Can explain the difference between ''engineering'' stress and strain and true stress and strain.

Question

Can explain the difference between ''engineering'' stress and strain and true stress and strain.

Answer 1

Engineering Stress is calculated using emperical equations.  True Stress is done by test.  For example, if you calculating the axial stress of a column.  You would calculate it based on Force / cross-section area.  Based on the material being used, you could calculate the strain in the material.  Now if you take the take a column and put it under a compression test in which the column is subjected to a force across its cross section, you would then use a strain gage, a force gage to measure the force and displacement of the the material at every load increase.  You would then plot the material on a graph and get the approximate modulus of elasticity for the material and calculate stress and strain of the material.  This is true stress and strain.  The calculated values (engineering) will be different from experimented values (true).  Although they are different, they should be close enough.

Answer 2

Engineering stress and strain are calculated from the sample. They use the initial area of the sample and the average strain over typically a 2" (50mm) length.

True stress is based on the fracture area, where the sample necks down. So, if it necks to 1/2 the original area, you have twice the stress. Actual strain is the local strain that occurs, no reasonable way to determine. When you use the say 0.2% strain of the 2" section, most of it actually occurs in the tiny region that plastically deformed.

So, they are the same for elastic deformation, and different only for plastic deformation.

Answer 3

Stress is calculated as force divided by area. Engineering stress assumes that the area remains constant throughout the test, while true stress uses the instantaneous area as it changes.

Answer 4

engineering stress is the stress and strain of meterial.it is a mechanical property. true stress and strain is calculating the meterial stress.