venymäkäyriä

Venymäkäyriä, or strain curves, are graphical representations used in engineering and materials science to illustrate the relationship between stress and strain in a material subjected to tensile or compressive forces. These curves are fundamental for understanding a material's mechanical properties, such as its elasticity, plasticity, and ultimate strength.

The horizontal axis of a venymäkäyrä typically represents strain, which is the deformation of the material normalized by its original length. Strain is usually expressed as a dimensionless quantity or a percentage. The vertical axis represents stress, which is the force applied per unit cross-sectional area of the material. Stress is commonly measured in units of Pascals (Pa) or pounds per square inch (psi).

A typical venymäkäyrä for a ductile material begins in the elastic region, where stress is directly proportional to strain, following Hooke's Law. In this region, the material will return to its original shape once the stress is removed. Beyond the elastic limit, the material enters the plastic region. Here, deformation is permanent, meaning the material will not fully recover its original shape. Within the plastic region, there is often a yield point where the material begins to deform significantly with little or no increase in stress. As the stress continues to increase, the material reaches its ultimate tensile strength, the maximum stress it can withstand before necking begins. Necking is a localized reduction in cross-sectional area. Finally, the curve ends at the fracture point, where the material breaks. Brittle materials, on the other hand, typically fracture before significant plastic deformation occurs, resulting in a much shorter and straighter venymäkäyrä.