Enabling damage detection: Manufacturing composite laminates doped with dispersed triboluminescent materials

Triboluminescent materials are being harnessed to address the gaps in current structural health monitoring systems. Their innate ability to emit light when stressed or broken makes them ideal candidates for the ubiquitous and in situ monitoring of structures. The increasing use of advanced composites in critical structures, where subsurface damage initiation may go unnoticed, further highlights the urgency in developing efficient online monitoring technologies. This work looked at the manufacturing of composite laminates that have been doped with various concentrations (0 to 10 %wt.) of a triboluminescent material (ZnS:Mn). Laminates were manufactured using a vacuum infusion process. Dispersing the ZnS:Mn particulates was cumbersome because their density was higher than the resin that caused settling during resin infusion. The dispersion of ZnS:Mn is critical to their use in the health monitoring of the host structure. As such, a method for mechanical agitation using a rotational vacuum infusion apparatus was developed employing centrifugal motion. The degree of dispersion in the resulting laminates was determined using scanning electron microscopy and the energy dispersive scanning feature of the electron microscope for elemental mapping. A quantitative metric was established by computations of the Euclidean distance of EDS mapping. Studies of the effect of ZnS:Mn concentration on the tensile strength of laminates showed that increasing the ZnS:Mn concentration reduced the tensile strength. Key processing parameters were studied, and determined that curing kinetics were not altered by ZnS:Mn inclusion. © 2011, SAGE Publications. All rights reserved

Progress towards self-healing polymers for composite structural applications

Repair in composite materials is tending towards autonomic healing systems. This is a technological departure from the mechanical repair currently practiced in industry. For reinforced polymer matrix composites, failure tends to occur in the matrix or matrix-reinforcement interface. The most common failure mode is the formation and propagation of microcracks that reduce the material\u27s structural capabilities. Damage may be fixed through traditional bolted or bonded repair methods, but such repair requires temporary decommission of a part, collection of repair materials, and employee time and effort to enact the repair. This review describes methods of self-repair and healing for polymeric materials with a focus on structural applications of these self-healing materials. From intrinsically healing polymers to self-healing-enabled polymer composites with dispersed agents or vascular networks, this review examines the chemistries and mechanisms which enable self-healing

Multifunctional composites with triboluminescent sensors and photoactive materials

Advanced composites have non-traditional failure occurrences that can include composite delamination, fiber-debonding, and matrix cracking. A known weak focal point for continuation of damage is found in the matrix constituent. Damage detection will be most prominent at these sites for first occurrences and thus deemed as critical to detection for first response. The system under development uses the triboluminescence (TL) phenomenon as the energy (light) source, thus negating the need for any external energy source. Triboluminescence1 is a mechano-optical phenomenon of luminescence, where light emission occurs by rubbing or fracture. The composites become multifunctional when TL phosphors are incorporated as composite fillers and via nerve sensors. This effort investigates the harvesting of light energy through ubiquitous dispersion as well as concentrated photoactive optical fibers. Through inundation of a highly known TL material (ZnS:Mn), emissions were observed during flexural loading of casted resin and reinforced matrices. This work describes ongoing effort to harvest low-light energy using optoelectronic devices during quasi-static loading of concentrated composite systems

Mechanical Characterization of EuD4TEA‐ and ZnS:Mn‐Enhanced Composites

Triboluminescent (TL) materials are assessed as components in structural health monitoring (SHM) systems within polymer composites. Processing must be addressed due to particle characteristics such as density, morphology, and chemical makeup, all of which can affect polymer curing dynamics and thermo-mechanical properties. This study considers key processing parameters during incorporation of TL compounds into various polymers. The TL materials chosen for this study are zinc sulfide manganese (ZnS:Mn) and europium dibenzoylmethide triethylammonium (EuD4TEA). These crystals are dispersed within the liquid phase of polyvinyl ester (VE), polydimethylsiloxane (PDMS), and Dymax 9663 ultraviolet-curable (UV-curing) resins. Incorporation of the europium compound apparently slows the cure process, particularly in the UV-curing resin, while the zinc compound had a minimal effect on curing. Tensile testing shows a decrease in tensile modulus due to incorporation of TL crystals. Incorporation of the europium compound caused a 20–53% decrease in modulus; incorporation of the zinc compound caused a 7–66% decrease in modulus. Experimental results are used to create a multi-scale model using Digimat. Discrepancies in the found values may be due to sample quality (e.g. presence of voids in experimental samples)

