Seamus
They probably are the same and I'm struggling to find a term that describes the difference between the action of the high density EVA referred to and any of the PU rubbers such as Poron and Sorbothane. The following is taken from a sorbothane blog
http://www.sorbothane.com/blog/what-...ck-absorption/
Quote:
What Types Of Materials Are Best For Shock Absorption?
What Is Shock?
To understand what types of materials are best for shock absorption, one must understand shock, why shock absorption is important, and how shock energy is absorbed. What is shock? Shock is the effect on an object caused by the energy delivered to it by a force, usually an impact force, over a short time period. The effect of shock occurs when the energy of the impact is transferred from one individual or object to another. This wave of energy can cause injury or damage to the affected individuals or objects.
Why Is Shock Absorption Important?
Because shock is usually associated with adverse effects to objects or individuals, it will ultimately cause inefficiencies, such as waste, rework, and downtime. Shock absorption, therefore, increases the lifespan and/or the safe operation of the application.
How Is Shock Energy Absorbed?
A process called damping—the dispersion or disruption of the energy caused by shock’s impact forces—absorbs the energy from shock by decreasing the amplitude (strength) of the shock energy’s wave or by changing the wave’s frequency. Absorption reduces or eliminates the adverse effects, injury, or damage to an object or individual caused by shock.
What Are the Most Important Characteristics of a Shock Absorption Material?
To be effective, a shock absorption material must have the capacity to eliminate or reduce oscillations across a wide range of frequencies. To be effective in an industrial environment, a shock absorption material must perform well in a wide range of temperatures, even changing temperatures, regardless of the source of the shock, over an extended period of time.
What Is Sorbothane®?
Sorbothane is a proprietary, thermoset, polyether-based polyurethane material with visco-elastic properties—that is, it acts as a liquid to absorb shock and as an elastic solid when at rest. It performs by converting the impact of the shock energy to a small amount of heat.
As an industrial material, Sorbothane is resistant to fire and chemical solvents found in an industrial environment. It also performs through a wide range of temperatures and millions of cycles without degrading in performance.
Why Is Sorbothane the Best Material for Shock Absorption?
Sorbothane was specifically designed for shock absorption and is manufactured to outperform every other material available on the market. What makes Sorbothane the best material for shock absorption?
It absorbs more than 90% of shock energy and more than 50% of vibration energy;
It performs in temperatures ranging from –20° to 160° Fahrenheit (–29° to 72° Celsius)];
It performs at frequencies ranging from 10 to 30,000 Hertz;
It’s damping ratio is 0.344 at 2.34 HZ;
It doesn’t support bacterial or fungal growth and is relatively unaffected by industrial solvents such as diesel fuel, kerosene, and hydraulic fluid;
It has an extremely long shelf life; and
It has a superior damping coefficient.
Ok, we're all familiar with the properties of Poron and Sorbothane and they are certainly amongst the most popular choice for podiatrists who wish to provide some 'shock-absorption' for their patients, for example; plantar lesions; symptoms associated with atrophy/dysfunction of the plantar plate and calcaneal bursitis. I can't provide comparative analysis for the EVA as I don't know how to measure the force impact/damping effect (perhaps one of our lab gurus might..?) - but in my experience, therapeutically it far out performs any PU rubber materials in almost every aspect - the only 'negative' is that they need replacing every 4-6 weeks.
Think about it this way. If you were to jump out of an airplane without a parachute - what would be your preferred material in the LZ? Cardboard boxes or sorbothane? Both will 'absorb' the impact - but one will kill you in the process, the other you can walk away from.
Mark
PS - the jumper is Gary Connery who did the Bond jump with the 'Queen' in 2012. Spoke to Gary this morning - the reason he chose cardboard boxes is that it is the displacement of air within the structure at impact that provides the best shock absorption - the critical properties are the retention and displacement rate within the structure/material. The boxes are 3' deep - stacked seven high and are unsealed. As he points out, it doesn't work quite so well jumping onto 21' stacked flat-packed cardboard - or sorbothane for that matter. Apologies I can't provide a more scholarly explanation, but I'm sure there are a few who can...
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