{"id":6592,"date":"2020-06-03T14:51:50","date_gmt":"2020-06-03T11:51:50","guid":{"rendered":"https:\/\/fractory.com\/?p=6592"},"modified":"2024-01-26T15:43:10","modified_gmt":"2024-01-26T13:43:10","slug":"stress-strain-curve","status":"publish","type":"post","link":"https:\/\/fractory.com\/stress-strain-curve\/","title":{"rendered":"Stress-Strain Curve"},"content":{"rendered":"

The stress-strain curve is one of the first material strength graphs we come across when starting on the journey to study materials.<\/p>\n

While it is actually not that difficult, it may look a bit daunting at first. In this article, we shall learn about the stress and strain curve to understand it better.<\/p>\n

But before we get there, we will try to explain a few key concepts for better comprehension.<\/p>\n

Loading<\/h2>\n

A metal in service or during manufacturing is subjected to different forces. Depending on the magnitude of these forces, the metal may or may not change its shape.<\/p>\n

The act of applying the force is known as loading. There are five different ways in which these forces may be applied on a metal part.<\/p>\n

\"Load<\/p>\n

The five forms of loading are:<\/p>\n

    \n
  1. Compression<\/li>\n
  2. Tension<\/li>\n
  3. Shear<\/li>\n
  4. Torsion<\/li>\n
  5. Bending<\/li>\n<\/ol>\n

    Metals are elastic in nature up to a certain extent. When subjected to loading, the metal undergoes deformation but it may be too small to discern without special tools.<\/p>\n

    When this applied force is removed, the metal regains its original dimensions (unless the force exceeds a certain point). Just like a balloon, for example, regains its original shape after a force is removed after application.<\/p>\n

    What Is Stress?<\/h2>\n

    Stress is defined as the ratio of the applied force to the cross-sectional area of the material it is applied to.<\/p>\n

    The formula for calculating material stress:<\/p>\n

    \u03c3=F\/A, where<\/p>\n

    F is force (N)<\/p>\n

    A is area (m2<\/sup>)<\/p>\n

    \u03c3 is stress (N\/m2 <\/sup>or Pa)<\/p>\n

    For example, a force of 1 N applied on a cross-sectional area of 1 m2<\/sup>, will be calculated as a stress of 1 N\/m2<\/sup> or 1 Pa. The unit can be displayed as N\/m2 or Pa, both of which represent pressure<\/a>.<\/p>\n

    Stress can be understood as an internal force<\/strong> induced in the metal in response to an externally applied force. It will try to resist any change in dimension caused by the external force.<\/p>\n

    When the cross-sectional area changes, the same force will induce greater or smaller stresses in the metal. A smaller cross-sectional area will result in a larger stress value and vice versa.<\/p>\n

    What Is Strain?<\/h2>\n

    Strain is defined as the ratio of the change in dimension to the initial dimension of the metal<\/strong>. It does not have a unit.<\/p>\n

    There are three types of strain: normal, volumetric, and shear.<\/p>\n

    Normal strain (or longitudinal strain) concerns itself with the change in only one dimension, say length for example.<\/p>\n

    The formula for calculating strain is:<\/p>\n

    \u03b5=(l-l0<\/sub>)\/l0<\/sub>, where<\/p>\n

    l0<\/sub> is starting or initial length (mm)<\/p>\n

    l is stretched length (mm)<\/p>\n

    For example, if a certain force changes a metal\u2019s length from 100 mm to 101 mm, the normal strain will be (101-100)\/100 or 0.01.<\/p>\n

    Normal strain may be positive or negative depending on the external force\u2019s directions and therefore effect on the original length.<\/p>\n

    For the sake of simplicity, we shall only talk about normal strain in our article. Thus, every time we use the word strain, it will refer to normal strain. Once we understand normal strain, it is easy to extend the same understanding to the other two.<\/p>\n

    Stress and Strain<\/h2>\n

    Whenever a load acts on a body, it produces stress as well as strain in the material.<\/p>\n

    Let’s use a football as an example. When you try to squeeze it, it offers resistance. The resistance offered is the induced stress while the change in dimension represents the strain.<\/p>\n

    Strain causes stress. When applying force that leads to deformation, a material tries to retain its body structure by setting up internal stresses.<\/p>\n

    How Is a Stress-Strain Curve Plotted?<\/h2>\n

    The most common method for plotting a stress and strain curve is to subject a rod of the test piece to a tensile test.<\/p>\n

    This is done using a Universal Testing Machine. It has two claws that hold the two extremes of the rod and pull it at a uniform rate.<\/p>\n

    The force applied and the strain produced is recorded until a fracture occurs. The two parameters are then plotted on an X-Y graph to get the familiar graph.<\/p>\n

    Stress-Strain Curve<\/h2>\n

    \"stress-strain<\/p>\n

    The stress-strain curve is a graph that shows the change in stress as strain increases. It is a widely used reference graph for metals in material science and manufacturing.<\/p>\n

    There are various sections on the stress and strain curve that describe different behaviour of a ductile material depending on the amount of stress induced.<\/p>\n

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