Research On Failure Mechanism Of Composite Laminates Based On Multiscale Method

In recent years,reliability improvement on composite structure digitized design makes the use of composite become more advanced and popuplar.However,composite is still applied cautiously and conservatively.Therefore,the outstanding characters of composites are not fully utilized.Predicition for composite strength in aviation structure is mainly based on experiments,which means that the strength theory is immature and cannot be used to guide the design for engineering.In order to assess composite strength theory,Hinton,Soden and Kaddour organized the World Wide Failure Exercise,WWFE with the support from the UK's Engineering and Physical Sciences Research Council and the Institution of Mechanical Engineers in 1991.And they initiated the Second World Wide Failure Exercise,WWFEII in 2007.Assessment results from WWFE and WWFEII reveal that the existing strength theory is imperfect on the research of failure mechanism.Composite is heterogeneous,and its macro-mechanical properties are determined by microstructure and component materials.To explore the full benefits of designability,it is essential to reveal macroscopically mechanical properties based on the perspective of micromechanics.With the development of micromechanics,composite multiscale analysis method is becoming a research hotspot.This paper proposes a new micro failure criteria which is based on the physical failure mechanism.Synergistic multiscale method is established to couple macrolevel laminates and microlevel unit cell model.The failure criteria proposed from this paper is assessed based on the quantitative evaluation point of WWFE and WWFEII.On this basis,Numerical simulation of multiscale progressive damage on notched laminates and composite bolted joints is carried out and experiment verification is conducted.The main content of this paper includes:Composite macrolevel and microlevel failure criteria are summarized.Research about Multiscale analysis method and typical composite component is reviewed,including notched laminates and bolted joints.Based on physical failure mode of fiber,matrix and interface,a new micro failure criteria is proposed.The criteria is based on Mohr-Coulomb criteria and emphasizes damage type and failure mechanism under compressive load.This paper believes that compressive stress will prevent shear damage on the fracture surface.The fiber compressive failure mode is researched in depth.A concept of shear strength on fiber kinking surface is introduced in fiber kinking failure criteria.Synergistic multiscale method is established to couple laminates and unit cell model by homogenization and localization.Multiscale analytical framework is built on the ABAQUS/Standard platform.By User Subroutine and PDE,information transmission between macroscale FEM analysis and microscale unit cell is achieved and the damage of macrolevel and microlevel models is both propressive during the iterations.Failure prediction for all cases in WWFE is completed.According to the assessment procedure of WWFE,the quantitative evaluation on the failure criteria proposed by this paper is carried out.The prediction results are compared with Puck,Cuntze,Tsai,Chamis,Mayes and Huang criteria.The assessment results show that under the condition of biaxial load,the criteria of this paper ranks second.The effectiveness of multiscale analysis method and the criteria proposed in this paper are verified.Failure prediction and quantitative evaluation for lamina in WWFEII are carried out.The prediction results are compared with Puck,Pinho,Cuntze,Carrere,Tsai-Ha,Hansen and Huang criteria.The assessment results show that under the condition of tri-axial load,the criteria of this paper ranks first.The important divergence that whether the failure envelope is open or closed among each strength criteria in WWFEII is analyzed and discussed.This paper thinks there is no universally accurate answer,because it is effected by fibre volume fraction,mechanical properties,hydrostatic pressure and fracture angle under single compressive load.Component experiment of a certain type airplane structure is made,including tensile experiments of two kinds of notched laminates and six kinds of composite single bolt.During Multiscale analysis process,microlevel stress amplification factor is introduced.Before calling unit cell,reference points should be judged whether failure or not.Multiscale analysis for the notched laminates is carried out,both microlevel failure mode and macrolevel delamination are considered.Numerical results have a good consistency with the experimental results.The bolted joint laminate is divided into damage zone around the hole,no-damage zone and transition zone.Fine mesh is made in the damage zone and Multiscale progressive damage method is used to analyze the zone.No-damage zone adopts coarse mesh to carry out linear elastic analysis.Transition zone adopts structural multiscale analysis method,Arlequin method to couple the damage zone and no-damage zone.By user defined elements,the Arlequin method is embed into ABAQUS.Numerical simulation of single bolt,simple shear bolt joints is completed and verified by experiment.The results indicate that all the predicted strength agrees well with measured strength,and the simulative damage evolution process and the pattern of fracture are consistent with experimental results.