Modelling the microstructure and the viscoelastic behaviour of carbon black filled rubber materials from 3D simulations

International audienceVolume fraction and spatial repartition of fillers impact the physical properties of rubber. Extended percolating networks of nano-sized fillers significantly modify the macroscopic mechanical properties of rubbers. Random models that describe the multiscale microstructure of rubber and efficient Fourier-based numerical algorithms are combined to predict the material’s mechanical properties. From TEM image analysis, various types of multiscale models were proposed and validated, accounting for the non-homogeneous distribution of fillers: in the present work, aggregates are located outside of an exclusion polymer simulated by two families of random models. The first model generates the exclusion polymer by a Boolean model of spheres. In the second model, the exclusion polymer is a mosaic model built from a Johnson-Mehl tessellation. Here the exclusion polymer and the polymer containing the filler show a similar morphology, contrary to the Boolean model. Aggregates are then described as the intersection of a Boolean model of spheres and of the complementary of the exclusion polymer. Carbon black particles are simulated by a Cox model of spheres in the aggregates. The models rely on a limited number of parameters fitted from experimental covariance and cumulative granulometry. The influence of the model parameters on percolation properties of the models is studied numerically from 3D simulations. Finally, a novel Fourier-based algorithm is proposed to estimate the viscoelastic properties of linear heterogeneous media, in the harmonic regime. The method is compared to analytical results and to a different, time-discretized FFT scheme. As shown in this work, the proposed numerical method is efficient for computing the viscoelastic response of microstructures containing rubbers and fillers

Modelling the Microstructure and the Viscoelastic Behaviour of Carbon Black Filled Rubber Materials from 3D Simulations

Volume fraction and spatial repartition of fillers impact the physical properties of rubber. Extended percolating networks of nano-sized fillers significantly modify the macroscopic mechanical properties of rubbers. Random models that describe the multiscale microstructure of rubber and efficient Fourier-based numerical algorithms are combined to predict the material’s mechanical properties. From TEM image analysis, various types of multiscale models were proposed and validated, accounting for the non-homogeneous distribution of fillers: in the present work, aggregates are located outside of an exclusion polymer simulated by two families of random models. The first model generates the exclusion polymer by a Boolean model of spheres. In the second model, the exclusion polymer is a mosaic model built from a Johnson-Mehl tessellation. Here the exclusion polymer and the polymer containing the filler show a similar morphology, contrary to the Boolean model. Aggregates are then described as the intersection of a Boolean model of spheres and of the complementary of the exclusion polymer. Carbon black particles are simulated by a Cox model of spheres in the aggregates. The models rely on a limited number of parameters fitted from experimental covariance and cumulative granulometry. The influence of the model parameters on percolation properties of the models is studied numerically from 3D simulations. Finally, a novel Fourier-based algorithm is proposed to estimate the viscoelastic properties of linear heterogeneous media, in the harmonic regime. The method is compared to analytical results and to a different, time-discretized FFT scheme. As shown in this work, the proposed numerical method is efficient for computing the viscoelastic response of microstructures containing rubbers and fillers

Preserving the C7 spinous process in laminectomy combined with lateral mass screw to prevent axial symptom

AbstractBackgroundPreserving the C7 spinous process during cervical laminoplasty has been reported to prevent axial symptom. Some patients underwent laminectomy and fixation developed the symptom. The objective of this article was to investigate whether axial symptom can be reduced by preserving the C7 spinous process during cervical laminectomy and fixation with lateral mass screw.MethodsBetween 2005 and 2008, data of 53 patients who underwent laminectomy and lateral mass-screw fixation for multilevel cervical myelopathy were reviewed. Analysis consisted of the incidence of axial symptom, Japan Orthopaedic Association (JOA) scores, recovery rate, cervical lordotic angle, and atrophy rate of cervical posterior muscle. Axial symptom severity was quantified by a visual analog scale (VAS). Twenty-five patients were decompressed from C3 to C7 (group A) and 28 from C3 to C6 with dome-shape removal of the C7 superior lamina (group B).ResultsAnalysis of final follow-up data showed improvement in clinical outcome for both groups. No difference in recovery rate, cervical lordotic angle and atrophy rate was observed between groups. Postoperative axial-neck pain was significantly rarer in group B than in group A. Axial symptom severity was correlated with cervical posterior muscle atrophy rate; correlation coefficient was 0.665.ConclusionThe C7 spinous process might play an important role in preventing axial symptom, but there is a need for randomized, control studies with long-term follow-up to clarify the results

Haptic Teleoperation of UAV Equipped with Gamma-Ray Spectrometer for Detection and Identification of Radio-Active Materials in Industrial Plants

Large scale factories such as steel, wood, construction, recycling plants and landfills involve the procurement of raw material which may include radiating parts, that must be monitored, because potentially dangerous for workers. Manufacturing operations are carried out in unstructured environments, where fully autonomous unmanned aerial vehicle (UAV) inspection is hardly applicable. In this work we report on the development of a haptic teleoperated UAV for localization of radiation sources in industrial plants. Radiation sources can be localized and identified thanks to a novel CZT-based custom gamma-ray detector integrated on the UAV, providing light, compact, spectroscopic, and low power operation. UAV operation with a human in the loop allows an expert operator to focus on selected candidate areas, thereby optimizing short flight mission in face of the constrained acquisition times required by nuclear inspection. To cope with the reduced situational awareness of the remote operator, force feedback is exploited as an additional sensory channel. The developed prototype has been demonstrated both in relevant and operational environments

Functional neuroimaging of visual creativity: a systematic review and meta-analysis

Introduction: The generation of creative visual imagery contributes to technological and scientific innovation, and production of visual art. The underlying cognitive and neural processes are however poorly understood. Methods: This review synthesises functional neuroimaging studies of visual creativity. Seven functional magnetic resonance imaging (fMRI) and 19 electroencephalography (EEG) studies were included, comprising 27 experiments and around 800 participants. Results: Activation likelihood estimation meta-analysis of the fMRI studies comparing visual creativity to non-rest control tasks yielded significant clusters in thalamus, left fusiform gyrus, and right middle and inferior frontal gyri. The EEG studies revealed a tendency for decreased alpha power during visual creativity compared to baseline, but comparisons of visual creativity to non-rest control tasks revealed inconsistent findings. Conclusions: The findings are consistent with suggested contributions to visual creativity of prefrontally-mediated inhibition, evaluation and working memory, as well as visual imagery processes. Findings are discussed in relation to prominent theories of the neural basis of creativity