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

giver kic= 34 MPa m 12 crack length (2a) = 1 ซ) ๒ cylinder diameter (D)=10cm max. fluctuating shess (os= 30ompa at critical crack length (ac) KICE yo snad Shape of of crack is assumed to be elliptical 29 s D

Y is geometric factor givenas 13.69-0,6822+1,35213) & (indy Y = 1.9987-1.326d -- 0.tag² da crack length Diameter a - 11m 2 2x10x10 locm x = I = 0.005 200 Y = 1.98207 0.0172 Y = 1 9649 - for critical crack length (2.9.) Егс - Улаа => 345 1.9649 X 300 xrac raac 0,0.57 68 Та. 6. 003327 acao.oolim 20c a ca Toimm so crack length critical crack length is 200 = 2.2 mm

length e failure Crack shape assumption will not hold frue near the crack assumed elliptical shape is now de formed has taken shape a s a al most of a line.