Mechanical damage and strain in carbon fiber thermoplastic‐matrix composite,sensed by electrical resistivity measurement

The volume electrical resistivity of a unidirectional continuous carbon fiber thermoplastic (nylon‐6) matrix composite was found to be an indicator of strain and damage during repeated loading in the fiber direction. The through‐thickness resistivity irreversibly and gradually decreased upon damage (probably fiber‐matrix debonding) during repeated compression or tension. Moreover, it reversibly and abruptly increased upon matrix damage, which occurred reversibly near the peak stress of a stress cycle. In addition, the resistivity increased reversibly upon tension in every stress cycle, and decreased reversibly upon compression in every stress cycle. On the other hand, the longitudinal resistivity irreversibly and gradually increased upon damage. Moreover, it decreased reversibly upon tension in every stress cycle and increased reversibly upon compression in every stress cycle. The through‐thickness resistivity was a better indicator of damage and strain than the longitudinal resistivity.     

Evaluation of embedded optical fiber sensors in composites: EFPI sensor fabrication and quasi‐static evaluation

This article reports on the fabrication and evaluation of extrinsic Fabry–Perot interferometric (EFPI) sensors when embedded in fiber‐reinforced composites and tested under quasi‐static tensile and compressive mechanical loading. The EFPI strain sensors were embedded in carbon fiber composite test specimens, and their performance was compared against a surface‐mounted extensometer and electrical resistance strain gauges. When the composite was subjected to quasi‐static tensile loading, the sensors failed around a strain level of 0.5%; under compressive loading, the sensors survived until the failure of the composite at 1.1% strain. The EFPI sensors used in this study were fabricated in‐house and the issues relating to fabrication are discussed in the context of their performance when embedded in composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effects of tool‐embedded dielectric sensors on heat transfer phenomena during composite cure

The present study examines the effects that placement of tool‐mounted dielectric sensors in the composite cure assembly has on the local thermal and degree‐of‐cure fields. A nonlinear heat transfer model, incorporating appropriate thermoset cure and thermal property submodels, is used to simulate the cure of carbon and glass composites of various thicknesses. The model is validated against experimental data obtained during the cure of composite samples in a resin‐transfer molding tool. The results of the simulations show that embedding a sensor can have a significant effect on the thermal field, because of the thermal conductivity mismatch between the metal tool and the sensor substrate material. In the heating‐up stage of the cure profile, sensors embedded in the heated tool side intensify thermal gradients, which causes a corresponding lag in the progress of the reaction in the area adjacent to the sensor. Exothermic effects are also intensified by the sensor presence, especially in the case of thick composite curing. These results suggest that control strategies based on the utilization of embedded sensors should take these effects into account. POLYM. COMPOS., 28:139–152, 2007. © 2007 Society of Plastics Engineers.     

Evaluation of embedded optical fiber sensors in composites: EFPI sensor response to fatigue loading

Extrinsic Fiber Fabry‐Perot Interferometric (EFPI) sensors were fabricated and embedded within a 16‐layer cross‐ply composite. The composites with and without the embedded EFPI sensors were subjected to tension/compression loading. The presence of the embedded sensor was not found to have adverse effect on the tension/compression fatigue properties. However, the performance of the EFPI sensor was found to degrade with fatigue cycles, with the introduction of a compressive element in the loading regime; samples were tested using stress ratios of −1, −2.5, and −3. Although the reasons for this observed degradation in the response of the sensor to applied strain is not known at present, it is speculated that this may be due to debonding of the key components of the sensor. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Thermo‐mechanical and tribological properties of multi‐walled carbon nanotubes filled friction composite materials

