Investigation Of Constituents Damage And Interface Strength Of Laminate Made Of Carbon Fiber Woven Fabrics

Carbon fiber braided fabric reinforced resin matrix composites are widely used in aerospace,automobile and industrial products,owing to the low weight and high mechanical performance.However,mechanical properties and damage status are affected by the architecture of braiding,materials of fiber tows and matrix.Furthermore,the efficiency of laminate will be influenced.In this paper,the applicability of the modified 2D Hashin failure criterion was estimated based on the out-of-plane load experiment.The criteria was used for analyzing the damage status of laminate under specific loading condition.Furthermore,the failure of laminate under three point bending condition was analyzed.The degraded stiffness,matrix damage and residual modulus of the periodic repeated unit in mesoscale were studied when it was subjected to unidirectional load.Works and conclusions are as follows:(1)Out-of-plane load tests with different displacement were carried out,which was designed to identify the damage status of the laminate manufactured by braided carbon fiber and E51 epoxy resin.The failure of both fiber and matrix were estimated by the 2D Hashin failure criterion.It is concluded that the initial failure occurs in either the weft or the wrap,then the crack propagates along the alignment of the other fiber tows,leading to fiber fracture and matrix failure in different fiber tows.(2)Blocking phenomenon was existed in the fiber tows under arbitrary loading conditions,which may result in greater local stress,and then leads to premature failure.In order to predict the stress in tows as accurately as possible,a near-real 3D fiber undulation model(FUM)was established through combining the measurements(which reflect the undulation and the cross section bending degree)and the spatial geometric relationship(which denote the dimension relationship between tows and single laminate).Constitutive subroutine VUMAT was developed based on Fortran for calculating the degraded stiffness of matrix in fiber tows.Damage factors of matrix were derived from the simple rule of mixture(SROM),therefore,the degraded total stiffness matrices can be calculated.Consequently,accurate stress prediction was obtained.(3)In case of strength estimation of laminate interface,the geometrical continuum shell model and cohesive element were employed,thus,the combination of analysis of plane stress and interface strength were achieved.In addition,bilinear traction-separate law was employed to describe the mechanical behavior of interface elements.Failure of constituents was also calculated by the 2D Hashin criterion.Damage analysis of the AS carbon/epoxy and T300/PR319 laminate under the three-point bending test were carried out.In conclusion,laminate cured by matrix with lower stiffness and strength is more liable to transmit loads,and can be used for producing impact resistant or ductile parts.In contrast,matrix with higher stiffness and strength makes the composite stiffer,which can be used for fabricating structural products.