A tensor is a mathematical object which describes how a physical system changes shape when that system is stressed. Tensors are used in the analysis of a variety of physical systems, such as continuum mechanics and solid mechanics. A stress tensor, often referred to as a Cauchy Stress tensor, is used to define the amount of force that is applied to a material or object.
In the simplest case, a stress tensor is composed of three components corresponding to the three fundamental physical laws governing the behavior of materials. The first component is a normal stress which is the component of force which is applied perpendicular to the surface of the object. The second component is a shear stress which is the component of force applied parallel to the surface of the object. The third component is a moment stress which is the component of force applied parallel to the surface of the object but in a different direction than the normal stress.
The normal stress is usually referred to as the principal stress component and is particularly important as it controls the behavior of the material when it is in a homogenous strain. It is this component of force which is used to calculate the Cauchy stress tensor. This tensor can then be used to determine the behavior of a material under different levels of stress in a given direction.
Using the theory of stress tensors, engineers are able to determine the strength of a material in different directions. Increasing the normal stress component in a given direction will strengthen the material in that direction and reduce its strength in other directions. Similarly, reducing the normal stress component in one direction will have the opposite effect, with the material in that direction becoming weaker. Furthermore, the direction of the applied stress plays an important role in determining the final strength of the material.
Due to the presence of the moment stress component, the stress tensor does not need to be symmetric. Symmetric stress tensors, in which all three components have the same magnitude, are generally easier to interpret and use. However, in many cases it is more advantageous to use an asymmetric stress tensor as this more accurately models the actual behavior of a material in response to different levels of stress.
The effects of a stress tensor can vary significantly depending on whether it is elastic or plastic. Elastic tensors, which are normally made up of three components of stress, exhibit a linear relationship between the stress and strain of a material. That is to say that the material will only deform and return to its original shape when the stress is removed. Plastic tensors, on the other hand, are not linear and they can be used to measure the permanent distortion and shape of a material subjected to a significant amount of stress.
The application of stress tensors is extremely broad with many industries using them to assess the strength of materials. Understanding the concept and application of stress tensors is a fundamental prerequisite for any engineer involved in such work. By employing the stress tensor, engineers are able to understand the behavior of materials under different levels of stress and develop methods and materials that are stronger, more reliable, and more cost-efficient.