Study On Properties And Damage Control Of Interlayer Toughened Composites

Composite material has become more and more widely used in the aerospace industry due to its excellent characteristics.The thermosetting resin composites have excellent in-plane mechanical properties but poor toughness,and are susceptible to delamination damage after low-velocity impact.Therefore,the use of interlayer toughening to suppress the internal impact damage is of great significance to improve the toughness of the material.In this paper,carbon fiber reinforced epoxy resin composite?T700/6240?prepreg and self-made thermoplastic PEK-C films were used to prepare interleaved composites laminates with different thickness,position and number by autoclave method.The optimal interlaminar structure was obtained by analyzing the result of mode I fracture toughness test,low-velocity impact and compression after impact?CAI?test,bending performance test,interlaminar shear performance test,scanning electron microscope?SEM?observation as well as atomic force microscopy?AFM?characterization.Then,discrete interleaves were used to enhance specific area of the laminate.The impact of PEK-C films was studied by impact and CAI test combined with VIC-3D.The thickness of the interleaf obtained by dip-coating method increases with the increase of the thermoplastic resin solution's concentration.Mode I interlaminar fracture toughness,CAI and interlaminar shear strength of the composites increase with PEK-C films of different thickness.G_IC and shear strength are optimized at a film thickness of 10?m,increased by157.17%and 17.57%respectively.CAI reaches 186.67 MPa at a film thickness of 30?m.The flexural strength and modulus decrease with the increase of the thickness of the PEK-C film,from 1551 MPa,106 GPa when not toughening,to 965 MPa,79 GPa at the thickness of 30?m.Considering the influence of interleaf on mechanical properties and impact resistance,the optimal film thickness is 10?m.The interleaf sequence was altered to find out the optimal position.Compared with the untoughened laminate,CAI increases by 42.39%when interleaves were laid in the middle of the laminate,in which the maximum damage area appears.The number of toughening films laid between the layers was changed,and the relationship between the bending strength,CAI and the number of PEK-C were obtained respectively.Considering the total gain and the single-layer gain function,the optimum number of toughened films is finally determined to be 11 or 12.PEK-C films with shape of round and circular ring were used to put around the impact area.CAI test with VIC-3D was carried out,and the results show that the round toughening membrane can effectively alleviate the stress concentration during compression.The sample with round toughening film has a smaller damage area than that of the sample with circular ring,indicating its ability to control damage during impact.The cross-sectional damage morphology shows that the laminates with circular ring can control the crack propagation.