Jännityksenvenymäkäyrä

Jännityksenvenymäkäyrä, translated into English as the stress–strain curve, is a graphical representation of how a material deforms under applied tensile or compressive forces. The horizontal axis, strain, measures the relative change in length, while the vertical axis, stress, quantifies the internal force per unit area required to produce that deformation. By plotting these two quantities for a given material, engineers can assess properties such as elastic limit, yield strength, ultimate tensile strength, and ductility.

In classical mechanics the curve is derived from experimental tests, often using a universal testing machine; the specimen is stretched until failure while the applied load and elongation are recorded. For many homogeneous isotropic materials, the initial portion of the curve is linear, reflecting Hooke’s law, where stress is proportional to strain with the proportionality constant known as Young’s modulus. Beyond the elastic region the material exhibits plastic deformation until it reaches a peak stress; beyond this point the material typically fractures.

The stress–strain curve is central to material science and structural engineering, enabling the selection of appropriate materials for specific load conditions and informing the design of safety factors. It also informs finite element analysis models and guides failure analysis investigations. Variations of the curve are available for different loading modes, such as compression or bending, and for materials with anisotropic behaviors, such as composites and biological tissues. As such, the jännityksenvenymäkäyrä remains a foundational tool for understanding and predicting the mechanical response of materials under load.