Investigation Of Ballistic Impact And In-plane Punch Shear Damage Mechanism Of Three-dimensional Woven Composites

Three-dimensional woven composites have much higher damage tolerance than laminated composites when subjected to impact loadings for their high specific strength,good integrity,high fracture toughness and good delamination resistance as structural composites.Three-dimensional woven composites have been widely used in occasions where there is higher demand for impact damage tolerance.The mechanical properties and dynamic response of three-dimensional woven composites under dynamic loadings are quite different with quasi-static conditions,thus it is of great importance to study the damage mechanism of three-dimensional woven composites subjected to dynamic loadings.In this paper,both experimental and numerical methods are used to study the ballistic impact response and in-plane punch shear damage mechanism of three-dimensional woven composites.The main contents of this thesis include:Both light gas gun system device and 3D DIC technique are used to conduct ballistic impact tests of three dimensional woven composites.The damage initiation and propagation of 3D woven composites as well as the whole-field displacement field and strain field of the target plate are obtained in this paper.Both C-Scan and digital microscope technique are used to observe the damage type and failure characteristics of 3D woven composites.Besides,the energy absorption mechanism of 3D woven composites are studied in this paper.The results show that the main damage of 3D woven composites under ballistic impact loadings are matrix cracking,fiber breakage and fiber bundle cracking,the absorbed energy and the incident velocity have a liner relationship approximately.A progressive damage model at the fiber bundle/matrix scale based on the concept of continuum damage mechanics according to the micro structure of 3D woven composites.In this model,the Puck criteria is introduced to account for the major fiber failure and inter fiber failure modes while the parabolic yield criterion is adopted to characteristic the damage of matrix in which the influence of strain rate effect on the constitutive relation of matrix is considered.The damage process of 3D woven composites subjected to ballistic impact loading is simulated based on the commercial finite element software ABAQUS/Explicit combined with user material subroutine VUMAT,the influences of incident velocities on the damage of 3D woven composites is also discussed in this paper.The corresponding ballistic impact tests of3 D woven composites are carried out to verify the validity of the model.The simulation results showing good agreement with experimental observations.In order to study the in-plane punch shear damage mechanism of 3D woven composites,the specimen which realizes in-plane shear loading using traditional Hopkinson pressure bar device is designed in this paper,the in-plane punch shear mechanic properties of 3D woven composites under high strain rate loadings are studied using split Hopkinson pressure bar device.The stress-strain curves of 3D woven composites under different strain rates are obtained in this paper.In addition,this paper also studied the influence of size on the in-plane impact shear properties of3 D woven composites.Based on the in-plane punch shear experiments,the mesoscopic finite element model which has the same size of specimen is established to simulate the damage failure process of 3D woven composites under in-plane punch shear loading.The propagation process of stress wave in 3D woven composites as well as the damage failure process of component materials are studied in this paper,therefore,the damage mechanism of 3D woven composites under in-plane punch shear loading is better revealed.By comparing the simulatin results and experimental results,the validity of the finite element model is verified.