| As a second generation fiber metal laminate,GLARE laminates have a variety of excellent performance on combination of composite materials and metal materials.And the theory and technology of the preparation,the formation of complex components and the evaluation of service performance about such laminates have become the current research hotspot.Therefore,in this paper,the forming technology of the curvature parts of the fuselage skin is systematically studied,which can provide theoretical basis and engineering guidance for the application of GLARE laminates in large aircraft.Primarily,the basic forming properties of GLARE laminates were studied by experiment.The results showed that n yσ=σ +Kε was proved the most suitable model to fit the true stress-strain curves of three variants and.GLARE 2A laminate exhibited the strongest resistance to deformation and it was less prone to deformation in the thick direction,resulting in poor calenderability.Furthermore,the minimum relative bending angle of the GLARE 6A laminate was the smallest,and the springback of the GLARE 6A laminate was also the smallest,which indicated that it had better bending performance.Secondly,the force and springback of the GLARE laminates during the roll bending process were analyzed theoretically.The Hill yield criterion and the exponential reinforcement model were used to describe the anisotropic aluminum alloy sheet.The stress-strain,the bending moment,the theoretical springback radius and the springback angle of the GLARE laminates were calculated and analyzed during the bending process.The analytical model of the roll bending process was established.The accuracy of the analytical model was verified by experiments,which showed that the established analytical model had a certain applicability.Then,the influence on the springback was studied about the three parameters,such as the displacement of the top roller,the direction of fiber and the thickness of laminates by test.The results showed that the deformation of the GLARE laminate became larger and the springback became smaller with the increase of the displacement of the top roller.And the relationship between the displacement of the top roller and the radius of curvature of the laminate was also a power function.GLARE 2A exhibited the highest springback,followed by GLARE 3 and the smallest was GLARE 6A laminate under the same top roller displacement.As the thickness of the GLARE layer increased,the amount of springback was gradually reduced.In addition,the residual stress distribution of the aluminum alloy layer in the GLARE was analyzed by the etching method.The results showed that the aluminum alloy layer on the outer surface was in the compressive stress state.But the variation of the residual stress of the aluminum alloy layer on different type of GLARE laminates was not obvious.Finally,the damage characteristics of GLARE laminates was observed and analyzed by SEM after roll bending forming.The critical top roller displacement and the radius of curvature were obtained.The results exhibited that glass fiber reached the ultimate strain when the top roller displacement reached 12 mm.Therefore,it can be determined that the critical displacement of the top roller is 11 mm and the corresponding critical bending radius of curvature is 150.62 mm during the roll forming process.When the top roller displacement reached 12 mm,a certain degree of damage failure occurred on the three kinds of GLARE laminates in the process of roll bending.The main type of failure was resin matrix cracking and fiber breakage,but there was no interface delamination failure phenomenon.When the GLARE layer structure evolved from 3/2 to 4/3,5/4,6/5 structure,the bending performance decreased slightly.With the increasing of the number of layers,the degree of failure will also become larger. |
