Development Of Real-time Optical System For Displacement Filed Measurement

Material testing machine is an important instrument of scientific experiments and widely applied to the study of material properties, however, due to the limitation of the extensometer, the complete displacement field distribution on surface of samples cannot be provided in tension, compression or fatigue test, and large deformation of sample cannot be measured too. By features of non-contact, real-time and the whole audience information provided by the optical measurement system, this article established the real-time displacement filed optical measurement system that can measure large deformation of specimen and observe the crake moment. Adopting Basler CCD camera as image sensor for image acquisition, using the Camera Link data cable to transfer data to the NI PCIE capture card and adopting labview parallel processing technology and RAID0storage mode, the system can reach120frame/s data acquisition velocity and nearly240M per second velocity of storage.This article implemented two displacement field calculation methods:automatic mesh method and digital correlation method. Automatic mesh method adopts the change of center coordinate displacement of each point in the grid lattice to reflect the change of displacement field. While combining advantages of geometric center with gray gravity, a new method is used to calculate the center coordinates of the grid points and make the calculation speed and accuracy achieve balance. In the aspect of grid lattice coding, this article adopted an improved one-dimensional code method to make calculating much faster and more adaptable. Digital correlation method does not require the production of lattice grid and acquire the deformation through analyzing changes of speckle.The calibration results through high precision calibration plate show that the measurement stability of the system is0.5um, the measurement error can reach7umafter eliminating distortion. By combining with Instron, Shimadzu, MTS and other materials testing machine, this paper obtain results of the sample tensile test on the aluminum, rubber, iron and other materials. The results show that the system can acquire distribution of plane displacement field real time and the image processing velocity can reach10frame/s; at the same time, this system can observe crack on line, and the velocity of observation and storage can reach120frame/s.