Sensing strain and damage in polyurethane/MWCNT nano-composite foams using electrical measurements

Abstract

The addition of carbon nano-fillers (nanofibers (CNF), nanotubes (CNT) etc.) into plastics has been shown to affect the various properties of the resulting material and effectively increase the electrical conductivity of the system by several orders of magnitude [1]. This is attributed to the formation of a conductive network of the conductive nanofillers, which can be described as a percolated network. The increased electrical conductivity of the nano-reinforced materials has given rise to their use in various applications [2]. Polymeric foams (e.g. Rigid PolyUrethane (PUR)) represent a very interesting and useful sub-group, finding vast range of applications due to their versatility. In structural applications, they are commonly used due to the weight saving capabilities they can offer in the design (e.g. as sandwich cores). Combining nano-fillers with foam materials, nanoreinforcement of foams has been developed and studied the past decade, but mainly focused on the mechanical and thermal properties. Electrical conductivity of nano-composite foams is much less studied. Works on the electrical properties of nanoreinforced polymeric foams are rather sporadic [3][4][5][6][7][8][9][10]. The relationship between the resulting electrical conductivity and the density of the rigid foams for given CNT concentrations was reported in [6] but only recently described further [10]. 40Sensing strain and damage in polyurethane-MWCNT nano-composite foams using electrical measurements A. Baltopoulos, N. Athanasopoulos, I. Fotiou, A. Vavouliotis Abstract. This work deals with the damage identification in polymeric foams through the monitoring of the electrical resistance of the system. To assess this idea electrically conductive rigid Poly-Urethane (PUR) foams at various densities were prepared. Multi-Wall Carbon Nanotubes (MWCNT) were dispersed in the host polymer at various concentrations through high shear mixing to provide electrical conductivity to the system. The PUR/MWCNT foams exhibited varying electrical conductivity on a wide range of densities and nano-filler contents. The prepared foams were subject to compression tests. Electrical resistance was recorded online during the tests to monitor the change of the bulk property of the materials. A structural-electrical cross-property relation was exhibited. The distinctive phases of foam compression were successfully identified from the electrical resistance profile recorded during the tests. A characteristic master curve of the change of electrical resistivity with respect to load and damage is proposed and analyzed. It was shown that the found electrical resistance profile is a characteristic of all the MWCNT contents and depends on density and conductivity. MWCNT content contributes mainly to the sensitivity of electrical sensing in the initial stage of compression. Later compression stages are dominated by foam microstructural damage which mask any effect of CNT dispersion. Micro-structural observations were employed to verify the experimental findings and curves.Keywo...

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