18.2 : Stress-Strain Diagram

A stress-strain diagram is a crucial tool that graphically displays a material's mechanical characteristics. This diagram is derived from a tensile test performed on a carefully prepared cylindrical specimen. The specimen has two gauge marks inscribed on its central part, and the distance between these marks is known as the gauge length. The cylindrical specimen is placed in a testing machine, which applies an increasing centric load. As this load grows, so does the gauge length. This change in length, or elongation, is recorded for each value of the load using a dial gauge. In many cases, a second dial gauge is used concurrently to measure changes in the diameter of the specimen.

The stress is then computed by dividing the load with the original cross-sectional area of the specimen. Meanwhile, the strain is determined by dividing the elongation by the initial gauge length. These calculated values are then plotted on a graph, with strain represented on the abscissa and stress on the ordinate, creating the stress-strain diagram. Notably, stress-strain diagrams can vary significantly across different materials. Even within the same material, results can vary due to a range of factors, such as the temperature of the specimen at the time of testing and the speed at which the load is applied.