Investigating The Effect of Carbonaceous Nanofillers on Strength Properties of Adhesive Lap Shear Joints

Abstract

Adhesive joining presents a compelling substitute to traditional joining techniques, like welding and mechanical fastening. Adhesive bonding offers several advantages, such as the capability to construct lightweight and stiff structures, the ability to join various types of materials, offer improved fatigue performance, and a decrease in heat effects zones commonly associated with welding. However, lack of structural redundancy and moderate strength offered by adhesive joints still makes it an area of exploration for researchers as joint strength is significantly influenced by geometric, surface, manufacturing, and environmental parameters. In recent times, modification to the properties of host resin by the addition of nanofillers is a non-geometric parametric technique proven to be effective in improving the mechanical performance of adhesive joints. In literature, the effects of various fillers (metallic, nonmetallic) have been studied with varying rates of success. The conducted research aims to fill the gap in the non-metallic category by performing a systematic study of the effect of graphene nanoplatelets (GNPs), multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) addition on a high viscous, high strength structural adhesive at various weight fractions of the nanofiller addition. The nanofillers including the functional components of GNPs and MWCNTs (COOH and NH2 functionalized) were added in weight fractions of 0.25, 0.5, 0.75 and 1 wt% in the adhesive. A comprehensive mixing method based on solution mixing technique was developed for uniform mixing of nanofillers in the host resin. The effects of filler addition on the dispersion characteristics, mechanical response of nanofiller/adhesive composite and strength characteristics of two different lap joint configurations were then investigated. The joints were fabricated using aluminum 5083 alloy where adherends were electrochemically treated prior to joining. Lap shear tests were conducted on Universal Testing Machine (UTM). Fourier-Transform Infrared Spectroscopy (FTIR) was utilized for the analysis of functional groups and chemical interaction of nanofillers with the adhesive. Variation in the cure kinetics was investigated using Differential Scanning Calorimetry (DSC). Ultraviolet-Visible Spectroscopy (UV-VIS-Nir) was carried out to quantitatively quantify the dispersion characteristics of nanofillers. ANOVA study was performed for the evaluation of data variation and interaction. Optical and Scanning Electron Microscopy (SEM) was utilized for the analysis of fracture surfaces, and the correlation between nano-reinforcement and strengthening mechanisms was critically discussed. A comprehensive comparison of thex mechanical behavior of bulk adhesive specimens and strength characteristics of lap joints reinforced with GNPs, MWCNTs and RGO was established. The novelty of the research is that, it introduces a pioneering exploration into the combined effects of functional and non-functional components of Carbon Nanotubes (CNTs), Graphene Nanoplatelets (GNPs), and Multi-Walled Carbon Nanotubes (MWCNTs) within high viscous structural adhesive. Unlike previous independent studies, our approach considers filler concentration, dispersion behavior, and diverse lap joint configurations, providing a holistic understanding of their impact on mechanical properties. The developed solution mixing technique ensures uniform nanofiller dispersion, and advanced characterization techniques offer unprecedented insights. This research not only addresses critical literature gaps but also provides a roadmap for tailoring adhesive properties, with wide-ranging implications for automotive, aerospace, marine, and construction industries. The result of the study depicted that the role of non-functionalized GNPs, MWCNTs in improving failure parameters in lap joints was superior to that of nonfunctionalized ones in general. This is a consequence of their superior dispersion properties and higher cross-linking density with the adhesive. However, in comparison between fillers, the strength improvement of lap joints reinforced with MWCNTs was superior to both GNPs and RGO. This is due the lateral length of the MWCNTs particles being greater than GNPs and MWCNTs which provided maximum shearing resistance out of the three nanofillers. The findings of this research can be applied to the aerospace and automotive sectors, construction and infrastructure and general adhesive industry where adhesive joints play a critical role in structural integrity. By incorporating carbonaceous nanofillers into epoxy adhesives, it is possible to enhance the strength and durability of adhesive bonds, resulting in improved performance and safety