Research On High Velocity Impact Damage Of Composite Laminates

Fiber-reinforced composites are used extensively in defense engineering, aeronautics andastronautics industry due to their extraordinary mechanical properties, which greatly contribute toreduce the structure weight and improve the ballistic resistant capability. Study of the ballisticperformance and falilure mechanism of composites under high velocity impact loading are importantcontent of the survivability research of aircraft, which would lay a solid foundation for optimizationof aircraft structure design. Therefore, the damage analysis of composites under high velocity hasbeen focoused by many international researchers in the domain of composites mechanics. In thisthesis, systemic studies including dynamic constitutive equation, engineering analyses and numericalsimulations on ballistic performance and damage characteristics of composite laminates under highvelocity impact are conducted. The main contents are as follow:(1)Based on conservation of energy,a simple model to analyze the high velocity impact damageof thin angular plied composite laminates was established by the analytical approach, coupled withthe existed experimental observation. In the model, different damage and energy absorbingmechanisms, such as tensile failure of primary yarns, matrix cracking, delamination, conedeformation and deformation of secondary yarns during penetration were identified. The strain wavetheory was used for calculating the size of the deformation area and the strain field of compositelaminates. Then, energy absorbed in each time interval and the residual velocity of the projectile weredetermined. The influences of the impact velocity, the projectile diameter and the layer angle ofcomposite laminates to damage characteristic were detailedly discussed.(2)According to macroscopic and microscopic structure of composite laminates, a rate-dependentconstitutive equation for composite laminates was deduced by by considering the fibre as linearelastic rate-independent and the matrix as viscoelastic. By combining with Hashin failure criteria, a3D rate-depengdent continuum damage constitutive model(CDM) was established for modeling thedynamic properties of unidirectional fiber-reinforced composite laminate. The first-order sheardeformathion laminate theory under high strain rate was developed for modeling thin compositelaminate. By combined with2D Hashin Failure Criteria, a2D rate-depengdent continuum damageconstitutive model(CDM) was established.(3)Based on2D rate-dependent CDM, a numericial model to simulate ballistic performance anddamage characteristic of thin composite laminate was established by using nonlinear FEM method and coupled with ABAQUS software and the material user subroutine VUMAT. In this FEM model,the strain rate effect of composite material properties under high-velocity impact was considered, andcombined with Hashin Failure Criteria, the damage process of the laminate during the ballistic impactwas simulated. The influences of related parameters on the ballistic proformance and damagecharacteristics of composite laminate wass discussed.(4)Considering the microstructure of composite laminates, interface unit is introduced into theFEM model to stimulate the delamination of composite laminates. By using the strain rate-depentdent3D-CDM to model the dynamic properties of composite laminates, a3D FEM model was establishedunder ABAQUS software platform for analyzing the ballistic performance and damage characteristicsof thick composite laminates. Results from the numerical simulations were used to analyze theballistic damage mechanisms.The influence of related parameters on ballistic resistance of laminatewas analyzed and discussed by aseries numerical calculationgs.Some valuable conclusions areobtained, which is valuable for the target design and material improvement.(5)Based on ABAQUS software platform, FEM model for analyzing damage of stiffenedcomposite panel under high velocity impact are constructed.The influence of stiffener's parameters onballistic resistance and the damage characteristics of the stiffened composite panel were investigateddetailedly.