Strength Analysis And Fatigue Life Research For The Patch-repaired Composite Laminates

With the wide application of composite materials in the fields of aircraft,automobiles,and ships,there are more and more cases of damage suffered by composite materials in the process of use.Therefore,there is an increasing need to repair the composite material to restore some of its mechanical properties.At the same time,with the application of carbon fiber composites in the primary and secondary load-bearing members of structures,more and more attention has been paid to the structural repair and fatigue problem.In this paper,the tensile strength and fatigue life of patch repaired carbon fiber composites are experimentally investigated and numerically simulated to provide theoretical references for their engineering applications.Firstly,the tensile properties of composite laminates with holes,single-bonded and double-bonded patch repair were investigated experimentally.Then,the tensile strength simulation models of composite laminates with holes,single-bonded and double-bonded patch repair were established and the damage processes of the laminate,adhesive layer and patch were analyzed.The effect of structural parameters on the tensile strength of the patch repair structure was investigated.The results show that patch repair significantly improves structural strength,and double-bonded patch repair is more effective;the change of patch thickness did not have a significant effect on the tensile performance of the patch repair structure;the tensile strength increased with the increase of patch radius;the best repair effect was achieved when the thickness of the adhesive layer was 0.08 mm.Secondly,the fatigue life and damage of composite laminates with holes,singlebonded and double-bonded patch repair under different stress levels were investigated experimentally.The results show that fatigue failure of laminates occurs in the middle and late stages of fatigue life,with fatigue failure occurring first in the plies and substrate and finally in the fibers,leading to fatigue damage;the average fatigue life of the specimens was improved by 33.4% and 46.5% after single-bonded and doublebonded patch repair of laminates,respectively;the fatigue damage of the specimens under different stress levels was compared,and it was found that the higher the stress level,the more similar the fatigue damage morphology of the specimens was to that of the tensile test;the lower the stress level,the more intense the fatigue damage of the specimens was,and the damage area was larger.Finally,a fatigue life prediction model for composite laminates with holes,singlebonded and double-bonded patch repair was developed,and the UMAT subroutine was written to perform fatigue progressive damage analysis on the laminate.The fatigue test results were compared with the simulation results to verify the feasibility of the fatigue life prediction model.The fatigue life prediction was performed for the optimized solution of the double-bonded patch repair structure,and the results showed that the fatigue performance of the optimized solution of the double-bonded patch repair structure was significantly better than the non-optimized,and the fatigue life was improved by 9.12% on average.