The bias-extension test for the analysis of in-plane shear properties of textile composite reinforcements and prepregs: a review

The bias-extension test is a rather simple experiment aiming to determine in-plane shear properties of textile composite reinforcements. However the mechanics during the test involves fibrous material at large shear strains and large rotations of the fibres. Several aspects are still being studied and are not yet modeled in a consensual manner. The standard analysis of the test is based on two assumptions: inextensibility of the fibers and rotations at the yarn crossovers without slippage. They lead to the development of zones with constant fibre orientations proper to the bias-extension test. Beyond the analysis of the test within these basic assumptions, the paper presents studies that have been carried out on the lack of verification of these hypothesis (slippage, tension in the yarns, effects of fibre bending). The effects of temperature, mesoscopic modeling and tension locking are also considered in the case of the bias-extension test

Sparsity-aware multiple relay selection in large multi-hop decode-and-forward relay networks

In this paper, we propose and investigate two novel techniques to perform multiple relay selection in large multi-hop decode-and-forward relay networks. The two proposed techniques exploit sparse signal recovery theory to select multiple relays using the orthogonal matching pursuit algorithm and outperform state-of-the-art techniques in terms of outage probability and computation complexity. To reduce the amount of collected channel state information (CSI), we propose a limited-feedback scheme where only a limited number of relays feedback their CSI. Furthermore, a detailed performance-complexity tradeoff investigation is conducted for the different studied techniques and verified by Monte Carlo simulations.NPRP grant 6-070-2-024 from the Qatar National Research Fund (a member of Qatar Foundation)Scopu

Sparse Equalizers for OFDM Signals with Insufficient Cyclic Prefix

The cyclic prefix (CP) is appended in orthogonal frequency division multiplexing (OFDM) signals to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) induced by the communication channel, which limits its spectral efficiency. Therefore, inserting an insufficient CP and equalizing the resulting ICI and ISI is a method that has been circulating the literature for a while, aiming at increasing the efficiency of OFDM systems. In this paper, we propose a reduced-complexity sparse linear equalizer and a decision-feedback equalizer for OFDM signals with insufficient CP. A performance-complexity trade-off is highlighted, where we show that it is possible to equalize the received signal with a reduced complexity equalizer while having a limited performance loss. Our proposed equalizer designs are not only less complex to realize, but are shown to provide a higher data rate. The proposed equalizers are further evaluated in terms of the worst-case coherence, a metric determining the effectiveness of our used approach. Numerical results show that we can significantly and reliably reduce the order of the design complexity while performing very close to the conventional complex optimal equalizers. 2013 IEEE.This work was supported by GSRA from the Qatar National Research Fund (a member of Qatar Foundation) under Grant 2-1-0601-14011. The statements made herein are solely the responsibility of the authors.Scopu

Prédiction par simulation des défauts de plissement lors de la mise en forme des matériaux composites mono et multiplis

Lors de la mise en forme des renforts de composites l’apparition des plissements fait parti des défauts les plus courants. Ces plissements sont fréquents en raison des très faibles raideurs en flexion dues aux mouvements relatifs entre les fibres constituant chaque mèche. Il est nécessaire de détecter leur apparition, ainsi que leur évolution au cours de la phase de préformage, et ce afin de s’assurer qu’ils ne s’étendent pas à la partie utile de la pièce. La simulation des renforts de composites textiles en cours de mise en forme se fonde sur une forme simplifiée du travail virtuel des efforts internes de chaque cellule élémentaire, découplée en une énergie de tension, de cisaillement dans le plan et du moment fléchissant. L’influence des trois rigidités (traction, cisaillement dans le plan et flexion) sur l’apparition des plissements lors de la simulation est analysée. Même si la raideur en cisaillement dans le plan joue un rôle principal sur leur apparition, il n’y a pas de corrélation directe entre l’angle de cisaillement et les plis. Le plissement est un phénomène global dépendant autant des déformations, des raideurs et des conditions aux limites. La raideur en flexion joue un rôle principal sur la forme que prendront ces plis, et il n’est pas possible de simuler proprement un pli avec une approche membranaire seule

Simulation of the forming of tufted multilayer composite preforms

International audienc

On I/Q imbalance effects in full-duplex OFDM decode-and-forward relays

We analyze the outage probability of dual-hop full-duplex decode-and-forward relaying for an orthogonal frequency division multiplexing system in the presence of I/Q imbalance. We derive accurate analytical approximations which quantify the outage probability's functional dependence on the I/Q imbalance level and the residual loopback self-interference average power level. In addition, we derive the condition at which direct transmission outperforms full-duplex decode-and-forward relay-assisted transmission in the presence of I/Q imbalance. Finally, our numerical results confirm the accuracy of our analysis. 2014 IEEE.Scopu

Simulation of wrinkling during bending of composite reinforcement laminates

International audienc

I/Q imbalance and loop-back self interference effects in full-duplex OFDM DF relays

We analyze the outage probability of dual-hop full-duplex decode-and-forward relaying for an orthogonal frequency division multiplexing system in the presence of I/Q imbalance. We derive accurate analytical approximations which quantify the outage probability's functional dependence on the I/Q imbalance level and the residual loopback self-interference average power level. In addition, we derive the condition at which direct transmission outperforms full-duplex decode-and-forward relay-assisted transmission in the presence of I/Q imbalance. Furthermore, we propose an opportunistic relaying approach and demonstrate its robustness against the detrimental effects of I/Q imbalance and residual loopback self-interference. Our numerical results confirm the accuracy of our analysis. 2015 IEEE.Scopu

OFDM Full-Duplex DF Relaying under I/Q Imbalance and Loopback Self-Interference

We analyze the outage probability of dual-hop full-duplex (FD) decode-and-forward (DF) relaying for an orthogonal frequency-division multiplexing (OFDM) system in the presence of in-phase and quadrature-phase (I/Q) imbalance (IQI). We derive tight analytical approximations that quantify the outage probability's functional dependence on the IQI level and the residual loopback self-interference (LSI) average power level. In addition, we derive the condition at which direct transmission outperforms FD-DF relay-assisted transmission in the presence of IQI. Furthermore, we investigate an opportunistic relaying (OR) approach and demonstrate its robustness against the detrimental effects of IQI and residual LSI. Our numerical results confirm the accuracy of our analysis. 2015 IEEE.Scopu