Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints

Abstract

Carbon nanotubes (CNTs) embedded polymers are of increasing interest to scientific and industrial communities for multi-functional applications. In this article, CNTs have been introduced to high-strength epoxy adhesive for enabling in-situ strain sensing in adhesively bonded aluminium-to-aluminium single-lap joints to accurately indicate the onset and propagation of adhesion failure to the evolution of piezo-resistivity in varying mechanical loads. The CNT modified adhesive in bonded joints and the CNT modified adhesive alone have been tested under monothonic and cyclic tensile loads up to ultimate failure. The changes in the piezo-resistivity induced by the CNTs have been monitored in situ with respect to loading. A novel interpretation method has been developed for progressive, instantaneous adhesion failure estimation under cyclic tensile stresses from a resistivity baseline. The method indicates that the in-situ resistivity changes and the rate of the changes with strain, i.e. sensitivity, strongly correlate with the adhesion failure progression, irrespective of the CNT dispersion quality. Moreover, the effect of bond thickness on the evolution of piezo-resistivity and adhesion failure have been studied. It was observed that relatively thin adhesive bonds (0.18 mm thickness), possessing higher CNT contact points than thick bonds (0.43 mm thickness), provide 100 times higher sensitivity to varying cyclic loads.

Adhesive Joint Integrity Monitoring Using the Full Spectral Response of Fiber Bragg Grating Sensors

“…Instead of directly looking for defects, there are relatively more economical techniques suitable for real-time monitoring of the integrity degradation of adhesive joints. These include strain/stiffness monitoring using back face strain gages [21][22][23], resistance monitoring of adhesive joints made conductive by adding carbon nanotubes [24,25] and optical fiber sensors signal surveillance [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Strain gages can only be applied to the outer surface, but they will disrupt an otherwise smooth surface and are susceptible to environmental degradation.…”

Mechanical properties of carbon nanotubes/epoxy nanocomposites: Pre-curing, curing temperature, and cooling rate

“…12 By using nanofiller, it is possible to produce a polymer composite with multi functionalities; 13 for example, conducting nanofiller may act as self-sensing material in composite. 14 In order to achieve the optimum reinforcement of nanofiller, several factors need to be considered, such as the properties of each constituent (e.g., nanofiller and polymer matrix), the morphology of the filler, 5 the interface between the filler and the polymer matrix, 15 and the dispersion of the nanofiller. 16 Carbon nanofillers such as carbon nanotube and graphene have shown excellent mechanical properties thus can be used as reinforcement of polymer matrix.…”

Development and testing of carbonaceous tin-based solder composites achieving unprecedented joint performance

“…via heating, chemical treatment or ultra-violet radiations), the bonding formed during adhesive joining (so-called secondary bonding) is not a metallurgical bond, rather, it is a chemical bond (i.e., Van der Waals bond) [6]. However, the polymer bonding poses problems in curing time, inspection, disassembly and environmental degradation [7][8][9][10][11][12], as well as the challenge to assure bond quality [13,14] Joining aluminium for structural applications has proven to be challenging using traditional welding and brazing practices due to its high coefficient of thermal expansion (CTE). The thermally induced residual stresses at the interface leads to excessive strains causing CTE mismatch between the substrate and the joining material [15].…”

“…Contrarily, during adhesion [17,18],the same procedure would require highly controlled surface treatment and possible process-induced tight disbond. Similar to adhesive bonding, the main parameters affecting the solder joint is the wettability which in turn influences the interfacial strength of the soldered joint that is characterised using techniques such as the single-lap joint shear test [12].…”

“…The study includes a comprehensive analysis of data from microstructural characterisation, thermal analysis and mechanical shear performance of soldered joints utilising the pristine solder, and carbon nanomaterials reinforced solder with 0.01 and 0.05 wt.% loading contents. The joint strength was evaluated using standard single-lap soldered joints made of aerospace grade aluminium substrates, and under quasi-static loading conditions [12,25].…”