Multi‐walled carbon nanotubes (MWCNTs) filled graphite lubricated phenolic‐based friction composites reinforced with combination of lapinus/Kevlar fibers have been fabricated and subsequently evaluated for their dynamic‐mechanical and tribological properties. The experimental results indicated that the higher MWCNT content enhances the thermal stability, whereas, lower MWCNT content enhances the thermo‐mechanical properties of the friction composites. The tribo‐performance evaluation has revealed that with the increase in MWCNT content, the friction‐fade and friction‐recovery performances are enhanced. The friction‐stability and friction‐variability coefficients are influenced by the combination of MWCNT, graphite, lapinus, and Kevlar constituents. The wear performance decreases with the increase in lapinus and MWCNT, whereas, it increases when the amount of Kevlar or graphite is increased in the composites. Wear surface morphological studies have led to the qualitative characterization of the topographical attributes and the nature of the frictional contact patches which is crucial in understanding the role of MWCNT on friction and wear mechanisms of the investigated automotive brake friction materials. POLYM. COMPOS., 38:1183–1193, 2017. © 2015 Society of Plastics Engineers     

Experimental characterization of interfacial adhesion of an optical fiber embedded in a composite material

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material. The present paper reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A simple system composed of optical fibers embedded in an epoxy vinylester resin was first studied to evaluate the influence of embedded length, curing temperature and curing time. Pull-out tests on optical fibers bonded in epoxy vinylester/glass fiber composite material were carried out to measure the effect of glass concentration on the fiber bonding. The pull-out results showed no effect of both embedded length and curing temperature. However, an increase of the interfacial debonding stress is reported with increased curing time. For the optical fiber/composite system, a linear evolution of interfacial debonding stress with increasing glass fiber concentration is reported.     

Bio‐based hyperbranched polyurethane/multi‐walled carbon nanotube nanocomposites as shape memory materials

Mesua ferrea L. seed oil based hyperbranched polyurethane/multi‐walled carbon nanotube nanocomposites were prepared by solution polymerization technique. The multi‐walled carbon nanotubes were modified with the polyoxyethylene octyl phenyl ether (Triton X‐100). The transmission electron microscopy and Fourier transform infrared spectroscopic study revealed the homogeneous distribution of the multi‐walled carbon nanotubes in the polymer matrix and the presence of strong interfacial interaction between them, respectively. The tensile strength (5.5–21.5 MPa) and scratch resistance (3–6.1 kg) increase with the increase of the content of carbon nanotubes (0 to 2 wt%). The thermo‐gravimetric analysis result showed the increment of thermal stability (240–275°C) of the nanocomposites. All the prepared nanocomposites exhibited the excellent shape fixity and shape recovery. The shape recovery time decreases (127–73 s) with the increase of the concentration of carbon nanotubes in the nanocomposites. Thus the prepared nanocomposites might be utilized as advanced shape memory applications. POLYM. COMPOS., 35:636–643, 2014. © 2013 Society of Plastics Engineers     

Emulsion‐electrospinning n‐octadecane/silk composite fiber as environmental‐friendly form‐stable phase change materials

The ultrafine n‐octadecane/silk composite fibers as form‐stable phase change materials were successfully developed by the emulsion‐electrospinning method. The effect of n‐octadecane content in the emulsion on the morphology and thermal energy storage capacity of the composite fibers were scientifically investigated. Scanning electron microscopy images show that the composite fibers display cylindrical shape with smooth surface and uniform diameter. Differential scanning calorimetry results demonstrate that the composite fibers exhibit reversible phase transition behavior, high thermal energy storage capacity, and good thermal reliability. Meanwhile, the composite fibers exhibit the capability to regulate their interior temperature as the ambient temperature alters according to the thermo‐infrared images. In addition, the composite fibers are friendly to the environment due to the biodegradability of silk. Therefore, the n‐octadecane /silk composite fibers have the great potential application of serving as form‐stable phase change materials for thermal energy storage and thermal regulation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45538.     

Thermal interaction between polymer‐based composite friction materials and counterfaces

Attempts have been made to improve the performance of polymeric composite friction materials for eliminating undesirable mechanical and thermal effects on the opposing surfaces. Elastic compression modulus and thermal conductivity of the moulded friction materials were found to be the most effective parameters upon the thermal interaction between the disc and brake pad. Effects of elastic modulus on temperature accumulation of the interface have also been studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 364–369, 2001     

Simulation of Real‐Valued Discrete‐Time Periodically Correlated Gaussian Processes with Prescribed Spectral Density Matrices

Abstract. In this article, we provide a spectral characterization for a real‐valued discrete‐time periodically correlated process, and then proceed on to establish a simulation procedure to simulate such a Gaussian process for a given spectral density. We also prove that the simulated process, at each time index, converges to the actual process in the mean square.     

