Plastic products and Impact Resistance
When my wife dropped her old cell phone from the balcony to the concrete-paved yard, the phone took a few bounces and distributed itself then in several pieces around it. That was it, I thought. But as we collected the pieces, snapped them together and turned the power on, the phone worked perfectly again despite the few scratches it had gained. Excellent job on mechanical design, I had to conclude (the phone was, by the way, an ancient Nokia).
Impact resistance (or impact strength) describes a material’s or a product’s ability to absorb shock or impact energy without breaking.
Something that feels strong and stiff might be surprisingly easy to break with a bump to the right spot. Resistance against impacts is one of the key requirements in plastic product design. It is clear that a helmet or a ski boot should have high impact resistance, but almost every plastic product is subjected to impacts at some point of its service life and the consequences are often irreversible. All products should preferably be impact resistant to a degree for more reasons than one. They may fall down from store shelf before they ever meet the customer, to begin with.
Impact resistance is in fact one of the key strengths of plastics. It is why they are used in e.g. helmets, riot shields and sports gear. They replace glass in many applications, and in some cases they can be more durable than metals; if you kick a metal bucket, for example, you easily make a dent in it. A well designed plastic bucket would take the impact with no problem. Impact resistance is not, however, an inherent material property to all plastics grades. Some grades are rather poor in withstanding impact, as we all may have noticed with cheap plastic toys or other similar products.
Selecting the right material is in main role when designing impact resistant products but the mechanical design/geometry makes a big difference as well. Tips on material selection and mechanics can read by pressing the links below.