How to measure shock absorbtion?

[Speedy]

Folks,

What is the most effective way to measure shock absorbtion of a material; Accelerometer, MDA (Dynamic Mechanical Analysis) or Resilience (% height loss in bouncing metal ball)?

The material in question is a very soft elastomer used in a prosthetic device to limit shock loads transferring to the human skin.

From my understanding DMA measures the energy loss per cycle, this derieved from the Tan Delta value. Resilience measures the loss in kinetic energy of the bouncing ball, I imagine that the mass and diameter of the ball would be significant here especially if there is permanent deformation at the contact area. Accelerometers, I guess, measure the force transmitted to the other side of the material.

Apprecaite any help,

Speedy

 

[FINN_imported]

I deal with vibratory shockmounts daily and the only two devices I have ever used are a meter for determining the Durometer of the elastomer which can be related to a springrate in lbs/inch of deflection and also an accelerometer for determining vibration transmission through an isolator.
I would assume you are looking for comfort and control versus dampening of a vibration. Keep in mind that the softer the elastomer the more deflection you get. The trade-off to softer material is control.
I hope this helps.

 

[Speedy]

Finn,

Thanks for that.

We are testing different materials at present. I have sourced some 'piezo film' sensors and I will experiment with those.

The product in question will be worn by below knee amputees and the greatest shock load will occur during 'heel strike' as the person's foot strikes the ground. It is this shock that we want to insulate the limb from as much as possible. We are particularily concerned with high localised shock at boney promenences etc.

I have noticed that similar products on the market vary considerably in the visco-elastic nature of the material. In fact the best selling product is very elastic, which is puzzling. This material is extremely soft though and will creep easily under load so interface static pressure at the skin distributes very evenly. Other products then, seem to have great damping (slow recovery) but don't seem to sell all that well. I guess the ideal product would do both, creep easily and have good damping.

I would appreciate any other help.

Speedy

 

[Boothby171]

Speedy--Check out the material Santoprene, from "Advanced Elastomer Systems" Very resilient, and promises not to take a set:

http://www.santoprene.com/

Also: "Sorbothane":

http://www.sorbothane.com/

You may also want to check our EAR:

http://www.earsc.com/materials/index.html

(though I think their material may be too soft & foam-like for your applications. But I could be wrong...