Homework Help: S-N diagrams

1. Aug 10, 2011

qwerty0123

how do i plot the follwing S-N diagram, i am having trouble with what im 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?

2. Aug 10, 2011

SteamKing

Staff Emeritus
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. Aug 11, 2011

qwerty0123

ok.....so how would i go about doing that?

4. Aug 11, 2011

qwerty0123

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. Aug 11, 2011

SteamKing

Staff Emeritus
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. Aug 14, 2011

qwerty0123

well.....i've decided to plot stress against the logarithm of the N-values? could you please show me how im supposed to deal with the figures 3 and 3.7?

7. Aug 14, 2011

SteamKing

Staff Emeritus
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. Aug 15, 2011

qwerty0123

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