Mohr developed a generalised form of the theory around the end of the 19th century. Coulomb's contribution was a 1773 essay entitled " Essai sur une application des règles des maximis et minimis à quelques problèmes de statique relatifs à l'architecture" The Mohr–Coulomb theory is named in honour of Charles-Augustin de Coulomb and Christian Otto Mohr. An alternative view derives the Mohr-Coulomb criterion as extension failure. By conservation of energy the sum of these must be zero and this will make it possible to calculate the failure load of the construction.Ī common improvement of this model is to combine Coulomb's friction hypothesis with Rankine's principal stress hypothesis to describe a separation fracture. This makes the strength of the material determinable by comparing the external mechanical work introduced by the displacement and the external load with the internal mechanical work introduced by the strain and stress at the line of failure. It can be shown that a material failing according to Coulomb's friction hypothesis will show the displacement introduced at failure forming an angle to the line of fracture equal to the angle of friction. According to the principle of normality the stress introduced at failure will be perpendicular to the line describing the fracture condition. Mohr's circle is used to determine which principal stresses will produce this combination of shear and normal stress, and the angle of the plane in which this will occur. Coulomb's friction hypothesis is used to determine the combination of shear and normal stress that will cause a fracture of the material. In structural engineering it is used to determine failure load as well as the angle of fracture of a displacement fracture in concrete and similar materials. In geotechnical engineering it is used to define shear strength of soils and rocks at different effective stresses. Generally the theory applies to materials for which the compressive strength far exceeds the tensile strength. Most of the classical engineering materials follow this rule in at least a portion of their shear failure envelope. Mohr–Coulomb theory is a mathematical model (see yield surface) describing the response of brittle materials such as concrete, or rubble piles, to shear stress as well as normal stress.
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