The Strength Analysis Method Of Adhesively Bonded Composite Repair Structures

From the1960s, the composite material has been widely used in manyareas particularly on aircraft structures. Meanwhile, the repair ofcomposite structures is becoming increasingly important. Adhesivelybonded repair is the main repairing method, including lap repair and scarfrepair. This paper studies the strength analysis method of the repairedcomposite structures by double-sided repairing and scarf repairing.Two models were established including analytical model and finiteelement model to analysis the static strength of the composite adhesivelybonded structures. The analytical model is a2-D model, in which thecomposite layers are considered linear elastic material, and assuming thereis no shear deformation, while there is only shear deformation in theadhesive material. Using the maximum strain criterion for the adhesivelayer and the first layer failure criterion for the composite material, thestrength and the stress distribution of the composite adhesively bondedstructures can be obtained. The FEA model is a3-D progressive damagemodel, in which The composite laminates was modeled with theorthotropic constitutive, and the onset of damage was predict by3DHashin’s fiber failure criterion，Puck’s matrix failure criterion and Yecriterion. Damage variables were introduced to characterize the damageextension. The adhesive layer was modeled with the isotropic constitutive.A square criterion based on three direction shear strains to predict thestarting of the adhesive layer’s damage and a degradation functionassociated with the stress and strain was defined to degenerate the stiffnessof the damaged material. The numerical prediction was compared with the experimental results, and the ultimate load correlate well, which verifiedthe method and model can effectively predict the tensile ultimate strengthof the double sided repaired composite laminate structures.