113_2009_HW6_sols

113_2009_HW6_sols - UNIVERSITY OF CALIFORNIA College of...

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Unformatted text preview: UNIVERSITY OF CALIFORNIA College of Engineering Department of Materials Science and Engineering Assigned 11/3/09 Due 11/10/09 Fall 2009 MSE 113 Mechanical Behavior of Materials Prof. Ritchie PROBLEM SET 6 SOLUTIONS Problem 1 a) Crack deflection crack deflect by, for example, a weak interface (wood, bone) and lowers the local applied K at the crack tip Transformation toughness a material transformation causes an additional compressive stress in the material, lowering the K at the crack tip. Example: partially stabilized zirconia. Microcrack toughening a microcrack zone ahead of the crack tip causes a compressive stress, lowering the K at the crack tip. Example: bone Crack bridging bridges behind the crack tip cause partial crack closure, which lowers the K at the crack tip. Example: fiber composite with cracks running perpendicular to the fiber orientation. b) Intrinsic vs. extrinsic toughness : Intrinsic toughness is toughness of the material itself, whereas extrinsic toughness lowers the stress intensity felt at the crack tip and is not caused by the material toughness (if one would have a toughened and un-toughened ceramic the pure material has the same toughness in both cases, but the mechanisms...
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113_2009_HW6_sols - UNIVERSITY OF CALIFORNIA College of...

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