How is a stress strain curve obtained?

Answer 1

From the origin O to the point called proportional limit, the stress-strain curve is a straight line. After reaching the proportional limit, the curve shows less stress until it gets to the ultimate strength, where the stress decreases.

Answer 2

Typical is not exactly a good word. A stress-strain curve can look very different depending on the material that is being tested.

Stress-strain curves will have a modulus of elasticity, the slope leading up to the yield point. Along this line, a material can take the pressure and will only elastically deform. Meaning, the material will go back to its original state without a change in its properties or dimensions. Its like bending a paperclip, the paperclip be slightly bent without the shape changing. Once you bend the paperclip far enough, the paperclip will reach its yield point and begin to plastically deform. Plastically deform means you have permanently altered the shape and now you begin to effect the strength of the material. If stress is continually applied, lets say as a tensile test, then an ultimate tensile strength will have been reached. This is where plastic deformation continues and worsens. And eventually a breaking point for all materials will have been reached, when discussing most metals, the breaking point is less than the ultimate tensile strength due to the loss in cross sectional area.

There are many materials that will also break at its own yield point, which can include glass, some plastics, and cast iron. The actual stress-strain curve really depends on the material that is being tested.

Answer 3

It is usually obtained by taking a rectangular bar of the material with known area cross section ( width x height). It is gripped on its ends in a tensile test machine that measures laod with a load cell as it is applied. The bar has a straijn guage extensometer on it as the load is applied, measuring strain (displacement/length). Output is through softeware to obtain the load vs. strain curve. Since stress is load/area, you now have a stress strain curve