(1) \"Big Dig\" tunnel ceiling collapse in Boston started as: (a) fatigue failur
ID: 693956 • Letter: #
Question
(1) "Big Dig" tunnel ceiling collapse in Boston started as: (a) fatigue failure (b) crack expansion from stress concentration, (c) creep failure, (d) shock failure (2) Materials with Poisson's ratio of zero are called: (a) auxetic materials, (b) incompressible materials, (c) functionally graded materials, (d) classified as Silicene (3) Calculate the value of the "Bulk Modulus" in terms of the Young's modulus E when the Poisson's ratio is (1/3): (a) 3E (b) E/3 (c)E (d) 2E/3 (Hint: read on bulk modulus first) (4) Stress in a material varies with strain as -cam (that is strain to the power of (1/2)) , where is the strain and is the stress. Calculate the toughness of the material if it fails at a strain of (9/4):(a) 2/3 (b) 9/4 (c) 4/27 (d) 3/4 (5) The average diameter of indentation when testing the Brinell hardness of a material was found to be 6 mm. Diameter of the indenter is 10 mm, then the Brinell Hardness number is given as: (a) Pa 10 ) (b) 2P7x (c) 2P/(101) (d) 2P/(St) where P is the force. (6) Generally, fracture occurs: (a) above the glass transition temperature (Tg) but below melting (c) below Tg (d) it can happen at any temperature, (b) any temperature above Tg temperature (7) Most of the gas pipe explosions we discussed in the class very likely occurred when the atmospheric (or ground) temperature (a) went above the melting temperature of the pipes, (b) went below the freeing temperature of the pipes, (c) went below the brittle-ductile transition temperature, (d) below the Brill-transition temperature of the pipes (8) An isotropic material with a Poisson's ratio 0.3 is subjected to a stress of 10' psi in the axial direction. Its modulus of elasticity is 10 psi, then the magnitude of lateral (perpendicular to the axial direction) strain is: (a) 0.3 (b) 0.03, (c) 3 (d) 0.003 (9) For a material with a critical stress intensity factor Kir for all types of cracks, an engineer found two cracks at two different locations - a tunnel crack and a penny crack. For an applied stress of o, which statement is the best regarding which crack is the critical one (meaning with the same crack size, which would initiate fracture): (a) tunnel crack, (b) penny crack, (c) both are equal in this regard, (d) none of these, we need a wedge-opened crack (10) If the critical stress intensity factor for a tunnel crack Kie is 30 MPa-m2 with an yield strength of 500 MPa. If the thickness of this material is 1 cm, what is the applied stress when it fails under fracture if the tunnel crack has a le (c) 300 MPa (c) 100/ ngth of length 2a . 0.02/s meters? (a) 30 MPa (b) 300 MPaExplanation / Answer
(1) Option C poor creep is the reason behind the collapse
(2) Option C. Functionally graded materials
3) E = B (1-2n) = B (1-2/3) , B = 3E
option a is correct
answering only 3 due to time constraint and policy guidelines .
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