Effect Of Stacking Sequence On Low-velocity Impact Response Of Braided Composite Laminates

Carbon fiber reinforced polymer（CFRP）have been gradually entered people’s life and replaced some traditional metals used in major structural components in the aerospace,marine,automotive,and other engineering fields,which is inseparable from their excellent properties,such as high strength,incredible stiffness,lightweight,superior fatigue resistance and corrosion resistance.However,during their service period,they always face the danger of the low-velocity impact from foreign objects.Because their load-bearing capacity in the direction of thickness is not ideal,they will suffer varying degrees of damage.After the structure absorbs energy,different failure behaviors occur.The common injuries are matrix cracking,fiber and matrix splitting,delamination,and fiber fracture.Not only are these damage processes very complex,but mechanical properties such as residual strength are significantly reduced.There are many factors that affect the impact resistance of composite laminates.In terms of fiber structure,braided structure has a great improvement in impact resistance.Therefore,it is particularly important to study the low-velocity impact mechanical properties and damage failure behavior of mixed laminates with different braided structures.In this paper,the influence of different hybrid biaxial/triaxial carbon fiber braided composite laminates on the impact response at low-velocity was studied by combining experiments and numerical simulations.In terms of testing,to compare the impact resistance of triaxial braids on the impact side,non-impact side and the middle layer of the specimen,three different mixed structure braided plate specimens（[（±6 0^*）₂/（0/±60^*）₂],[（±60^*）/（0/±60^*）]_s,[（0/±60^*）₂/（±60^*）₂]）were first designed,abbreviated as BBTT,BTTB,and TTBB,respectively.Where B was a biaxial braid and T was a triaxial braid.Then,the low-speed impact test of the hybrid braided plate was completed under the collision energy of 23.62 J,43.62 J and 63.62 J,respectively,and the effective signal collected was automatically extracted.After that,the super-depth optical camera was used to study the damage morphology of the surface and interior of the specimen,the crack analysis of the surface crack of the specimen was extracted by Image J software,the damage status between the layers of the specimen was explored by an ultrasonic detector,and the residual performance of the specimen after impact was obtained by the universal testing machine.In terms of numerical simulation,the impregnated yarn and matrix model were established on the Tex Gen software based on Python script,the partitioned voxel grid was imported into ABAQUS/Explicit to complete the impact event model.The mesoscopic finite element model in this paper was used to captured the damage state,stress distribution and failure mechanism within the area of interest of the specimen during the dynamic process.In terms of the research conclusion,in the low-velocity impact test,the T structure would cause different structural deformation,damage appearance and stress distribution when T structure was located at different positions of braided laminates.In the BBTT sample,the bottom T structure had earlier fiber fracture under the high tensile stress caused by bending deformation.This was due to the high yarn curl that provided lower in-plane tensile performance and straight shaft yarns,which were most likely to reach the tensile limit of carbon fiber and break at higher deflection and fewer constraints.In addition,the matrix cracks of structure B with poor in-plane compression resistance tended to expand in the thickness direction,resulting in more concentrated damage areas,resulting in smaller delamination areas and smaller residual compressive strength.For TTBB specimens,the matrix crack spread on the impact surface was wider.This was because the axial yarn could effectively suppress the propagation of cracks in the thickness direction,forcing the cracks to propagate in the axial yarn direction.Thereofore,the specimen was more prone to global damage,delamination tended to the upper side,and its residual properties was severely degraded.The T structure in the BTTB specimen was placed in the middle,which delayed the sudden failure of the T structure caused by axial yarn breakage,and sacrifices the B structure to absorbed more energy to ensure that the specimen had better integrity,thus obtaining better impact resistance and the best residual performance.Therefore,selecting the appropriate stacking sequence for structural design is beneficial to enhance the impact resistance of the composite.