Study On The Effect Of Modification On The Mechanical Performance Of GF/pCBT And Foam Core Sandwich Composites

Fiber reinforced plastic(FRP)composites have many desirable characteristics such as the high strength to mass ratio,high modulus to mass ratio and design ability.Compared with the conventional materials,FRP composites also face the issues that including hygrothermal aging,temperature aging and low impact toughness etc.Thus,this paper will study the mechanical performance of composites under various service environments.The aim is to find out an effective approach by which the anti-aging performance of FRP composites can be enhanced.Meanwhile,finding out an effective way to increase the impact tolerance of composites is also the target.The main contents of this paper are as follows:1.This paper firstly investigated the catalyst contents used during the polymerization process of cyclic butylene terephthalate(CBT)resin.Based on the mechanical.performance of the polymerized specimens,the suitable catalyst content was selected.Afterwards,modifications that including blending nano-SiO2,nano-TiO2,nano-graphite and short carbon fiber with CBT resin were performed.Thermal behaviors and mechanical performance of the modified materials were studied by thermo,mechanical and scanning electron microscope(SEM)technologies.By the comparison results between the specimens before and after modification,the effect of nano particles on the thermal behaviors and mechanical performance of CBT resin was found out.2.By physical vapor deposition(PVD)technology,nano-SiO2 particles were coated on glass fiber surface,and the nano-silica content in the composites was respectively 0.5wt.%and 2wt.%.The modified/un-modified glass fiber reinforced polymerized cyclic butylene terephthalate(GF/pCBT)composite laminates were manufactured by vacuum assisted mold pressing(VAMP)processing.The fundamental mechanical properties such as tensile,flexural and interface performance of the obtained composites were tested.To investigate the mechanical performance of modified and un-modified composites in various temperature conditions,three-point-bending tests on the obtained composite laminates in different temperatures were carried out.Effect of fiber surface nano-silica modification on GF/pCBT composites was studied.The failure mechanism of the composites in different temperatures was obtained with assistance of SEM technology.3.The modified and unmodified specimens were exposed in various hygrothermal environments for up to 3 months.By comparison results obtained in the tests,the mechanical performance of the composites in hygrothermal environments was achieved.According to the variation tendency of mechanical performance,failure mechanism of the composites in hygrothermal condition was obtained and effect of nano-fillers on the hygrothermal performance of the composites was analyzed.Based on the data obtained in the experiments,the relationship between mechanical strength decline ratio(SDR)and aging duration was obtained,and this relationship can be used to predicate the lifetime of the composites as well as to accelerate the aging process to save aging duration.4.Interply hybrid modification on fiber reinforced pCBT resin composites was performed.Failure mode and damage mechanism of the hybrid composite laminates under low-velocity impact load were analyzed.The processing adopted to manufacture the pure and interply hybrid pCBT resin based composites is VAMP.The impact parameters of the composite panels in low-velocity impact events are achieved through the experiments and ABAQUS/Explicit finite element methods.In the simulation work,the 3D damage criterion of the composite panels was compiled in VUMAT program,and this subroutine is based on stiffness progressively decline theory.Simulation and experiment results match well,and the stress distribution cloud of the panel as a function of contact time in the impact event was observed in the simulation results.5.Foam core filled hybrid composites facesheet sandwich panels were manufactured by vacuum assisted resin injection(VARI)processing,and the low-velocity impact tests of the sandwich structures were performed.The six types of the sandwich structures are respectively[C4/Foam core/C4],[C2/G2/Foam core/G2/C2],[G2/C2/Foam core/C2/G2],[G/C]2/Foam core/[C/G]2,[G/C2/G/Foam core/G/C2/G]and[G4/Foam core/G4].The effect of hybrid facesheets on the impact performance of the sandwich structures under low-velocity impact load was obtained according to the impact data.By SEM observation,the failure mode of the sandwich panels was analyzed.The compression after impact(CAI)test was also performed,and the residual strength,damage mode and mechanism of the specimens were obtained.