Wear and thermal effects in low modulus polymer‐based composite friction materials

The wear properties of low modulus polymer‐based friction materials were studied. The wear equation W = K P^a V^b t^c was used to correlate the wear of polymer‐based friction material sliding against cast iron with the wear coefficient (K), load (P), speed (V), and time (t). The parameters were determined experimentally by varying only one variable at a time and keeping the other two variables constant. The wear rate of selected polymer‐based friction material was compared with cast iron friction material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1181–1188, 2005     

Piezoresistivity in continuous carbon fiber polymer‐matrix composite

Piezoresistivity involving the volume resistivity of a continuous unidirectional carbon fiber epoxy‐matrix composite in the fiber direction decreasing reversibly upon tension in the fiber direction was observed by the four‐probe method, due to an increase in the degree of fiber alignment. Use of the two‐probe method resulted in measurement of the contact resistance rather than the volume resistance. The contact resistance increased reversibly upon tension.     

Highly sensitive nano-aerosol detection based on the whispering-gallery-mode in cylindrical optical fiber resonators

Highly sensitive detection of nanoscale aerosols, or nano-aerosols, is a difficult challenge. Here, we report a fiber optical technique that is capable of detecting trace-level nano-aerosols. Our method is based on monitoring the nano-aerosol-induced resonance shift due to the optical Whispering-Gallery-Mode (WGM) in a cylindrical optical fiber resonator. A nearly linear relationship between the WGM resonance shift and the aerosol coverage ratio of silica nanoparticles (40–50 nm dia.) on the fiber resonator was identified in the low coverage regime. Our experimental results imply sensitivity at the level of ～2 nanoparticles per μm² deposited on the fiber resonator, which corresponds to pg-level sensitivity in the total aerosol mass within the effective detection area. The response of this fiber optical sensor is further confirmed by using silica nanoparticles deposited on the fiber surface via electrostatic self-assembly. The fiber optical technique for nanoparticle detection may ultimately lead to an instrument capable of real-time in situ aerosol detection with ultrahigh sensitivity.

Copyright © 2016 American Association for Aerosol Research     

Waste‐derived low‐cost mycelium composite construction materials with improved fire safety

Mycelial growth attracts academic and commercial interest because of its ability to upcycle agricultural and industrial wastes into economical and environmentally sustainable composite materials using a natural, low‐energy manufacturing process able to sequester carbon. This study aims to characterise the effect of varying ratios of high silica agricultural and industrial wastes on the flammability of mycelium composites, relative to typical synthetic construction materials. The results reveal that mycelium composites are safer than the traditional construction materials considered, producing much lower average and peak heat release rates and longer time to flashover. They also release significantly less smoke and CO₂, although CO production fluctuated. Rice hulls yielded significant char and silica ash which improved fire performance, but composites containing glass fines exhibited the best fire performance because of their significantly higher silica concentrations and low combustible material content. Higher concentrations of glass fines increased volume‐specific cost but reduced mass‐specific and density‐specific costs. The findings of this study show that mycelium composites are a very economical alternative to highly flammable petroleum‐derived and natural gas‐derived synthetic polymers and engineered woods for applications including insulation, furniture, and panelling.     

