| High performance fiber reinforced composites have the advantages of high specific strength and modulus,good fatigue resistance,corrosion resistance and so on,under the background of energy saving and emission reduction,lightweight and high-strength properties of composites makes it become the star material for transportation tools,which are paid more and more attention.However,due to the high cost of raw materials and manufacture process,the large-scale application of composites is seriously hampered.At present,the primary methods to reduce the cost focus on the production process and raw material,while the process optimization mainly includes technical innovation and rapid automation of production equipment,and reduction of material consumption is the main way to reduce raw material costs by optimizing the stacking-sequence design,the use of low-cost fiber and resin,and the development of hybrid composites.In this paper,based on the cost reduction of composites,the mechanical properties of interlayer and intralayer hybrid composites were evaluated systematically,and the performance cost is analyzed.To explore the advantages and disadvantages of the mechanical properties of these two hybrid forms and to provide some reference for practical introduction.In this paper,the hybrid forms of composites were studied firstly,and it was found that more researches focus on interlayer hybrid forms,and many types of reinforcement are adopted,including woven fabrics,unidirectional warp knitted fabrics,unidirectional prepreg and so on.However,there were few studies on the intralayer hybrid composites,which primarily contains woven intralayer hybrid,winding intralayer hybrid,of which most of the woven intralayer hybrid fabrics are only used as decorative parts,and the hybrid structure in the winding intralayer hybrid form is unstable,which leads to the poor predictability of mechanical properties.Therefore,in this study,a series of novel unidirectional warp-knitted hybrid fabric(NCF)were developed using carbon fiber and glass fiber,and this type of NCF fabric is commonly used in the automobile and the wind power industry.In order to compare the mechanical properties of interlayer and intralayer hybrid composites,layup schemes of interlayer and intralayer hybrid composites were designed,and the test specimens were prepared by VARTM process.Due to particular boundary condition of the intralayer hybrid composites,the cutting scheme of the intralayer hybrid testing samples was discussed.The filling process of composites reinforcement is determined by the viscosity of the resin and the permeability of the fabric.While the permeability of carbon fiber is weaker than that of glass fiber,thus,the permeability of hybrid fabric can be improved by adding more glass fiber.In this paper,the permeability of the hybrid reinforcements was studied by means of the experimental test,theoretical calculation and finite element analysis.It was found that the experimental permeability of the hybrid fabric decreases linearly as the carbon fiber content increases.The permeability values obtained by the theoretical calculation and finite element analysis are in agreement with the experimental values,and decreases as the carbon fiber content increases,which make it feasible to obtain the permeability of intralayer hybrid fabrics via the theoretical method and finite element analysis.Tensile property is one of the most excellent mechanical properties of composites,firstly,the tensile failure modes of hybrid composites were analyzed,and the synergistic effect and failure acceleration effect have been found.Then,the tensile properties of interlayer and intralayer hybrid composites with various mixed ratios and layup structures were analyzed systematically,it was found that the tensile modulus of interlayer and Intralayer hybrid composites is mainly determined by the C/G mixed ratio,and it exhibits a linear increase with the increase of carbon fiber content.The tensile strength is influenced by the layup structures and the mixed ratios,which increases as the carbon fiber content increases.The tensile strength of interlayer hybrid composite is the maximum as the carbon fiber is sandwiched with glass fiber,while,due to the cutting position of the specimen,the tensile strength of the intralayer hybrid composite with maximum dispersion degree is the minimum.The experiment and Rule of Mixture(ROM)tensile properties of the interlayer and intralayer hybrid composites are compared,it is found that the tensile modulus of the interlayer and intralayer hybrid composite is almost the same as that of the ROM,showing a weaker positive mixed effect,while the tensile strength presents a relatively high positive hybrid effect.Due to high tensile strength of the high-performance fiber,the tensile properties of composites are excellent.However,the compression properties of composites are relatively weak as fiber and resin both shares the compression load.In this paper,the compression properties of interlayer and intralayer hybrid composites are studied,including the compression strength,modulus and fracture strain.It was found that the compression modulus of interlayer and Intralayer hybrid composites is the same as that of the tensile modulus,which is mainly affected by the mixed ratio,and increases linearly with the increase of carbon fiber content,while the compression strength of interlayer hybrid composites is mainly influenced by the layup structure,which shows that the compression strength of hybrid composites is the highest with the interlayer structure glass fiber sandwiching carbon fiber.On the contrary,the compression strength of hybrid composites is lower with the carbon fiber sandwiching glass fiber or with the asymmetric structures.However,the strength of the intralayer hybrid composite is mainly affected by the C/G mixed ratio,and the layup structures have no obvious impact on it.Finally,the results of the compression properties of interlayer and intralayer hybrid composites are analyzed.With the increase of carbon fiber content,the compression modulus of interlayer and intralayer hybrid composites is linearly increased,and there is a weak negative mixed effect,while the compressive strength presents positive mixed effect which is influenced by the layer structures.In view of the different tensile and compression properties of composites,the tensile and compression properties of interlayer and intralayer hybrid composites were analyzed.It was found that the tensile and compression modulus of hybrid composites are basically the same,while the tensile modulus of the intralayer hybrid composite is slightly larger than the compression modulus.However,the tensile strength of hybrid composites is significantly larger than the compression strength,and with the increase of carbon fiber content,the ratio of the tensile to compressive strength(T/C)of interlayer and intralayer hybrid composites increases gradually.The T/C of interlayer hybrid composites reaches the maximum in the case of glass fiber sandwiching carbon fiber,while the T/C of intralayer hybrid composite is mainly determined by the mixed ratio.Flexural property is important to evaluate the mechanical properties of composites,the flexural properties of interlayer and intralayer hybrid composites were studied in this paper,and the progressive failure modes were analyzed.The results showed that the flexural modulus of interlayer hybrid composites is greatly influenced by the layup structure,and it can be improved obviously by the reasonable layup design,for example,the flexural modulus of [C/G/G/C] is almost the same as that of the carbon fiber composites,while the flexural modulus of intralayer hybrid composite is mainly affected by the mixed ratio,which increases with the increase of carbon fiber content and exhibits a weaker negative hybrid effect.The effect of the layup structure on flexural strength of interlayer hybrid composites is larger than that of intralayer hybrid composites,and the flexural strength of intralayer hybrid composites is between carbon fiber and glass fiber composite,while the flexural strength of some interlayer hybrid structures is obviously greater than that of carbon fiber composites or glass fiber composites.Finally,through the force-deflection curves,light transmission method and fracture sound method,the failure process of hybrid composites was analyzed,it was found that the layup structure of the interlayer hybrid composites has an effect on its failure modes,while the C/G mixed ratios is a decisive factor for the failure modes of intralayer hybrid composites.Finally,the mechanical Performance/Cost of interlayer and intralayer hybrid composites was analyzed,it was found that due to the high cost of carbon fiber,the tensile and compression specific modulus/cost of interlayer and intralayer composites decreases as the carbon fiber content increases,while the flexural specific modulus/cost of interlayer hybrid composites is greatly affected by the layup structures,for the intralayer hybrid composites,the performance-cost of the flexural specific modulus is mainly affected by the mixed ratio.Meanwhile,the C/G mixed ratio is decisive factor of the Performance/Cost of tensile and compression specific strength,and the mixed ratio and the layup structure both impact the Performance/Cost of the flexural specific strength for the interlayer hybrid composites,while the Performance/Cost of the intralayer hybrid composite is determined by the mixed ratio.Therefore,it is possible to improve the Performance/Cost of hybrid composites by reasonable selection of the mixed ratios and layup structures. |
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