113_2009_HW7_solns - UNIVERSITY OF CALIFORNIA College of...

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UNIVERSITY OF CALIFORNIA College of Engineering Department of Materials Science and Engineering Assigned 11/19/09 Due 12/03/09 Fall 2009 MSE 113 Mechanical Behavior of Materials Prof. Ritchie PROBLEM SET 7 SOLUTIONS Problem 1 a) Any 4 out of the following are acceptable: Corrosion Fatigue Crack initiation is facilitated by corrosion, especially pitting, and the crack grows under cyclic loads. Sometimes, debris from the corrosion process gets stuck at the crack tip and helps to force the crack open during the cyclic loading, thereby increasing the crack growth rate. Stress Corrosion Cracking (SCC) oxides that form on the crack surface are more brittle than the material underneath and crack under lower applied stresses than KIC for the metal. Once the oxide cracks, one of two things can happen: either anodic dissolution at the crack tip or the formation of more oxide. Either the anodic dissolution itself or cracking of the newly formed oxide will advance the crack tip forward. Hydrogen-Assisted Cracking (HAC) Hydrogen can enter a system in a variety of ways (metal is in a hydrogen-rich environment, H is inside the metal due to high pressure, or the metal is in an acidic environment). Once the H is near a crack tip, it can lead to the following embrittling mechanisms: reduction of surface energy (enabling cracks to form easier), enhancing dislocation mobility/attacking local bonds in the metal, or by the formation of brittle metal hydrides. Hydrogen Attack
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113_2009_HW7_solns - UNIVERSITY OF CALIFORNIA College of...

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