# Maximum Shear Stress Theory: Tresca Theory of Failure

Maximum shear stress theory provides failure criteria for mechanical components made of ductile material. This failure criterion is developed by the French mechanical engineer, Henri Tresca, and based on his name maximum shear stress theory is also known as the Tresca theory of failure. Due to their enormous contribution to the field of plasticity, Henry Tresca is popular as the father of the field of plasticity.

Maximum shear stress theory is one of the two main failure criteria that are widely used in recent times for predicting the failure of ductile materials. To establish the failure criteria of material, all failure theories compare a specific parameter with the same parameter for the uniaxial tension test. The maximum shear stress theory is no exception and the parameter for comparison in Tresca theory is maximum shear stress.

“The maximum shear stress theory states that the failure or yielding of a ductile material will occur when the maximum shear stress of the material equals or exceeds the shear stress value at yield point in the uniaxial tensile test.”

## Maximum shear stress theory formula

Let’s deduce the mathematical form of the above-mentioned Tresca theory statement.
Considering principal stresses, at the yield point, the principal stresses in a uni-axial test, σ1y; σ2 = 0 and σ3 = 0.
So the maximum shear stress at yielding: σsy1/2. Therefore σsy = σy/2

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Now assuming σ123; the maximum shear stress for the material is given by:

### τmax=(σ1 -σ3 )/2

Now comparing these to maximum shear stresses following Tresca theory, failure will happen when τmax>=σsy

## Safe Design Condition as per Tresca’s theory of failure

So the design of a mechanical component should be based on the following maximum shear stress theory equation

### τmax<=σsy or (σ1 -σ3)<=σy

The factor of safety (N) can also be calculated based on maximum shear stress theory and given by N=σsymax

Hence, the maximum permissible shear stress for designing a component as per maximum shear stress theory is given by τmaxsy /N

The failure envelope for Tresca’s theory of failure is provided in Fig. 1 below:

## Steps for using the Maximum Shear Stress Theory

To use the maximum shear stress theory in problem-solving the following steps are necessary to be followed:

• Step 1: Determine the three principal stresses (σ1,σ2, and σ3) from the tri-axial stress system using principal stress equations or Mohr’s circle method.
• Step 2: Find out the maximum (σ1) and the minimum (σ3) principal stresses.
• Step 3: Determine the value of the maximum shear stress τmax=(σ1 -σ3 )/2.
• Step 4: Find out the allowable stress value of the material; allowable stress= σsy /N or σy /2N as mentioned above (N=Factor of safety)
• Step 5: Compare the value calculated in step 3 with the allowable value found in step 4. If the Value at step 3 is less than the allowable value at step 4, then the design is safe as per the maximum shear stress theory.
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## Maximum Shear Stress Theory vs Von Mises Stress Theory

Von Mises and Tresca’s failure criteria are normally presented jointly with little discrimination between them. However, there are a few differences between them which are tabulated below:

The failure envelope for Tresca theory and Von Mises theory is given in Fig. 2:

## Limitations of Maximum Shear Stress Theory

• The maximum shear stress theory does not give accurate results for the state of pure shear stresses developed by the Torsion test.
• The Tresca theory provides conservative results leading to an increase in component cost.
• This theory is not applicable to brittle materials.

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

## One thought on “Maximum Shear Stress Theory: Tresca Theory of Failure”

1. Sathyanath says:

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