Week-7 Head Impact

OBJECTIVE : 

CASE 1 :

1. To simulate the simple head impact with the rigid wall creating the simple elastic material model .

CASE 2 :

2. To simulate the head impact of the given headform  with the rigid wall at an angle of 35-75 degrees.

3. To plot the stress / strain and the acceleration for the same.

CASE 3 :

3. To simulate the head impact of the given headform with the given meshed hood at an angle of 35-75 degrees.

4.  To plot the stress/strain and the acceleration for the same.

5.  To use the aluminium material properties for the hood. 

6. To use thekeyword *INCLUDE, *INCLUDE_TRANSFORM, *DEFINE_TRANSFORMATION for organizing a multi-include model in CASES 2 & 3.

 

DELIVERABLES :

1. Comparison of the HIC values between different cases .

2. Plotting Stress-Strain in case of the Head Impact with the Rigid Wall.

3. Plotting Stress-Strain in case of the Headform Impact with the Meshed Hood.

 

CASE SET UP :

CASE 1: IMPACT OF THE SIMPLE HEAD ON TO THE RIGID WALL

1. Creating the Rigid Wall 

      The Rigid Wall is created through the create entity tool in the tool bar. The Planar form of the rigid wall is created through the 1n+L option and selecting the node on the simple head form. The normal to the headform is created in the direction opposite to the velocity of the simple head form.

Fig 1 Creating the Rigid wall

2. Applying the Intial Velocity to the Simple Headform

     The Intial Velocity card is created in the keyword manager and the intial velocity is applied by selecting all the nodes of the simple head form and giving the velocity in the direction opposite to the normal to the rigid wall. An intial velocity of 15.64 mm/msec(35 Kmph) is entered for the VZ . All the nodes of the Simple head are selected and created as the Node set for the NSID in the Intial Velocity card.

Fig 2 Applying the Intial Velocity to the Simple Head

3. Creating the Material Card for the Simple Head 

         The Material card is created in the Keyword manager for the simple head form. The Material card chosen for the Simple Head form is the 001_Elastic Card. All the properties such as the density, Young's Modulus & Poisson's ratio.

Fig 3 Creating the Elastic material card for the Simple Head form

4. Creating the Section for the Simple Headform

          The Shell Section card for the simple head form is created in the keyword manager in which the tickness of the shell elements is entered. 

Fig 4 Creating the Section card

5. Assigning the Section ID and the Material ID to the respective Parts 

     The Created section ID and the Material ID are assigned to the respective Parts and the Part ID cards. 

 

Fig 5 Assigning the Section and the material to the Simple Head form

 

6. Creating Automatic_Single_Surface Contact card for Self contact in case of the Simple Head form

      The Self contact for the Simple Head form is created by creating the Automatic_Single_Surface card. The Master and the slave nodes are the same .i.e, the simple head form.

Fig 6 Creating the Self contact for the Simple head form

 7. Creating the database card for the Output

       i. ASCII Card

         The ASCII card with the options for the GLSTAT, MATSUM & NODOUT are checked with timestep at which these outputs must be written is entered. 

       

 Fig 7 Creating the ASCII output card in the database

         ii. Binary D3Plot

                 The binary D3plot card is created for the animation output with the timestep for which the output should be generated.

Fig 8 Creating the Binary d3 plot card in the database

         iii. Extent_Binary card for Strain

                  The Strain flag in the Binary extent has to be entered as 1 for getting the strain outputs.

 Fig 9 Entering the Strain flag for Strain Output

8. Creating the Control termination card for assigning the run time for the simulation

          The  time for which the simulation has to be peformed is assigned by creating the control termination card and entering the value for the Endtime.

