is used.

Case 1:

• The starter file is imported using the Import solver deck option. The property card is checked and the parameters are kept to the recommended values. The material card is opened and the Law 2 material is kept. With its default values, the analysis is performed.

Case 2:

• For case 2, the failure card is defined with Ifail_sh = 1, Ixfcm = 1 which enables the element to delete / crack upon failure and to view the crack propagation as the element fails. With the Law 2 material, the analysis is performed.

Case 3:

• For this case, the failure card is completely deleted, i.e. failure for the material is not defined. The analysis is performed with the Law 2 material.

Case 4:

• In case 4, the Law 2 material is used with the Eps_p_max deleted meaning the plastic failure strain is changed to radioss default (10^30). With these parameters, the analysis is performed.

Case 5:

• In case 5, the same density, modulus of elasticity & poisson’s ratio are used but with Law 1 material. With all other parameters kept same, the analysis is performed.

Case 6:

• For this case, we will use the LAW 27 starter file. The starter file is imported using the Import solver deck option. The material card is kept as Plast_BRIT. This is the material card for a brittle material.

Case 7:

• The case 7 analysis is performed with Law 36 Plas_TAB material. The values for E, rho, nu are given. Also the Eps_p_max, Eps_t, Eps_m & Eps_f values are given.

 

The output files, plot files & simulation files for each simulation are saved separately and the results are viewed & analysed.

 

RESULTS:

Case 1:

• From the plot, we can see that the hourglass energy & kinetic energy are almost zero. There is a small amount of kinetic energy after 3.6 ms, but the hourglass energy remains zero.
• There is a linear increase in the total energy & internal energy upto 3.8 ms. At about 4 ms, there is a small dip in the internal energy and from hereon, the internal energy & kinetic energy have slight differences.

 

• From the plot it can be seen that the resultant tangent force is completely zero. The total resultant force has a steep increase in the beginning upto 5.7 kN and thereon there are ups & downs in the curve. The amount of dips decrease as the analysis progresses.
• While nearing the 4th ms, there is a steep decrease in the total resultant force to 0.35 kN. From 4th ms, there are slight increases & decreases and during the 4.8th ms, it becomes zero for some while and again there is an increase. After 5 ms, as the analysis stops, the curve is cut off. 

 

Case 2:

• As seen in the previous case, the hourglass energy is again zero throughout the analysis. There is a small amount of kinetic energy after 4 ms which also becomes zero afterwards. There is a linear increase in the total energy & internal energy upto 3.8 ms.  At about 4 ms.

 

• As in case 1, the resultant tangent force is completely zero. The total resultant force increases steeply in the beginning upto 5.7 kN . After that, there are ups & downs in the curve.
• At about 3.8 ms, there is a steep decrease to 5 kN. From here, there is a small hike and then an even steeper fall in the force.
• From about 4.4 ms, the force starts to fall steeply to 0.25 kN. Then there is a small steep increase and decrease. The resultant force then reaches zero at one point and then starts to increase again.

Case 3:

• As seen in the first case, the hourglass energy is again zero throughout the analysis. There is a small amount of kinetic energy before 4 ms which wavers afterwards.
•  There is a linear increase in the total energy & internal energy upto 3.8 ms.  After that, the total energy becomes almost same but the internal energy wavers upto the end.

 

• In this case, the resultant tangent force & resultant normal force are zero throughout the analysis. The total resultant force has a steep increase as in the previous cases upto 5.8 kN. Then there is a bit steeper decrease and thereon the curve progresses with ups & downs.
• At about 3.9 ms, there is a steep fall in the total resultant force and it reaches almost equal to 0.2 kN. Afterwards, there is again an increase & decrease in the total resultant force. After 4.8 ms, the total resultant force becomes zero.

 

Case 4:

• In case 4 we can see that there is zero hourglass energy throughout. The total energy & internal energy are almost the same and we cannot find any difference between the two. The total energy & internal energy curves have a linear increase from the beginning of the analysis.

