Modern aerospace engineering increasingly prioritizes the integration of lightweight materials to improve performance and reduce fuel consumption. A recent study explores the optimization of joints between carbon-Kevlar polymer matrix composites and AA 7075 aluminum alloy using friction riveting, a method recognized for its energy efficiency and minimal environmental impact.
The research conducted by Vignesh N.J., Navasingh R.J.H., and Pitchumani S.V. from Metmech, Chennai, demonstrates significant advancements in mechanical properties for hybrid materials, with notable joint capacities of 5.83 kN for tensile strength and 2.95 kN for shear pull-out tests.
The joining process utilized multi-material specimens subjected to mechanical tests, providing insights on how these materials interact under stress. Friction riveting enables the fusion of polymers and metals without the need for additional adhesives or mechanical fasteners, which can add weight and reduce performance.
The authors applied hybrid Taguchi-Grey relational analysis to optimize process parameters, pinpointing the ideal conditions at 6000 revolutions per minute (rpm) for rivet speed, 0.2 megapascals (MPa) for reaming pressure, and 6 seconds for reaming time. This optimization revealed the rivet speed as the most influential factor affecting joint strength, followed closely by the friction time and the applied pressure.
The friction process generates heat through the rotation of the rivet, which enhances the bonding by creating semi-viscous polymeric composites at the joint interface. The study noted the maximum interface temperature reached was 189 °C, substantially increasing the ductility of the aluminum rivet, thereby improving the joint formation.
Microstructural investigations provided additional clarity on the bonding mechanisms at play. The results indicated effective mechanical interlocking and potential chemical bonding between carbon fibers and AA 7075. Conversely, the bonding characteristics of Kevlar fibers were less favorable, exhibiting weaker interlocking and more frequent fiber pull-out behavior during tensile tests.
The experimental methods included T-pull tensile tests and lap-shear pull-out tests, which assessed how well the rivets held during stress. The mechanical tests confirmed the strength and viability of the joints formed through the low-speed friction riveting machine developed for this research.
Results indicate improved performance of the carbon-Kevlar composite joints when friction riveting techniques are utilized. The findings could significantly impact aerospace applications, where the strength-to-weight ratio is of utmost importance.
While the research provides promising results for the use of friction riveting, the authors point out the necessity for future studies to evaluate the longevity of these joints under varying environmental influences, such as humidity and corrosion resistance. Further experimentation could lead to optimized joining designs and the exploration of alternative polymer-metal combinations.
Overall, this study highlights the potential of friction riveting as not only a method for joining metals and polymers effectively but also as a key process to utilizing advanced materials for enhanced performance and sustainability in aerospace applications.