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# Mechanical Impact

#### mikes

##### New member
Hello there,

I got this little project I am working on, it maybe simple to you , but I have a hard time getting some useful results.

I have an assembly, it looks like a square box(section) 6 inches long, with a cylinder attached to one end.

On the end I have the possibility to attach a sleeve made of a rubbery material (I use relatively soft , Shore 80 A Santoprene) . The measured weight of the assembly is 3.77 lbs.

In my experiment I attached this assembly to an arm (67 inch long), which can swing like a pendulum.

The arm is rotating on a pin with a bearing on it

I bring the arm horizontally, and let the assembly swing in the gravity field, initial speed 0.

At 90 degree (arm vertical) the assembly impacts a concrete wall and bounces back.

The impact area of the assembly is the ream of the sleeve.

In reality, the contact is not a cylindrical ring because the contact is not always centric.

I have instances when the contact is a segment of a ring, since the initial wall-ring contact is an edge of the ring ; under impact forces the edge deforms and at times folds (changing the area of contact) and changing the bounce speed of the assembly.

To complicate the things, I have some small masses attached to the assembly through some miniature connectors.

The fashion these masses are attached to the assembly is in such a way that the inertial forces generated at impact pulls them out of the connectors, overcoming the retaining forces. The connecting pins are parallel with the impact force vector.

I did my homework and I

It isn't a simple problem and it would rquire a very lengthy response, but impossible with the information provided. I would recommend a book to you: Vibration Analysis for Electronic Equipment, by Dave S. Stainberg and published byJohn Wiley & Sons.

ISBN 0-471-63301-1

Perhaps you'll find it at your local engineering school library.

It will help you understand the results of your experiment.

Martin

So kind of you to share your problem-solving thoughts with this forum. What purpose does this experiment serve? What are you trying to prove? Is this a school project?

Hello all again,

I got some answers to my initial problem.

The experiment I did(and explained in my initial post) was not a school exercise but a real life project.

I designed a flashlight and the customers were complaining that the light bulb comes off as they hit axially the facecap of the flashlight as they go through buildings(hitting the door frames, hard objects, etc.). The flashlight normally is strapped to their waist with a special band/strap, so the impact is mostly happening horizontally.

The light bulb is held by two connectors which have an insertion force of about 3.8 N each.

The existing facecap is made of ABS which is pretty rigid (about 90 Shore A durometer).

My approach is two prong; I have to make the facecap from a softer material to cushion/diminish the impact force and , if needed, to change the connectors I am using now with a higher withdrawal force connectors.

The light bulb I am using has two contacts 0.028