Independent Research Project

Aim:

To perform a helmet visor integrity test and asses whether the provided specimen is fit for Snell rating.

Theory:

• The test is carried out by a shooting a high velocity projectile(polycarbonate pellet) at the visor(polycarbonate) and assessing the damage to the visor.
• Visor integrity test beds can shoot pellets at speeds between 45-200m/s.
• Snell rating is granted to helmets typically used for racing purposes and indicates more stringent conditions under which the specimen has to maintain it’s integrity as compared to DoT or ECE ratings.

For the purpose of this simulation the pellet velocity is estimated at 138.889m/s or 500kmph.

Procedure:

For the purpose of this simulation the visor design model has been created from scratch and is imported into spaceclaim.

The model consists of 2 major parts: The Visor and the pellet.

The pellet has a diameter of 2.2mm and is positioned to make contact with the visor perpendicular to it’s centerline.

Upon inspection of the model in spaceclaim and verification of it’s integrity with respect to the initial design we can set up the experiment.

We begin by assigning the material to the parts, the visor made of polycarbonate amd the pellet made of structural steel.

The simulation is an explicit dynamics simulation and on opening the mechanical module our first step is to rename and assign the materials to the parts.

We then delete all manual contacts and setup a new coordinate system with the origin at the center of the spherical pellet.

Meshing: We provide 2 body sizing features to the mesh where one focuses on the visor and the other on the pellet.

We provide a velocity to the pellet of 138.889/s and fixed supports to the visor at the mounting surfaces.

Explicit Dynamics simulations require only the end time to be specified which is 0.001s

The visor is provided with an element size of 2.1mm and the pellet with an element size of 0.1mm

Results: We request the module for outputs of Directional Deformation on the visor, stress developed on the visor, strain generated in the visor and the force reaction.

Directional Deformation

Equivalent Stress

Equivalent Elastic Strain

Sr No.	Directional Deformation (mm)	Equivalent Stress (Pa)	Equivalent elastic strain (mm/mm)
1	15.001	136.01	0.0783

Conclusion:

The proposed visor does not clear the safety requirements to be rated with a Snell rating.

Project Link : https://drive.google.com/file/d/1jv5THaE4ce-uUHNYEOEz38ofaTpaHTHg/view?usp=share_link