Week-7 Head Impact

Aim:

To perform head Impact simulation and calculate HIC values for 3 cases

• Simple Head with rigid wall
• Headform rotated with rigid wall
• Headform rotated with meshed Hood

Case setup:

There are 3 files provided  in the model - Simple head, headform and meshed Hood. These files should not be edited and should be included in our model using 

keyword -> Include (or)

keyword -> Include -> Transform (To invoke transformation)

keyword -> Define -> Transformation (to rotate the headform by 45 degrees)

We are following mm, ms, kg units in this assignment

Section

The simple head and Hood are shell components. So a shell section is created  with 2.5mm thickness and ELFORM 2 for simple head and shell thickness of 1.5mm thickness and ELFORM 16 for Hood. Headform already has section properties assigned so no need to create one. 

Material

A steel material is assigneed for the simple head. Headform already has material properties assigned so no need to create one. For the meshed hood, Aluminium properties are provided.

Assign section and mat properties to part

The material and section cards created are now assigned to the respective Part

create rigid wall

A rigid wall is created underneath the simple head using

Create entity -> Rigidwall -> Rigidwall -> Create (Using planar and 1N+L define vector with one point and normal)

Now open

Keyword -> Rigidwall -> Planar 

and input 0 in Nodeset ID NSID which makes all nodes in the model as slave nodes

contacts

Automatic Single surface is created to avoid penetrations during imact. Slave set ID value is given as 0 to include all surfaces in the salve set 

Control

Termination time is given as 20ms

Initial velocity

For the Simple head case, Intitial velocity of 40kmph=11.11m/s is imparted to the model in the negative z direction using 

Initial -> velocity

For the Headform with meshed hood, velocity of 40kmph of the headform is resolved into 2 components along negative z (-8.510m/s) and negative x direction (-7.142m/s) 

Boundary

For the meshed hood model, a nodeset is created with all the outer edge nodes of the hood. An SPC set is created and all translational DOF are constrained 

Database

ASCII_option: GLSTAT, NODOUT, RWFORC

Binary D3 Plot: DT of 0.5ms is provided

History node: A node in the shell is selected to get information about the node in the NODOUT file

Extent Binary: STRFLG is changed to 011 to get strain data

Post Processessing:

Stress Plots

In the forst case, as the wall is rigid and cant absorb energy from the impacting headform, the headform experience a large amount of stress compared to the fleible hood. As the hood absorbs the crash energy from the Impacting headform, stores it as potential energy while getting crushed and slows down the headform. Henceforth the headform experiences less stress with the hood.

Strain plots

As the hood is flexible and deformable, it absorbs energy from the impacting headform. Hence, the strain value is lesser in the hood model compared to the rigidwall model.

Acceleration plot with HIC

As it can be seen, HIC value is very less in the hood model compared to the rigid wall model which indicates there is less probability of severe damage to head with the hood model.

Conclusion:

All the results shows flexible hood is safer to pedestrian head than the rigidwall.

Hence the hood should be designed in such a way to absorb as much energy as possible from the pedestrian head to minimize the risk of severe damage. Below the hood lies the rigid engine. So the hood should not designed with so much compliance as well.