MadSci Network: Physics

Re: How much stress is exerted on an object withing a calapsing cavity?

Date: Tue Jul 20 07:15:55 1999
Posted By: Bob Novak, Other (pls. specify below), Sr Process Research Engineer, Carpenter Technology
Area of science: Physics
ID: 931538720.Ph

Hi David,

Most materials expand when heated.  The coefficients for metals can be 
found in the Handbook of Chemistry and Physics, which most libraries should 

The shere, when heated uniformly, will expand at the same rate in all 
directions, so the volume at the center will decrease.  The coefficient of 
expansion for iron is 12 parts per million per degree centigrade, so the 
change in volume that results from heating the sphere will be very small.

Caution!  This experiment could be very dangerous.  A one foot diameter 
sphere will not heat uniformly without very special equipment.  As the 
temperature gradient builds up within the sphere it creates a stress 
gradient.  Some metals can actually explode when the thermal stress exceeds 
the tensile strenght of the material.

A more pronouned change in the inside of the sphere will result from 
heating of the gas at the center.  The change in pressure is directly 
related to the change in temperature.  The pressure will increase very 
quickly as the sphere is heated!

Bob Novak
Specialist, Process R&D
Carpenter Technology

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