How Can I Calculate Energy Absorbed by a Shin Guard During Impact?

In summary: The downward slope of the graph indicates that the striking mass was dropping at a slower rate than the shin guard. This was likely because the shin guard was absorbing some of the energy from the impact.The y-axis shows the acceleration measurements recorded by the accelerometer, the x-axis shows the time. The downward slope of the graph indicates that the striking mass was dropping at a slower rate than the shin guard. This was likely because the shin guard was absorbing some of the energy from the impact.
  • #1
ClapClap
24
0
Hi,

I am doing a drop impact testing on a football shin guard. I know how to find the impact force but how do I determine the energy absorbed by shin guard during impact?
 
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  • #2
welcome to PF...
could it be loss in kinetic energy?
 
  • #3
Suraj M said:
welcome to PF...
could it be loss in kinetic energy?
Well that is what I thought. I'm not sure if it's equal to the kinetic energy of the falling body
 
  • #4
no, change in kinetic energy!
 
  • #5
Suraj M said:
no, change in kinetic energy!
This is going to sound really stupid and I'm sure that as soon as I see the answer I'll realized how obvious it was, but how would I find that?
 
  • #6
It might be a bit hard to do, but you should measure the velocity of the ball before and after the collision, if that's difficult, do it using the height to which the ball rises, with no horizontal component and then find the velocity, but with air friction, it's a bit difficult.
 
  • #7
Suraj M said:
It might be a bit hard to do, but you should measure the velocity of the ball before and after the collision, if that's difficult, do it using the height to which the ball rises, with no horizontal component and then find the velocity, but with air friction, it's a bit difficult.
I'm not sure how i can measure the height after collision as i am dropping a meta stud on it :/ as for the air friction that won't matter as i won't be considering it
 
  • #8
Do you have means of finding the velocity of the ball after the impact?
 
  • #9
Yea. Can I assume that the impact velocity is the same as the rebound velocity or is that wrong?
 
  • #10
ClapClap said:
t the impact velocity is the same as the rebound velocity or is that wrong?
I think you mean SPEED, because velocity cannot be the same after the REBOUND.
Well theoretically, you can , assuming that the shin guard is as rigid as a wall. But still in reality you can't, however rigid it is, the coefficient of restitution cannot be =1, there will be some energy loss. Also if you assume that the magnitude of velocity remains same, you mean to say that no energy had been absorbed by the shin guard.
 
  • #11
you can test the shinguard either with a drop test, like at a helmet lab, with accelerometers in the headform, or on a simpler , self constructed pendulum apparatus. on pendulum put object on bottom of swingarm, hit without shinguard, take measurement of distance traveled , the with shinguard , take same measurement.
 
  • #12
You say you know how to find "the force." Are you measuring it, vs. time? If so, you should be able to calculate energy loss from that directly: the work done on the shin guard during compression of the impact, minus the work done by the shin guard during rebound, is the energy loss. To calculate this you'd either need to have displacement of the impacting object vs. time during the impact also, whether measured directly or from measuring the acceleration vs. time.
 
  • #13
I have actually been struggling reading my sensors measurements. I have attached an acceleration vs time graph i have developed with the measurements taken. Can you help me understand it?
 

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  • #14
That graph looks messy. And I cannot read the axis labels.
Do you have a sketch of the setup? Where is the sensor?
 
  • #15
Sensor was attached to a falling mass of 4.3 kg. The mass was dropped at different heights (this graphs shows acceleration measurements for impact drops of 20 cm). The striking mass was dropped onto a football shin guard which was placed on a metal flask. I assumed that the graph is messy because the weight bounced a few times on the guard.
The y-axis shows the acceleration measurements recorded by the accelerometer, the x-axis shows the time.
 

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Related to How Can I Calculate Energy Absorbed by a Shin Guard During Impact?

What is energy absorption from impact?

Energy absorption from impact refers to the process of converting the kinetic energy of an object into other forms of energy, such as heat or sound, when it collides with another object. This is an important concept in understanding the effects of impacts on various materials and structures.

Why is energy absorption from impact important to study?

Energy absorption from impact is important to study because it can have significant implications in a variety of fields, including engineering, materials science, and accident reconstruction. By understanding how different materials and structures absorb and dissipate energy during impacts, we can design safer and more effective products and structures.

What factors affect the amount of energy absorbed during an impact?

The amount of energy absorbed during an impact can be affected by several factors, including the velocity and mass of the objects involved, the stiffness and strength of the materials, and the angle and duration of the impact. Other factors, such as temperature and surface properties, can also play a role.

How can energy absorption from impact be measured?

Energy absorption from impact can be measured using a variety of techniques, such as strain gauges, accelerometers, and high-speed cameras. These tools allow scientists to measure the forces and deformations that occur during an impact and calculate the amount of energy that is absorbed by a material or structure.

How can we improve energy absorption during impacts?

There are several ways to improve energy absorption during impacts, depending on the specific application. Some common strategies include using materials with higher strength and stiffness, designing structures with energy-absorbing mechanisms, and incorporating protective features, such as airbags or shock-absorbing materials. Additionally, understanding the principles of energy absorption from impact can help inform the design and construction of safer and more resilient products and structures.

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