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•Nano particle aspect ratio, content, geometry and orientation affect piezoresistivity.•Piezoresistive behaviour becomes adjustable.•Filler content near the percolation threshold ...leads to the highest sensitivity.•Alignment of particles leads to higher linearity.
In this study, we investigate the piezoresistive response of carbon black and multi walled carbon nanotube/epoxy composites films and bulk specimens. The morphology of the nanocomposites has been influenced by variation of particle geometry, aspect ratio, filler content and AC-field induced alignment of the particles. This allows to understand the influencing parameters so the electrical resistance change (ERC) of the material becomes adjustable. All nanocomposites show a reproducible characteristic ERC vs. strain under quasi-static unidirectional tension, with a resistance increase, a maximum and a subsequent resistance decrease at high strains. Due to the occurring maximum in ERC two resistance values correlate to one strain level. This ambiguity of ERC is unfavourable for sensing purposes. Higher aspect ratios and filler contents shift the maximum to a lower strain level, while the sensitivity is reduced. Alignment of particles leads to a shift of the maximum to a higher strain level, a linear ERC and a gauge factor of about six, but reduces the conductivity. In the composites films the alignment of particles in load direction enhances the strain sensing capabilities.
The subject of this work is the investigation of the stress field around a unique void in a fibre-reinforced model composite under compression. Voids were introduced into the epoxy material by ...injection. The idea was to imitate a real void in fibre reinforced plastics (FRP) where voids appear between fibres and in resin rich areas. To investigate the mechanical response of the composite material under compression, a test jig was designed, which fits into a light microscope with an integrated photoelasticity device. That way in situ measurements were conducted. It could be demonstrated, that voids have a significant influence on the stress distribution in the matrix which leads to stress concentrations particularly around the end caps and the longitudinal side of the voids. Furthermore, different failure mechanisms like fibre matrix debonding and fibre buckling could be observed.
•Continuous-discontinuous sheet molding compounds show excellent fatigue properties.•Hybridization effects are stronger under fatigue than under monotonic loading.•Constraining effects lead to a ...higher fatigue strength of the continuous plies.•A cross-ply continuous reinforcement leads to an unfavorable damage evolution.•The S-N behavior of hybrid SMC can be approximated from the behavior of DiCo SMC.
This study is focused on the fatigue of sheet molding compounds (SMC) with a discontinuous (DiCo) glass fiber-reinforced core and continuous (Co) unidirectional (0/DiCo/0) or cross-ply (0/90/DiCo/90/0) carbon fiber-reinforced face layers. Tension-tension tests were conducted on the constituents (i.e., DiCo and Co SMC) and hybrid specimens. Hybridization effects were larger under cyclic than under monotonic loading. Constraining effects resulted in enhanced high fatigue strength of the Co plies in 0/DiCo/0. 0/90/DiCo/90/0 was more sensitive to fatigue than 0/DiCo/0 due to localized damage starting from 90°-ply cracks. The S-N behavior of the hybrid was approximated from the behavior of DiCo SMC.
The new ATLAS track reconstruction (NEWT) Cornelissen, T; Elsing, M; Gavrilenko, I ...
Journal of physics. Conference series,
07/2008, Letnik:
119, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The track reconstruction of modern high energy physics experiments is a very complex task that puts stringent requirements onto the software realisation. The ATLAS track reconstruction software has ...been in the past dominated by a collection of individual packages, each of which incorporating a different intrinsic event data model, different data flow sequences and calibration data. Recently, the ATLAS track reconstruction has undergone a major design revolution to ensure maintainability during the long lifetime of the ATLAS experiment and the flexibility needed for the startup phase. The entire software chain has been re-organised in modular components and a common event data model has been deployed. A complete new track reconstruction that concentrates on common tools aimed to be used by both ATLAS tracking devices, the Inner Detector and the Muon System, has been established. It has been already used during many large scale tests with data from Monte Carlo simulation and from detector commissioning projects such as the combined test beam 2004 and cosmic ray events. This document concentrates on the technical and conceptual details of the newly developed track reconstruction.
