Can help me on engineering stress, Explain the difference between ''engineering'' stress and strain

Question

Given the engineering stress - engineering strain for aluminum alloy initially 11mm diameter and 50mm in length.

Answer 1

Stress is force/area.

Strain is deltaL / L

Engineering stress is average stress, i.e. based on the original area. Actual stress is based on actual area, so after the sample breaks you take the cross sectional area of the fracture surface (projected area, ignore the up and down bumps).

Answer 2

In engineering, STRESS is the amount of load applied to a sample, while STRAIN the resulting deformation due to that stress.  Stress is proportional to strain.

Imagine setting up a steel beam so that it is held up by each end.  Then you start putting weight on the middle of the beam.  This is stress.  With each weight you add, the beam with bend downward (deform).  You can measure the distance the beam has curved from normal, which is strain.

To find stress, divide the force applied (load) by the area of the sample.  If you are loading in pounds, the resulting unit of stress will be PSI or "pounds per square inch."  This reduces the measurement of stress to the smallest unit possible, and makes the data applicable to all samples, regardless of size.

Stress=  force / Area

To find strain, divide the elongation of the sample by the original length of the sample.  Using inches again, this yeilds a measurement like "inch per inch."

Strain= total elongation / original length

All materials are tested in this way, and the results are charted on a stress/strain curve.  Given a stress, you can find the resulting deformation, and vice versa.  You haven't given enough information to solve your problem.  To solve for stress, you would need to know the force applied (you know the area of the sample).  To solve for strain, you would need to know the elongation or deformation (you know the original length).