Effect of multi‐walled nanotubes on the interlaminar shear strength of glass fiber/acrylate composite fabricated by stepwise ultra‐violet light curing

The interlaminar shear strength (ILSS) of glass fiber/acrylate composite with stepwise ultraviolet (UV) light curing was enhanced by adding multi‐walled carbon nanotubes (MWCNTs) into the resin matrix. The maximum content of MWCNTs that can be used in the process was investigated. Differential scanning calorimetry (DSC) results indicated that prepreg with MWCNTs of more than 0.5% by weight was difficult to cure by UV light because of its poor UV light penetration ability. The ILSS was improved obviously due to the improved resin toughness, crack propagation resistance and interfacial adhesion between the resin and glass fibers according to SEM images. Experimental results suggested that the addition of MWCNTs is an effective method to improve the ILSS of UV stepwise curing composites. POLYM. COMPOS., 38:2113–2118, 2017. © 2015 Society of Plastics Engineers     

Refractive materials for interlayer optical contacts with TiO2‐based organic/inorganic hybrids

Organic/inorganic hybrid materials were prepared by synthesizing from titanium tetraisopropoxide (TTIP), diethanolamine (DEOA), and water. Formulating the materials with thermosetting polymers, the composites were designed for refractive optical contacts with heat lamination of a film having >50 μm thickness. Inherent difficulties of TiO₂ and sol‐gel reaction of TTIP, i.e. photocatalytic properties and prompt sol‐gel reaction to form large TiO₂ particle, were avoided by stabilizing Ti with use of DEOA. The reactivity of the sol‐gel reaction and formation of TiO₂ crystal structure were suppressed by DEOA. However, suppression of the photocatalytic properties was not enough and needed a use of anti‐oxidant agent, 2,6‐di‐t‐butyl‐p‐cresol (BHT). The titanium‐based organic/inorganic hybrid materials and its epoxy composites were transparent in visible wavelength region and gave in the range of 1.66 to 1.73 of refractive indices depending on stoichometric parameters of TTIP, water, and DEOA for the hybrid materials. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Preparation and characterization of epoxidized soybean oil‐based paper composite as potential water‐resistant materials

Epoxidized soybean oil‐based paper composites (ESOPCs) were prepared by fabricating poly epoxidized soybean oil (PESO) with paper. With boron trifluride diethyl etherate as catalyst, epoxidized soybean oil was in situ polymerized on the surface of the paper and within the interspaces of the paper cellulose fibers. Fourier transform infrared analysis confirmed the polymerization of epoxidized soybean oil. Scanning electron microscopic analysis showed that ESOPCs had nanostructured wrinkle morphology on the surfaces and the PESO combined tightly with the paper cellulose fibers. The tensile strength of ESOPCs was 17.3–24.8 MPa, which was higher than that of most vegetable oil‐based neat polymers. Thermogravimetric analysis indicated that ESOPCs were thermally stable up to 360°C in a nitrogen atmosphere. Water vapor permeability (WVP) tests revealed that the WVP of ESOPCs was 3.52–4.45 × 10^?12 g/m/s/Pa, significantly lower than many of other biobased polymeric materials, which would promote the application of vegetable‐based polymers as potential water‐resistant materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41575.     

Core–shell type multi‐arm azide polymers based on hyperbranched copolyether as potential energetic materials in solid propellants

A series of novel multi‐arm azide copolymers (POGs) with the same hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] core (PEHO‐c) and different content of linear glycidyl azide polymer shell (GAP‐s) have been synthesized by sequential cationic ring‐opening polymerization and azidation. Detailed structural information of these copolyethers was deduced from Fourier transform infrared, ¹H NMR and inverse gated decoupled ¹³C NMR spectroscopies, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry, gel permeation chromatography and elemental analysis. The molecular weight of POG having GAP‐s and PEHO‐c with a molar ratio 14.95:1 (R_s/c) was around 31 000 g mol^?1, far above that of linear GAP (around 4000 g mol^?1). The apparent viscosity and glass transition temperature (?51 to ?23 °C) decreased first and then slightly increased with increasing molecular weight. Thermal analysis revealed that all the obtained POGs exhibited excellent resistance to thermal decomposition up to 220 °C. Moreover, the energetic properties, investigated using oxygen bomb calorimetric measurements, indicated that the enthalpy of formation of the POGs was higher than that of general linear GAP, but similar to that of branched GAP under reasonable R_s/c. The compatibilities of the POGs with common materials used in solid propellants were studied using differential scanning calorimetry and the results indicated that the POGs had good compatibility with these materials. © 2017 Society of Chemical Industry