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# Mudzm14 - Muddy Card Responses Lecture M14 Why are we rotating coordinate systems There are many reasons Here are two Materials tend to fail as a

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Muddy Card Responses Lecture M14 Why are we rotating coordinate systems? There are many reasons. Here are two. Materials tend to fail as a result of the stresses acting on them. Brittle materials fail due to the maximum tensile stress, ductile materials (including most metals) fail due to the maximum shear stress. As part of assessing structural integrity it would be useful to be able to determine the maximum values of stress at a particular location. A second reason is that we sometimes need to specify directions for making joints between sheets of material, or for putting in structural reinforcement (stiffeners or fibers in a composite) and we will want to be able to analyze the stresses as a function of direction. Unclear as to why we need to transform the stresses onto a different set of axes. See comments above. Other than maximum and minimum stresses what information does Mohr’s circle give us/ what is the point of drawing it? How do you get equations from it? The maximum and minimum stresses are pretty important in their own right. Being able to resolve stresses into different directions is also important. If you draw a Mohr’s circle in terms of an arbitrary state of stress and then look at the state of stress at an angle q from the original axis directions, you will recover the equations we derived from the triangular element. Would we ever transform to a different coordinate system, ie. From rectangular to polar? Or are transformations simply for orthogonal coordinates. If so why do we transform in the first place? You can certainly transform coordinates from cartesian to polar, but we are not going to examine that in Unified. The reasons for needing to being able to rotate coordinates are given above. Mohr’s circle – needs more exposure and explanation of what it does. Understood. We will cover it in recitation tomorrow and also do some examples in lecture. Still a little fuzzy on how to get stresses from reading Mohr’s circle. See above. We will do more examples.

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## This note was uploaded on 02/20/2012 for the course AERO 16.02 taught by Professor Charlescoleman during the Winter '12 term at MIT.

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Mudzm14 - Muddy Card Responses Lecture M14 Why are we rotating coordinate systems There are many reasons Here are two Materials tend to fail as a

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