Effect of water aging on the mechanical properties of flax fiber/bio-based resin composites

Present work investigates the effect of hydrothermal aging of flax fiber-reinforced bio-based epoxy resin laminates on the mechanical and thermomechanical properties of the composites. Three different types of bio-based resins were used. Plates reinforced with eight layers plain weave flax fibers of 150 g/m², manufactured using Resin Transfer Molding (RTM), compression molding or autoclave technique depends on type of the resin. One dimensional Fickian behavior shows a good fitting to the experimental data derived from weight measurements. The water uptake at the equilibrium state in the case of 60 °C temperature was slightly greater than that at 40 °C. The mechanical properties after hydrothermal aging show a significant reduction and do not return to their initial values even after the drying process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48787.     

Markov Chains for Damage Accumulation of Organic and Ceramic Matrix Composites

A systematic presentation of the concept of a well-defined stochastic damage accumulation model for fatigue calculation is attempted; the model is applicable for both organic and ceramic matrix composites. Stationary and nonstationary, with one or more blocks, discrete time and finite state Markov chain models are employed. They are found appropriate for yielding fatigue life probability distributions and damage evolution information at different stress levels. The structure, applicability, flexibility, and limitations of the model are examined in detail. The theoretical concepts are elucidated by the incorporation of data from a comprehensive testing program.     

On the Viscoelastic Response of Composite Laminates

The present work deals with the determination of theviscoelastic properties of composite laminates based on the viscoelasticbehaviour of the single lamina. A viscoelastic lamination theory isdeveloped assuming that the lamina stiffness matrix is fully complex andfrequency dependent.For the measurement of the complete setof frequency dependent viscoelastic properties of the single lamina(i.e. complex moduli and Poisson's ratio) a new methodology has beenintroduced, based on the free and forced vibration of unidirectional and[45/–45] _ns composite laminates.Allmeasurements have been performed both in air and in vacuum. Since thevibration amplitude was very small, in order to fulfil linearityrequirements, the results do not show any significant difference due toair damping.The effects of experimental errors on theevaluation of the viscoelastic properties of the single lamina have alsobeen discussed.     

The Effect of CNT‐modified matrix of cyanate ester CFRPs on the hydrothermal behavior of the material. Evaluation of the water uptake using electrical resistance measurements

In this work, reference and nanomodified unidirectional cyanate matrix, carbon fiber‐reinforced polymers (CFRPs), were exposed to distilled water at 80°C. Water uptake was investigated as a function of the carbon nanotube CNT wt% content up to saturation level. In parallel the variation of glass transition temperature (T_g) was also monitored using dynamic mechanical analysis tests. The distilled water absorption process was modeled following the Fick's law, and the experimental results were found to be in very good agreement with the theoretical predictions up to saturation. Finally, during the tests and, at defined time intervals the variation of the electrical conductivity of the materials under investigation was studied and a correlation between the water absorption and the variation of the electrical conductivity was established. It was shown that the presence of CNTs into the cyanate matrix affects the water absorption mechanism, since an important amount of additional interfaces has been introduced. POLYM. COMPOS. 37:1072–1077, 2016. © 2014 Society of Plastics Engineers     

Failure mechanisms analysis of 2D carbon/carbon using acoustic emission monitoring

The present work aims toward the application of an innovative methodology for the analysis of acoustic emission (AE) activity monitored during the quasistatic tensile loading of centre-hole carbon/carbon. An in-house developed algorithm is proposed, which utilises the results of unsupervised pattern recognition classification of AE data. Correlation between clusters and specific material failure modes was achieved, using algorithm results and cluster activation parameters. During the analysis a dependence of AE activity on the hole diameter was observed.     

