Cauchy Stress Tensor in Applied Strength of Materials

In summary, the conversation discusses the use of stress tensors in both mechanical engineering and relativity. The Cauchy stress tensor, commonly used in engineering, is a 3D representation of stress while the stress-energy tensor in relativity is a 4D extension with a time component. The stress tensor used in engineering is different from the relativistic one due to terms representing momentum carried by bulk flow of matter. The book "Classical Field Theory" by Davison E. Soper is recommended as it covers both 3D and 4D topics in the development of Lagrangian densities, which utilize Lorentz invariance.
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dsaun777
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I am in a course in applied strength of materials and we often use the 3D stress tensor for stress analysis of materials i.e. Mohr's circles, bending, torsion, etc. Is the stress-energy tensor in relativity basically a 4-d extension to the Cauchy stress tensor commonly used in mechanical engineering? Cauchy with the addition of a time component? Are there any engineering courses that would use the relativistic energy tensor or is that more towards the theoretical side of things?
 
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The stress tensor used in engineering is the space-space components of the stress energy tensor in the rest frame of the material. In other words the engineering one is different from the corresponding components of the relativistic one by terms that represent the momentum carried by the bulk flow of matter across a surface.
 
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I might recommend a book, “Classical Field Theory” by Davison E. Soper. Dover 2008. The book covers areas like continuum mechanics while skipping things more of interest in quantum field theory. All things are derived from Lagrangian densities where Lorentz invariance is used. The development covers both 3 and 4 dimensional topics.
 
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FAQ: Cauchy Stress Tensor in Applied Strength of Materials

1. What is the Cauchy stress tensor?

The Cauchy stress tensor is a mathematical concept used in the field of solid mechanics to describe the distribution of forces and stresses within a material. It is a 3x3 matrix that represents the stress state at a specific point within a material, taking into account both the magnitude and direction of the stresses.

2. How is the Cauchy stress tensor calculated?

The Cauchy stress tensor is calculated by taking the derivative of the total force acting on an infinitesimal volume of material with respect to the area of that volume. This results in a 3x3 matrix with 9 stress components, which can then be used to determine the stress state at any point within the material.

3. What is the significance of the Cauchy stress tensor in applied strength of materials?

The Cauchy stress tensor is a fundamental concept in the study of solid mechanics and is used to analyze the mechanical behavior of materials under various loading conditions. It allows engineers and scientists to predict how a material will respond to external forces and to design structures that can withstand these forces.

4. How does the Cauchy stress tensor relate to the strain tensor?

The Cauchy stress tensor and the strain tensor are related through Hooke's law, which states that the stress in a material is proportional to the strain. This relationship allows for the calculation of strain from stress and vice versa, providing a more complete understanding of the mechanical behavior of materials.

5. Can the Cauchy stress tensor be used for anisotropic materials?

Yes, the Cauchy stress tensor can be used for both isotropic and anisotropic materials. However, for anisotropic materials, the stress tensor is not a simple 3x3 matrix and requires more complex mathematical formulations to accurately describe the stress state at a specific point within the material.

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