Mohr circle:the fundemental principle of finite strain measurements

Finite strain measurement,the quantitative analysis instead of the qualitative analysis of deformed rocks,was founded in studying deformed rocks, and structure of orefield with the foundation of plate tectonic theories in 1960s.The main mark of the quatitative analysis was that the Mohr circle construction was introduced from mechanics into structural geology,and was improved and developed from then on. The finite strain Mohr cirle was established for analysing large deformation problems,and the polar Mohr circle was established later for analysing general shear deformation of rocks which distributed widely in the field.The famous chinese geologist Lee J S was the first people who introduced the stress Mohr circle and the Coulomb criterion from the field of mechanics into structural geology. Some chinese geologists made their contribution in improving and developing the polar Mohr circle method.The basic conceptions and construct methods of Mohr circle were introduced simply and popularily in this paper with some exercises and their explanations.