Effects Of Parameters Preformed With Hot Press On The Properties Of Composites Manufactured With Vacuum Assisted Resin Infusion

At present,autoclave molding has been widely used in the field of aviation composite materials due to the increasing amount of composite components,however,two main problems have been exposed when autoclave molding was applied.First,the cost is high including the investment of autoclave equipment for operation,the transportation and storage for prepreg.Second,large components can't be manufactured with molding in integral which possessed long production cycle and low efficiency.In order to overcome these disadvantages and meet the requirements for cost and time efficiency,the process of dry fiber placement with resin infusion are developed.In the work,the continuous thermal plastic fiber as the setting material was laid among carbon fiber fabrics according to the simulated principle of dry fiber placement.Then fabric preform was prepared with hot-pressing conditions,and composite components was manufactured by vacuum assisted resin infusion(VARI).The detailed contents and conclusions in this study are as follows:The preform of different hot-pressing conditions and various contents of polyurethane setting fibers are fabricated,and the permeation characteristics of preforms are studied.The results show that the pre-setting materials' content is higher than about 3.6% when the preforming pressure is under 0.1MPa and temperature is below 140?.The fabricated preform has better permeability characteristics which is beneficial to the impregnated of resin.The preforms compression characteristics with different hot-pressure conditions and various contents of polyurethane setting fibers are studied.The preform possesses higher compression rigidity and better resistance deformation ability as the increasing preforming pressure and temperature.The compression rigidity of preform increase first then decrease with the increasing content of preform fiber.The preform rigidity is optimum when the content of polyurethane fiber is about 2.4%.The preform of different preforming pressure is produced,and the composites are fabricated by VARI.The thickness,fiber volume fraction and mechanical properties are tested.The fiber volume fraction of composites increase with the preforming pressure and tend to stable when the preforming pressure up to 1MPa,and the fiber volume fraction is 65%.The 0° tensile and flexural modulus increase continuously with the preforming pressure,and the ultimate modulus is 150 GPa and 125 GPa,respectively.However,the 0° tensile strength and short-beam shear strength present the tendency of increasing first then decreasing,and when the preforming pressure up to 0.6MPa,the 0° tensile strength and short-beam shear strength are getting the maximal value which are nearly 1900 MPa and 28 MPa respectively.The 90°tensile modulus and tensile strength nearly remain stable.The properties of composite sample are characterized which are prepared under different preforming temperature and microstructure is investigated.The mechanical properties including tensile performance,short-beam shear strength,flexural modulus and 90° tensile performance increase with the preforming temperature when the preforming temperature is below or within limits of the setting materials' softening temperature.However,when the preforming temperature higher than the softening temperature of the material,the setting material would be soften and even melted which lead to the insufficiency impregation of the resin as a result,the strength of the composites decrease due to the exist of defects.The effect of polyurethane fiber contents on the thickness,fiber volume fraction and mechanical properties of the composites are studied,and the microstructure of composite sample is also investigated.The tensile performance and short-beam shear strength of the samples both decreased as the polyurethane fiber contents increasing which cause thickness increasing and the carbon fiber volume fraction decreasing.The polyurethane fiber among the carbon fiber form,the resin enrichment area which make the carbon fiber volume fraction decrease and cause the composites mechanical properties decrease.