Research On The Secondary-Damage Inhibition Strategies For The Carbon Fiber Composite Components During Jointing

Composite laminates consisting of carbon fiber reinforced plies are now widely employed in the aircraft manufacture by the virtues of high specific strength,high specific stiffness,and outstanding designability.At present,the main joint form of aircraft composite load-bearing components is bolted joint.However,due to the constraints of forming and processing technology,composite components are prone to warpage and deformation.They would lead to the assembly gap in the assembly process,which would expand under the effect of component stress and result in the secondary-damage.The secondary-damage will seriously affect the mechanical properties and reliability of composite components,and even lead to aircraft damage in service.In view of the above problems,the experiments research and simulation analysis of the composites bolted joints with various prefabricated assembly gap and shimming compensation strategies are carried out in the paper.The influence of the secondary-damage caused by the assembly gap on the performance of the composites bolted joints was discussed with experimental test and numerical simulation.The effect of different shimming compensation strategies on the secondary-damage were compared and analyzed in order to provide theoretical and technical basis for the realization of high-quality bolted joints in composite components.The main work of this paper is as follows:(1)By combining the progressive damage analysis method with cohesion model,the improved Hashin damage criterion and the continuous damage degradation scheme are programmed into the external subroutine.Based on ABAQUS,finite element simulation models of tensile,compress,and three-point bending of carbon fiber composite laminate were established.The relevant experiments are carried out,and results of numerical simulation are in good agreement with the experimental results,which verifies the effectiveness of the composite analysis methods in the paper.(2)The bending experiments of the carbon fiber composite joints with no gaps,2mm gaps and 4mm gaps are carried out,and the corresponding finite element models are established.The differences of the macro mechanical properties,micro damage morphology and the stress distribution in the connection area of different components are analyzed.The results show that the assembly gap will lead to the secondary-damage such as the decrease of the mechanical properties,the stress concentration of the connecting holes and the damage of the hole walls.And the larger the assembly gap is,the more serious the secondary-damage is.(3)With liquid shim as the gap compensation,the bending experiments of composite bolted joints with total shimming,center shimming and side shimming are carried out.The corresponding finite element model are established for simulation analysis.The secondary-damage of different composite joints is studied.The results show that the mechanical properties of the components are improved and the stress concentration in the connection area and the laminate damage are also suppressed after the liquid shim is applied in the assembly gap.Using liquid shim to compensate the assembly gap can effectively restrain the secondary-damage of the composite bolted joints.