Question

A crack, 1 mm long on the surface, is discovered in a 6061-T651
Al alloy cylindrical support beam using the eddy current technique. The beam’s
diameter is 10 cm. The beam is situated in a aircraft such that it is under a
uniform normal stress that is fluctuating. The maximum stress on the beam is
300 MPa. What shape would you assume the crack has? What length would
would the crack need to grow to along the surface by fatigue in order for it
become unstable (catastrophic fracture)? Based on your estimate of the critical
crack length, would your crack shape assumption probably still hold just before
the beam completely fractures?

Answer 1