Identification Of Fan Blade With Single Crack

Mine ventilators provide continuous fresh air for downhole operators to regulate the amount of air,humidity and temperature required for downhole,and to dilute and remove toxic and hazardous gases,improve working conditions,and are critical in mine production effect.Blade as a key component of the fan,its reliable operation is essential.Once the cracks occur in the blade,it often poses a great threat on the operation of the fan unit,and even lead to the occurrence of major accidents,so the crack monitoring and identification of the blade is of great significance.In order to study the blade crack quickly and effectively,this paper presents a simple and reliable method for fan blade crack identification.And the test system platform is built,and the modal test is carried out to verify the feasibility of the proposed method.The main work is as follows:(1)The damage theory of blade crack and the theory of blade vibration are introduced.The characteristic equation of transverse vibration of cracked blade is obtained.The natural frequencies of cracks in different positions and different depths are obtained,and the influence of crack location and crack depth on the inherent characteristics of the blades is summarized.(2)Based on the analysis of the vibration dynamics equation of the discretization of the blade structure,it is deduced that the "frequency variation squared" of the arbitrary order mode of the blade structure includes the information of the same unit damage.In this paper,the method of identifying the position of the blade based on the natural frequency change is proposed,that is,using the natural frequency change squared ratio confidence criterion as the basis for judging the similarity between the two conditions to determine the location of the crack.(3)By separating the pulse or free vibration response of the system into local response corresponding to each stiffness region,a system identification method based on bilinear system is proposed.The natural frequencies are extracted from each of the local responses after separation,and the presence or absence of the respiratory crack is determined by comparing the difference in the percentage of the natural frequencies of the two groups.(4)A verifying experiment was carried out by using the structure of the blade structure.The vibration response is obtained by hammering method,and the natural response is recognized by the DASP software.The natural frequency of the two local responses is obtained by the data processing in MATLAB.The natural frequency of the first five order is obtained from the global response,and the square ratio of the natural frequency of the blade structure and the cracked blade structure are obtained.The crack location is determined from the similarity compared with the simulated data.The percentage difference of the local response and the nature of the monotonic change with the depth of the crack are used to quantify the depth of the crack.Experimental verification shows that the proposed method of blade location and depth is feasible.