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Unformatted text preview: MechEng 382 Winter 2009 Homework #8 Solutions 1. [ Dowling , Prob. 8.5] Define the following concepts in your own words: (a) Modes I, II, and III, (b) cracktip singularity, (c) stress intensity factor, (d) strain energy release rate G , and (e) fracture toughness K Ic 1 MechEng 382 Winter 2009 Homework #8 Solutions 2. [ Dowling , Prob. 8.6] A centercracked plate of AISI 1144 steel has dimensions, as defined in Fig. 8.12(a), of b = 40mm and t = 15mm . For a safety factor of three against brittle fracture, what is the maximum permissible force P on the plate if the crack halflength a is (a) 10mm, and Solution P = 1 . 49 × 10 5 N = 149kN . (1) (b) 24mm? Solution P = 7 . 44 × 10 4 N = 74 . 4kN . ( 1 ) 2 MechEng 382 Winter 2009 Homework #8 Solutions 3. [ Dowling , Prob. 8.8] A tension member is made of AISI 1045 steel (Fig. 8.7) heat treated to a hardness of HB = 400 . It has a width of b = 120mm and a thickness of t = 12mm , and there may be an edge crack through the full thickness, as shown in Fig. 8.12(c). (a) If the edge crack has length a = 18mm , what tension force P can be allowed for a safety factor against brittle fracture of 3.0 in stress? Solution P = 1 . 259 × 10 5 N = 125 . 9kN . (2) (b) For the force calculated in (a), what is the safety factor against fully plastic yielding?...
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 Winter '08
 Thouless
 Strain, Stress, Fracture mechanics, N. E. Dowling

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