18.2:
Stress-Strain Diagram
Consider a cylindrical specimen placed in a system to measure its tensile strength.
Two gauge marks are inscribed on the central portion of the specimen. The length between the marks is known as the gauge length.
Then, a tensile load is applied on both ends of the specimen.
As the load increases, the gauge length increases, and the elongation is recorded for each load value.
The change in the diameter of the specimen is also recorded simultaneously.
Stress is computed by dividing the load by the original cross-sectional area of the specimen. Strain is calculated by dividing the elongation by the original gauge length.
A stress-strain diagram is then obtained by plotting strain as an abscissa and stress as an ordinate.
It is observed that stress varies linearly with strain during the initial loading. However, as the load increases, small changes in the stress lead to significant changes in the strain values for most materials.
Depending on their temperature and loading speed, the results vary for some materials.
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.