 

• As for the rigid wall forces, the resultant tangent force is completely zero. The total resultant force as in the previous cases, see a steep increase in the beginning upto 5.6 kN. Then the force increases slowly. There are no major falls & rises in the curve, as in the previous cases.
• From the curve, we can see an average rise and then an average fall which is stopped at 5 ms as the analysis is stopped. If the analysis would have run for some more time, we could have seen the results further.

 

• From the simulation, we can see that the failure of elements in all the cases from the first frame. But for case 4, the failure of elements has not happened till frame 4.

• The failure starts to happen from frame 5 only. This is due to the plastic failure strain value (Eps_p_max). Since the value is deleted, the default value `10^30` was automatically assigned. As a result, the failure is delayed in this material. 

• The strain is maximum in case 4.

• From the contour, we can see the maximum strain which is 0.401. 

 

Case 5:

• For case 5, as in previous cases, internal energy & total energy have a linear increase from the beginning. At the ending of the analysis, it starts to stabilise but as the analysis is ending at 5 ms the curve has stopped abruptly. As seen in previous plots, the hourglass energy is completely zero.

 

• The rigid wall forces plot for this case is different from those of other cases. Just like the internal & total energy, the total resultant force also sees a linear increase. The steepness of the total resultant force curve is less. It is more flexible than the internal & total energy curve.

• One more point to note is that, since the material is elastic, there is elastic deformation and no elements fail.

  

Case 6:

• In this case also, the total & internal energy have a linear increase from the beginning. After about 4.2 ms, the two curves are visible separately. Upto that time, they are exactly superimposed on each other.
• The hourglass energy is completely zero. The kinetic energy is also zero but after 4.3 ms, we can see a slight increase. There is a small amount of kinetic energy till the end of the analysis.

 

• In the rigid wall forces plot, the resultant tangent force is zero throughout the analysis. The total resultant force as in other cases, sees a steep increase upto 6.4 kN. Then there is a decrease.
• Afterwards, there is a continuous rise and falls in the curve. After 4 ms, the fall steepens and reaches almost zero. After that, again there is a steep increase & decrease from threon. The curve abruptly stops at 5 ms as the analysis ends.

 

Case 7:

• From the above plot, the total energy & internal energy have a linear increase upto 3 ms in contrast to that of 4, 4.3 ms in other cases. After this point, the internal & total energy can be seen separate.
• The internal energy sees a slight fall after 3 ms, then increases upto 3.8 ms. From thereon, it becomes almost constant with slight ripples. One more interesting point to note is that the kinetic energy, which was almost zero in other cases increases after 3 ms.
• From this point, there is a small amount of kinetic energy existing. We can also see the kinetic energy which will exist if the analysis is extended.

 

• The total resultant force sees a less steep increase in the beginning of the analysis as contrast to an even steeper increase in other cases. But the force in this case is very high as compared to other cases. The reason behind this is the lab test data provided for the stress & strain values, plastic failure strain & other parameters.
• These force values are very similar to the real-life testing. Then the curve falls steeply after 3 ms. After this there are small peaks and further there is a fall. After this point, the force reaches zero multiple times during the course of the analysis.

 

• As for displacement of elements, the law 36 material (case 7) sees the most displacement of the elements. 

• When seeing the results in contour, we can see the maximum displacement of elements. The maximum displacement in case 7 is 59.84 mm at node 3688. 

 

• Since we have given the stress values for corresponding strains based on lab tests, this case resembles the actual test result. 

 

 

Case	No. of cycles	Energy error (Min. & Max.)	Mass error	Simulation time
1	49380	-0.6 to 1.3 %	0.00 %	69.28s
2	49217	-0.6 to 4.5 %	0.00 %	77.82s
3	49408	-0.6 to 1.2 %	0.00 %	74.40s
4	49304	-0.6 to 1.2 %	0.00 %	77.91s
5	47969	-0.6 to 4.0 %	0.00 %	76.21s
6	49508	-0.7 to 1.0 %	0.00 %	82.69s
7	53161	-1.2 to 0.6 %	0.00 %	72.21s

CONCLUSION:

• From the analysis simulations & output plots, we can conclude that the analysis data is more realistic when the real-time data for material stress & strain for different strain rates are given. 
• For elastic material, the total resultant force absorbed by the material is the highest when compared to other materials.