Crash Worthiness of Rail Elements Using Hypermesh and Radioss

1.Objectives:

     To compare the result of the base simulation and improve shell element properties.

2.Explanation :

  2.1 Simulation 1 :

  • First, 0000.rad file is imported to the Hypermesh.
  • To get a minimum of 25 animation files, frequency is set as 2.2 for 55-time steps.
  • The analysis is done using Radioss and thread at -nt 4 .
  • Thus after running the simulation we can find in 0001.out file that energy errors are exceeding above -5% which is not acceptable.

   2.1.1 GRAPH:

  • The resultant graphs are shown below.

                                                                                         Simulation 1

 

  • Kinetic Energy - The kinetic energy is high at the start regarding the energy of mass in motion with respect to the time and it's gradually decreasing due to the elements collide each other and stops the possibility of the element to move further.
  • Hour Glass Energy - since the properties are not assigned according, the graph shows the clear result that hourglass energy is not stabilized and causes improper deflection of the elements.
  • Contact Energy - There is no contact or friction between the surfaces, so the contact energy is not exceeded in this simulation and it can be seen that the contact energy curve is at zero for the entire simulation.
  • Total Energy -  Total energy is a combination of initial total energy and external work. The total energy is high at the start and reducing gradually due to the reduction of (k.E+I.E + HG.E) and also there is no external load acting upon.

    2.1.2  ERRORS :

        NEGATIVE ERRORS are caused when energy is dissipated from the system. There could be a lot of reasons for the same, it could be because of damping or hourglass, etc. The damping, hourglass, and shear energy are caused due to the properties assigned for the component. It is acceptable that energy errors must be less than negative of 5%.

     

                 

                                                  Energy Errors for Simulation 1

  2.1.3:  MASS ERRORS are caused due to the imposing of high time steps.

 

2.2  Simulation 2:

  • Now the same rad file is imported and frequency is set as 2.2 for 55-time steps.

  2.2.1 PROPERTIES:

  • Then the properties are assigned for material components.

               

     Ishell =24 With one-point integration formulation, if the non-constant part follows exactly the
state of constant part for the case of elastoplastic calculation, the plasticity will be
under-estimated due to the fact that the constant equivalent stress is often the
smallest one in the element and element will be stiffer. Therefore, QEPH, defining
a yield criterion for the non-constant part seems to be a good idea to overcome
this drawback. 

     Ismstr = 2, full geometric nonlinearities. It is applicable for the material that undergoes drastic deformation. During the deformation, the time function remains constant whereas the Gaussian quadrature point change which results in the change in stress, strain, deflection, etc.

     Ish3n =2, This is for the three noded elements. since the component has meshed with four noded, there is no use of assigning properties.

     N=5 is the number of integration points set through the thickness which helps in increasing the accuracy for calculating the bending moment.

     Ithick =1, The thickness changes is taken into the account. Since material after reaching the yield point, the material loses elasticity and gains elasticity. after the elasticity region the thickness reduces due to necking, so considering the thickness at the necking region will result in the better output.

     Iplas =1, Iterative plasticity for good accuracy, since the Von Mises is bigger than the yield stress, the strain through-thickness integration point is been updated in an iterative way, also the thickness that has been changed is updated and taken into the consideration. 

   2.2.2  Running the Simulation:

  • After the properties have been assigned, then run the simulation using the same method 
  • Analysis -- Radioss--Option(-nt 4)--Run the simulation.
  • Thus it creates the same number of the animation file(25).
  • Now change from Hypermesh to Hyperview 
  • Contour -- Result type-- von mises stress or any other stress can be selected.
  • By selecting it, different loads acting upon the material component is visible and also the how much deflection has been carried out is found and where exactly can also be recognized.
  • After the simulation, the errors are noted 

             

  • Thus it produces errors is of -0% which mean the simulation is accurate due to the elimination of hourglass. 

    2.2.3 Graphs :

  • The graph shows the exact results after assigning the properties

      

  • Kinetic Energy - The kinetic energy descends sharply for the process of impact. The elements keep on moving till the impact ends. The maximum deflection of elements is 350mm and the kinetic energy ends at the last time cycle.
  • Hour Glass Energy - since the properties are assigned, the graph shows there is no hourglass energy due to the assigning of Ishell = 24. Thus reducing the hourglass energy and making the simulation stabilized.
  • Contact Energy - There is no contact or friction between the surfaces, so the contact energy is not exceeded in this simulation and it can be seen that the contact energy curve is at zero for the entire simulation.
  • Total Energy - The total energy remained constant throughout the process of impact.

 

3.Conclusion:

  • Thus the base simulation is executed.
  • And found out simulation 2 is better than simulation 1 comparing the results of errors and graph plotted.
  • The simulation 2 is better because of the properties assigned.

 

 

 

https://drive.google.com/open?id=1kx6l_MZpksN-m6qHfFlN0RYh7vR-WPjs


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