Roof Crash simulation with NEON BIW components

AIM :

       To simulate the frontal crash using the body in white components, make a model as per the given requirement and extract the required results in the post-processing.

OBJECTIVES :

       Transform the impactor to the desired location.

       Create a Type 7 contact interface between impactor and car.

       Create a boundary condition for the suspension shock tower.

       Create an impactor boundary condition.

       Apply an imposed displacement for the impactor.

       Create control cards.

       Set the termination time, nodal & element-time step.

       Extracting all output animation as requested.

       Extracted all output plots as requested.

INTRODUCTION :

       Roof crash testing helps us to evaluate how well a vehicle roof might be strong while the car gets rollover accidents. Due to a rollover accident, a passenger gets in serious injuries or even death also. This is also called quasi-static testing because a load is applying gradually on the roof

       Automotive companies are using two methods to conduct crash tests such as physical crash tests & Virtual crash tests.

Physical roof crash test:

       In a physical crash test, we using the new original car to conduct the roof crash testing. All wheels are holding with help of a unique device, a car doesn't move at all while conducting the roof crash testing.

A rigid wall keeps at some inclined position & move with constant displacement towards the vehicle roof with the help of a hydraulic system.

       For each crash test, have to use the new vehicle. It will lead to an increase in the cost & time.

Virtual roof Crash test:

       In a Virtual crash test, by using powerful computers we can perform the same roof crash analysis and get the proper results whatever we want. But, we have to set up the model as same as in real crash scenarios & get the results.

       Keep the rigid wall body wherever we want, run the simulation properly & get the results and compare with industry standards.

       We can perform an N number of tests with some changes as per our requirement. Eventually, we save a lot of money & time.

       But, the accuracy of the results is slightly changed then the physical test.

       

PROCEDURE FOR OBTAINING THE OBJECTIVES :

1) Import the given files :

      Open a HyperWorks software, select the "Radioss" as an Explicit solver and then switch to "HyperMesh". Followingly, import the appropriate files through the import solver deck which are NEON BIW & FMVSS impactor components.

     After importing both models, it will be showing in the Hyperworks graphical window as below.

     

2) Transform the impacted as desired location:

      By using rotation & Translation options we can be relocating the impactor from the initial position to the suggested location.

      Make sure, the impactor is located as same as a given reference image.

      Make sure to keep the minimum gap between the impactor and roof.

      After relocating the impactor to the desired location, it has looked as below.

      

3) Create a Contact interface:

      First of all, delete all default predefined contacts under which Type 7 contact interface.

      Create a self contact under the Type 7 contact interface, select the car components for the slave ground node id.

      Similarly, select the car components only for the master surface id.

      

       Then Create another new contact for the car & impactor.

       Select the car components as slave nodes.

       Select the impactor components as master nodes.

      

      Now, give the parameters as per the recommended crash application & then provide 0.2 as the coefficient of friction.

Igap : Determines how the size of the gap is calculated.

An "Igap = 2" is a set variable gap to take into account the true distance between parts.

GAPmin : Minimum gap for activation of the interface.

A "GAPmin = 0.5" is a specify the minimum thickness of the model to avoid numerical issues. Typically, it takes half of the thinnest part.

Inacti : Action to takes if initial penetration exists.

An "Inacti = 6" is to remove initial penetrations where possible. Elsewhere, reduce to less than 30% of the defined gap value and adjust the gap with the "Inacti" parameter.

Istf : Affects how the stiffness of the interface is calculated.

An "Istf = 4" is to set stiffness of interface based on the softer of master and slaves.

Iform : Friction formulation. 

A "Iform = 2" is sliding forces are computed using the stiffness of the interface, which usually results in a bigger time step.

Stmin : Minimum stiffness to use in the interface.

A "Stmin" is a specify a minimum stiffness in the contact to avoid too soft contact

Idel : Behaviour of slave and master segment if an element fails.

An "Idel" is removed slave nodes from contact because of element deletion.

 

Have changed the contact card image as per the requirement as below for both contact interface.

      

4) Create a boundary condition for suspension shock tower:

     As per requirement, we have to create an RBE2 element & constraint the Z translation & rotational degree of freedoms.

     Select the "rigids" sub-panel under the "1D" main menu panel.

     Change into "multiple nodes" as independent nodes & change into "calculate node" as the dependent node.

     

     Select the nodes around the inner hole, click the middle mouse button to create Cluster type RBE2 elements like as below.

     

     Similarly, we have to create the same type of rigid elements in the remaining two regions.

     After creating the cluster RBE2 for three regions, it has looks like as below.

     

5) Create an impactor boundary condition:

    First of all, create a new moving skew as a reference for defining the boundary condition.

    Select the first node as the origin node, select the second node as the axis node & then select the third node as the Plane node. Make sure the z-axis should lie downwards.

    

    After creating the moving skew for the impactor, it will look as below.

       

   Create a new boundary condition in the solver browser & name it as impactor. Select the appropriate master node of the impactor rigid body as below.

   Constraint the all possible degree of freedoms except z translation.

   Make sure to define the created moving skew for this.

    

    Then create another boundary condition & name it as mass. Select the three master nodes as below.

    Constraining all possible degrees of freedom.

    In this case, we constrained all degrees of freedom so don't need to define the skew for this.

    

    Similarly, create another new boundary condition & name it a spring.

    Constraining all possible degrees of freedom.

    In this case, we constrained all degrees of freedom so don't need to define the skew for this.

    

6) Applying the imposed displacement:

     As suggested, a displacement should be applied linear from 0 to 200 ms over the period of time.

     So, create a new curve manually as below.

     

     Create an imposed displacement in the solver browser, select the master node of the impactor rigid body as an entity id.

