GFRP composites with MWCNT modified eproxy resins II : low velocity impact performance

• Main Author: Lim, Guo Hui.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Aeronautical engineering::Materials of construction
• Online Access: http://hdl.handle.net/10356/53565
• Institution: Nanyang Technological University

Glass Fiber Reinforced Plastics (GFRP) has become a popular choice in replacement of traditional materials such as aluminium and wood, particularly in the aerospace and marine industry. The inherent weakness of GFRP in the traverse direction makes it extreme susceptible to knocks or tool drops. Thus, it is of paramount importance to develop enhancement to the GFRP to strengthen its out of plane mechanical properties. The study first investigate the process of dispersing multi-walled carbon nanotubes (MWCNT) in epoxy for used in later fabrication of the MWCNT enriched GFRP. The objective was to identify critical parameters that will lead to the quality dispersion of MWCNT. The time and process parameters by sonication and homogenisation were investigated along with type of solvent to be used. It was indentified that acetone was an ideal selection given the processing constraints. A longer sonication time could significantly reduce the amount of agglomerates in the dispersion. After the determination of the process parameters, Epolam 5015 epoxy resin was used in the fabrication of the MWCNT enriched GFRP. Laminates panels of size 300 x 300 mm were fabricated using the wet layup technique by varying two importance parameters. The different concentration by weight of 0%, 0.4%, 0.75% and 1.1% and stretching level of the glass fabric at 0KG, 1.27KG and 2.47KG at the 0% and 0.75% concentration were investigated. The prepared laminates were first cured at room temperature before being post cured at elevated temperature. The burn off test conducted in accordance with ASTM standard reveals consistent fiber volume fraction of 0.5, which is an ideal ratio required in our investigations. Specimens were then machined to 100 x 100 mm specimens subjected to low velocity impact testing. For each MWCNT concentration, samples are subjected to 9J, 16J and 22J of impact energy in accordance to ASTM standards. The 3 time profiles (load, energy absorbed and velocities) together with load-displacement profile for all specimens were collated. The 3 domain of parameters (loads, energies and displacements) were quantitative compared and discussed. The load displacement profiles of the same configuration under quasi static (1mm/min) loading were compared to those of the low velocities impact as well. Fractography analysis by means of digital imaging, optical and scanning electron microscopies and Computed Tomography Scans were made to identify the fracture mechanisms from macro to nano scale. They were also conducted to substantiate the quantitative data obtained from the impact test. The quantitative analysis, coupled with substantiation from fractography assessment, concluded that 0.75% MWCNT offers the best damage resistance to all investigated low velocities impacts. When stretching level were assessed independent of MWCNT, the same conclusion could be applied to the highest stretch level of 2.47KG-0%MWCNT. However, when the optimum concentration of MWCNT (%MWCNT) was coupled with fabric stretching, the interaction appears to have led the laminates to take both heavier localised and laminate damage over non stretched laminates. The comparison between quasi static indentation and low velocity impact reveals 2 main observations. Firstly, all except two configurations’ flexural properties and damage progression in the elastic region is independent of the loading rate. 1.27KG-0%MWCNT laminates display increasing flexural modulus with increasing loading rate. Second, the observation of the increase in load carrying capability with increasing %MWCNT is only observed for dynamic impact – a trend that is not reflected in quasi static condition. Overall, this study has shown that the modification of GFRP with MWCNT do lead to significant improvement in low velocity impact resistance. The study between quasi static and dynamic behaviour bring insights into mechanical properties in which specified configuration maybe best applied for the expected loading rate. Further investigations can be done to study %MWCNT and fabric stretching interaction to bring out the best impact resistance properties beneficial to the related industrial applications.