Impact Testing 2

[Newguy2011]

Hi Gentlemen,

I am a new engineer working on designing a probe. In simple terms, the probe has a tube like structure which is made of 2 piece injection molded nylon66 (left side and right side)assembled together with 6 screws. It has brass tubing housed inside this plastic structure and the brass tubing protrudes out of the plastic sturcture. The whole probe is about 8 inches long, 1.375" maximum diameter. The probe will be mounted on the clamp on the end opposite to the brass tube protution. I would like to study the how much impact will the probe be able to take on the brass tube end before noticable failure.

Can you someone point me in direction to learn more about impact testing, any standard procedures or equipment thats already out there. I was thinking about using a pnematic cylinder to impact the probe at different pressures. I am hoping this will allow me to develop a test plan, starting from a small pressure value (Which will transform to a small force) on the working end of the cyclinder and keep incresing the pressure (thus increasing the force in steps since area is the same) to get some good data until the probe fails.

My thoughts are since the flow rate of air to the cylinder is going to be constant, I will not be able to change the velocity of impact?

Isn't impact velocity a greater indication of impact resistance?

It will be great if I will be able to change the impact velocity in steps until the probe is damaged. Is this possible through this cyclinder set-up or do I have to think of something else different?

 

[hydtools]

A simpler rig may be like the pendulum impact or vertical weight drop impact. Adjustable mass and adjustable velocity. Constant gravity. No air pressure variation, no seal drag variation.

Ted

 

[IRstuff]

I think you're putting the cart a bit before the horse.

You need answer what kind of impact are you trying to claim resistance to? Different types of impacts have different time behaviors. You cannot necessarily use a single setup to simulate different types of impacts. A falling impact is different than a point impact, which is different than a crushing impact.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Newguy2011]

IRstuff,

Thanks for your input. The probe will be mounted on a robot arm and the primary concern in the impact from crashing on to something.

 

[IRstuff]

OK, so whatever setup you wind up with, it needs to simulate the inertia of the robot arm and whether there's any impact mitigating characteristics from the mount or the robot arm. You might also want to consider whether you actually need a hard mount, and whether a softer mount would provide sufficient shock isolation.

In many systems, you'd actually need to replicate the robot arm and mount to get a more realistic simulation of the actual scenario, otherwise, you run the risk of overstressing the design and having to re-design for a more severe environment that your system won't ever see in real life.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize