Damage Behaviors Investigation Of Layer-to-layer Angle Interlock Woven Composites

Three-dimensional(3D)woven composites have been widely used in aviation,aerospace,sports,medical,automotive and so on due to their high specific stiffness and strength,excellent impact resistance,fatigue resistance,and good structural designability.However,the premise of the application is to be able to evaluate the performances accurately.It is challenging to evaluate their mechanical properties and investigate the damage mechanism due to the structural complexity and the inconsistent properties of the component materials.In this paper,the research status of 3D woven composites at home and abroad is introduced in detail from experimental research,mechanical analysis model,damage criterion and damage degradation model,firstly.The main research directions and ideas of mechanical properties of 3D woven composites are given.On the mesoscale,the continuous damage model is applied to study the mechanical properties,damage evolution process and failure modes of layer-to-layer angle interlock woven composites(a kind of 3D woven composites)under various load conditions by combining with experimental analysis and numerical simulation.The main contents of this thesis include:Firstly,the uniaxial warp tension,warp compression,in-plane warp shear and weft shear experiments under quasi-static conditions are carried out for the layer-tolayer angle interlock woven composite.According to the experimental results,the elastic modulus and strength of the layer-to-layer angle interlock woven composites under tension,compression and shear are obtained.The main failure modes under these loads are obtained by optical microscope and digital image correlation(DIC).This part lays the foundation for the later research.Then the progressive damage behavior of layer-to-layer angle interlock woven composites under tension is investigated by numerical simulation method.From the mesoscale scale,the representative volume unit(RVU)is extracted and the periodic boundary conditions are applied to the RVU.Combined with the failure modes under static tension,different failure modes of the component materials are considered: fiber longitudinal fracture,fiber tows transverse fracture,matrix crack and fiber towsmatrix interface debonding.Different damage criterion are applied to different damage modes.The damage variables which characterize different damage modes are introduced into the flexibility matrix of the component materials.The tensile stiffness and strength are predicted,and the progressive propagation process is analyzed.The effect of interfacial properties on the tensile properties of the materials is discussed.The main failure modes of layer-to-layer angle interlock woven composites under compression are fiber kinking,fiber tows transverse crack,fiber tows-matrix interfacial debonding and matrix crack based on the above experiments.The compressive damage behavior of layer-to-layer angle interlock woven composites is investigated by using the mesoscopic damage model.Due to the current manufacturing technique,the fiber initial misalignment angle will inevitably occur in the manufacturing process of the woven composites.This is an important cause of fiber kinking failure under compression.As a result,the fiber initial misalignment angle is considered in the compressive damage model.The effect of misalignment angle on compression performance is analyzed.In order to study the damage behavior of layer-to-layer angle interlock woven composites under in-plane shear,an in-plane shear damage model is proposed.The finite element model with the same size as the shear specimen is established through the finite multiphase element method.At the beginning of the calculation,the material is identified by the position judgment module,and the fiber tows and the matrix are meticulously distinguished.The 3D Hashin failure criterion considered shearing effect is used to judge the initial damage.The shear nonlinearity of the fiber tow is considered in the form of damage factor.The progressive damage behavior of layerto-layer angle interlock woven composites is studied under in-plane shear.The shear performance and the damage propagation process of the component materials are obtained.Compared with the macroscopic shear test results in this paper,the reliability of the model is verified.