Study On The Delamination Behavior Of Carbon Fiber Braided Composite Laminates By Interface Angle

New materials are the key industry in the 21 st century,and compound is an important trend of the development of new materials technology.Advanced composite materials have become an important direction of the development of new materials.Composite materials have been classified as four major material systems with metal materials,polymer materials and ceramic materials.With the development of society,more and more composite products of composite materials,the use of technology is more and more advanced,people have developed a number of such as carbon fiber,silicon carbide fiber,alumina fiber and other high performance reinforcement materials,and the use of high performance resin,metal and ceramic matrix made of advanced composite materials.Because of its high specific strength and modulus,light weight and strong designability,advanced composite materials with carbon fiber as reinforcement materials have been widely used in aerospace,national defense,construction,sports,automobiles and other fields,and have broad development prospects.However,in its service life,composite materials also have a very serious shortcoming.In other words,there are manufacturing defects or instability after stretching under external load,which is easy to produce stratified failure,thus threatening the structural stability and safety of composite automobile/aircraft.Due to the high frequency of type Ⅰ fracture in practical engineering problems,it is necessary to study the stratification behavior of carbon fiber composite laminates in the case of type Ⅰ fracture and analyze the reasons for stratification,so as to provide theoretical support for the damage structural tolerance design of carbon fiber composite laminates.In this paper,the delamination behavior of carbon fiber laminates with different braided angles is studied by means of experiment and numerical simulation.In the test aspect,firstly,three kinds of laminates with different braided angles are designed:45//45:[PW/45/PW/45//S];PW//45:[PW/45/PW/45//AS];PW//PW:[45/PW/45/PW//S]PW is a plain weave fabric,45° is a braided fabric,"//" represents the prefabricated crack location,"S" represents symmetry,and "AS" represents antisymmetry.During the experiment,we found that it is difficult to measure the actual crack length and record the dynamic crack growth length.In order to solve this problem,an industrial high-speed camera is used to record the whole test process.Combined with advanced deep learning,an automatic crack identification system based on STDC semantic segmentation is developed to measure the real-time crack growth curve,which provides technical support for the calculation of fracture toughness.Subsequently,the mechanical response curves of these three samples were analyzed under the double-cantilever beam(DCB)test,and acoustic signals were collected by acoustic emission(AE)device to detect the damage and record the damage evolution process.In the process of acoustic signal processing,features with small correlation coefficients were selected according to the person correlation coefficient for K-means clustering.In the aspect of numerical simulation,ABAQUS/Explicit is used to establish the finite element macro model to capture the damage state,stress distribution and failure mechanism of the sample in the dynamic process.In terms of the research conclusion,it is found that the interface Angle has a great influence on the damage starting point and fracture toughness under the double cantilever beam stratified test.In terms of fracture toughness,the 45//45 structure is superior to the other two structures,among which the fracture toughness of PW//45 sample is the least,which can be attributed to the asymmetry of the layered interface of this sample,resulting in a low degree of adhesion between the fiber bundle and the matrix.The cracks spread in a bonding mode,and the stratification is more likely to occur.The fracture toughness of sample 45//45 is relatively high,which can be attributed to the existence of transverse Angle fibers that can resist the occurrence of delamination behavior.The large void between fibers will result in more resin-rich regions in the structure,which will lead to the crack propagation in the internal polymerization mode instead of bonding mode,and the resin-rich regions will consume more energy in the delamination process.Resulting in higher fracture toughness.PW//PW structure has a symmetrical interface,so its fracture toughness is higher than that of PW//45 structure,but the void between the fibers is smaller,so the resin-rich zone of PW//PW structure is less than that of 45//45 structure,resulting in slightly weaker fracture toughness than 45//45 structure.By observing the fracture surface with ultra-depth of field three-dimensional optical microscope,it can be found that the surface of PW//PW and 45//45 structures are rough and uneven.Due to their high fracture toughness,the structural stiffness degradation is also serious after the damage.The fracture surface of PW//45 structure is relatively flat and smooth,and the degradation of PW//45 structure is relatively slight after the occurrence of layered damage,which is mainly progressive damage.Therefore,it is necessary to choose an appropriate braided Angle for structural design.From the results of finite element simulation,the load-displacement curve formed by simulation is basically consistent with the experimental results,and the damage morphology of cohesive layer corresponding to the first large scale load drop is also consistent with the structure,which proves that the numerical simulation method is more reliable to predict the layered damage.