Pultruded fiber-reinforced polymer (FRP) composite is expected to be widely applied for civil infrastructures due to its advantages of lightweight, anti-corrosion, and industrial manufacturing. Its long-term performance has attracted increasing attentions from academia and industry. This paper presents a comprehensive review on experimental studies investigating the mechanical performance of pultruded FRP composites subjected to long-term environmental effects, including water/moisture, alkaline solutions, acidic solutions, low/high temperatures, ultraviolet radiation, freeze-thaw cycles, wet-dry cycles, and in situ environments. Over 1900 experimentally determined mechanical properties of FRP materials were collected, including tensile, compressive, flexural and shear strength and moduli. The reported test data were highly dispersed, and no uniform conclusions could be drawn from these data. Exposure to water and water-based solutions (alkaline and acidic solutions) had detrimental impacts on the mechanical properties of pultruded FRP materials, whereas other environmental effects induced various levels of degradation. The degradation mechanisms for each environmental effect were discussed, and the existing design approaches were presented. Based on the findings from this review, recommendations were proposed for future works. The database presented herein, which is the largest in the available literature, enables a comprehensive understanding of the degradation behavior of pultruded FRP composites. Moreover, this work can serve as a foundation for deriving predictive models for pultruded FRP materials exposed to long-term environmental effects.

A comprehensive review on mechanical properties of pultruded FRP composites subjected to long-term environmental effects

The physical processes producing electron particle transport in the core of tokamak plasmas are described. Starting from the gyrokinetic equation, a simple analytical derivation is used as guidance to illustrate the main mechanisms driving turbulent particle convection. A review of the experimental observations on particle transport in tokamaks is presented and the consistency with the theoretical predictions is discussed. An overall qualitative agreement, and in some cases even a specific quantitative agreement, emerges between complex theoretical predictions and equally complex experimental observations, exhibiting different dependences on plasma parameters under different regimes. By these results, the direct connection between macroscopic transport properties and the character of microscopic turbulence is pointed out, and an important confirmation of the paradigm of microinstabilities and turbulence as the main cause of transport in the core of tokamaks is obtained. Finally, the impact of these results on the prediction of the peaking of the electron density profile in a fusion reactor is illustrated.

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Particle transport in tokamak plasmas, theory and experiment

A general feature of particle transport in the core of tokamak plasmas is that when core particle sources are small, a stationary peaked density profile is provided by a balance of outward diffusion and inward convection, driven by either neoclassical or turbulent mechanisms. The turbulent contribution to the off-diagonal elements of the transport matrix is very sensitive to the type of dominant instability of the background turbulence. We present here a detailed quasi-linear gyrokinetic analysis of stationary turbulent particle transport by means of analytical and numerical calculations to show how the actual parametric dependence of the stationary normalized density gradient can strongly vary between an ion temperature gradient (ITG) dominated turbulence and a trapped electron mode dominated turbulence regime. It is also shown how the maximal achievable normalized density gradient is reached when the turbulence regime is in a mixed state. This result is interpreted as the interplay of different physical mechanisms arising from (linear) wave–particle resonances. The results presented here are addressed to interpret some of the still unresolved issues in interpreting known experimental results.

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The role of ion and electron electrostatic turbulence in characterizing stationary particle transport in the core of tokamak plasmas

This overview summarizes the latest developments in plasma turbulence simulations and their impact on transport modelling. The traditional approach, based on the mixing length estimate, is presented first. The self-regulation of a plasma turbulence through the formation of structures is then emphasized. It is shown that zonal flows and large-scale transport events play an important role. Also the latest results concerning the dimensionless analysis are presented. The implications for transport modelling are then assessed.

