Question

16. Consider 7075-T6 aluminum with fatigue crack growth properties as given in Table 6.3. Assuming that 1=0.5 in the Walker equation, @. estimate da/dN versus AK equations in the form of Eq. 6.22a for R=0.4 and 0.8. 6. plot the equations from (a) on a log-log scale along with the R=0 equation. Keep in mind the proper region I limits of the equation. 169x10-5 ©. For a given AK, by what force does the crack growth rate, da/dN, increase if R is increased from 0 to 0.4? If it is increased from 0 to 0.8? 6.22 a da n ACAK) (I-R) "(1-1) A (Ok)" ملح

Consider 7075-T6 aluminum with fatigue crack growth in Table

Answer 1

63 Given d=0.5 da du ACAK? (T-Ronche) ~ll A =2.7X10 n=3.7 for R=0.4 da -14 2.7810 7x10 3.7 (ok) 761-0.5) dN (1-0.4) 3.74 11 3.7 da dh = 6.94x10. Cak) for R=0.8 3.7 da dN 2 2.7x10 CAK? 3.7(los) 1-0.8) -10 3.7 2 da dH 8.3810 CAK) Ocoley b putting Rao in the equation gives. Cox) 3:1 2 da a 2.7 x 10 du Applying log on on both sides 7x20) 3.7 log ( daha log CAK) + log (2-7x10 doy cle3.7 log(ok) - 10 508 CS Scanned with CamScanner

logeda (2.85 log (OK) -10.56 Constant Ak a for da net) Ci- Rq) du ni-7 da (L-Ra) R=0.4 4 given R=0 'da 37(1-0) (1-0.4) IN rda dN :) rda AN 2.57 Cape da will increase increase by a factor of 2.57. dh CS Scanned with CamScanner

for Rao to 0.8 3.7x0.5 da dN (1-0.8). 'da dh ) , rda d N ) = 19.6 dN 1 of 19.6. a factor da du will increase by CS Scanned with CamScanner