Fiber orientation tensors (FOT) are used as a compact form of representing the mechanically important quantity of fiber orientation in fiber reinforced composites. While they can be obtained via ...image processing methods from micro computed tomography scans (μCT), the specimen size needs to be sufficiently small for adequate resolution – especially in the case of carbon fibers. In order to avoid massive workload by scans and image evaluation when determining full-field FOT distributions for a plaque or a part, e.g., for comparison with process simulations, the possibilities of a direct interpolation of a few measured FOT at specific support points were opened in this paper. Hence, three different tensor interpolation methods were implemented and compared qualitatively with the help of visualization through tensor glyphs and quantitatively by calculating originally measured tensors at support points and evaluating the deviations. The methods compared in this work include two algebraic approaches, firstly, a Euclidean component averaging and secondly, a decomposition approach based on separate invariant and quaternion weighting, as well as an artificial intelligence (AI)-based method using an artificial neural network (ANN). While the decomposition method showed the best results visually, quantitatively the component averaging method and the neural network behaved better (that is for the type of quantitative error assessment used in this paper) with mean absolute errors of 0.105 and 0.114 when calculating previously measured tensors and comparing the components. With each method providing different advantages, the use for further application as well as necessary improvement is discussed. The authors would like to highlight the novelty of the methods being used with small and CT-based tensor datasets.
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•Four different tensor interpolation methods applied to fiber orientation tensors.•Methods include linear algebraic decomposition method and artificial neural network.•Orientation field of plaque determined in significantly less time with scarce data.•Could replace time-consuming high amount of μCT scans.
Hybrid continuous-discontinuous sheet molding compound (SMC) composites are considered suitable candidates for structural automotive applications, due to their high mass-specific mechanical ...properties combined with high geometrical flexibility and low costs. Since structural automotive parts are subject to repeated loading, profound knowledge of their fatigue behavior is required. This paper presents an experimental study on the bending fatigue behavior of hybrid SMC with discontinuous glass fibers in the core and unidirectional continuous carbon fibers in the face layers. Effects of hybridization on the S-N behavior and stiffness degradation have been analyzed in constant amplitude fatigue tests under 3-point bending load at different temperatures and frequencies. Microscopic investigations on polished specimen edges were used to study the damage behavior. The ultimate flexural strength at quasi-static (UFSS) and fatigue strain rate (UFSF) of the hybrid composite was 54 % and 59 % higher than that of discontinuous SMC, respectively. In contrast, the flexural fatigue strength at 2.6⋅106 cycles increased by 258 %. The relative stiffness degradation of the hybrid composites was smaller during most of their fatigue lives due to the continuous carbon fiber reinforcement. The carbon fiber ply on the compression loaded side was the first ply to fail. Fatigue stress significantly decreased at 80 °C due to early kinking of the continuous carbon fiber-reinforced ply on the compression loaded side. Variation of frequency had no significant effect on the fatigue behavior of both discontinuous and continuous-discontinuous SMC.
