A machine part is made from 2024-T351 aluminum plate. For each cycle of the machine the part undergoes a tensile stress that varies from 0 to 1/2 of the material’s tensile yield strength. The machine...

A machine part is made from 2024-T351 aluminum plate. For each cycle of the machine the part undergoes a tensile stress that varies from 0 to 1/2 of the material’s tensile yield strength. The machine cycles 20 times per minute, 24 hours per day, 365 days per year. At the last inspection of the machine the part was found to have a central crack 1.7 mm long. The machine is inspected every six months. Estimate the expected crack length at next inspection. The values of the coefficient and exponent in equation 6.4 for this material are A = 4.8 x 10-11 (mm/cycle) and n = 3.5.