Bending Stress on a Protective Cover

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SUMMARY

The discussion centers on calculating the force and bending stress on a protective cover when a 30kg pallet falls from a height of 2m. The force exerted on the cover is calculated to be 294.3N, resulting in a pressure of 1.094Pa when distributed over an area of 269m². The bending stress formula, bending stress = mc/I, is referenced but not fully explored due to missing parameters. The conversation highlights the complexities of impact forces, emphasizing that the peak force during impact is influenced by the cover's flexibility.

PREREQUISITES
  • Understanding of Newton's Second Law (F=ma)
  • Knowledge of pressure calculations (P=F/A)
  • Familiarity with kinetic energy concepts (KE=mgh)
  • Basic principles of bending stress (bending stress = mc/I)
NEXT STEPS
  • Research the effects of material flexibility on impact forces in protective covers.
  • Explore advanced calculations for bending stress in composite materials.
  • Learn about dynamic loading and its implications in structural engineering.
  • Investigate the principles of damped oscillators in impact scenarios.
USEFUL FOR

Mechanical engineers, structural analysts, and students studying dynamics and material science will benefit from this discussion, particularly those focused on impact analysis and protective cover design.

Jesse Niekamp
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Homework Statement


A 30kg pallet falls from a height of 2m onto a protective cover. The cover has an area of 269m² and an overall thickness of 10.9mm.

upload_2018-11-6_11-58-22.png


a. What is the force/pressure on the cover?

b. What is the bending stress on the cover?

Homework Equations


F=ma
bending stress = mc/I
P=F/A
Vf^2=Vi^2+2ad
KE=mgh
Wnet=1/2m(Vf)^2-1/2m(Vi)^2

The Attempt at a Solution


F=ma=(30)(9.81)=294.3N
P=F/A=294.3/269=1.094Pa
Vf^2=0+2(9.81)(2)...Vf=6.264m/s
KE=mgh=(30)(9.81)(2)=588J
 

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Jesse Niekamp said:
F=ma=(30)(9.81)=294.3N
P=F/A=294.3/269=1.094Pa
That F will be the steady state force. It does not take into account the impact from the fall.
During impact, force will be a function of time, increasing up to some max then dropping back down (the mass might even bounce). The peak force will depend on the flexibility of the cover, which we are not given. The more flexible, the longer the duration of the impact and the less the peak force. It will be a damped oscillator.

As for the pressure, I see no suggestion that the mass spreads right across the cover. The localised pressure could be much higher.

Where does this very flawed question come from?
 

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