Manufacturing,Characterization,and Selfhealing Of Microchanneled CFRP Composites

Light weight,superior strength and high stiffness carbon fiber reinforced polymeric(CFRP)composites were developed to replace conventional materials to boost the function of existing aerospace structures,and they performed well.Now the next-generation airframes demand smart and multifunctional composite structures that can fulfill certain critical mechanical,chemical and thermal requirements simultaneously.Introduction of microchannels within composites is one of the promising techniques that can effectively produce additional functionality of self-sensing,selfhealing or active-cooling within a composite structure.Among them,self-healing is of great importance as it significantly reduces the risks associated with barely visible damages,most common and threatening problem of composites.However,these added benefits are often adjoined with loss of structural strength,due to their presence,that depends on the channel diameter,channel spacing,channel density,orientation,type of channel and manufacturing method through which channels are created.Additionally,merely a handful of techniques are available to create microchannels within composites,and most of them can create only basic and straight channels that result in higher loss of structural strength,not desirable in self-healing applications.Hence,there is a need for new advantageous methods and processes that can generate simple as well as complex microchannels with minimum loss in structural strength upon their addition,for broader range of applications.It is also necessary to assess the effects of microchannels inclusion and associated factors such as channel diameter and channel distance on the mechanical properties and considers these effects in design to build functional composite structures with enhanced safety and reliability.Moreover,self-healing via self-healing agent filled microchannels is still new and more research is required for self-healing of various damage types under diverse loading conditions,to extend its potential in different applications.The aim of this thesis is to introduce a novel cost-effective processing approach to produce microchannel embedded CFRP composites with minimum impact on the mechanical properties for self-healing of distinct damages.The specific research contents and the main research achievements are as follows:(1)In this thesis,a common and modest method,insertion of hollow glass tubes(HGTs)and two novel,low-cost,highly compatible methods,selective polymer degradation(SPD)and step-molding(SM),were applied to create plain and intricate microchannels within CFRP composites during their manufacturing by resin infusion.Among them,HGT created straight microchannels with great ease;SPD created simple and straight microchannels that caused a lower mechanical loss due to the presence of channels,whereas SM generated intricate microchannels for a broader range of applications.In SPD,microchannels were created within CFRP composites by selective degradation of the especially chosen polymer,whose solid-preforms were placed at specific locations within dry fabric layers during composite manufacturing by resin infusion.The proposed approach of SM essentially comprises of two steps of composite molding.In first step,microchannels are first generated on the composite laminate during composite molding,and later this composite laminate with microchannels(on the surface)is adhered with the other composite laminate insitu second step composite molding.By this approach,microchanneled CFRP composites with simple and complex shape,varying diameter and varying path were fabricated that can be potentially used in structural health monitoring,self-healing,light weight heat exchanger,biological and chemical micro-reactors applications.(2)In order to mechanically characterize the microchanneled CFRP composites,microchannels with 300 ?m,500 ?m and 900 ?m diameters and 5 mm,10 mm and 15 mm distance between two microchannels were created in CFRP composites by insertion of HGTs.Standard interlaminar shear strength(ILSS)and three-point-flexural tests were performed on these plain and microchanneled CFRP composites samples to determine the effect of microchannels inclusion and associated factors such as channel diameter and channel distance on ILSS and flexural properties of CFRP composites.In addition to these,microchannels with 700 ?m,1100 ?m and 1600 ?m diameters were also created in CFRP composites by SPD.ILSS and three-point-bend flexural tests were carried out(under same testing conditions)on these CFRP composites with microchannels to assess their effect on the structural strength.The results showed that inclusion of microchannels within CFRP composites weakened the composite structure and decreased their ILSS and flexural strength that decreased steadily with the increase in channel diameter and decrease in channel distance.The mechanism for these observed results was found to be the creation of resin-rich areas,microchannels(as cavities),and lessened fiber content by the addition of microchannels.Hence,diameter and location of microchannel must be wisely selected to get maximum structural strength possible along with added functionality.These mechanical testing results were also compared with the results of CFRP composites with microchannels,inserted by HGT,and it was found that the new applied strategy(SPD)was quite effective in introducing microchannels within CFRP composites with reduced mechanical loss and provided more space for additional functionality.(3)In addition to ILSS and flexural testing,CFRP composites embedded with microchannels by HGT were also subjected to a range of low-velocity impact(LVI)and mode-I delamination(M1D)testing to seek the effect of LVI and M1 D damage on the flexural strength of microchanneled CFRP composites.Furthermore,a self-healing approach was employed to recover their lost flexural strength due to these damages and influence of LVI,M1 D damage and healing on the flexural failure behavior of microchanneled CFRP composites was investigated as well.The results of flexural after impact(FAI)and flexural after delamination(FAD)showed that LVI has a more deleterious effect on the flexural strength of CFRP composites than M1 D damage.Additionally,the loss in flexural strength increased linearly with the increase in both impact(by higher impact energies)and delamination damage(by longer delamination lengths).Scanning electron microscopic(SEM)study revealed that self-healing agent,stored in HGTs placed within CFRP composites effectively repaired both LVI and M1 D damage with excellent healing efficiencies.