Calculate creep elongation and stress required

In summary, the problem involves determining the maximum stress that can be applied to a 10 inch long 316 stainless steel structure at 1200°F in order to meet the maximum creep elongation allowed in 500 hours. The minimum creep rate vs. applied stress is known at 1100 and 1300°F, and by interpolating the values, an equation for 1200°F can be found. The accuracy of this calculation is uncertain due to the given data and the resulting zero stress value obtained when plugging in the strain rate. The likelihood of accuracy may be low and further analysis may be needed.
  • #1
daskywalker
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Homework Statement



A 10 inch long 316stainless steel structure is in service at 1200°F. The maximum creep elongation in service permitted is 0.05 inches in 500 hours. The minimum creep rate vs. applied stress is known at 1100 and 1300°F and given by the following equations σ = 31.91[itex]\dot{\epsilon}[/itex]^(0.1292) (1300°F) and σ = 68.23[itex]\dot{\epsilon}[/itex]^(0.1142) (1100°F). Assuming the exponent and log of the pre-exponent for 1200°F are interpolated averages of the values at 1100 and 1300° determine the maximum stress that can be used to obtain this creep lifetime. Explain the likelihood of the accuracy of this calculation in light of the data given.

Homework Equations



Given in problem

The Attempt at a Solution



I wrote down the 2 equations and took the log of both sides, found the equation for 1200F to be σ=46.66[itex]\dot{\epsilon}[/itex]^(146.79)
But then plugging in the strain rate (0.05/1800000s) gives me zero for stress
 
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  • #2
. Is this correct or am I missing something? Also, what does it mean by explain the likelihood of the accuracy of this calculation?
 

Related to Calculate creep elongation and stress required

What is creep elongation?

Creep elongation is the gradual and permanent deformation of a material under constant stress over time. It is a type of material failure that can occur in metals, polymers, and other materials.

How is creep elongation calculated?

Creep elongation is typically calculated by measuring the change in length of a material over a specified period of time while under a constant stress. This can be done through laboratory testing or by using mathematical models that take into account the material's properties and the applied stress.

What factors affect creep elongation?

There are several factors that can affect creep elongation, including the material's composition, temperature, applied stress, and duration of stress. Materials with higher melting points and stronger bonds tend to have lower creep elongation rates.

What is the relationship between creep elongation and stress?

The relationship between creep elongation and stress is directly proportional, meaning that as the applied stress increases, the amount of creep elongation also increases. This is because higher stresses cause more rapid and extensive deformation in the material.

Why is it important to calculate creep elongation and required stress?

Calculating creep elongation and required stress is important for understanding the long-term behavior and durability of materials under different conditions. This information is crucial for designing structures and components that can withstand constant stress over extended periods of time without experiencing excessive deformation or failure.

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