How to Calculate Nut Velocity After Tensile Test Failure?

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SUMMARY

This discussion focuses on calculating the velocity of a nut after tensile test failure, specifically when a threaded bar reaches a failure point of approximately 300kN. The energy stored in the threaded bar primarily contributes to the velocity of the nut, as little energy is retained in the nut due to its elastic properties. The kinetic energy of the nut upon ejection can be derived from the potential energy stored in the elastic portion of the bar, particularly when considering the material properties of the threaded rod and nut, such as ductility.

PREREQUISITES
  • Understanding of tensile testing and failure mechanics
  • Knowledge of stress-strain diagrams and energy storage in materials
  • Familiarity with the concepts of kinetic and potential energy
  • Material science principles, specifically regarding ductile and brittle materials
NEXT STEPS
  • Research the calculation of kinetic energy from potential energy in elastic materials
  • Explore the implications of ductility and brittleness in tensile testing
  • Learn about the stress-strain relationship in different materials
  • Investigate the dynamics of ejected components in mechanical testing scenarios
USEFUL FOR

Mechanical engineers, materials scientists, and professionals involved in tensile testing and failure analysis will benefit from this discussion.

BruceD
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Hi, so when doing a tensile test let's say on a threaded bar and a nut. The nut thread reaches failure and shoots off. How would you calculate that velocity and the actual force that it would hit say a wall 20cm away. just for information the failure point was at about 300kN
 
As tension is increased, almost all energy will be stored in the threaded bar and the elastic properties of the testing machine's framework. Very little energy will be stored as axial compression in the nut.
If the thread on the nut and/or bar strips due to tension, the failure will usually be a slow creep and not shoot-off fast. The stored energy is expected to go into deforming the contact material. The situation will be different with glass or metals that are not ductile.

Integrate the stress strain diagram to find the total energy stored in the threaded bar. That energy is stored evenly along the bar. If the bar then fails suddenly, the proportion of the length of elastic bar still attached to the nut will accelerate towards the nut, then carry the mass of the bar and nut from the machine. The kinetic energy of the ejected mass will be slightly less that the potential energy stored as tension in that part of the elastic rod.

What material is the threaded rod and nut ? Is it ductile or brittle ?
 

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