Lecture_Failure_Criterion

Lecture_Failure_Criterion - Class Workbook and Handouts -...

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Class Workbook and Handouts - MME 412: Mechanics of Materials Prepared by: Kumar V. Singh -75- Strength Theories (Criteria for material failure): Structural failure prohibits the structures to perform their indented functions hence while designing structure for a given loading conditions we should be able to predict the circumstances under which failure is likely to occur. Depending upon the loading conditions and material behavior the structures can have different types of failure modes. (a) Fracture: Crack initiation or growth (b) Yielding: Permanent Deformation (c) Excessive deflection or linear deformation: Vibration or dynamic loading (d) Buckling: Instability or sudden change in the structural configuration In this topic we will learn failure theories that are used to predict: Yielding in ductile materials o Maximum Shear Stress theory or Tresca criteria o Maximum distortion energy theory or Von-Mises criteria o Maximum Principal Stress theory o Maximum Principal Strain theory o Maximum Octahedral Shear Stress theory Fracture in brittle materials o Maximum Normal Stress theory o Coulomb-Mohr theory Figure 7.3-2 [1] Figure 7.3-1 [1]
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Class Workbook and Handouts - MME 412: Mechanics of Materials Prepared by: Kumar V. Singh -76- Yielding: It occurs at the microscopic or atomistic level due to the slip (dislocation) of the layers of atoms along those slip planes which are the weakest to shear resulting the beginning of plastic flow and permanent deformation. Hence yielding criterion must be based upon the shear
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Lecture_Failure_Criterion - Class Workbook and Handouts -...

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