Study On Structures And Properties Of Structural Damping Polymer Matrix Composites

A huge challenge was presented on mass reduction and noise reduction of the traditional structural material with development of aerospace vehicles toward high-speed, light mass and multi-function. In recent years, with the rapid increases of fiber-reinforced composite materials in the proportion in aerospace applications, development of the new structure-damping multifunctional materials with both high mechanical properties and high vibration damping performance has become a hot topic of research. Structural damping composite is one of the integration composites of structure and function. Meanwhile, its application scope is widespread, involving aviation, mechanical power, transportation, power electronics and instrumentation industry and other fields. Therefore, it is playing an important role in the development of national economy and improvement of the quality of people’s lives.Traditional preparation of structural damping material is through inserting viscoelastic materials with high damping into structural materials. In this case, material strength and stiffness were provided by the structural material, and the damping performance was benefit from viscoelastic material. However, the present main problems of the co-cured composites with viscoelastic materials exposed are the degradation of the mechanical properties and heat resistant performance of structure and weakening of manufacturability and service. In addition, there were some drawbacks such as increase of thickness, weight or cost in the latest development of other co-cured composites (honeycomb, intelligent materials, metal foam, and nanometer material). This paper argues that key problems in the development of structural damping materials is selection of the matching damping layer material to the structure and forming good interface structure. From the material level, on the one hand, the damping material should have good interface bonding force and no conflict of the molding process with the structural material; on the other hand, the damping material should have relatively high mechanical properties, damping properties and heat resistance. From the structure level, interpenetrating network structure should be constructed between the structure and damping layer because this can reduce the concentration of interface stress, and at the same time improve the stress transfer efficiency in order to give full play to the damping effect of damping layer.In addition, the damping performance of material is close to fracture toughness, so the relatively mature toughening technology can be used for the development of structural damping composites, especially through ex-situ toughening with thermoplastic polymer with excellent mechanical properties or nanoscale carbon materials toughening such as carbon nanofibers and carbon nanotubes. In fact, the basic idea of this paper is filtering some matching materials who have a good toughening effect with matrix resin from the material level such as several kinds of porous thermoplastic non-woven fabrics (this paper chooses two kinds of nylon and aramid fiber non-woven fabric) as toughening materials and damping materials at first. Then through co-curing with the structure materials and forming multiphase sequential interpenetrating network structure between them to accomplish the ex-situ toughening modification and improvement of damping properties at the same time. Additionally, in order to further improve damping property and fracture toughness of the system, thermoplastic polymer PVDF with good crystallization and nano-material VGCF with excellent mechanical properties were loaded on the non-woven fabrics to research synergistic toughening and damping modification of materials between different toughening and damping materials. In addition, the development of the green composites in recent years more and more attracted the people’s attention, and also environmental protection design principle should be considered in the development of structural damping materials. Therefore, in this article, ramie fiber and jute fiber with relatively good mechanical properties and damping properties were sifted for the preparation of green structure damping composites.In addition, because the addition manners of damping layers and their damping properties have a direct impact on the damping properties of co-cured composites, in order to further study the change rule, this paper developed two kinds of virtual damping test via the finite element simulation analysis with ANSYS software on the basis of experiment. In other words, it was very convenient to investigate how the variation of the damping layer’s physical properties shows impact on the overall performance of composites. It is no doubt that the virtual test technology has a strong practical performance as a result of greatly shortening the cycle time of the development of material and providing convenience for the research of structural damping materials through finite element analysis.The following conclusions are reached mainly in this paper:1) PNF can toughen the composites and increase the loss factors of the composite significantly and at the same time it didn’t cause a significant drop of the mechanical properties of composites obviously. Among them, the damping properties and mechanical properties of the composites were closely related to the position and volume fraction. Through loading PVDF on the PNF can further improve the vibration damping performance and interlaminar fracture toughness. The loss factor of the co-cured composite with 7 layers of PNF/PVDF is 0.0121, which was 152.1% higher than that of the control sample. In addition, the GⅠC and GⅠC reached 1700.0 J/m2 and 2829.0 J/m2, respectively, which were 4.6 times and 2.9 times over the control one. Additionally, through loading PVDF/VGCF on PNF the heat resistance and the damping properties at high temperature of composite materials, conductive performance can be further improved. However, the mechanical properties of the composites aren’t obviously improved, and this may be related to the poor dispersion of nano materials which are prone to agglomeration.2) ANF can also improve the fracture toughness and damping properties of composites synchronously in the premise of not reducing the mechanical properties. Compared with the ones with PNF, ANF co-cured composites have better mechanics performance damping performance, but interface associativity is relatively poor and the GⅠC, GⅠC and CAI value is low.3) The contradiction between the damping properties and the mechanical properties could be balanced by the hybrid plies of the ramie fiber cloth and the glass fiber cloth or the carbon fiber cloth. Therefore it could realize the controllable regulation of the damping properties and the mechanical properties and give full play to remarkable designing advantages of composites. Among them, the composite with "RCRCR" lay-up achieved loss factor 0.0057,2.2 times more than the pure glass fiber cloth composites, and tensile strength 381.6 MPa,4.6 times more than the pure ramie fiber cloth composites. Loss factor and tensile strength of the composite with "RGRGR" lay-up were 0.0101 and 278 MPa, respectively, which were 1.4 times more than the pure glass fiber cloth composite, and 3.0 times more than the pure ramie fiber cloth composites, respectively.4) Two virtual damping performance test methods were developed with ANSYS software, namely virtual free vibration attenuation method and virtual sweeping frequency forced resonance method, respectively. The feasibility of the finite element simulation methods were verify through comparison between the measured results and the virtual test results of the damping factors, the resonance frequencies and modal loss factors of the three kinds of structural damping composites. At the same time, the effect of different mixing ways of damping layers and various physical properties on the performance of structural damping composites are studied in detail. Results show that the stiffness of the composite is closely associated with the most outer layer material modulus, while the damping performance is related to the volume fraction and distribution of the damping layer. When the damping layers are located in the surface of the composite with maximum normal stress and the neutral plane with maximum shear force, the damping effect were made full use.