Test Research on Measurement Parameters of Digital Image Applied to Fatigue Monitoring

Fatigue monitoring of steel structure is an important part of steel structure health monitoring system.In recent years,under the rapid development of image acquisition and data remote transmission technology,the application of non-contact digital image measurement technology in fatigue monitoring has attracted the attention.In order to achieve the goal of detecting the fatigue anomaly by means of the identification of certain parameter changes in the digital image before the appearance of identifiable cracks,Q345qD steel specimens were designed and processed for fatigue test.During the test,the ARAMIS optical measurement system was used to take pictures of the observation area dynamically and continuously to obtain the whole fatigue process image,and the image was converted into data inside the measurement system as the measured value.By comparing and analyzing the mechanical indexes and collection methods during the whole fatigue process,the shape and application feasibility of the strain and displacement parameters of the digital image were studied.Comparing the results of electrical strain gauge with image strain measurement in static load test to make sure that the accuracy of digital image measurement was satisfied or not.The strain and displacement changes of the specimen during fatigue process were studied.The sensitivity analysis of various parameter of the image with fatigue process was carried out.The optimal parameter index and the way to collect them were studied.Finally,the feasibility and implementation scheme of the application of digital image technology to fatigue monitoring are verified meanwhile both of objectivity and automation were in consideration.
It was shown that the ARAMIS optical measuring techniques can collect dynamically the image data of the measured surface without contact.The obtained 3D strain values meet the accuracy requirement.The nominal strain of cross-section can be obtained by average value method of cross section line.The fatigue abnormal information obtained from the displacement parameter is relatively late,which is unacceptable for fatigue monitoring.While it is acceptable to take the strain parameter as the monitoring object of digital image.It is proposed that the maximum strain eigenvalue on the equivalent cloud image can be intercepted as a numerical series for fatigue monitoring.The obtained data are objective,effective and practical,and are the optimal measurement parameters for the application of digital image to fatigue monitoring.