Ultra-low electrical percolation threshold in carbon-nanotube-epoxy composites

Staff members at Los Alamos National Laboratory (LANL) produced a summary of the structural health monitoring literature in 1995. This presentation will summarize the outcome of an updated review covering the years 1996 2001. The updated review follows the LANL statistical pattern recognition paradigm for SHM, which addresses four topics: 1. Operational Evaluation; 2. Data Acquisition and Cleansing; 3. Feature Extraction; and 4. Statistical Modeling for Feature Discrimination. The literature has been reviewed based on how a particular study addresses these four topics. A significant observation from this review is that although there are many more SHM studies being reported, the investigators, in general, have not yet fully embraced the well-developed tools from statistical pattern recognition. As such, the discrimination procedures employed are often lacking the appropriate rigor necessary for this technology to evolve beyond demonstration problems carried out in laboratory setting.

A review of structural health monitoring literature 1996-2001

Carbon nanotube-reinforced epoxy-composites: enhanced stiffness and fracture toughness at low nanotube content

Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties

Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications.

Flexible Nanodielectric Materials with High Permittivity for Power Energy Storage

In conductive polymer compounds, the filler volume fraction at which a network of touching particles is formed is not a constant but depends on the manufacturing process. By applying three main features—particle-particle interaction, dynamics of agglomeration, and structure of agglomerates—which are well known in colloid science to filled polymers, the electrical percolation behavior can be understood. Thus, it is possible to explain the hitherto found low percolation thresholds of less than 0.5 vol% in carbon-black-filled resins and, hence, further reduce the threshold to 0.06 vol%. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1741–1746, 1997

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

Damage detection in CFRP by electrical conductivity mapping

ac and electrical properties of carbon-black–epoxy composites measured in the frequency range of 100 Hz to 1 MHz are reported. Experimental results are in remarkable disagreement with the predictions of the statistical percolation theory for real and imaginary parts of the conductivity. They both exhibited, in particular, an abrupt variation at a given fraction of carbon black. The evolution of these transport quantities with the volume fraction of carbon black can only be explained considering a phase transition from a dispersed to an agglomerated state of the conducting fillers. This transition has been successfully verified by optical micros-copy of thin polished sections of cured samples. A simple model based on electrostatic repulsion between the carbon-black particles is proposed to interpret such a singular insulator-to-conductor transition. S0163-18299901718-X

https://hal.archives-ouvertes.fr/hal-01653704/document

Anomalous percolation transition in carbon black-epoxy composite materials

The conditions to form a conductive network in carbon black filled epoxy resin were examined. It was found that the formation is controlled by particle-particle interaction which can be influenced by shear forces or by the ionic concentration of the resin. Therefore the network morphology and thus the percolation threshold depends strongly upon the processing route. On best conditions the percolation threshold was reduced to 0.06 vol.-%. That a continuous network can form with such a low volume fraction can be explained by the fractal dimension of agglomerates the network is made of.

Percolation in carbon black filled epoxy resin

Carbon fibers used in advanced composite structures are piezoresistive. These fibers are inherently sensors because of this property. Therefore, carbon fiber reinforced polymer (CFRP) composites can be considered a self-monitoring material without any need for additional sensing elements. However for this to become reality the conductivity map of the entire structure needs to be constructed and relationship between the conductivity and various usage and damage related variables need to be established. Experimental results are given to demonstrate that internal damage, such as fiber fracture and delamination, decreases the conductivity of the composite laminates. In general the information about the damage size and position can be obtained by utilizing electrical impedance tomography (EIT). But the traditional EIT is not capable of extracting this information when the medium possesses highly anisotropic electrical conductivity. Above a certain level of anisotropy it is advantageous to modify the traditional EIT. This paper presents preliminary results from the modified EIT applied to highly orthotropic (unidirectional) CFRP. These results indicate that a practical EIT has a potential of being a cost effective health and usage monitoring technique (HUMT) for CFRPs.

Ruediger Schueler

Papers

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

Damage detection in CFRP by electrical conductivity mapping

Anomalous percolation transition in carbon black-epoxy composite materials

Percolation in carbon black filled epoxy resin

Conductivity of CFRP as a tool for health and usage monitoring