 

Fig 10 Creating the Control termination card for assigning the run time for the simulation

 CASE 2 : IMPACT OF THE HEADFORM ON TO THE RIGID WALL USING THE KEYWORDS *INCLUDE_TRANSFORMATION & *DEFINE_TRANSFORMATION

1. Importing the Headform and transforming the Head form using the Keyword *INCLUDE_TRANSFORMATION & *DEFINE_TRANSFORMATION

     i. Defining the transformation for the Head form  

        The Head form is rotated by an angle of 60 deg along the Y- axis by creating the Tranformation card   under the keyword *DEFINE and the transformation is defined as TRANSID. 

Fig 11 Defining the Transformation for the Head form

          ii . Using the Keyword *INCLUDE_TRANSFORM card for Including the Head form file 

                    The path for the Head form file is given in the Include_Transform card and also the Transformation ID created for the rotation of the Head form is included/entered in the card.

Fig 12 Including the Head form file with transformation

2. Saving and closing the Main.k file

          The existing file is saved as the Main.k file after including the Head form file and then closed so that when the Main.K file is opened again the Head form can appear as the model.

3. Creating the Rigid Wall

       Similar to the CASE-1, the Rigid wall is created with the normal pointing in the direction opposite to the velocity of the Head Form. 

Fig 13 Creating the rigid wall for the Headform

4. Applying the Initial Velocity to the headform

           The Initial Velocity is applied to the entire Head form through the local Coordinate already defined in the *Included file for the Head form . All the nodes of the Head form are incorporated in the Box id.

Fig 14 Applying the Initial velocity to the Headform

 5. Creating the Database card for the Out put

        Similar to CASE-1, the database card for the ASCII output and the Binary d3plot for the Binary Output of the simulation is created. The Option for the NODOUT is also checked as the node in the accelerometer inside the Headform is chosen for the time history in the *INCLUDED file of the Headform. 

Fig 15 Creating the database for the Output

    Also, the History_Solid card is created for getting the Eleout option for the ASCII PLOT. The Element for which the stress and strain plots are to be generated, that element is selected.

Fig 16 Creating the History_Solid card

             The ELEOUT option in the ASCII Card has to be checked for getting the effective stress and the effective strain for the element . 

6. Creating the control termination card for the simulation run time

            Similar to CASE-1, the control termination card with the ENDTIME is created for deciding the run time for the simulation.

 7. Existing Keywords in the inclued in the headform file.      

*MATERIAL, * CONTACT, * SECTION, *PART, *HOURGLASS, *DEFINE_CO-ORDINATE & *SET_NODES keywoords already exist in the Included keyword files of the Head form.

 

CASE-3 : IMPACT OF THE HEAD FORM WITH THE MESHED HOOD USING THE *INCLUDE_TRANSFORMATION, *INCLUDE & *DEFINE_TRANSFORMATION 

     All the steps mentioned in CASE 2 are same except the  step 3 i.e the creation of the rigid wall is not required in CASE 3 . In addition to the above steps following steps are to be added for the case set up:

Step 1 : Creating the LINEAR_PIECEWISE_PLASTICITY material card for the meshed hood .

          In the meshed hood file which is to be included later in MAIN file, the LINEAR_PIECEWISE_PLASTICITY material card is created with all the properties of the Aluminium for the meshed hood.

 

Fig 17 Creating the Lnear_Piecewise_Plastic material for the Hood

Step 2 : Creating the section for Hood Mesh

                The section card is created in the meshed Hood file for the mesh of the hood. The SHELL card is created under the keyword *SECTION and the thickness for the Hood mesh is assigned .

Fig 18 Creating the Section for the Shell Mesh of the hood

Step 3 : Assigning the MatID and the SectionID to the PARTID

             The newly created material card and the section card assigned to the HOOD Part ID in the PART card.

Fig 19 Assigning the Material and the section ID's to the HOOD part

Step 4 : Including the meshed hood file in the Main file

              The meshed hood is included in the main file using the card *Include . The path of the Meshed Hood file is entered in the *INCLUDE card.

Fig 20 Including the Meshed Hood file in the Main file

Step 5 : Creating the boundary condition for the Hood

             The Hood is Constrained through Single Point Constraint Set (SPC SET) card using the all of the nodes at the periphery/Edge  of the Hood. The Nodeset is constrained in all the degrees of freedom.

