Research On The Damage Of Wind Turbine Blade Composites Based On Acoustic Emission Technique

Wind energy as a kind of renewable energy,in the national energy development strategy plays an important role,wind turbine is the wind energy into electrical energy key equipment,its safe and smooth operation is the wind energy can be effectively-converted into electrical energy prerequisites.But the wind turbine blade in the production,transportation installation and operation process will be affected by various factors,these factors will cause the wind turbine blade damage or even fracture,and the damage detection is to detect the blade internal material may exist in the microscopic damage and defects,for the blade damage detection need to use nondestructive testing technology.This paper is based on acoustic emission technology to monitor the damage process of wind turbine blade composite material under the action of external load,the purpose of this research is to use acoustic emission technology to study the signal change characteristics of wind turbine blade composite material in the damage process and characterize the damage process and identify different damage modes.The main research contents and conclusions of this paper are as follows.(1)In this paper,firstly,pure epoxy resin and composite tensile specimens were fabricated and damage signal acquisition was performed.The signal attenuation characteristics within the material were tested on the composite specimens prior to testing.It was shown that the further the distance from the sensor,the greater the signal attenuation rate and the smaller the relative attenuation rate.(2)It was found that the mechanical curve of the pure epoxy resin material fluctuated very little and the maximum load was 3.2 kN;the maximum strain of the composite part decreased with increasing loading speed but the maximum stress increased.The cumulative energy values exceeded 420,000 mv*us for all three velocities during the period before fracture to complete fracture;when the amplitude value was 90-95 dB,the count value reached more than 30,000,the energy value reached about 35,000 mv*us,and the duration value reached about 40,000 us.The normalized cumulative counts and cumulative durations were found to be the basis for determining the development of material damage,and the normalized cumulative energy parameters were used to characterize the occurrence of material damage from the time before fracture to the time of complete fracture.The Pearson correlation coefficient was used to analyze the parameters and found that the correlation coefficient values were above 0.8,which is a strong correlation.(3)The signal types were classified into four damage types using k-means clustering and waveform analysis:matrix fracture,fiber matrix debonding,fiber fracture and delamination and the amplitude ranges were 40-70 dB,58-80 dB,75-95 dB and 85-100 dB,respectively,with peak frequencies corresponding to different value ranges.The rise time values of delamination damage were 83.5%higher than fiber matrix debonding,58.2%higher than fiber fracture and 20.8%higher than matrix fracture,and their duration values were 62.2%higher than fiber matrix debonding,53.1%higher than fiber fracture and 17.7%higher than matrix fracture;microstructure photographs of the four different damage patterns were used to establish a micromacro connection with the previous study,and the four types of damage corresponded to The rise time,duration and peak frequency of the waveforms were well distinguished.The analysis using Hilbert yellow transform found that the characteristics of the parameter change trends of different damage time periods are consistent with the characteristics and trends of the parameter changes of the material in the damage process analyzed in Chapter 4,which further verifies the reliability of the analysis process and research results,which has practical significance for the judgment of blade damage in engineering applications.