Effect of stress ratio on fatigue-crack growth in 7075-T6 aluminum-alloy sheet

摘要: Abstract Axial-load fatigue-crack-propagation tests were conducted on 12 in. (305 mm) wide sheet specimens made of 7075-T6 aluminum alloy. These at stress ratios R (ratio the minimum to maximum stress) ranging from −1.0 0.8 and levels 5 50 ksi (34–340 MN / m 2 ) study effects ratio fatigue-crack growth. The data analyzed using Paris' stress-intensity analysis. negative values fell into a relatively narrow scatterband along with results = 0 plot rate against stressintensity range. Apparently, compression portion loading cycle did not significantly affect crack growth in these tests. different positive discrete bands plots. varied systematically , that is, higher given value ΔK This spread rates was small lower range, but became progressively larger as range increased. Semiempirical equations developed by Forman et al ., Broek Schijve, Paris fitted this investigation least squares fit. Forman's equation gave best fit data. fracture surfaces changed normal mode shear within reasonably for all values. transition approximately constant ratios. adequately represented variation between