The two dimensional size measurement device was introduced in the low-cycle impact fatigue tests of SS400 smooth and notched bodies, which enabled us to clarify the local strain variation of a specimen easily and precisely for long test time duration over 24 hours. In the experiments, a circular test area of 40mm's diameter was provided by the sensor device, and the smallest cross-section area of a specimen was automatically chosen, and its size was recorded out with the time intervals of 40ms to is to a portable computer. The time variation of the specimen' s longitudinal strain was then able to be estimated by using the smallest cross-ection area size and the incompressible condition of test materials.