     Define the appropriate curve, make sure to keep the Z as a direction.

     Make sure to define the moving skew as created previously.

     

7) Creating the control cards:

    By using previous projects engine files to defining the same parameters in this project too.

Title card:

    

SPMD:

    

IOFlag card:

    

Analysis Flags:

    

Default shell:

    

Default solid:

    

8) Set the termination time & time steps:

Termination time:

     In this project, we have to run the model up to 200 milliseconds. Select the "Engine_run" parameter & provide the number of 200 as a termination time.

    

Time steps:

DT_ELTYPE_KEYWORD_IFLAG_SUPPORT:

     In this option, we can create different types of time step control options such as INTER, NODA, BRICK, QUAD, SHELL, TRUSS, BEAM, SPRING & other few.

     After, we have to select the type of time step control such as CST, CST1, CST2, AMS, STOP, DEL.

     In this case, we have created INTER & NODA as a type of time step option

ENG_DT_INTER:

     This method is used for controlling the time step from the element.

     A Type of time step option is "INTER" and the time step control type is "DEL"

     Keep the 0.67 as a scale factor on the time step.

     Keep the 0.0005 ms as a minimum time step.

     If the model time step is reduced below the minimum time step, this algorithm will add some mass to the element so which will lead to maintaining a time step which more than the minimum time step.

    

ENG_DT_NODA:

      This method is used for controlling the time step from the Node.

     A Type of time step option is "NODA" and the time step control type is "CST"

     Keep the 0.67 as a scale factor on the time step.

     Keep the 0.0001 ms as a minimum time step.

     As same, If the model time step is reduced below the minimum time step, this algorithm will add some mass to the node so which will lead to maintaining a time step which more than the minimum time step.

    

 

ANALYSIS OF THE MODEL :

     Select the "Radioss" sub-panel under the "Analysis" panel, save the file in the separate folder, and click the radioss button to solve the problem by solver itself.

     After calculating the model, a solver is generated different files such as the Starter listing file, Engine listing file, Animation files, Time history file and then restart file.

     

        As we know, a time step is calculated in each & every cycle. If the model time step value is less than 0.001, a solver will take a default time step value which 0.001. Because we enabled "CST" which means the solver will use default constant time step if model time step value falls below minimum nodal time step value. To keep the time step constant, it will add some mass on the node for which control the time step.

      A mass error has gone beyond the acceptable range because of quasi-static analysis.

      Initial energy error starts from 0 and ends up with negative errors which means some energy has been dissipated.

       

       As the time step value is decreasing more, a mass added percentage also be increasing more. A difference between model time step & minimum time step is inversely proportional to mass adding a percentage on the node.

 

POST-PROCESSING :

      Post-processing is a process of extracting useful data from the solved model.

Hyperview :

      After completion of solving, switch to "Hyperview" from the "HyperMesh" section.

      Select the appropriate file in an "h3d" format and open the same file in the Hyperview interface.

Contour plot of Displacement:

       A maximum displacement reached up to 256.4 mm after 200 milliseconds ran.

      

Contour plot for Von Mises :

      More stresses are generated on the roof corners & pillars. And then stresses are generated over the sides of the car & cross rails.

      A maximum von mises stress reached up to 0.274 KN/mm^2 after 200 milliseconds ran.

    

Contour plot for Nodal mass:

     A maximum nodal mass is added on the node up to 0.931kg

    

Contour plot for plastic strain:

     

 

Hyperview :

      Switch to the "HyperGraph 2d" interface instead of the "Hyper View" interface for plotting the required data.

      Import the appropriate time history file.

Energies plot:

      Internal energy is gradually increased on the body over a period of time because of quasi-static analysis. Energy starts from 0 at 0 milliseconds & reached up to 650 at the termination time.

      A displacement distance is maintained constant to time, so kinetic energy is also maintained as constant over the period of time.

      There's no hourglass energy has been generated because since we are using QEPH element formulation in the property card.

      The total energy is the sum of kinetic energy & Internal energy.

      

Displacement with respect to time:

      Switch to "Hyperview" & import the appropriate file into that.

      Open the "Build plot" option, keep "displacement" for result type and then select any one node from the impactor. Make sure to select the resultant as magnitude.

      

      After applying it. we get a plot for displacement vs time. By default, a solver has been split the screen into two halves.

      

      Select the left screen, switch to hypergraph & then import the appropriate file.

      Select the "Interface" as a Y Type, select "car vs impactor" as a Y request & then select the "Total resultant force" as Y component.

      Click apply to get a plot like as below.

      

      Select the "MATH" option from the main menu, choose "Cross plot" through the "two curves" option.

      Select the displacement curve for "Curve X" and select the force curve for "Curve Y". Click apply to get the curve for force vs displacement.

      A Total resultant force is a resultant of components of X, Y & Z.

      

Gross mass of the vehicle is 160 kg 

Gravitational force is 9.81 m/sec^2.       

Gross weight of the vehicle = 160*(9.81/1000)

                                        = 1.5696 KN

                                        = 1569 N

FMVSS 216 Target load of 47000 N = 3*1569

                                                   =   4708 N

We got a 4708N from the roof crash simulation which is only 10% of FMVSS 216 target load because the model is reduced due to software limit restrictions. Probably, we get the proper solution which is equal to FMVSS 216 target load of 47000N if we run the roof crash simulation with the original model without any node reductions.

If simulation results go beyond the 47000N, then the vehicle will be failed.

CONCLUSION :

       Successfully ran the Roof crash simulation as per the given requirements on the given BIW components with the rigid impactor.

      Calculated all the outputs requests such as force versus displacement, energies versus time.