Low-velocity impact behavior of glass fiber-MWCNT/polymer laminates exposed to seawater and distilled water aging

The influence of seawater (SW) and distilled water (DW) aging on low-velocity impact behavior of glass fiber/polymer laminates with and without multiwalled carbon nanotubes (MWCNTs) is experimentally investigated. To this aim, unidirectional glass fiber fabrics were coated with 0.75 wt% MWCNTs by airbrushing, infused with resin (epoxy or vinylester), and cured. Then, composite laminates with and without MWCNTs were cut into specimens for low-velocity impact testing and exposed to hydrothermal aging by immersing them to SW and DW at 60 degrees C for 2000 h. After that time of conditioning, dry and wet specimens were tested using a drop-weight tower with an impact energy of 15 J. Results showed that the moisture absorption content of composite laminates exposed to SW and DW aging is considerably higher on epoxy-based specimens with respect to vinylester ones. The impact tests revealed that the measured impact peak force and absorbed energy in wet specimens are significantly lower compared to dry specimens due to plasticizing effect of the matrix. With the incorporation of MWCNTs into the laminates, the absorbed energy is increased due to additional damage mechanisms induced at CNT-rich regions during the impact loading. It was also found that the damage area of the laminates after impact tends to be more prominent for laminates fabricated using vinylester resin than for those using epoxy resin as a result of its brittle behavior during impact loading. Post impact damage analyses by ultrasonic C-scan imaging and scanning electron microscopy showed that matrix cracking, fiber breakage, fiber/matrix debonding, and delamination are the main damage mechanisms induced in the dry and wet specimens during impact.