Tensile samples are divided into proportional samples and non-proportional samples. The gauge length is related to the cross-sectional area of the proportional specimen: under the root sign, L0=k times A0, and the constant k is usually 5.65 and 1 1.3. The former is called short specimen and the latter is called long specimen.
Extended data:
In the mechanics of materials, the research object is regarded as a uniform, continuous and isotropic linear elastic object. However, in practical research, it is impossible to have materials that meet these conditions, so it is necessary to compare materials with various theoretical and practical methods.
In many engineering structures, members often fail under the influence of complex loads or complex environments. For example, the bar is damaged by fatigue under alternating load, by creep under high temperature and constant load, or by the impact of high-speed dynamic load.
These failures are the main reasons for the loss of working ability of mechanical and engineering structures. Therefore, material mechanics also studies the fatigue properties, creep properties and impact properties of materials.