The Sonic Characteristics And Detection Technology Research Of Defects In Steel Strand

In the prestressed structure,the steel strand is the main force-bearing component,and the high-strength steel wire is the component unit of the steel strand.When the high-strength steel wire has defects,the location and degree of damage is uncertain,and will lead to the reduction of the strength of the steel strand,which will further affect the durability and overall safety of the prestressed structure.In order to ensure the normal use of steel strands,it is necessary to detect the defect size and location of a single high-strength steel wire and whole strands during the process of production and use.Acoustic detection is an important technical means of nondestructive testing.Through acoustic detection of high-strength steel wire and steel strand,the acoustic signal received is processed and analyzed to extract acoustic characteristic parameters that can reflect the state of defects,so as to achieve quantitative judgment of highstrength steel wire and steel strand defects.Based on sound spectrum analysis method,this paper studies the acoustic characteristics and acoustic detection technology of defects of highstrength steel wire and strand.The main research contents and results are as following:(1)The influence of defect depth and location on acoustic propagation characteristics of high-strength steel wire was studied.Taking a single high strength steel wire as the research object,we used the finite element to simulate the acoustic wave propagation process in different defect status of high strength steel wire,and through the extraction of time-domain signal of the single node,Fourier transform and Hilbert transform were achieved,thus the frequency domain signals and power spectrum were gained,and then from the different depth of defect,the characteristic parameters were extracted-the signal in frequency domain signal integral ω,Characteristic parameters-power mean γ and power maximum λ-were extracted from power spectrum signals at different defect locations.In addition,the time-domain signals of different defect states were processed by wavelet transform to obtain the influence of defect states on the modal distribution of guided waves.The results show that ω decreases linearly with the increase of defect depth,γ and λ increase with the increase of defect location distance,and L(0,1)modal signal is sensitive to defect.(2)The influence of defect depth and location on acoustic propagation characteristics of steel strand was studied.With steel strand as the research object,we used the finite element to simulate the acoustic wave propagation process in the different defect states steel strand.By extracting the time-domain signal of the receiving point and analyzing it,the parameters based on time domain signal were extracted and defined as time-domain attenuation ratio μ,and Fourier transform was also performed on the time-domain signal,and the parameters based on the frequency-domain signal were extracted,which was defined as the frequency-to-peak-topeak ratio β.In addition,when the sound of direct wave and echo was extracted from the time domain signal,the calculation of sound velocity and sound time difference was carried out.The results show that μ and β are sensitive to steel strand defects.μ increases with the increase of damage degree,and β increases with the increase of integrity degree.The location of defects can be determined by calculating the acoustic time difference and acoustic velocity.(3)The detection test of steel strand defect depth and residual bearing capacity was carried out,and the relationship between acoustic characteristic parameters and steel strand defect depth and residual bearing capacity was established.Acoustic tests were carried out on the steel strand models with different defect depths,and the received acoustic signals were compared and analyzed in time domain and frequency domain.After that,tensile tests were carried out on the steel strand models with different defect depths to establish the relationship between acoustic characteristic parameters and residual strength of the steel strand.The results show that μ and β can effectively reflect the damage condition of steel strand,and can be used to quantitatively determine the depth of defects in steel strands.and there is a positive correlation with the residual bearing capacityIn this paper,the relationship between acoustic signal characteristic parameters and damage of high-strength steel wire and strand is established by finite element simulation and test,which provides a basis for quantitative judgment of defects of high-strength steel wire and strand.