Research On Phased Array Detection Method Of Aerospace Composite Laminates Drilling Stratification Defects

Composite materials as an important new materials of this age,is widely used in aviation,aerospace,military and many other important areas.But its unique interlayer structure makes it easy to produce delamination defects around the borehole during drilling and in-service use.The damage has a great influence on the bearing capacity and fatigue strength of the composite structure.However,the traditional non-destructive testing technology has low resolution,it is difficult to find the generation of small tiered defects.Therefore,it is very important to explore a reliable and high-resolution detection method for the drilling stratification of composite materials.Full Matrix Capture(FMC)technology based on ultrasound phased array acquisition can capture complete defect information.And through the method of Total Focusing Method(TFM)fully restore the detection information of defect.So it can greatly enhance the characterization of defect features and has high detection resolution of drilling layered defect.This paper begins with the mechanism of drilling hierarchical defects and the methods or research status of the commonly used methods at home and abroad.The ultrasonic sound field model was established by means of mathematical modeling,and the characteristics of the ultrasonic sound field were studied by numerical simulation.By studying the influence of the element width,the array spacing,the number of elements and the depth of focus on the sound field of the law found that the change of element width directly affects side lobe effect;the change of element spacing has a great influence on the lobe effect;under the condition of certain depth of focus,as the number of elements increases,the beam bandwidth becomes narrower and the beam direction is enhanced,but if the depth of focus is too small should not stimulate the array element too much,easily lead to the production of side lobes;the higher the focus depth is,the better the beam directivity is,under the same excitation element number.This study provides a theoretical basis for the subsequent optimization of ultrasonic phased array detection parameters.Secondly,based on the full matrix data capture model and the total focusing method imaging theory,the full focus imaging detection of the cross-hole in carbon steel was realized by simulation and experiment.Based on the definition of Array Performance Indicator(API),investigated the influence of effective aperture variation on the image quality.The experimental results show that increasing the number of elements or increasing the pitch of the elements can improve the image quality,and the number of array elements can increase the array spacing to improve the imaging effect significantly under the condition that the calculation time does not increase.After that,carry out the experimental study on the phased array imaging of the composite drilling laminates.Set up the conventional phased array experimental platform,firstly,based on the study of optimal parameter selection,determined the interval range of the optimal detection parameters for composite delamination detection.Then,constructed a full matrix data experiment capture system,determined the parameters of the experiment.Comparing the results of total focusing method imaging with the results of conventional phased array imaging,it is found that total focusing method imaging detection technology compared to conventional ultrasound phased array detection of layered defects have a significant advantage,and can be a very comprehensive characterization of defect characteristics.Finally,use the time-domain finite difference method to simulate the layered defects of different depths in the carbon fiber composites,and carry out ultrasonic phased array full matrix capture respectively.The total focusing method imaging results show that this technology has a maximum resolution of 0.3 mm for the bottom layer of carbon fiber delamination.For the layered defects with a distance of less than 0.3 mm,although the imaging results show that the stratification defects cannot be separated from the bottom surface,the image at the hole shows an upturned trend.