MSE 243A Final Exam (3 hours) Fall 2015

MSE 243A Final Exam (3 hours) Fall 2015 Prof. Kanji Ono Students can consult the slide files distributed through CCLE as 243-xx (xx = 1 to 14, some with suffix letter), including own handwritten notes. Janssen’s book (or its copy) is also allowed. Calculator and a ruler can be used. 1. (50) a. Using the data from the attached graph, determine KQ of the samples A and B. The specimen geometry is the standard compact tension type per ASTM E399 (or its subsequent versions like E1820) with the thickness of 1.00” and a/W = 0.50. b. Do these satisfy the condition with respect to the maximum load? c. What level of the yield strength is required to qualify these KQ as KIc (ignoring other conditions that may disqualify)? (Get 2 values as KQ is likely to be different.) d. What is the maximum allowable pre-cracking fatigue maximum load? e. Are there other conditions that need to be satisfied? Name at least 2. 2. (9) Select the best answer (circle one) a. Most likely source of SCC initiation is fillet corrosion pit scratch blister extrusion b. R value for the cyclic loading of a rotating axle is -10 -2.0 -1.0 -0.5 0.1 0.5 1 c. In wrought alloy plates, the lowest fracture toughness is generally found in L-T orientation T-L orientation S-T orientation 3. a.(21) Describe the macroscopic types of fracture; i.e., fibrous, shear and flat. b. (10) Summarize the main features of cathodic SCC (or hydrogen embrittlement) mechanism. 4. (30) a. A J vs. Δa plot is used for getting JIc. Here, the so-called blunting line is defined. Describe it and define parameters appearing in the equation for the line. Also explain how this is related to the crack tip deformation. b. What is its role in the determination of JIc? c. Describe briefly other important steps in the determination of JIc. 5. (25) In a very large 7178-T651 sheet, a through-crack is found with a length of 2a = 7 mm. This structural part will be used with exposure to salt water where stress corrosion plays a role. The incubation time for the material can be ignored as this part has been already exposed to the environment. Information about the stress corrosion crack growth rate is given below and assume that da/dt at Stage III is equal to that at Stage II. For the geometry of the part the stress intensity as a function of crack length a is given by KI = σ √πa. The part will be subjected to a constant nominal stress equal to 130 MPa. Estimate the remaining lifetime of the part (in seconds) if possible crack growth is allowed up to KI = KIc = 24.0 MPa√m. Note log da/dt ranges from -12 to -5. 6. (30) a. Describe leak-before-the-break concept. b. Examine the fractograph below. Identify the origin of fracture, pointing precisely with an arrow. Do you think fatigue played a part in this failure? Give your reason for either yes or no. c. What is meant by the upper shelf energy? How can it be used in estimating KIc? 7. (30) Using the fatigue data below, obtain the Manson-Coffin relation for 1045 steel. 8. (20) a. Is there a way to distinguish anodic dissolution (anodic failure) and hydrogen embrittlement (cathodic failure)? Explain. b. Obtain the stress intensity factor for an embedded circular crack of radius 0.005 m subjected to 100 MPa stress normal to the crack plane.

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