Plotting S-N Diagram with Cycles to Failure

In summary, scientific notation is important when plotting S-N curves. It is recommended that a log-log plot be used.
  • #1
qwerty0123
17
0
how do i plot the follwing S-N diagram, i am having trouble with what I am supposed to do with the 'cycles to failure' figures:
stress amplitude ... cycles to failure
(y axis)- .... (x axis)
170 ...... 3.7 x 10^4
148 ...... 1 x 10^5
130 ...... 3 x 10^5
114 ...... 1 x 10^6
92 ..... 1 x 10^7
80 ...... 1 x 10^8
74 ...... 1 x 10^9


im confused about what to do with the 3.7 and 3?
 
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  • #2
Do you understand scientific notation?

Due to the nature of the data, it is recommended that a log-log plot be used for S-N curves.
 
  • #3
SteamKing said:
Do you understand scientific notation?

Due to the nature of the data, it is recommended that a log-log plot be used for S-N curves.

ok...so how would i go about doing that?
 
  • #4
SteamKing said:
Do you understand scientific notation?

Due to the nature of the data, it is recommended that a log-log plot be used for S-N curves.

why would you recommend a log-log plot? can i not just plot it as stress against logarithmic scale of the cycles to failure?
 
  • #5
You can. But often if a log-log plot is used, the S-N curve plots as a straight line, which is really handy.
 
  • #6
SteamKing said:
You can. But often if a log-log plot is used, the S-N curve plots as a straight line, which is really handy.

well...i've decided to plot stress against the logarithm of the N-values? could you please show me how I am supposed to deal with the figures 3 and 3.7?
 
  • #7
For example, in the table in the OP, a stress amplitude of 170 correlates with 3.7 x 10^4 cycles to failure. 3.7 x 10^4 is scientific notation, and this figure equals 3.7 x 10000 = 37000 cycles. In your plot, assuming you do a log-log plot, the x value of this point is log (37000) = 4.568, and the y value is log (170) = 2.230

I strongly urge you to study and refresh your knowledge of scientific notation.
 
  • #8
SteamKing said:
For example, in the table in the OP, a stress amplitude of 170 correlates with 3.7 x 10^4 cycles to failure. 3.7 x 10^4 is scientific notation, and this figure equals 3.7 x 10000 = 37000 cycles. In your plot, assuming you do a log-log plot, the x value of this point is log (37000) = 4.568, and the y value is log (170) = 2.230

I strongly urge you to study and refresh your knowledge of scientific notation.

yeah I am sort of new to this so its taking a while. thanks
 

1. What is an S-N diagram and how is it used in engineering?

An S-N diagram, also known as a stress-life curve, is a graphical representation of the relationship between stress (S) and the number of cycles to failure (N) for a material. It is commonly used in engineering to determine the fatigue strength and lifetime of a material under cyclic loading conditions.

2. What is the process for creating a plotting S-N diagram with cycles to failure?

The process for creating an S-N diagram involves conducting a fatigue test on a material to determine its stress-life relationship. This involves subjecting the material to varying levels of stress for a certain number of cycles until it fails. The results are then plotted on a graph with stress on the y-axis and number of cycles on the x-axis. A line is then drawn connecting the data points to show the relationship between stress and cycles to failure.

3. What factors can affect the accuracy of an S-N diagram?

The accuracy of an S-N diagram can be affected by several factors, including the testing conditions (such as temperature and loading rate), the material's microstructure and surface conditions, and the shape and size of the specimen used in the fatigue test. It is important to carefully control these factors to ensure the accuracy of the diagram.

4. How is the information from an S-N diagram used in engineering design?

The S-N diagram provides valuable information for engineers to design and select materials for components that will be subjected to cyclic loading. It helps them determine the maximum stress levels that a material can withstand for a specific number of cycles, and therefore, the expected lifetime of the component. This information is crucial for ensuring the safety and reliability of engineering structures and products.

5. Can an S-N diagram be used for all materials?

No, an S-N diagram is specific to a particular material and cannot be used for all materials. The stress-life relationship of a material depends on its composition, microstructure, and processing, and therefore, each material will have its own unique S-N diagram. It is important to use the correct S-N diagram for the specific material being tested to ensure accurate results.

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