Research On The Influence Of Defects Associated With Automatic Laying On The Mechanical Properties Of Composite Materials

With the increasing size of aircraft,the consumption if composite materials increases gradually and the size of composite materials increases continuously.The manufacturing of composite materials gradually change from manual laying to the automatic laying of high automatic,such as automated fiber placement(AFP)and automated tape placement technology.The automated fiber placement technology optimizes the path of unidirectional composite wire bundles,but it may lead to the introduction of defects(gaps?overlaps?wrinkle defect,etc)When the complex shape mechanism is applied.These defects are often a key factor limiting the performance of components.These defects usually become the starting point of failure of composite lamination and reduce the bearing capacity of components.Therefore,it is of great significance to study the influence of the defects in the automated fibre placement on mechanical properties of components.The main research work of this paper is as follows:(1)In this paper,the specimens are manufactured by an automated fiber machine which enables 2 prepreg fiber tows to be draped simultaneously.The prepreg used was cycom5320-1FP/T40/800B,the width of the tow is 6.35 mm and the thickness is 0.125 mm.Developed according to the Nanjing University of Aeronautics and Astronautics with setting of the process parameters of laying head in addition to the embedded defects as far as possible to avoid the occurrence of other defects,set the fibre in the laying temperature of 40 ?,promote tow liquidity and viscosity of the resin material,laying pressure is set as standard pressure.The spreading speed is set at 10mm/s.The test piece after automatic laying is made into shape by hot pressing tank.After tensile failure,the specimen was observed with lycra microscope,and it was found that the fracture of the specimen was spread along the direction of the embedded defects.(2)Automated fibre placement(AFP)enables the trajectory of unidirectional composite tape to be optimized,but laying down complex shapes with this technology can result in the introduction of defects.The specimens are manufactured by an automated fiber machine which enables 2 prepreg fiber tows to be draped simultaneously,gap and overlap embedded defects are introduced on two cross-ply layups of[(90°/0°)5/90°]and[(0°/90°)5/0°].Autoclave cure without a caul plate results in local thickness variation and microstructural changes which depend on the defect type.This has a strong influence on mechanical performance.Use of a caul plate improves these variations.In the case of gap defects with fiber angle 0°,the tensile strength of the plate with caul plate increased by 218.50/%.In the case of overlap defects with fiber angle 0°,the tensile property of the plate with a caul plate is 69%higher than the plate without a caul plate.On the direction of 90° fiber,the 90°direction fiber is not the main bearing layer,the caul plate is less effective in the defects with a block of 90° plies.But the tensile property of the gap and overlap defect specimen with a caul plate is improved by 3.20%and 15.6%respectively.(3)Aiming to investigate the influence of wrinkle manufactured by automated fiber placement,the failure of a composite laminate containing an embedded wrinkle defect was investigated under tension loading.The wrinkle was created in the central region by inserting thin 90°ply strips adjacent to the full-length 90°plies in certain locations through the thickness of the laminate.The specimens are introduced on the cross-ply layup of[(0°/90°)2]s and manufactured by an automated fiber machine which enables 2 prepreg fiber tows to be draped simultaneously.Tensile tests of specimens with 6 sizes of defects are conducted and puts that the level of wrinkle is measured by wrinkle angle.It is found that the wrinkle angle is the most important factor to measure the influence of the embedded wrinkle on the properties of laminate.The tensile property declines with the rise of the level of wrinkle.The tensile strength of the specimen with a wrinkle angle of 10°is 31.74%lower than that of a wrinkle angle of 4°.