# Impact force of a pendulum hitting a fixed block

#### Danje

Hi all,
I have just started work experience at an engineering company in the design department. I've be tasked to develop a test rig, Similar to a charpy rig. Intended to measure the impact strength of materials.

The design will consist of an A-frame structure with swing arm attached to the top axle, on the end of the swing arm is an anvil mass. The arm will swing and strike test pieces which are fixed to a solid, flat steel block fixed at the point of 0°

These numbers are just an example for the purpose of understanding how to do it and as accurately as possible.

Length of swing arm (inc anvil) =2m
Mass of anvil = 250kg
Size of anvil = 200x200x300mm
Mass of swing arm = 30kg
Starting position of swing arm = 90°
Strike point is 0°
Bearings on axle = 100mmOD.. 50mmID
Bearing friction = 0.002ų
Everything will be made from hardened
steel

My initial thought was the impact force wouldn't be overly difficult but after some research it seems to be much more complicated. I am begining to think I've been setup with lack of information. Any help or advice on how to go about this problem/ what variables are missing would be much appreciated. Attached a rough sketch In case there's any confusion on the construction.

Many thanks

Jay

#### studiot

So what exactly is your question?

You should consider a momentum balance to determine the impact energy and force.

topsquark

#### ChipB

PHF Helper
Impact strength is the energy (not force) that a material can withstand without fracturing. It's easy to calculate the energy being imparted into the sample from the data you've provided, based on KE = mgh. You can keep increasing mass of the anvil and/or the length of the swing arm until the sample breaks. The energy loss due to friction of the bearing can be estimated by integrating the weight of the swing arm plus anvil times mu times the radius of the bearing times the cosine of the angle of displacement over the range from 0 to 90 degrees.

topsquark