These ambitious research objectives call for authoritative materials tests, which can only be achieved with high-precision measurement technology. High-quality optical extensometers are increasingly used in order to obtain reliable results when testing metals, even in the rugged environment of continuously operating automated materials testing systems.
One such extensometer is the laserXtens Array developed by Zwick which is already providing reliable service to leading steel producers. This laser speckle extensometer combines a large measurement range with high resolution for tracking gage marks in compliance with EN ISO 9513. Automatic application of the laser speckle gage-marks, plus automatic setting of the initial gage-length enable a wide range of specimens to be tested automatically with no need for specimen preparation. In some cases two opposed measuring heads are used to measure deformation on two sides of the specimen and, where necessary, to compensate exactly for horizontal deformation or displacement of the specimen. Installing an additional video camera in the laserXtens housing and mounting a backlight screen in the opposed housing allows transverse strain to be measured. The combination of non-contact measurement and a total absence of moving parts is a crucial advantage for use in continuous operation, particularly with regard to wear and long-term accuracy.
Close collaboration between Zwick’s experts and the steel producers during the ongoing development of optical measurement systems allows practical experience to be channeled directly into product design.