Assignment 4-RADIOSS Material Laws Challenge

AIM:

To apply different material types to the simulation model and compare the behaviour of the material with different element and failure formulations.

PROCEDURE:

CASE 1:

Import the provided 0000.rad file into the HyperMesh workspace and change the properties to the recommended properties for shell elements.

Save the model and run the simulation without changing the failure card.

Material and failure cards for the simulation.

0001.out file at the end of the simulation.

From the above image the total number of cycle at the end of 5ms is 49480 and energy error is 0.2% which indicates that the simulation is stable and there is no energy created in the simulation and mass error is 0.0.

Energy graph.

the above graph shows the internal, kinetic, hourglass and total energy in the simulation. from the graph it can be seen that their is no hourglass energy produced in the simultion, the internal energy increases as time increases this is because of elements absorbing the forces acting on them. 

plastic strain contour graph

in the above image we can see that the elements are deleted when they reach 15% plastic strain after the yield stress value.

it can be seen that the elements are being deleted when they reach the 15.1% plastic strain arear after the yield stress of 290Mpa, the maximum stress in the simulation is 287.6MPa.

elements break because the Johnson-Cook failure criteria model is applied to the simulation model which considers both tensil and compressive failure into account, when the elements plastic strain reaches Eps_p_max value they are deleted from the simulation, which is seen in the model above. 

Case 2:

change the failure card as shown below.

edited failure card

here Ifail_sh is Shell failure flag set to 1 which will generate crack in the shell element when Ixfem is set to 1, Dadv is the criterion for the crack advancement.

images above show the energy error, mass error, number of cycles and the time.

 energy error is +4% which is acceptable result. the simulation time taken is 75.86s which is higher than the previous simulation.

Plastic strain contour plot.

image above shows elements being cracked at the centre before getting deleted.

the maximum stress in the simulation is 294.7MPa which is higher than the previous simulation. crack developement can be seen in the simulation.

 since the crack advancement is set the maximum value of 1 and Ifail_sh is activated for shell elements, we can see the crack being generated in the simulation. 

CASE 3:

Delet the failuer card from the smulation and run the simulation.

energy error is at 0.8% which is less than 15%, hence the result is acceptable. time elapsed for this case is more than the previous two simulations.

hourglass energy in the simulation is zero, this is due to QEPH24 element formulation, the internal energy in the model increses with time similar to both the previous simulations

hourglass energy and kinetic energy in the system are 

Plastic strain contour.

the elements are deleted in this simulation.

the maximum stress in the model is 270.5MPa, and their is no crack observed in the simulation.

CASE 4:

Running the model with zero  EPS_p_max value.

material card image.

energy and mass errors are in acceptable range.

time for the simulation is less than other three simulations.

the above images shows that their is no hourglass energy generated in the simulation and internal energy and total energy of the simulation model intecepts eachother and increases with time.

in this simulation model the elements do not fail as the their is no failure criteria applied to the model, and Eps_p_max (Failure plastic strain) value is deleted which sets it to the default value of 10^30, and the maximum stress value is set to 425MPa due to which the maximum stresses in the model is seen to be 424.7MPa, and their are no elements deleted in the model.

CASE 5:

Changing the law 2 (elasto-plastic material) to law 1(linear elastic material)with same values of E (youngs modulus), density and poissons ratio.

Material card for the simulation.

energy error and mass error are in the acceptable range, and time elapsed for the simulation is 70.33s which is least compaered to previous four cases.

no hourglass energy generated in the simulation and internal energy and total energy of the simulation model intecepts eachother and increases exponentially with time.

since the material law applied is linear elastic, their is no plastic region in the material hence no elements fail and no plastic strain is recorded in the simulation.

the material has no maximum stress defined and the stress strain relation is linear, hence their is no failure of the elements.

CASE 6:

change the material card to Law 27 ( elasto-plastic Johnson-Cook material model with an orthotropic brittle failure model )

this law combines johnson cook material with the brittle failure method, this law is  applicable only for shell elements.

material card for LAW 27.

where, 

EPS_t1 is tensile failure strain at which stress starts to reduce in the principal strain direction 1.

EPS_m1 is maximum tensile failure strain in principal strain direction 1 at which the stress in the element is set to a value dependent on dmax1

EPS-f1 is  maximum tensile strain for element deletion in principal strain direction 1

dmax1 is maximum damage factor in principal strain direction 1 which is at default value of 0.999.

EPS_t2, EPS_m2 and EPS_f2 are for direction 2.

energy error and mass error values are in acceptable range for the simulation, time for elapsed for the simulation is 78.31s which is second heighest afetr case 3.

their is no hourglass energy in the simulation model, the internal energy and total energy increase with time and then tends to flaten after 4ms as seen in the image above.

elements are deleted in the simulation due to EPS_t, EPS_m and EPS_f values.

the maximum stress developed in the simulatioon is at 277.3 MPa, which is below the Plasticity yield stress value of 290 MPa.

the material breakes after the cracks reach the end of material boundary as seen in the simulation image. 

CASE 7:

Law 36 which is a isotropic elasto-plastic material using user-defined functions (curve).

create a curve with to apply in the material model N_funct.

Material card selection and curve selection.

N_funct is Number of functions which can be between 1 and 100 depending on the requirments of the simulation.

Fscale default value is 1.

energy error and mass error are in acceptable range for the simulation, and time elapsed is 76.07 s.

their is no hourglass energy generated in the simulation model, the internal energy increases with time as seen in the imag.

Once the EPS_p  (plastic strain) reaches EPS_p_max , in one integration point, the element is deleted.

elements behaviour in different cases.

stresses devloped in diefferent material formulation.

based on the stresses developed in the material, and given material data for aluminum with yield stress of 290Mpa and maximum stress of 425MPa, case 2 presentes the on-field scenario compaired to rest of the cases.

conclusion:

comparison between different material cards and failure cards has been carried out by applying them to the given simulation model. Element behaviour and stress development has been discussed. Based on the observation of results: case 2 presents the best on-field scenario in the simulation.