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In continuum mechanics, the Cauchy stress tensor (symbol , named after Augustin-Louis Cauchy), also called true stress tensor [1] or simply stress tensor, completely defines the state of stress at a point inside a material in the deformed state, placement, or configuration.
In continuum mechanics, the most commonly used measure of stress is the Cauchy stress tensor, often called simply the stress tensor or "true stress". However, several alternative measures of stress can be defined: [1] [2] [3] The Kirchhoff stress (). The nominal stress ().
Describing the stress, strain and deformation either in the reference or current configuration would make it easier to define constitutive models (for example, the Cauchy Stress tensor is variant to a pure rotation, while the deformation strain tensor is invariant; thus creating problems in defining a constitutive model that relates a varying ...
The second Piola–Kirchhoff stress tensor for a hyperelastic material is given by = where = is the right Cauchy–Green deformation tensor and is the deformation gradient.
Thus the stress state of the material must be described by a tensor, called the (Cauchy) stress tensor; which is a linear function that relates the normal vector n of a surface S to the traction vector T across S. With respect to any chosen coordinate system, the Cauchy stress tensor can be represented as a symmetric matrix of 3×3
The effect of stress in the continuum flow is represented by the ∇p and ∇ ⋅ τ terms; these are gradients of surface forces, analogous to stresses in a solid. Here ∇p is the pressure gradient and arises from the isotropic part of the Cauchy stress tensor. This part is given by the normal stresses that occur in almost all situations.
where is the Cauchy stress tensor, is the infinitesimal strain tensor, is the displacement vector, is the fourth-order stiffness tensor, is the body force per unit volume, is the mass density, represents the nabla operator, () represents a transpose, () ¨ represents the second material derivative with respect to time, and : = is the inner ...
For an isotropic material the Cauchy stress tensor can be expressed as a function of the left Cauchy-Green tensor =.The constitutive equation may then be written: = (). In order to find the restriction on which will ensure the principle of material frame-indifference, one can write: