# Wanting to do some impact force experiments

• B
• LT72884
B) do an FFT on the video data to get the frequency and amplitude of the vibration. The frequency will be very near the natural frequency of the block. Then calculate the force from the stiffness of the block.3) Use a "force hammer". This is a known mass moving at a known velocity before it hits the block. The velocity is measured using a strain gage on the hammer, and the mass is known, so the kinetic energy is known. Then measure the velocity of the hammer after the impact (strain gage) and calculate the kinetic energy after the impact. The difference is the energy loss in the impact, which is equal to the energy dissipated in the block. The force

#### LT72884

I have 3d printed some 25mm cubes all with the same parameters. what i want to do is take some different weight dumbells, and drop them all from half a meter onto a cube. My goal is to collect data and see at what impact force the cube fails. For me, failure will be when layers break apart, not a total destruction of the part.

since the weights will be falling, it has KE, and we know that at the top, before the fall, PE=KE, meaning, milliseconds before the weight hits the cube, all the PE is now KE. This allows me to find its velocity right before impact. Since i now have its velocity, i can find KE on impact. All the KE will be transferred into the cube. A transfer of energy is work done

ok, so we all know that work done = force(distance) so force =work done/distance.

Here is my issue, i don't know distance. Usually distance is some sort of deformation or if the weight falls on a nail, its the distance the nail is driven into the wood. So i am not sure what to use as my distance?? should i use a value close to 0, but not 0??

i do not have access to a izod or charpy tester, nor do i have the time to make one.

i want to try it out this way and see what happens. Ill plot the data in excel and see what i can find:)

thanks

Delta2
The impact does not transfer all the energy into the cube because energy is dissipated in heat and sound. We should use the loss of momentum. The formua to use is: Force x time = velocity x mass. I have done this experiment using a pointed cone made of soft clay (Plasticine UK). The stopping distance can then be measured and the duration time of the impact can be found.

Delta2
I am not sure that I agree with the premise that yield stress (in units of pressure) can be accurately assessed by a measurement of average force.

russ_watters
jbriggs444 said:
I am not sure that I agree with the premise that yield stress (in units of pressure) can be accurately assessed by a measurement of average force.
I would usually agree with you on your exact argument, however, today i must not haha. I am specifically looking for impact force. Same method as the crumple zone of a falling car, or a person falling of a 4ft high bed. Except, we use 0.75 inches as the deform distance for a human body. I have a reason for this experiment haha

tech99 said:
The impact does not transfer all the energy into the cube because energy is dissipated in heat and sound. We should use the loss of momentum. The formua to use is: Force x time = velocity x mass. I have done this experiment using a pointed cone made of soft clay (Plasticine UK). The stopping distance can then be measured and the duration time of the impact can be found.
isnt force*(time) impulse? So if i follow you, i should do F=vm/t and since i know the v based on my equations above, of the weight, the mass of the weight and since i can find time based on v, i will have all i need?

v= sqrt(2gh)

thanks

The impact force will also be spread onto an area. Preassure could be a better idea to investigate.

drmalawi said:
The impact force will also be spread onto an area. Preassure could be a better idea to investigate.
what kind of idea are you thinking? Once i find the force, i can find the pressure? I like that idea. Main reason, i am 3d printing parts soon that need to take a lot of force and pressure.

thanks

LT72884 said:
Once i find the force, i can find the pressure?

Then you need to find the contact area, which is not that easy to do I think. Why don't you consider something more static? Find a small bolt which you can fix in position, then apply weight on the bolt until your object cracks

might be hard to balance it, though.

LT72884
drmalawi said:
Then you need to find the contact area, which is not that easy to do I think. Why don't you consider something more static? Find a small bolt which you can fix in position, then apply weight on the bolt until your object cracks
View attachment 303903
might be hard to balance it, though.
i thought of this, but its all pinpointed to one spot. Its like walking on snow with your tippy toes, rather than using the entire snowshoe. Thats how my brain is thinking of it. I may be incorrect with my thinking on that analogy though

The impact of the dumbell kan also be on "one spot" depending on how it drops. Dumbells can have many shapes, and if you want to controll the outcome of the result, you have to make sure the area of the impact is the same each time.