https://iopscience.iop.org/article/10.1088/0741-3335/43/12A/319/pdf

Turbulence in fusion plasmas: key issues and impact on transport modelling

The entropy production rate is calculated for an interchange driven turbulence both in fluid and kinetic regimes. This calculation provides a rigorous way to define thermodynamical forces and fluxes. It is found that the forces are the gradients of density and temperature normalized to their “canonical” values, which are Lagrangian invariants of the flow. This formulation is equivalent to expressing the fluxes in terms of “curvature pinches,” where the curvature pinches are proportional to the logarithmic gradient of canonical profiles. Off diagonal terms in the transport matrix are found, which correspond to thermodiffusion and its Onsager symmetrical contribution to the heat flux. Hence, if thermodiffusion is significant, a heat pinch due to the density gradient also exists. The entropy production rate is found to be minimum when the profiles are equal to their canonical values. This property yields a generalized form of profile stiffness. However, a state where all profiles match their canonical values is not attainable because it is linearly stable.

Turbulent fluxes and entropy production rate

Issues such as energy generation/transmission and greenhouse gas emissions are the two energy problems we face today. In this context, renewable energy sources are a necessary part of the solution essentially winds power, which is one of the most profitable sources of competition with new fossil energy facilities. This paper present the simulation of mechanical behavior and damage of a 48 m composite wind turbine blade under critical wind loads. The finite element analysis was performed by using ABAQUS code to predict the most critical damage behavior and to apprehend and obtain knowledge of the complex structural behavior of wind turbine blades. The approach developed based on the nonlinear FE analysis using mean values for the material properties and the failure criteria of Tsai-Hill to predict failure modes in large structures and to identify the sensitive zones.

Simulation of Mechanical Behavior and Damage of a Large Composite Wind Turbine Blade under Critical Loads

Evaluation of durability of composite materials applied to renewable marine energy: Case of ducted tidal turbine

Damage prediction of horizontal axis marine current turbines under hydrodynamic, hydrostatic and impacts loads

Composite materials have vast range of engineering applications because of their outstanding mechanical performance, low density and cost effectiveness. Marine industry and naval structures are one of the applications where composites are gaining importance rapidly however, there are confronted with extreme environmental conditions in addition mechanical behaviour. Therefore, it is important to comprehend the behaviour of these materials not only under mechanical loads but also under environmental effects. For that reason, the objective of this paper is to study the effects of hygrothermal aging phenomenon on the behaviour of adhesively bonded composite joints at high strain rates. Dynamic compressive properties and microstructural damage progression is analysed utilizing the Split Hopkinson Pressure Bars (SHPB) technique. The stress-strain behaviour of composite specimens subjected to severe hygrothermal conditions have been studied at high strain rates ranging from 445 to 1240 s−1. In addition, Keyence and scanning electron microscopic (SEM) is used to study the significant damage modes. The results indicated change in dynamic properties and damage behaviour because of the environmental effects.

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An investigation of hygrothermal aging effects on high strain rate behaviour of adhesively bonded composite joints

The diffusion coefficient in phase space usually varies with the particle energy. A consequence is the dependence of the fluid particle flux on the temperature gradient. If the diffusion coefficient in phase space decreases with the energy in the bulk of the thermal distribution function, the particle thermodiffusion coefficient which links the particle flux to the temperature gradient is negative. This is a possible explanation for the inward particle pinch that is observed in tokamaks. A quasilinear theory shows that such a thermodiffusion is generic for a tokamak electrostatic turbulence at low frequency. This effect adds to the particle flux associated with the radial gradient of magnetic field. This behavior is illustrated with a perturbed electric potential, for which the trajectories of charged particle guiding centers are calculated. The diffusion coefficient of particles is computed and compared to the quasilinear theory, which predicts a divergence at low velocity. It is shown that at low veloci...

D. Saifaoui

Papers

Simulation of Mechanical Behavior and Damage of a Large Composite Wind Turbine Blade under Critical Loads

Evaluation of durability of composite materials applied to renewable marine energy: Case of ducted tidal turbine

Damage prediction of horizontal axis marine current turbines under hydrodynamic, hydrostatic and impacts loads

An investigation of hygrothermal aging effects on high strain rate behaviour of adhesively bonded composite joints

Anomalous particle pinch in tokamaks