Research On The Mechanism And Influencing Factors Of Crack Heating Of Concrete Slab Under Ultrasonic Excitation

Cracks are common diseases of concrete structures and an important indicator of structural health state.In recent years,a large number of transportation infrastructure has been put into operation,and crack detection methods of structures have attracted more and more attention from experts and scholars.Aiming at the shortcomings of the existing defect detection methods for concrete structures,an ultrasonic infrared thermography detection method for concrete cracks is introduced.The main research results and conclusions are as follows:(1)The domestic and foreign research results of ultrasonic infrared thermography detection method were summarized,and the heating mechanism of cracks under ultrasonic excitation was deduced and explained.(2)Through prefabricated concrete slab specimens with cracks,the ultrasonic excitation system,infrared thermal imager and computer control system are selected to realize the detection and identification of concrete slab cracks under laboratory conditions.It is proved that the ultrasonic infrared thermography detection method is feasible for the detection and identification of concrete cracks.(3)Increasing pre-tightening force,prolonging excitation time,increasing excitation intensity and increasing excitation frequency can promote crack heating;the smaller the crack width,the better the crack heating effect and the stronger the sensitivity to excitation parameters;the defect characteristics of thermography obtained from experiments are easily covered up by noise,which will affect crack identification;the continuous friction loss of the crack may make the crack heating effect worse.(4)Considering self-vibration characteristics,material damping and contact effects,a model was established,based on finite element software ANSYS/LS-DYNA.The calculation results show that the crack heating is determined by the contact collision effect and the friction slip effect of a node on the crack surface.The acoustic chaos effect and the resonance of the specimen promote the crack heating.The standing wave resonance suppresses the crack heating,and the crack position generates strong stress concentration under the vibration state,which promotes the crack heating.