LT72884
drmalawi said:
The impact of the dumbell kan also be on "one spot" depending on how it drops. Dumbells can have many shapes, and if you want to controll the outcome of the result, you have to make sure the area of the impact is the same each time.
excellent information. I agree.

LT72884 said:
I am specifically looking for impact force.
There are several ways to measure impact force.

1) Mount a load cell under the cube, and measure force vs time for the impact. A sample rate of about 10,000 samples per second would be about right depending on the stiffness of the block. It's easy to make a simple load cell if you know how to work with strain gages. The load cell will need its natural frequency to be at least 10 times higher than the duration of impact.

2) Use high speed video to observe the impact. You will need a frame rate at least 1000 frames per second, and possibly faster depending on the hardness of the block. (A) Measure position vs time, and calculate peak acceleration, and calculate the peak force from the mass and peak acceleration. Or (B), assume a constant spring constant (not a good assumption with elastomers), measure the peak deflection, calculate the spring constant from ##KE = 0.5kx^2##, and calculate the peak impact force from ##F = kx##, where ##x## is the peak deflection.

LT72884
I have done a very similar experiment simulating a vehicle crash using an air track. I use a cone made of soft clay to take the impact. I actually make two identical cones, then subject one to the impact and the second to a static force which I adjust to give the same deformation. The impact deceleration can be found from the stopping distance, then we apply Pt=mv to find the force. We then compare this with the deformation of a second cone with a static load.

jrmichler said:
Use high speed video to observe the impact.
I'm a little bit lost. If you have a high speed camera why use anything else? Measure the acceleration profile and your done, right?
tech99 said:
Does a cone of soft clay produce a particularly constant acceleration? I understand it will provide inelasticity but what is P in equation? Lost again!

LT72884
well, here is what i think. for a free falling object, such as a metal dumbbell, F=MA. We also know that V=GT and since we know V and T then G works out to be 9.8, so all i need to do is take the mass of my metal dumbbell and multiply it by G and i will have the force, or in other words the weight of the object because MA is the same as the weight of a free falling body and now I am lost hahaha

working in english units for a moment. If i drop a 10 Lb metal block onto a cube, and it doesn't break. I know it can handle 10Lbs of force, but that's incorrect thinking because having 10Lbs just rest on me is not the same as having 10Lbs fall on me

jbriggs444
LT72884 said:
well, here is what i think. for a free falling object, such as a metal dumbbell, F=MA. We also know that V=GT and since we know V and T then G works out to be 9.8, so all i need to do is take the mass of my metal dumbbell and multiply it by G and i will have the force, or in other words the weight of the object because MA is the same as the weight of a free falling body and now I am lost hahaha

working in english units for a moment. If i drop a 10 Lb metal block onto a cube, and it doesn't break. I know it can handle 10Lbs of force, but that's incorrect thinking because having 10Lbs just rest on me is not the same as having 10Lbs fall on me
Correctly observed. The force required to support an object at rest is not the same as the force required to stop it in an impact. Not even close.

Perhaps "force" is not the parameter of interest for an impact. Perhaps neither "peak force" nor "average force" are the right parameters either.

Maybe damage done during an impact is more complicated than that.

LT72884

## What is an impact force experiment?

An impact force experiment is a scientific investigation in which an object is subjected to a sudden or intense force, typically in order to measure the amount of force exerted and its effects on the object.

## Why would someone want to do an impact force experiment?

Impact force experiments can provide valuable information about the strength and durability of materials, as well as how they respond to various types of force. This information can be used to improve the design and safety of products and structures.

## What types of materials are typically used in impact force experiments?

Common materials used in impact force experiments include metals, plastics, and composites. These materials are chosen because they are commonly used in various industries and can provide insights into their performance under different types of force.

## How are impact force experiments conducted?

Impact force experiments typically involve using a specialized machine, such as a drop tower or pendulum, to deliver a controlled amount of force to the object being tested. The force is measured using sensors and the results are recorded and analyzed.

## What are some potential applications of impact force experiments?

Impact force experiments have a wide range of applications, including in the automotive, aerospace, and construction industries. They can be used to test the strength and durability of materials in products such as cars, airplanes, and buildings, as well as in research for developing new materials and technologies.