Assignment 4-RADIOSS Material Laws Challenge

Objective –

Run the given Models in Radioss as per the required parameters and compare them using the plots and animations.

• Given model – impact of a rigid ball on sheet of metal, for all these cases the material laws are changed for the sheet.

Case 1 – Law 2 with EPS Max Failure and Failure Johnson card

Case 2 - Law 2 with EPS Max Failure and Ifail =1, Dadv =1 and Ixfem = 1 (crack)

Case 3 – Law 2 with deleted Fail Johnson card

Case 4 – Law 2 with deleted Fail Johnson and EPS Max Failure

Case 5 - Law 1 with density, E, nu

Case 6 – Law 27 with EPS based Failure

Case 7 – Law 36 with Strain rates curve

Same Property parameters are given for all the cases.

Case 1

Procedure block

• Import the starter file into radios block
• Provide the shell properties to the component in this case the sheet of metal
• Provide the material and failure to the component in this case Law 2 and failure Johnson card.
• Run radios and wait for the run to complete without any errors.
• Open the engine out file for energy error (should be less than 15% max) and mass errors (should be less than 1%)
• Open hyperview to observe the animations and contour plots from H3d file.
• Open hypergraph 2d for observing the energy plot data from TA01 file.

• In this case, – /MAT/LAW2 (PLAS_JOHNS) Johnson Cook material is used with EPS failure and Johnson failure card.
• This model represents the material stress as a function of plastic strain, strain rate and temperature.
• Built-in failure criterion based on the maximum plastic strain (EPS max) is used in this case.
• Since build in failure criterion does not take care of compression fails, a Failure card is applied- For three typical loadings (example: pure tension, pure shear or pure compression) material parameter D1 D2 and D3 are defined in failure card along with EPS max value. Reference strain rate is also given.
• In this case Ixfem=0, so element is deleted if it reaches the rupture criteria.
• Animations and Plot explanation.
• We can observe that elements are getting deleted as the maximum plastic strain values are reached in the elements.But the crack propagation cannot be observed well as Ixfem is 0 in this case.

Energy error and mass error are within the limits - (less than 15% and 1% respectively )as the recommended shell properties are applied to the component. (same can be observed in all the cases)

We can observe from the plots that the Internal energy reaches its peak value value just before the elements are getting deleted at 3.9ms. 

Case 2

• In this same material is used except that in this case Ixfem=1, so element is cracked if it reaches the rupture criteria. (Failure John card) can be used only on shell elements
• Ifail_sh =1, shell failure flag of Ixfem =1 ; Dadv = 1 (max accumulation damage value D, used for crack initiation),
• Using this criteria we can see the crack propagation more than the case 1 before element deletion. And we observe due to Dadv, certain elements getting elements when another crack arrives at its boundary.
• Animations and Plot explantion. Cumulative damage law based on the plastic strain accumulation is the failure model used here. Along with that Ixfem =1 hence crack propagation can be visible in this case before the elements gettting deleted.

We can observe from above plots that the internal energy peaks at around 4.5 ms , which is later than in case 1 its because of Ixfem and Dadv parameters which allow for deletion of elements only after crack propagation. And the total resultant force declines by steps unlike what is observed in case 1.

Case 3

• Same material but failure card is deleted.
• Eps max failure criteria is considered .Elements are deleted once the (15.1% True plastic strain value)
• When strain reaches the value of Eps max in one integration point, the corresponding shell element is deleted.
• Animations and Plots Explantion
• From the animation we observe the that the elements are deleted the moment it reached Eps max value as inputed.

The plots above are quite same as in case 1. The impact of rupture due to the crack is not very noticable as compared to case 2 , where total resultant forces were declining in a step manner.

Case 4

• Same material but with failure Johnson and Eps max deleted.
• Since the Failure card is been deleted,hence the solver sets Eps max is set to the default value (10³⁰)
• Now there is no failure criterion for the elements.
• Animations and Plots explanation – Elements are not getting deleted,  failure criterion is default value. We can observe the max von mises stress is comparatively higher than the above cases.

Energy plots and Resultant Forces can be similiar to to case 3.

Case 5

• In this case /MAT/LAW1 (ELAST) with density, E, nu is used.
• isotropic, linear elastic material using Hooke's law. This law represents a linear relationship between stress and strain. It is available for truss, beam (type 3 only), shell and solid elements.
• Hence this law is used to model only elastic materials.
• Animations and Plots Explanation. – Elements are not getting deleted.
• Since we have selected a elastic material, behavior is very linear and there is no failure criteria for element deletion. (These types of materials are not suitable for impact type analyiss)
• And max von mises are way higher than in cases above

From the above plot we can see that internal energy and resultant forces on the rigid ball is even higher than in case 4 . There no peaks or valleys in the resultant forces it goes linearly until the simulation time.

Case 6

• In this case /MAT/LAW27 (PLAS_BRIT) is used. This law combines an isotropic elasto-plastic Johnson-Cook material model with an orthotropic brittle failure model. Material damage is accounted for prior to failure. Failure and damage occur only in tension. This law is applicable only for shells.
• In this model, the material behaves as a linear-elastic material when the equivalent stress is lower than the plastic yield stress. For higher stress values, the material behavior is plastic and the stress is calculated.
• Once the maximum tensile strain is reached corresponding elements are deleted.

The Sheet break into two parts showing its brittle nature . In terms of IE it reaches a peak value even after than we can see a rise in IE its due to the dissipation  of strain energy from stressed elements.( similiar to how a windshied glass breaks when its impacted by a stone) . Elements are delete once the failure criteria is reached.

Case 7

• In this case /MAT/LAW36 (PLAS_TAB) is used. This law models an isotropic elasto-plastic material using user-defined functions for the work-hardening portion of the stress-strain curve (for example, stress vs. plastic strain) for different strain rates.
• Since crashes (explicit) happens within 120ms, strain rates are very high so using this law user can input curves of true Plastic strain vs stress for different rates into the model.
• It can be used for all type of elements shell or brick
• Stress strain curves inputted should not intersect and for cases where the stress strain rates are not inputted, interpolation is done by solver for those cases.
• Law 36 can be used with Johnson cook fail card with no rupture parameters, but in this case Eps max failure is used (build in).

• Animations and Plot Expalantion.
• The IE and the resulatant forces increases relatively earlier compared all to all other cases, and elements gets deleted from the center portion completely.

Conclusion and Results

- Hourglass energy remained almost zero during all the cases.

- Mass error and energy error also were with limits due to the recommeded shell formulations.

- Case 1 and 6 are more realistic on field scenarios(due to failure card and build in strain failures covering compressin and shear stresses) . Case 2 with its crack propagation feature would be useful in small crack observations.

- Case 7 would be really useful for simulating ,if test data is available for different strain rates - would help in crash based analysis giving more realistic results.