Week-7 Head Impact
Objective:- To perform head impact simulation fpr the 3 different cases and calculate the Head Impact Criterion (HIC) values for the each case
Case-1 : Simple head model impacting against rigid wall.
Case-2 : Child headform dummy model impacting against rigid.
Case-3 : Child headform dummy model impacting against Hood.
Procedure :-
Case 1:- Simple head model impacting against rigid wall.
- The given head model imported into ls-dyna workspace using file- open- lsdyna keyword file
- Create section card, with an ELFORM 2 and 2.5mm thick.
- Create Piecewise_Linear_Plasticity material card
- Then assign MAT and Section card to the PART card by id
- Create Rigid_wall using create entity- rigid wall, Planner wall is created by defining vector with one point and normal. the rigid wall is then offsetted to a distance of 10mm
- The nodes of model are selected with an initial velocity of 11.11mm/ms (40kmph) in -Z direction.
- Create automatic surface to surface contact
- Run the simulation for 20ms, go to control-termination
- Generate animations for every 0.5ms, go to database-binory_d3plot
- Generate outputs for GLSTAT, MATSUM,NODOUT and RWFORCE with DT 0.5, go to Database- ASCII card.
- To find HIC value, we need NODOUT
- Without Node_history card NODOUT will not generate any results, here we will find HIC value for the node#68789
- The EXTENT_BINARY card useed with STRFLG =1, in order to Write plastic strain data to d3plot.
- Run the simulation, check for normal termination.
Case-2 : Child headform dummy model impacting against rigid.
- In this simulation open ls-prepost, go to model - keyword manager - Define_transformation
- Rotate about Y-axis by 45degrees
- Include the Child headform model and assign this transformation, go to include_Transform
- Mention TRANID
- Save the file as Main.k
- close the file and open in new ls-prepost, now child head form will rotate about y-axis by 45degrees
- There are 4 parts in pedestrain child head model
- Create rigid wall 10mm away from the sphere with normal force opposite to the direction of sphere
- Create a automatic surface to surface contact between Skull and Rigid wall
- The initial velocity of head is 11.11mm/ms (40kmph), head is acting on plane at 45degrees so give initial velocity in Z & X Directions
- Create Database, control cards as same as case1
- Run the simulation, check for normal termination.
Case-3 : Child headform dummy model impacting against Hood.
- Open ls-prepost, go to model - keyword manager - Define_transformation
- Rotate about Y-axis by 45degrees
- Include the Child headform model and assign this transformation, go to include_Transform
- Mention TRANID
- Save the file as Main.k
- close the file and open in new ls-prepost, now child head form will rotate about y-axis by 45degrees
- In this case, replace rigid wall with hood
- go to, keyword manager - include-include
- Save the file as Main.k, close the file and open in new ls-prepost
- Create Piecewise_Linear_Plasticity material card for the hood.
- Create section card, with an ELFORM 2 and 2mm thick.
- Then assign MAT and Section card to the PART(hood) card by id
- Automatic surface to surface contact created between skin and hood, skin as slave and hood as master
- A spc (single point constrain) is applied to the outer edges of hood in all 6 directions, in order to keep hood motion fixed.
- Give initial velocity to the pedestrain child head in X & Z direrctions as same as case2
- Create control,database cards as same as previous cases
- Run the simulation,check for normal termination
RESULTS
case1
Von mises stress
Effective Plastic Strain
- Energy plots
HIC 36 value for node #68789
- From the results, von mises stress is 3.858e-1mpa and effective strain is 5.167e-2 at the time of impact and the HIC value is 4.235e+7
case 2
Von mises stress
Effective Plastic Strain
Energy plots
HIC 36 value for node #25679
- From the results, von mises stress is 9.712e-3mpa and effective strain is 6.476e-3 at the time of impact and the HIC value is 1.677e+4
case 3
Von mises stress
Effective Plastic Strain
Energy plots
HIC 36 value for node #25679
- From the results, von mises stress is 3.657e-1mpa and effective strain is 1.017e-2 at the time of impact and the HIC value is 1026
CONCLUSION
-
Model has been simulated for the 3 different cases and calculate the Head Impact Criterion (HIC) values for the each case
Case-1 : Simple head model impacting against rigid wall.
Case-2 : Child headform dummy model impacting against rigid.
Case-3 : Child headform dummy model impacting against Hood.
-
The energy plot for the case1 &case2 shows a sudden drop of kinetic energy and increase of internal energy at the instant of the impact with the rigid wall, mainly beacuse the rigid wall is non deformable
- The energy plot for case3 shows a gradual change of energy, beacuse the hood is deformable
- HIC value for case 1 is extreamly high beacause impact occurers against non deformable rigid wall
- for case2 HIC value slightly reduced compared to case1
- HIC value for case 3 is very low compared to case1&2, beacause impact occurers against hood which is deformable
- The value of HIC depends on deformability of material, if deformability of material increases HIC value will be reduced
- To reduce the impact effect on pedestrain head, increase the deformability of hood material.