| Fiber metal laminates(FMLs)is an interlayer super hybrid composite structure formed by alternating laying of high-strength metal sheets and fiber composites and curing at a certain temperature and pressure.According to its resin matrix,FMLs can be divided into thermosetting FMLs and thermoplastic FMLs.Thermoplastic FMLs have good mechanical properties and formability,but limited by traditional forming methods,only simple curvature components can be formed at present.As a high temperature and air pressure forming process,hot gas bulging forming technology has the characteristics of high efficiency and low cost.Combined with the test and finite element simulation methods,this paper studies the influence law of the laying parameters of metal and fiber materials on the mechanical properties of thermoplastic FMLs,and then explores the influence law of key process parameters such as temperature and pressure on the forming and mechanical properties of curvature components of FMLs in the preparation process of hot gas bulging.Firstly,thermoplastic PA6 resin based FMLs were prepared by hot pressing curing method and their mechanical properties were analyzed.Based on the performance analysis of metal laminate and fiber composite substrate,the distribution ratio of each material used in thermoplastic FMLs was determined.The uniaxial tensile and three-point bending tests of thermoplastic FMLs prepared by hot pressing curing are carried out.It is found that the material parameters of fiber layer determine the damage tolerance of FMLs.The laying direction of prepreg in laminate has an important influence on its mechanical properties.Secondly,the single curvature and double curvature components of thermoplastic FMLs were prepared by hot gas bulging,and the effects of key process parameters on their forming properties were explored.It is found that single curvature structure and double curvature structure FMLs can be successfully prepared by hot gas bulging.Temperature and pressure are the key factors affecting their forming quality.The forming results show that the temperature range of single curvature and double curvature components of PA6 resin based FMLs prepared by hot gas bulging is 230℃-250℃;The forming pressure of single curvature member shall not be less than 3Mpa,and that of double curvature member shall not be less than 4MPa.With the increase of forming temperature,the uniformity of thickness distribution of formed parts decreases,which is due to the excessive flow of resin caused by too high temperature.However,the influence of pressure on the forming effect of the two components is different,which is mainly affected by the forming shape of the components.For the complex shape of hyperbolic components,the thickness uniformity of laminates is affected.The forming effect of complex curved surface FMLs formed by hot gas expansion can be enhanced by improving the die.Finally,the finite element simulation model of hot gas bulging FMLs is established by benchmarking experiment to study the changes of fiber layer and metal layer in the forming process of single curvature components.The thickness,fiber arrangement and stress-strain behavior of aluminum alloy were analyzed.It was found that the thickness of aluminum alloy was distributed in steps during the forming process,and the local accumulation behavior of resin and fiber occurred,but there was no failure.On this basis,the influence of temperature and pressure on the forming results in finite element simulation is deeply explored.It is found that the thickness change behavior of prepreg under temperature and pressure is consistent with the experimental results,and the thickness uniformity decreases with the increase of temperature and pressure.The establishment of the simulation model provides technical support for the follow-up in-depth discussion of the complex shape components of FMLs in hot gas bulging. |
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