1. The problem statement, all variables and given/known data Hi, I require some assistance using coffin's law. I have the strain range and cycles to failure but need coffins slope- 'c'. C2 can then be found after the other values are known. 2. Relevant equations Δε^pl=C2/N^c Where Δε^pl is plastic strain range, N is the cycles to failure and C2 and c are constants. 3. The attempt at a solution I have the strain range and cycles to failure data in excel. No problems here. It seems from the above graph that coffins slope-c is the slope of the Log(stress amplitude) and Log(cycles to failure) regression line. So I use excels slope function and get -0.05 The textbook and other sources say this value is usually +0.5. using the 'c' I attained in the equation results in lower cycles to failure for lower strains, the opposite of what is expected. Thanks for any help you can offer.