The Research On Low Energy Impact Damage And Residual Strength Of Composites With Initial Imperfection

Fiber reinforced composite laminate structure has the advantage of high strength anddesignability, which lead to the wide applications in the main bearing components of aircraftstructures. When the composite laminate structure is subjected to low velocity impact loads,delamination and matrix cracks will appear within the structure, which will reduce theresidual compressive strength. The initial imperfection raised during the manufacturingprocess will also affect the mechanical properties of the structure. Therefore, the research onlow velocity impact response of composite laminates, the evaluation of residual compressivestrength, and effect of initial defect on mechanical properties would contribute to theimprovement of the impact resistance and compressive strength of composite laminates.In this assay, the existing research models were compared and analyzed. Somedeficiencies of the existing models were proposed. By the introduction of new method such asprogressive damage evolution, cohesive contact and restart analysis, a new analytical modelwas proposed for the research of low velocity impact damage and residual compressivestrength.Drop-weight impact tests and residual compressive strength tests were conducted oncomposite laminates with different thickness. The damage behavior was discussed byanalyzing the result of the impact tests and nondestructive inspection. The residual strengthsof different specimens were compared to study the influence of the impact damage on theresidual compressive strength. Two failure modes of composite laminates under compressionload were proposed.Then, a finite element model was built base on the new analytical method proposed inthis paper. The method was verified to be accurate by comparing the calculated results withthe experimental results. At the same time, the FEM was used to study the low velocityimpact damage and residual compressive strength of composite laminates. The effect of theintroduction of delamination on calculated results was discussed. The relationship betweenmatrix cracks and delamination was clarified. The expansion form of damage during thecompression failure process was revealed. The optimized design was also conducted for thecomposite laminate structures.On the basis of the micromechanical method, a representative volume element ofcomposites with voids was built. A prediction of mechanical parameters was conducted forthe RVE model. The influence of porosity on the mechanical properties of composite laminates was discussed. The results show that as the addition of porosity, both impactresistance and compressive strength of the structure drop down.At last, the new analytical method proposed in this paper was used in the study of thelow velocity impact damage and residual compressive strength for a typical wing structure.Under the impact energy of8.1J, the damage area of the structure was very small. Theresidual compressive strength of the structure was almost the same as the nondestructivestructure.