This article presents a retrospective exposure assessment for 493 workers who were occupationally exposed to airborne hexavalent chromium, Cr(VI), at a Painesville, Ohio, chromate production plant ...from 1940-1972. Exposure estimates were reconstructed using a job-exposure matrix approach that related job titles with area monitoring data from 21 industrial hygiene surveys conducted from 1943 to 1971. No personal monitoring data were collected. Specifically, airborne Cr(VI) concentration profiles for 22 areas of the plant, termed job-exposure group (JEG) areas, were constructed for three distinct time periods (1940-1949, 1950-1964, and 1965-1972), with cut points based on known major plant and process changes. Average airborne Cr(VI) concentrations were the highest for the bridge crane operators (5.5 mg/m
3
) prior to 1965, although only four cohort members held this job title. Airborne concentrations for the rest of the production areas of the plant ranged from 1.9 mg/m
3
for packers in the 1940s to 0.012 mg/m
3
for ore mill operators after 1964. For nearly all JEG areas, exposures decreased over time, particularly after 1964. For example, average airborne concentrations in production areas of the plant decreased from 0.72 mg/m
3
in the 1940s to 0.27 mg/m
3
from 1950 to 1964, and the average was 0.039 mg/m
3
after 1964. Former workers were interviewed to determine activity patterns in the plant by job title. This information was combined with Cr(VI) monitoring data to calculate cumulative occupational exposure for each worker. Cumulative exposures ranged from 0.003 to 23 (mg/m
3
) × years. The highest monthly 8-hour average exposure concentration for each worker ranged from 0.003 to 4.1 mg/m
3
. These exposure estimates have been combined with mortality data for this cohort to assess the lung cancer risk associated with inhaled Cr(VI), and a positive dose-response relationship was observed for increases in lung cancer mortality with measures of cumulative exposure and highest monthly exposure.
In anticipation of the first LHC data to come, a considerable effort has been devoted to ensure the efficient reconstruction of vertices in the ATLAS detector. This includes the reconstruction of ...photon conversions, long lived particles, secondary vertices in jets as well as finding and fitting of primary vertices. The implementation of the corresponding algorithms requires a modular design based on the use of abstract interfaces and a common Event Data Model. An enhanced software framework addressing various physics applications of vertex reconstruction has been developed in the ATLAS experiment. Presented in this paper are the general principles of this framework. A particular emphasis is given to the description of the concrete implementations, which are dedicated to diverse methods of vertex reconstruction.
Aerographite (AG) is a mechanically robust, lightweight synthetic cellular material, which consists of a 3D interconnected network of tubular carbon 1. The presence of open channels in AG aids to ...infiltrate them with polymer matrices, thereby yielding an electrical conducting and lightweight composite. Aerographite produced with densities in the range of 7–15 mg/cm3 was infiltrated with a low viscous epoxy resin by means of vacuum infiltration technique. Detailed morphological and structural investigations on synthesized AG and AG/epoxy composite were performed by scanning electron microscopic techniques. Our present study investigates the fracture and failure of AG/epoxy composites and its energy absorption capacity under compression. The composites displayed an extended plateau region when uni-axially compressed, which led to an increase in energy absorption of ~133% per unit volume for 1.5 wt% of AG, when compared to pure epoxy. Preliminary results on fracture toughness showed an enhancement of ~19% in KIC for AG/epoxy composites with 0.45 wt% of AG. Furthermore, our observations of fractured surfaces under scanning electron microscope gives evidence of pull-out of arms of AG tetrapod, interface and inter-graphite failure as the dominating mechanism for the toughness improvement in these composites. These observations were consistent with the results obtained from photoelasticity experiments on a thin film AG/epoxy model composite.
In this study, we demonstrate the applicability of three-roll milling (TRM) process for carbon nanotube-epoxy dispersion in industrial scale and two methods to characterize the dispersion quality ...based on optical coherence tomography (OCT) and impedance spectroscopy were utilized. These methods are easily applicable for industrial continuous TRM dispersion process monitoring. Modeling impedance spectra with equivalent circuit enhances the possibility to quantify the grade of dispersion. We monitored the dispersion development over a complete seven step three-roll mill process for several batches. The gained results are in good accordance to the particle size measurements by grindometry. Results show, on the one hand, that the real part of impedance undergoes a minimum during processing. The most homogeneous dispersion state is not the favorable for gaining electrical conductive materials. On the other hand, imaginary part of impedance undergoes a maximum. High reactance correlates with small particle sizes as well as homogeneous distribution. A developed model from impedance spectra leads to an improved understanding of network formation. OCT results allow a qualitative analysis of the dispersion and detection of in-homogeneous agglomerate sizes.
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