Fatigue Damage Monitoring Research Of Wind Turbine Blades Based On The Acoustic Emission Technology

As a kind of green non-polluting new energy, Wind energy is paid more and more attention, and will become one of the main energy resources for the survival and development of human society in the future. The wind power industry has a broad and bright future. However, the safety of the wind turbine is an important factor that affects the efficiency of wind power generation. Especially the wind turbine blades, which operating in the natural environment wind farm for long term frequently failure. Once serious damage to the blades, repair work extremely difficult, which not only greatly reduce the working efficiency of the wind turbine a, but also cause huge economic losses to enterprises. The structural health monitoring of wind turbine blades is of great significance to the early warning of disaster, and has become the focus of research in the field of wind power in each country.At present, most of the wind turbine blades are detected by the nondestructive testing method. Acoustic emission(AE) technology is a kind of new dynamic nondestructive testing technology. It is sensitive to linear defects, and can detect the development of the defects in the interior of the materials under the external load. It also can effectively detect the quality level of composite materials and evaluate the actual harm degree of defects. Therefore, acoustic emission technology is increasingly being used in structural health monitoring of wind turbine blades.In this research, on the basis of the full understanding of the health problems of the wind turbine blades and the development of acoustic emission technology at home and abroad, Acoustic emission technique is applied to the structural health monitoring of wind turbine blades. The acoustic emission characteristics of composite material of wind turbine blade in the process of damage and fatigue damage are studied. The contents of the study include acoustic emission signal attenuation characteristics of the wind turbine blades composite materials, fiber breakage effect on the mechanical properties of glass fiber composite materials, and acoustic emission monitoring of wind turbine blades during fatigue loading.The results show that due to the presence of fiber- resin cycle interface, acoustic wave attenuation caused by scattering is more likely to occur in the direction perpendicular to the fibers. While propagating along the fiber direction, the acoustic emission wave meets fewer factors to promote the sound wave attenuation. Therefore, the lateral attenuation is much faster than the longitudinal attenuation. The tensile strength and tensile modulus of the material with surface fiber breakage are lower than those without fiber fracture. Acoustic emission signals of sample with surface fiber fracture are burst signals at all stages of the tensile. Signals with the amplitude in 80~ 90 dB have the maximum energy of 3.2×104~3.3×104mv*μs, the longest duration of 2.4×104μs, and the most ringing count of 3.4×104个. These signals indicate serious damage, such as fiber tearing, fiber / matrix debonding, fiber breakage, and so on.Acoustic emission signals of the specimen without fiber fracture is continuous signal at all stages of the tensile. The acoustic emission signals of most serious injury have the amplitude in 70~80dB, the maximum energy of 5.0×104mv*μs, the longest duration of 4.75×104μs, and the most ringing count of 4.3×104个. In the monitoring of fatigue damage, micro cracks have generated when the blade vibrates 200 thousand times and the frequency of the typical crack signals is 40 kHz and 80 kHz, the amplitude and the energy of the signals are low. When cyclic loading to 1.8 million times, cracks is expanding rapidly. Typical characteristics of fatigue damage also appeared, such as web debonding in a small range, and fibers delamination and so on. At this time, the amplitude and energy of acoustic emission signals are higher. The results of this research show that the AE technique can effectively detect the damage situation of wind turbine blade and glass fiber composite materials, and the acoustic emission sources can be well evaluated according to the results of parameters analysis and waveform analysis of the AE signals.