2. “Polymeric protective foams (e.g. protective foam layers) are widely used for impact force attenuation in a variety of safety-related applications. These include sport applications, military combat applications, automotive applications, footwear applications, etc. In general, a protective foam layer is placed adjacent or against a part of a person's body to protect a body part (e.g. a head) during an impact.
Protective foams function by absorbing and/or dissipating the impact energy from the force of an impact. An energy absorbing foam deforms or crushes on impact thereby consuming a portion of the impact energy to prevent its reaching the underlying body part. An energy dissipating foam also spreads the impact force over a larger surface area than the actual area of impact so the force per unit area is decreased for the underlying body part compared to that for the initial impact surface (e.g. the outer surface of the protective layer or a hard outer shell over the protective layer).
Traditionally, rigid foam pads are used in safety-related applications, made from foams that are non-recovering (i.e., they do not recover or rebound to any significant degree once they have been crushed) and do not provide comfort to the user. Such foams are not viscoelastic, and their structure essentially is destroyed on impact. Therefore, it is desirable to use semi-rigid protective foam pads that provide both comfort and energy-absorbing capabilities, and which are viscoelastic and recover (i.e. they re-expand to their pre-impacted shape) after impact.
Current energy-absorbing pads used in combat helmets can be made, e.g., by encapsulating an acceleration rate sensitive material with a non-porous coating that traps air and to a degree prevents compression of the coated foam. Such a design is the subject of U.S. Pat. No. 6,467,099. However, this structure has several significant disadvantages. First, the coating material used to cover the pads is both expensive and difficult to apply. In order for the pad to effectively attenuate an impact force, the coating must remain substantially continuous, non-porous and free from perforation. This can be difficult to guarantee, especially during combat conditions when repeated impacts may be likely. Second, the coating is often a sprayed on solvent-based material, as in the preferred embodiment of U.S. Pat. No. 6,467,099, which provides minimal resistance to chemicals and solvent-based products, such as insect repellants, acetone, etc. that may be encountered in the field. Third, the process of applying such a solvent-based coating involves specialized equipment tocapture the solvent vapors released when the coating is dried. “
[Moore and Novak, US Patent 3,999,085 (3/19/2013)]
1. A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.
Pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston.
The shock absorber absorbs and dissipates energy. One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most dashpots, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of dashpots, such as electromagnetic types, the dissipated energy can be stored and used later. In general terms, shock absorbers help cushion vehicles on uneven roads.
(Shock Absorbers, Wikipedia, 3/19/2013)
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Roger D. Corneliussen
Maro Polymer Links
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Copyright 2013 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 3/19/2013.