Experimental Study On Startup Time Difference Of Data Acquisition In High-Speed Photomechanics

The combination of high-speed imaging device and photomechanical analysis method is an important experimental method to investigate the mechanical behaviour of materials or structures under high-strain-rate conditions such as impact,explosion or dynamic instability.Some cases such as three-dimensional deformation measurement and mechanical behaviour analysis of structures usually require multiple high-speed imaging devices and high-speed electrical signal acquisition devices for joint measurement.Thus,the start-up time difference(STD)between multiple devices which worsens the synchronization of data acquisition will greatly affect the measurement accuracy.To sort out these issues,this paper develops a method to measure STD of high-speed data acquisitions based on optical and electrical coding technology,and investigates the law of different influencing factors on STD.The correction method of STD is proposed based on the related investigation.The paper investigates the method for time expression of high-speed data acquisition,and related system is constructed.Based on the principle of optical encoding for time and the oversampling decoding algorithm,a high-efficiency and high-precision method using coded optical signal to express time is developed.Moreover,an optical code system of high-speed image acquisition time is constructed,and the experimental calibration shows that the time positioning accuracy of this system is about 1/50 of the minimum resolution of time coding.Similarly,a method which uses coded optical and electrical signals to express time simultaneously is developed,and the availability is verified by numerical simulations.The system for expressing high-speed image / electrical signal acquisition time is constructed.The experimental calibration shows that the time positioning accuracy of this system is the same as that of time coding.Based on the above method and related system,this study carries out the measurement and correction of the STD between high-speed data acquisition devices.The measurement system of STD between high speed cameras,high speed camera and ultra-dynamic strain acquisition device are set up respectively.The influences of combination and triggering methods on STD are investigated.Combining with the measurement system and the factors that affect the STD,the correction method is provided.At the same time,the application example of correction the STD between the high-speed camera and the ultra-dynamic strain acquisition device in the SHPB tests is given.The present study on STD between high-speed data acquisitions is of great significance to improve the measurement accuracy of high-speed photomechanical method.It also provides experience for improving the accuracy of other high-speed photogrammetry method.