Fig 21 Creating the SPC Boundary condition for the Hood

Step 6 : Creating the contact between the Hood and the skin of the Headform

                      An AUTOMATIC_SURFACE _TO SURFACE_CONTACT card is created in which the Skin part is assigned as the slave where as the Hood part is assigned as the Master for the contact between the two.

Fig 22 Creating the contact between the Hood and the Skin of the Headform

  

EXECUTION :

  The Main files of all the three cases are run in the LS-RUN for obtaining the simulation results.

 

RESULTS :

1. Comparison of the HIC values between CASE-2 & CASE-3 

     i. Acceleration Plot and the HIC value in case of the Impact of the Head form on the Rigid wall

 

Fig 23 Acceleration Plot with HIC value for the Impact of the Head form on to the Rigid Wall

ii.Accleration Plot and HIC Value in case of the Impact of the Headform on to the Hood

 

 Fig 24 Acceleration Plot with HIC value for the Impact of the Headform on the Meshed Hood

INFERENCE :

   As compared to the CASE-2, the HIC value in CASE-3 is smaller since the material in the Hood is able to absorb more energy as compared to the rigid wall as a result of being a less stiffer material compared to the rigid wall. The Plastic deformation of the Hood material causes this absorption of the energy and hence the accleration(Maximum Value = 175 mm/`ms^2`) is less in the headform as compared to the acceleration( 1150 mm/`ms^2`)of the headform when it impacts on to the Rigid wall.

 2. Comparison of the Stress Strain plots between the Impact of the headform on the Rigid wall and the Impact of the headform on the Meshed Hood

     i. Stress Strain Plot for the Impact of the headform on the Rigidwall

 Fig 25 Stress Vs Strain Plot for the Impact of the Head on the Rigid wall

      ii. Stress Strain Plot for the Impact of the headform on the Meshed Hood

Fig 26 Stress Vs Strain Plot for the Impact of the Head on the Meshed Hood

INFERENCE:

 1. The Maximum Stress value in case of the Impact of the Headform on the rigid wall is  2.35E-04kg/`(ms)^2`mm as compared to the Impact of the of the Headform on the Meshed Hood which is 2.14E-04 kg/`(ms)^2mm`.

 2. The Stress value increases gradually and then becomes constant after reaching the maximum value in case of the head Impact on the rigid wall since the rigid wall is not able to absorb any energy from the incoming headform.

 3. The Stress value varies abruptly with strain in case of the head Impact on the Meshed Hood since the hood is readily able to absorb the kinetic energy from the incoming head form and undergo deformation.

 4. The  Headform undergoes more deformation in case of it's impact with the rigid wall as it is unble to abe more kinetic energy from the headform. The Maximum strain in this case is  2.35e-4 .

 5. The Headform Undergoes less deformation in case of it's impact with the meshed hood . The maximum strain in this case is 1.48E-4.

 6. It can be seen from both the plots that the head form is lot safer in case of it's impact with the Meshed hood since the headform experience stress which is of varying nature and is comparatively lot lesser. Also the Headform undergoes less deformation.

 

 NOTE: 

    The simulations for all the three cases i.e, i) Impact of the simple head on the rigid wall ii) Impact of the headform on the rigid wall & iii) Impact of the headform on the meshed hood  have been attached as Powerpoint file with the report.

 

 CONCLUSION : 

1. The simulation was run for all the three cases sucessfully by making use of the keywords such as *INCLUDE_TRANSFORM, *INCLUDE & DEFINE_TRANSFORMATIONS for organizing the files.

2. The HIC values for bpth the cases i.e, Impact of the Head on the Rigid wall and the Impact of the Head on the Hood were determined and compared successfully.

3. The Stress Strain Plots for the Impact of the head on the rigid wall and the Impact of the Head on the Hood were plotted succesfully.