Week-7 Head Impact
Objective- In this project, a children's headform model impacts with a rigid wall and also with a car Hood bonnet. the Stress / Strain plots and acceleration plot for both the simulation should be compared. From the simulation, the head impact coefficient must be calculated manually and with the help of LS-PrePost.
Simulation 1- Impact simulation of a simple head impact with the Rigid wall.
Methodology-
1. *Section_Shell is been selected as with thickness 20mm (with ElFORM2) with material as Elastic material given to the ball.
2. A Planar Rigid wall perpendicular to X-axis is created at a distance 10 mm from the ball
3. A node-set is being created from the ball and the initial velocity of 40km/hr is provided that is -11.11mm/ms along the negative X-axis toward the rigid wall.
4. During Impact, so as to avoid self contact, *Automatic_Single_surface has been used.
5. *Control_Termination was used with 20ms
6. In ASCII outputs, GLSTAT, MATSUM, SLEOUT, NODOUT, RCFORCE has been selected with dt 0.5ms.
7. A Node has been selected as an accelerometer in the ball to study the forces during Impact.
POST PROCESSING-
8. Stress, strain, energy plots, HIC etc will be shown below with discussions. Also, the Simulation video is attached.
From the above videos and Stress/ strain plots we can just say,it was a sample simulation in order to be on the process for further simulation advancements in this projects.
As in my Elastic material , it was a stiffer material with E=207 Gpa, the strain deformation was very less, the stress distribution was most in the x-direction because the velocity and the impact was in this direction.
From the MATSUM and GLSTAT plots, we can see that during the initial impact that happens when the ball hits the wall, the KINETIC and INTERNAL ENERGY goes through a change but after then it remains constant which during the rebound motion. Obviously the ball stopping after rebound scenario is not considered in this scenario. Also the HOURGLASS ENERGY is less than 5% of the TOTAL ENERGY, which means that this simple simulation is stable.
HIC (d) was plotted along with resultant acceleration, from the output results of the history node selected from *NODOUT. We can see it has a very high HIC , which is normal as it was just a simple elastic ball hitting a rigid wall at a speed of 40km/hr.
Simulation 2- Impact simulation of a headfoam with a Rigid wall.
In this case, a child-head model is been provided , so we would be replacing it with the sperical ball used in the above mentioned simulation. Now , we don't want the original mode to change in the .K file provided, but I want to incline the headmodel at 45 degree to the rigid wall because generally the angle of head hitting the car hood in at an angle of (35-75 degrees.) So, in order to change the angle of the model, I used DEFINE_TRANSFORMATION, the details of which are mentioned below
Now, As mentioned in the above paragraph, I don't want to save these changes in the original model , so I use *INCLUDE_TRANSFORM, in order to call the rotated model in a .dyn file and perform the simulation their with the rigid wall.
The headfoam section was selected as solid section
The other keywords such as *Automatic_Single_surface , Control_Termination and ASCII outputs, GLSTAT, MATSUM, SLEOUT, NODOUT, RCFORCE was kept same as used in Simulation 1 shown above.
POST PROCESSING-
Stress, strain, energy plots, HIC etc will be shown below with discussions. Also, the Simulation video is attached
During the Point of Impact , in the initial stages of simulation the maximum stress and strain value is achieved, after which it remains constant during the rest of the part of the simulation.
From the energy plot, we could see that during the impact the internal energy and Kineteic energy undergoes change but then remains contact. The hourglass energy remains lower than 5% of total energy. Thus, showing that the simulation is stable.
From the above plot, we can see the spike in resultant acceleration at the time of impact, the HIC(d) value is also found , its is considerably high as the Rigid was is more stiff then the skull , but still the HIC is lower than the spherical ball simulation as the headfoam model is used, with realistic properties.
Simulation 3- Impact simulation of a headfoam with a car hood.
In this simulation , the rigid wall of the previous two simulations are replaced by the car hood model,
Define Transformation and Include transform are used as shown in previous simulation.
Section Shell and MAT24 with properties of aluminium are used and defined in the car hood.
Automatic surface to surface contact has been used with the CAR HOOD as the MASTER and the HEADFOAM as the SLAVE
Rest of the definition of the simulation are same as SIMULATION 2 as mentioned above.
Post Processing-
Stress, strain, energy plots, HIC etc will be shown below with discussions. Also, the Simulation video is attached.
Fig1- Model view before the impact
Fig2- Effective strain contour during impact
Fig 3-Child headfoam hits car hood (Effective stress)
From the above plots we can say that During the Point of Impact , in the initial stages of simulation the maximum stress and strain value is achieved, after which it remains constant during the rest of the part of the simulation.
Fig 4- Energy plots
From the energy plot, we could see that during the impact point the stress increases and thus the internal energy gradually increases and Kineteic energy gradually decreases, but then remains constant throught the simulation after the point of impact and thus remains stable. change but then remains constant.
Fig 5- Resultant acceleration and HIC
From the above plot, we can see the spike in resultant acceleration at the time of impact, the HIC(d) value is also found , it looks more acceptable as the Car Hood(aluminium and mat24) is been used in comparision to the rigid wall used in previous two simulations.
Conclusion -
The HIC value is very large for SIMULATION 1 and SIMULATION 2, and considerably realistic for SIMULATION 3, This is because of the use of more realistic material properties and models in SIMULATION 3.
The Aluminium hood in SIMULATION 3 absorbs stress in comparison to the RIGID WALL in SIMULATION 2 , due to which HIC is higher when RIGID wall is used.
WIth this Project, I learned how by changing the various factors in the models , such as impact velocity, car hood material, impact angles, the simulation results can be achieved for future predictions, and also how to calculate HIC, and also to incorporate and manage different files together.