If you’re planning to use a living hinge, you should consider its life cycle. Living hinges serve the same purpose as traditional hinges: they allow one object to rotate away from another object. While they are both mechanical bearings, however, only living hinges are flexible. What determines the cycle life a living hinge exactly?
Material
The material from which a living hinge is made will affect its cycle life. Unlike traditional hinges, living hinges aren’t made of metal or hard plastic. Instead, they are made of a soft and flexible material.
Polypropylene is a popular choice because it combines flexibility with excellent resistance to bending. Living hinges made of polypropylene can flex repeatedly many times without succumbing to permanent deformation, resulting in a longer life cycle than those made of harder and less flexible materials.
Thickness
Another factor that affects the cycle life of a living hinge is thickness. Some living hinges are thicker than others. Most feature a thinner “core” surrounded by strips of thicker material. If the core section is too thick, it will require more force to bend during use. And the more force to which a living hinge is exposed, the greater the stress.
Heat and Cold Exposure
Exposure to heat and cold can affect a living hinge’s cycle life. Many soft materials change their behavior in extreme temperatures. In cold environments, they can become stiff. In hot environments, they can become particularly soft.
Living hinges can still withstand heat and cold, especially if they are made of high-quality materials. Nonetheless, repeated exposure to extreme temperatures may affect their cycle life.
Load
Living hinges are subject to loads. Light loads typically have minimal impact on its cycle life. Heavy loads, on the other hand, can shorten a living hinge’s cycle life.
And it’s not just the weight of the load that matters; alignment is equally important. The connected objects should move as intended while placing little or no sideways force on the living hinge. A misaligned load or opening force will expose the living hinge to greater stress, which can shorten its cycle life.
Sunlight
Sunlight can affect a living hinge’s cycle life. Most living hinges are used indoors where they are only subjected to artificial light. Some applications, though, involve outdoor use. When used outdoors, living hinges are exposed to UV-containing sunlight. Over time, exposure to these harsh UV rays can cause living hinges to soften or become brittle.