Equations for bending steel in a car crash?

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Discussion Overview

The discussion revolves around the equations and principles needed to determine the force required to create a dent in a car's body, particularly when considering the use of a carbon fiber bumper guard. The scope includes theoretical and practical aspects of material behavior during car crashes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks formulas to calculate the force necessary to dent a car, specifically with a carbon fiber bumper guard.
  • Another participant emphasizes that car body panels are designed to crumple to enhance safety during crashes, suggesting that an undentable car would be dangerous.
  • It is noted that the force required to dent metal can be significantly lower than the forces experienced in typical collisions.
  • A suggestion is made to research "sheet metal bending force" to understand the forces involved in bending car panels.
  • Consultation of literature on bending beams and plates, as well as yield criteria for metals, is recommended, including von Mises and Tresca criteria.
  • One participant points out that the crumpling process is not fully understood, particularly regarding energy dissipation in plastic deformations.
  • Concerns are raised about the behavior of carbon fiber compared to steel, noting that carbon fiber may shatter rather than dent, affecting energy dissipation differently.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of materials during impacts, particularly between steel and carbon fiber. There is no consensus on the specific equations or models to apply for calculating the required force to dent a car.

Contextual Notes

The discussion highlights limitations in understanding the crumpling process and the behavior of different materials under stress, as well as the complexity of determining force requirements due to varying geometries and conditions.

jetsfan83
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I wanted to know what formula's do I need to figure how much force is required to make a dent in a car. I am then placing a bumper guard made up of carbon fiber, and wanted to know what equation do I need to use to figure out how much force is required to make a dent with the carbon fiber bumper guard.
 
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1. you want the body panels, especially the bumper, to crumple ... that is what saves you in a crash: an undentable car would be a death trap.
2. it's very complicated ... there are no standards.
3. even quite gentle collisions or crushes can easily produce many times the minimum force needed to dent the metal.
https://plastics-car.com/Todays-Automobiles/Automotive-Safety/Physics-in-the-Crumple-Zone-2.html

You can get an idea by looking up "sheet metal bending force" ... force to bend sheet metal.
Extrapolate for the panel geometry of the bits you want to protect.
 
Consult the literature on bending beams and plates, and also the literature on quantitative yield criteria of metals. Look up von mises and Tresca yield criteria.
 
The process of crumpling is incompletely understood. Energy is dissipated in plastic deformations, especially in ridges and creases,.
BTW, carbon fiber doesn't behave like steel. It can shatter instead of denting or bending. Energy is still dissipated, but it may not be comparable to a standard bumper.
 

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