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Worldwide Face Shield: Impact Modeling to Improve Product Design

Honeywell Safety Products designed its new Worldwide Face Shield to meet the highest impact test standards specified by ANSI Z87.1-2010.  As such, it had to satisfy a part of the standard that requires the visor to remain fully attached to the crown protector when impacted by a large-mass pointed projectile dropped from 50 inches.  This proved to be a challenging requirement which demanded a full understanding of the detailed interaction between the face shield and the crown protector during impact.

Model of Face Shield & Projectile
Sideview of Face Shield & Projectile

Honeywell knew that images and video of the test could not provide enough detail so they asked CAE Associates to develop computer models that could replicate the behavior of the current face shield design and provide a good prediction of the behavior of future designs.  They also needed models that could provide detailed images of the response at all face shield-to-crown protector connection points, including images on the inside of the crown protector where cameras cannot be placed.

CAE Associates developed a finite element model of the face shield and crown protector using CAD geometry, material properties, and head attachment information supplied by Honeywell. The model was developed with both the ANSYS Workbench and LS-Dyna explicit dynamics software. The stiffness of the head suspension system was modeled with spring connectors and calibrated to static deflection tests. The attachment of the face shield to the crown protector was modeled as a preload phase prior to dropping the projectile.  The model showed separation of the face shield from the crown protector at both tab connectors, which was confirmed by testing. Reviewing the animated results helped Honeywell designers determine not only that additional stiffness was needed but precisely where it was needed.

A new design was proposed which included a reinforcement shelf in the crown protector.  The first model was then updated to include these changes. A dynamic analysis of the impact event predicted that the face shield would not separate from the crown protector. Honeywell also used High Speed Video to confirm CAE simulations, and performed high mass impact testing on handmade prototypes reflecting intended design changes. These combined results provided the confidence needed for Honeywell to move forward with the new design.  Physical impact tests with the new design later verified that the model predictions were correct.

These efforts helped remove a significant uncertainty and helped mitigate a significant design risk where the complex interactions of a system comprised of multiple components and materials could be better understood through concurrent theoretical modeling and physical verification.  It is estimated that the product development time would have taken 3 to 4 times longer had these approaches not been taken, which would have resulted in loss of revenue, not to mention critical time to market.