. Using the following concepts: torsion of a solid circular cross-section, Mohr's circle, and failure of brittle materials, explain why a cylinder of chalk shows a helical failure surface when it is...

Mechanics of materials

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Extracted text: . Using the following concepts: torsion of a solid circular cross-section, Mohr's circle, and failure of brittle materials, explain why a cylinder of chalk shows a helical failure surface when it is twisted till it breaks. See the figure below.