A polar exploration team based near the south pole is faced with an emergency in which a very important “housing and supplies” module must be lifted by a special 1 crane, swung across a deep glacial crevasse, and set down in a safe location on the stable side of the crevasse. The only means of supporting the 450-kN module during the emergency move is a 3.75-m long piece of steel with a rectangular cross-section of 4-cm × 25-cm, with 2 small holes as shown in Fig. 2. The holes are both 3-mm in diameter, and are located at midspan, 25-mm from the upper and lower edges, also shown in the figure. These holes were drilled for some earlier use, and careful inspection has shown a tiny through-the-thickness crack, approximately 1.5-mm long, emanating from each hole, as shown. The support member may be modeled for this application as s 3.75-m long simply supported beam that symmetrically supports the module weight at two points, located 1.25-m from each end, as shown. The material is known to be D6AC steel (1000◦F temper). Ambient temperature is about -54◦C. Is the beam predicted to fail or not? If not, what is the safety factor? Would you approve the beam to be used one time only for this purpose?
 

Enlarged view Crack 25 mm 225 kN 225 kN 1.25 m 1.25 m 25 m/2-1 Crack length 1.5 mm 1.25 m 3 mm D. hole 25 cm -4 cm RL 1.88 m RR 3.75 m -3 mm D. hole Enlarged view 25 mm -Crack length 1.5 mm Crack re 2: Support beams with two small holes with cracks emanating from holes.