On the sensitivity of the vibrational response of the human head

A parametric study based on finite element analysis is performed in order to investigate the sensitivity of the eigenfrequency spectrum of the human head system upon variation of its constitutive material properties. This study stems from the ever increasing medical interest connected to early diagnosis of brain edema and the lack of existing accurate and non-invasive diagnostic methods to achieve it. The present computational work aims to resolve the question of whether or not such a spectrum shifting is detectable with current experimental procedures. The human head is modeled as a prolate spheriod consisting of confocal shell representing the scalp-skull system, in contact with the subarachnoidal space which surrounds the brain. The skull is modeled as an isotropic elastic material whereas the brain is assumed to be a frequency dependent viscoelastic body.     

A wavelet-based Markov random field segmentation model in segmenting microarray experiments

In the present study, an adaptation of the Markov Random Field (MRF) segmentation model, by means of the stationary wavelet transform (SWT), applied to complementary DNA (cDNA) microarray images is proposed (WMRF). A 3-level decomposition scheme of the initial microarray image was performed, followed by a soft thresholding filtering technique. With the inverse process, a Denoised image was created. In addition, by using the Amplitudes of the filtered wavelet Horizontal and Vertical images at each level, three different Magnitudes were formed. These images were combined with the Denoised one to create the proposed SMRF segmentation model. For numerical evaluation of the segmentation accuracy, the segmentation matching factor (SMF), the Coefficient of Determination (r²), and the concordance correlation (p_c) were calculated on the simulated images. In addition, the SMRF performance was contrasted to the Fuzzy C Means (FCM), Gaussian Mixture Models (GMM), Fuzzy GMM (FGMM), and the conventional MRF techniques. Indirect accuracy performances were also tested on the experimental images by means of the Mean Absolute Error (MAE) and the Coefficient of Variation (CV). In the latter case, SPOT and SCANALYZE software results were also tested. In the former case, SMRF attained the best SMF, r², and p_c (92.66%, 0.923, and 0.88, respectively) scores, whereas, in the latter case scored MAE and CV, 497 and 0.88, respectively. The results and support the performance superiority of the SMRF algorithm in segmenting cDNA images.     

Realising an application environment for information-centric networking

It has been argued by many that the Future Internet should address information at the core of its operation. Prototypes have emerged to embody this new paradigm. Applications for such networks, however, are noted primarily by their absence. In spite of an appetite for Information-Centric Networking (ICN) applications, relatively little has come to fruition. We suggest that this is due to an unfavorable development environment, requiring applications to interface with the ICN substrate directly. This paper aims to answer this shortcoming by providing a middleware layer that aids the development of more advanced applications. We also present an application that leverages the middleware and answers a real-world problem concerning personalised media delivery. We argue that the development of this, and potentially other, application(s) is aided by the presence of such an application environment.     

Resistive heating of multidirectional and unidirectional dry carbon fibre preforms

The electrical conductivity (EC) of continuous carbon fibre (CF) layers is highly anisotropic and is expressed by a second order tensor. In the present work, using continuity equation for anisotropic media, the electrical conductivity of a dry CF multilayer preform can be predicted. Hence, the electrical conductivity tensor of the CF preform can be calculated for any stacking sequence. By means of the calculated electrical conductivity tensor of the multilayer preform, the elliptical form of the governing equation can be solved numerically. Based on this, the generated heat (Joule effect) can be determined. Introducing the generated heat into the heat transfer equation, the temperature field over the CF preform can be predicted. For the experimental verification, a thermal camera was used to record the temperature field developed on a CF multilayer preform under given electric potential field. The experimental results were compared to the respective numerical calculations of the temperature field, where the electrical conductivity tensor was calculated analytically based on the proposed methodology. In all the tested cases the calculated electrical conductivity tensor leads to a numerical model which is in excellent agreement with the experimental results.     

Haptic Rendering of Visual Data for the Visually Impaired

We introduce a force-field haptic rendering method for converting visual data to haptic data. The method includes a novel framework to convert specialized 3D map models into force fields. We generate the final force fields by using structure from motion and implicit surface approximation algorithms. Visually impaired people then can learn to navigate with these maps, using off-the-shelf haptic