Abstract
An Eulerian extensometer which gives Eulerian description of displacement has been proposed by the author for displacement measurement in material testing, and it has been shown that PC mouse, which is now an indispensable computer input device, can also serve as an Eulerian displacement meter. However, in material testing, Lagrangian description of displacement is needed to obtain specimen elongation and nominal strain. In the present study, Lagrangian velocity, i.e. the material derivative of displacement has been expressed as the sum of Eulerian velocity and the product of the displacement gradient in material coordinate system and Eulerian velocity. On this basis, a simple algorithm has been devised to obtain nominal strain as well as Lagrangian description of displacement in real time from the output of Eulerian displacement meter in one- and two-dimensional displacement field. Numerical verification has also been carried out to demonstrate the validity of the proposed method.
