Child Head Impact simulation with Hood

Aim:

• To simulate the impact of Pedestrian Headform with Hood and compare the results with the impact simulation of the Headorm with a rigidwall
• To calculate the Head Injury Criterion (HIC), Stress & Strain plots for different impact simulations

The units system used here is mm-kg-ms.

The following conditions are maintained for all the cases:

Angle of impact = 45 degrees

Velocity of the Headform = 40 km/h = 11 mm/ms

Case 1 - Simple Headform impact with rigidwall

Case Setup:

The headform used in this case is a sphere.

A rigidwall is created in the XY plane near the simple headform as shown

The material used for headform is as follows

A thickness of 2 mm is given to the shell elements of the Headform.

The velocity of Headform is defined by INITIAL_VELOCITY_GENERATION card in which velocity vector of 11 mm/ms is acting at an angle 45 degrees to X & Z axes.

The X an Z-component of velocity vector is calculated by

`V_x=V*cos(theta)`

`V_x=V*cos(theta)`

Results:

Effective Stress

• Von mises strain is used for this contour
• The max stress of 1.19 GPa is experienced at the point of contact
• The stress is distributed to entire headform after the contact

Effective Strain

• Strain used in this contour is Elastic effective strain
• Max strain of 0.3% is seen at the point of contact
• The headform rebounds after hitting the rigidwall

HIC

• A HIC of 2.4e+6 is obtained for the impact between simple headform and a rigidwall at angle of 45 degrees
• The node used to calculate HIC in this case is taken randomly at the opposite end of the contact
• This value is very much greater than 1700 implying that the impact results in fatal injuries to the head(predicted by EURONCAP)

Energy plot (GLSTAT)

• We can see that the kinetic energy is not absorbed by the rigid wall
• Kinetic energy contributes to about 95% of total energy of the system

Case 2 - Child Headform impact with rigidwall

Case Setup:

LSTC Child Headform is used in this case to impact it with rigidwall

INCLUDE keyword is used to inpuut the Child headform key file to our key file

Velocity card and rigidwall cards are defined similar to that in the above case so that the headform impacts the rigidwall at an angle of 45 degrees and with a velocity of 11 mm/ms.

The X an Z-component of velocity vector is calculated by

`V_x=V*cos(theta)`

`V_x=V*cos(theta)`

Results:

Effective Stress

• Max stress of 0.011 GPa is attained at the point of contact of Headform and rigidwall at time 2.5 ms

Effective Strain

• Max strain of 1.8% is obtained at time 2.5 ms

HIC

• HIC of 1.89e+4 is obtained for the impact of child headform with a rigidwall
• The node use to calculate HIC in this case is the Accelerometer node defined in the headform key file
• This value is very much greater than 1700 implying that the impact results in fatal injuries to the head(predicted by EURONCAP)

Energy plot (GLSTAT)

• Kinetic energy of 210 J is absorbed at the contact to reduce it to 130 J after the heaform rebounds off of the rigidwall
• As a result the internal energy of the system is increased to 80 J

Case 3 - Child Headform impact with Hood

Case Setup:

The LSTC Child headform is impacted with the hood at 45 degree angle of impact.

INCLUDE_TRANSFORM and DEFINE_TRANSFORM are used to tranform headform close to the centre of hood as shown below

The material of hood is defined as follows

A thickness of 2 mm is given to the shell section of hood.

The boundary nodes of hood are constrained in all DOF using BOUNDARY_SPC_SET

Since the hood is at an angle of 10 degrees to the X-axis and the angle of impact should be 45 degrees, the angle between velocity vector of headform and X-axis will be 35 degrees.

The X an Z-component of velocity vector is calculated by

`V_x=V*cos(theta)`

`V_x=V*cos(theta)`

A CONTACT is also defined for the contact between hood and the skin of headform as shown below:

Results:

Effective Stress

• Max stress of 0.135 GPa is experienced by the hood at time 11.1 ms

Effective Strain

• Max strain on the headform is 0.63% at time 10.8 ms
• The strain on the hood is in th order of e-9

HIC

• A HIC of 546 is obtained for the impact of child headform with hood
• This value is less than 650 implying that the impact results in only mild injuries to the head(predicted by EURONCAP)

Energy plot (GLSTAT)

• The kinetic energy of the headform is absorbed by the hood to decrease it from 210 J to 75 J
• Internal energy of the system is higher in this case than the kinetic energy at 105 J
• A part of kinetic energy is also converted to sliding energy of 25 J
• Hour glass energy is very minimal

Conclusions:

• HIC of 546 for the impact of child headform with hood indicates that the hood material used is good for vulnerable pedestrian safety
• The other two cases includes impact with a rigidwall which ends in fatal injuries
• The hood absorb the kinetic energy of the headform and deforms to minimize the impact of the contact
• The stress attained for the rigidwall case is lower and concentrated t the impact on the headform, while it is distributed on the hood for the hood case
• The strain for the rigidwall case is 1.8% on the headform whereas it is only 0.6% for the hood case as the hood also strians on impact in this case