Study On Real-time Monitoring Of Drilling Strain And Temperature Around Borehole Of CFRP Laminate

A large number of holes and riveting holes in Carbon Fiber Reinforced Plastics(CFRP)are mainly connected by drilling,and high quality hole making is particularly important for assembly of composite structure parts.However,the anisotropy and low interlaminar strength of the composite material lead to defects such as delamination and avulsion.Once the machining quality doesn't meet the standard,the expensive composite components will be scrapped due to inability to repair,or because of the deterioration of mechanical properties,a serious safety hazard will appear.So it is an effective way to ensure the safe operation of composite structures by real-time detection of defects in drilling process and prevention of CFRP.In this paper,the two physical quantities of temperature and strain around the borehole are selected to solve the problem of drilling defects in carbon fiber composite laminates.The mechanism and on-line monitoring of the layer defects are carried out to provide an important means for the high efficiency drilling and processing parameters optimization of the carbon fiber composite laminates.The main contents of the thesis include the following aspects:(1)The drilling technology of CFRP laminates and the mechanism of defects are summarized,detection methods of the defects in carbon fiber composites are compared and analyzed,and the detection methods of drilling defects based on temperature and strain are selected.(2)Based on the distributed optical fiber sensing technology,the pave of an array arrangement of optical fiber sensor is designed,and the strain sensitive optical fiber temperature sensing technology is developed by using the thermal conductivity capillary package,study the influence of the distance between the optical fiber and the whole temperature field around the borehole,then optimizing the embedding process and the lay spacing of the optical fiber.(3)The MATLAB software is used to establish the data reconstruction model of the distributed optical fiber sensor,to build the temperature distribution around the drilling hole in the CFRP drilling process,and then to analyze the diffusion process of the cutting heat in the drilling process,study the distribution of the maximum temperature of the hole with the different drilling parameters.(4)An experimental system based on optical frequency domain reflection(OFDR)was built,and a special fixture was developed.The unidirectional and 0degree /90 degree CFRP laminates with optical fiber sensors were used for drilling experiments with different drilling parameters.The temperature distribution around the borehole was obtained by using the established data reconstruction model and the temperature distribution around the borehole was obtained.The temperature and strain separation at the inlet and outlet were studied,and the influence of drilling parameters on delamination defects was studied.(5)The ultrasonic C scanning technique(C-SCAN)is used to detect the delamination defects of the orthogonal test holes of the T300 composite board.By means of the image processing method,the stratified factor which involves the maximum layer diameter and the stratified area factor is evaluated by the image processing method,and then the temperature and the stress produced by the drilling process parameters are analyzed.The influence law of the change to the delamination.