Finding impact force on Steel ball drop test

In summary, the conversation discusses a simple steel ball drop test on glass and the difficulties in calculating the impact force due to the non-elastic nature of the steel ball and the rigidity of the glass. The conversation also mentions the use of pressure pads and accelerometers for measuring impact force and the need for understanding the elastic properties of materials when conducting such tests.
  • #1
voltexx
2
0
I am doing a simple steel ball drop test on glass to see if the glass passes the standards.
We are dropping 1.18 inches (0.535kg) steel ball at the height of 51inches (1.295m).
Now, I can calculate final velocity at the impact, but cannot calculate the actual impact force.
One of the method is using F=(mgh)/s where s is the distance traveled after the impact as described in http://www.engineeringtoolbox.com/impact-force-d_1780.html
However since steel ball is non-elastic so the traveled distance after the impact on rigid glass will be nearly ZERO, then the impact force becomes infinite.
There must have been a report or analysis on this simple ball drop test.
Can anyone help me?
And please don't tell me about you need to know the elastic properties of materials or how long the bodies are in contact and others craps. It is straght forward situation I think anyone can assume assumptions and conditions. A Steel ball droping onto glass!
 
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  • #2
However since steel ball is non-elastic so the traveled distance after the impact on rigid glass will be nearly ZERO, then the impact force becomes infinite.
That is correct ... an absolutely rigid impact involves infinite forces. Well done.

There is no such thing though ... you'll find the glass bends a lot under the impact (unless it breaks).

We'd normally do impact tests with a pressure pad at the impact site measuring force vs time... or an accelerometer inside the ball.
 
  • #3
Simon Bridge said:
We'd normally do impact tests with a pressure pad at the impact site measuring force vs time... or an accelerometer inside the ball.

"Simon Bridge" Does that mean in this practical situation, evaluating impact force by mathematical model using only the known variables such as mass and height is invalid?

I do have a force gauge (Mecmesin Advanced Force Gauge 500N) but not sure if this device is valid to measure the impact force. What do you normally use for pressure pad and when you say force vs time does time means overall time taken during the impact? - it will be in milliseconds :(
 
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  • #4
"Simon Bridge" Does that mean in this practical situation, evaluating impact force by mathematical model using only the known variables such as mass and height is invalid?
Yep - you don't have enough information to do the prediction. You could predict the result using listed Youngs modulus and brittleness for the materials.

For a pressure sensor I'd normally just use whatever my boss bought for the job - there are lots of different kinds.

For force vs time I plot a graph of force sampled at some small time interval. The specific impulse is the area under this graph. The force is not usually constant throughout the impact (the graph is usually a quadratic - but it needn't be) ... here's an example of containers subject to blast-impacts (the researchers shot them!)
http://ars.sciencedirect.com/content/image/1-s2.0-S0141029607003781-gr19.jpg [Broken]
... just to show you what I mean. Of course the collisions were nowhere near elastic.

As a force gauge - I have tended to rig them up from torsion bars and capacitors... stuff like that. You may be able to use the glass sheet as a torsion bar :)

You need to be able to record what your gauge says as something is in the process of pressing into it ... if it just gives a number on a screen then perhaps take a high-speed movie and play-back frame-by-frame? It also needs to be very responsive... you can't be hitting it and a few seconds later it tells you how hard you hit.

I've had to conduct this sort of test on playground soft-fall surfaces ... in that case I used a hollow steel ball a bit bigger than my fist with an accelerometer inside it. Knowing the mass of the ball and the sampled acceleration data with the sample rate gives my F vs t graph etc. i.e. there are commercial devices designed for this sort of testing.

Looking below I see a lot of discussions about impact testing - have you had a look to see how other people solved similar problems?
 
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  • #5
Colleagues, I am trying to determine the Young's Modulus of a fibre reinforced polyester composite subjected to a drop impact test. I am trying to look for a relationship or formula to use but I am finding none. I have tried to use the relationship in the flat disc clamped around the edges with a central load. This seems to be wrong since the stead and impact load applications are different.

Any help please?
 
  • #6
  • #7
Thanks, Simon. Will try that.

Cheers.

Grain.
 
  • #8
@gmmunakaampe: how did you get on?
 
  • #9
I would like to run a similar experiment. Where would I be able to purchase a steel ball with an accelerometer in it?
 

1. What is the purpose of the steel ball drop test?

The steel ball drop test is used to determine the impact force of a falling object on a surface. It is commonly used in materials testing and engineering to evaluate the strength and durability of a material.

2. How is the impact force calculated in a steel ball drop test?

The impact force is calculated by measuring the height from which the steel ball is dropped, the mass of the steel ball, and the depth of the indentation it creates on the surface. Using the formula F=ma, the impact force can be calculated as the product of mass and acceleration due to gravity.

3. What factors can affect the impact force in a steel ball drop test?

The impact force can be affected by various factors such as the height from which the steel ball is dropped, the surface material and its properties, the shape and size of the steel ball, and any external forces acting on the system. It is important to control these variables to obtain accurate results.

4. How is the steel ball drop test used in product development?

The steel ball drop test is commonly used in product development to test the durability and impact resistance of materials. It can help engineers and designers determine the strength of a material and make necessary improvements to ensure its reliability and safety in real-world applications.

5. Are there any safety precautions to consider when conducting a steel ball drop test?

Yes, there are safety precautions that should be taken when conducting a steel ball drop test. Proper protective gear should be worn, and the test should be conducted in a controlled environment to avoid any potential hazards. It is also important to follow proper procedures and protocols to ensure accurate and safe results.

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