Creep calculations - application of Norton's power law
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- Опубликовано: 8 сен 2024
- In this video I show you how to apply the Norton equation for calculating the n and Q parameters. These are typical exam questions, so it is good to know them.
Steps:
1; Rearrange the creep equation so you will be able to plot and fit linear equations.
2; Calculate all the data which can be calculated for the rearranged equation. For example: log(sigma), log(de/dt), 1000/T(in Kelvin), etc.
3; Get n by plotting log(sigma) vs log(de/dt). The slope of the fitting gives n.
4; Rearrange the equation, so you will get a linear-type of equation.
5; Using the freshly obtained n, calculate log(de/dt)-n*log(sigma). This will be on the Y-axis. The X-axis will be 1000/T, where T is given in Kelvin. Plot it.
6; Fit a linear on your plotted data. The slope (m) is the "-Q/(2303*R)" in the equation. Rearrange and express Q. Done!
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thank you very much for the video. The only resource on the internet that eexplained this for me. I have one question ... Let's say I would like to calculate constants for the temperature I don't have a data for. I assume that if I have Q from the other temperatures I can just simply put any temperature in T variable but what about other constants n and Bo?
thanks
Hi! Since the second plot is along a line, I believe that you can inter/extrapolate to other temperatures if you know all the other parameters. Just be careful when you rearrange the equations.
To calculate B0, would you just take the Norton creep law and plug in the constants n and Q and the stress and strain rate at the corresponding temperature and then solve for B0? Thank you
Yes, if you have the above mentioned parameters, you just have to rearrange the equation.
Hi, If I use Ln for the linearization the Q values are the same that using log?
Hi! Could you rephrase your question? I don't exactly understand what you mean. I explained in the video that when we "cancel" out the exponential, we need to use ln(), but the rest is log(). Natural vs. 10-based logarithm.
Please take a video about Norton-Bailey law! Pleas..
How can I get the strain rate from creep modulus? Creep modulus is the inverse of creep strain at constant stress but not sure how to make strain rate from the strain. Thanks in advance for your thoughts...
If we "go back to the basics", creep is just a diffusion-assisted or dislocation motion-assisted deformation of the material. If you put a load on a specimen kept at a high temperature, it will creep. The creep will cause the elongation of the specimen. This elongation will happen at a specific rate. The elongation can be compared to the original length of the specimen which is actually the strain: ΔL/L0 = ε. If you are curious about the rate then it is simply just dε/dt. In this interpretation, I think the creep rate and strain rate are the same. So, according to the above expression, you just need to differentiate the creep curve and you get the strain (creep) rate.
Sir, i have T, σ and ε΄ data from tensile test for an alloy of my interest. I want to simulate creep in Ansys with the use of Norton's creep law. May i use this procedure to derive constants for the Temperature that i have more data ? How accurate is such an approach for modeling creep response ?
Hi! I am not familiar with creep modelling so I cannot really answer your questions. But you can of course evaluate the data for the temperature where you have more data. In this demonstration, I also only evaluated for the 700°C case.
@@CuriousScientistThank you for your response! Would it be more accurate if I calculate constants for each and every temperature that i have data ?
It is always good to rely on more data. It depends on what you want. You could see in the video, that one range was already enough to define the slope (n). But if you have more data, you can confirm your numbers with the rest of the slopes for example.
@@CuriousScientist Thank you!
hello. from where have you taken the sigma ? is it Ultimate tensile stress or flow stress ?
Hi! None. It is the applied stress in the creep test.
Hey. Thanks for the reply. I also have some other doubts . I am a student and working on my thesis currently. Is it possible to contact you by email ? Or should I ask my doubts here ? Will be waiting for your reply
You're welcome! I suggest you to talk to your supervisor if you have troubles with your thesis work.
Sir what is the unit of creep rate?
It is usually strain over time. The unit of time is usually adjusted to the length of the process. Strain is unitless.