Triboluminescence multifunctional cementitious composites with in-situ damage sensing capability

Structural health monitoring of civil infrastructure systems like concrete bridges and dams has become critical because of the aging and overloading of these CIS. Most of the available SHM methods are not in-situ and can be very expensive. The triboluminescence multifunctional cementitious composites (TMCC) have in-built crack detection mechanism that can enable bridge engineers to monitor and detect abnormal crack formation in concrete structures so that timely corrective action can be taken to prevent costly or catastrophic failures. This article reports the fabrication process and test result of the flexural characterization of the TMCC. Accelerated durability test indicated that the 0.5 ZnS:Mn/Epoxy weight fraction ITOF sensor configuration to be more desirable in terms of durability. The alkaline environment at the highest temperature investigated (45 °C) resulted in significant reduction in the mean glass transition and storage moduli of the tested ITOF thin films. Further work is ongoing to correlate the TL response of the TMCC with damage, particularly crack opening. © 2012 SPIE

Photoenergy harvesting with 3D solar cell (3DSC) for damage sensors: A nanotechnology approach

Solid state 3DSCs have been developed using thermally-stable and highly conductive a) titanium micro-wires (TM) and b) carbon nanotubes yarns (CNYs). These studies result in two different types of cells: a) TM-CNY and CNY-CNY systems. Two types of working electrodes (WEs) have been developed using TM and CNY separately. Highly inter-aligned, ultrastrong and flexible CNYs with excellent electrical conductivity, mechanical integrity and catalytic property have been successfully used as counter electrodes (CEs). The open circuit voltage and current density of the cells can remarkably be improved through optimizing the numbers of CNYs and engineering of CNYs-TiO2 interface. Optimizing the number of CNYs in the electrodes yields a photoconversion efficiency of 0.1959 % (TM-CNY 3DSC) and ∼ 1.5 % (CNY-CNY 3DSC) with prolonged-time stability. The cells are able to transport photocurrent over a significant distance using a simple cell configuration with a wide range of structural flexibility

Multifunctional cementitious composites with structural and damage monitoring capabilities for smart bridges

Aging and overloaded critical civil infrastructure systems such as bridges pose great risks to the hundreds of millions of daily users. Limited resources for their repairs and replacements have necessitated the need for the development of multifunctional composites with both structural and in-situ damage monitoring capabilities. An in-situ triboluminescent optical fiber (ITOF) sensor with an integrated sensing and transmission system has been developed. The ITOF sensor has been incorporated into reinforced triboluminescent multifunctional cementitious composites (TMCC) to allow for real time structural health monitoring of bridges. Results are reported on the performance characterization of the sensor under flexural loading and show that the integrated sensor is able to detect localized damage (cracks) before the failure of the TMCC beams. This will enable early damage detection that will lead to prompt repairs thereby resulting in significant life and cost savings. Copyright 2013 by Aurora Flight Sciences

3D Wire-Shaped Dye-Sensitized Solar Cells in Solid State Using Carbon Nanotube Yarns with Hybrid Photovoltaic Structure

A novel 3D solid-state wire-shaped dye-sensitized solar cell (DSSC) with a hybrid photovoltaic (PV) structure is demonstrated. Carbon nanotube yarn provides excellent interfacial and electrocatalytic properties. The quantum dots (QDs) have been applied due to their high photon absorption coefficient. Finally, the cell shows an outstanding operational flexibility with an efficient photovoltaic efficiency (7.39%)