Residual stresses in thick walled cylinders (autofrettage)]

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In summary, the conversation discusses the relative merits of the empirical Tresca and von Mises approaches for analyzing open-ended thick-walled cylinders from a design engineer's perspective. It also explores the potential effects of non-elastic recovery on residual stress distributions and the main benefits of the autofrettage process for thick-walled cylinders. The Tresca criterion is better suited for more ductile materials, while the von Mises criterion is more conservative. The Tresca criterion is better suited for linear structures, while the von Mises criterion is better suited for shells. The open ends of the cylinders do not significantly impact the choice of failure criterion.
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azzamut
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Homework Statement



1. from a design engineers point of view identify consisely the relative meris of the emperical TRESCA and VON MISES approaches as applied to open ended thick walled cylinders.

Hence specify with reasons what you believe to be the most appropriate approach.

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2. Discuss factors which can cause recovery to be non elastic. In qualititive terms what effects might such anelasticity have upon the residual stress distributions


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3. List and discuss the main benefits of the autofrettage process as applied to thick walled cylinders.



Ans...

1.

2.

3. Tensile stresses are lower at the bore
 
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You've just written out the question. We can't help you until you also show some effort towards answering it. Please read the forum guidelines.
 
  • #3
thats because I am stuck with these questions! some advise please of where to start
 
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anyone
 
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What does your text/notes have to say about the Tresca and von Mises criteria? Which is better suited to more ductile materials? Which is more conservative? Which one is better suited to linear structures, and which one to shells? What is the relevance of the open ends? Does that make any difference to the choice of failure criterion?
 

1. What is autofrettage and how does it affect residual stresses in thick walled cylinders?

Autofrettage is a process used to increase the fatigue strength and pressure capacity of thick walled cylinders by inducing compressive residual stresses on the inner surface. This is achieved by initially over-pressurizing the cylinder and then relieving the pressure, causing the inner surface to yield and expand. As the pressure is released, the outer surface of the cylinder restrains the inner surface, resulting in compressive residual stresses.

2. What factors contribute to the development of residual stresses in thick walled cylinders during autofrettage?

The amount of initial overpressure, the material properties of the cylinder, and the geometry of the cylinder (such as wall thickness and inner and outer radii) all play a role in the development of residual stresses during autofrettage. Additionally, the number of autofrettage cycles and the time between cycles can also affect the magnitude and distribution of residual stresses.

3. How do residual stresses impact the mechanical properties of thick walled cylinders?

Residual stresses can significantly increase the fatigue strength and pressure capacity of thick walled cylinders. However, they can also lead to stress corrosion cracking and reduce the ductility of the material. Additionally, residual stresses can cause distortion and warping of the cylinder, which can affect its overall performance.

4. What are some methods used to measure residual stresses in thick walled cylinders?

There are various methods used to measure residual stresses in thick walled cylinders, including X-ray diffraction, neutron diffraction, strain gauge rosettes, and hole-drilling techniques. Each method has its own advantages and limitations, and the choice of method will depend on the specific application and desired accuracy.

5. How can residual stresses in thick walled cylinders be mitigated or controlled?

There are several techniques that can be used to mitigate or control residual stresses in thick walled cylinders. These include post-autofrettage heat treatment, shot peening, and controlled overpressure cycling. These methods can help reduce the magnitude and improve the distribution of residual stresses, resulting in a more reliable and durable cylinder.

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