Load carrying capacity of material without excessive deformation or failure is characterized by a term, “stress”. Stress is defined as, “force experienced per unit area, expressed in pressure units.
Stress cannot be measured directly. Therefore, it is normally calculated from the changes in mechanical dimensions and the applied load. Strain is measured as mechanical deformation formed due to stress with the help of strain gauge measurement devices. Linear strain is the ratio of change in length to the original length.
The strain gauge element is defined as, transducer or device used to measure dimensional change on the surface of a structure under test. ” Strain gauge gives indication of strain at only one point.