Fouad Erchiqui

Pressure gradient and electroosmotic effects on two immiscible fluids in a microchannel between two parallel plates

A model of the flow of two immiscible fluids in a microchannel between two parallel plates was made. The concept of pumping a nonconducting fluid using interfacial viscous shear stress was applied while taking into account the combined effect of the pressure gradient and electroosmosis. To determine the electric potential and flow parameters, the Poisson–Boltzmann equation and modified Navier–Stokes equations were solved for a steady fully-developed laminar flow. The results obtained demonstrate the influence of the pressure difference, the dynamic viscosity ratio, the wall and interfacial zeta potentials, the interface location and the interfacial shear stress on the flow characteristics of both fluids. A comparison of results was performed to validate the developed approach.

Mechanical and structural properties of a novel melt processed PET–hemp composite: Influence of additives and fibers concentration

The mechanical and structural properties of novel melt processed poly-ethylene terephthalate (PET)-hemp fiber composites for engineering applications were investigated. First, four reinforcement formulations were compared with the PET modified with poly-epsilon-caprolactone: hemp, Clay/hemp, pyromellitic dianhydride/hemp and glycidyl methacrylate/hemp. Next, the effect of hemp fibers concentration as well as the effect of heat treatment was analyzed. A significant difference was observed in the mechanical and structural properties of the composites. Moreover, we observed a good fiber–matrix interface without the use of a coupling agent, particularly in the absence of additives. Our data suggest that a careful trade-off between the additives, the hemp fiber concentration and the desired engineering applications is key requirement for the applications of high melting polymers-reinforced with natural fibers.

Damage Characterization of Bio and Green Polyethylene–Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions

Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing.

Characterization of Polymeric Membranes Under Large Deformations Using Fluid-Structure Coupling

The mechanical properties of Ogden material under biaxial deformation are obtained by using the bubble inflation technique. First, pressure inside the bubble and height at the hemispheric pole are recorded during bubble inflation experiment. Thereafter, Ogdens theory of hyperelasticity is employed to define the constitutive model of flat circular thermoplastic membranes (CTPMs) and nonlinear equilibrium equations of the inflation process are solved using finite difference method with deferred corrections. As a last step, a neuronal algorithm artificial neural network (ANN) model is employed to minimize the difference between calculated and measured parameters to determine material constants for Ogden model. This technique was successfully implemented for acrylonitrile-butadiene-styrene (ABS), at typical thermoforming temperatures, 145°C. When solving for the bubble inflation, the recorded pressure is applied uniformly on the structure. During the process inflation, the pressure is not uniform inside the bubble, thus full gas dynamic equations need to be solved to get the appropriate nonuniform pressure to be applied on the structure. In order to simulate the inflation process accurately, computational fluid dynamics in a moving fluid domain as well as fluid structure interaction (FSI) algorithms need to be performed for accurate pressure prediction and fluid structure interface coupling. Fluid structure interaction solver is then required to couple the dynamic of the inflated gas to structure motion. Recent development has been performed for the simulation of gas dynamic in a moving domain using arbitrary Lagrangian Eulerian (ALE) techniques.

3D Numerical Simulation of Thawing Frozen Wood Using Microwave Energy: Frequency Effect on the Applicability of the Beer–Lambert Law

In this article, the frequency effect on the applicability of Beer–Lamberts law for thawing frozen wood using the microwave energy was analyzed. To this end, we use Maxwells equations to determine the absorbed power and characterize the critical slab thickness L crit of three Canadian eastern wood species: trembling aspen (Populus tremuloides Michx), yellow birch (Betula alleghaniensis), and sugar maple (Acer saccharum). The critical thickness L crit above which the Beer–Lambert law is valid is estimated as a hyperbolic function in the frequency domain: L crit = m/f n (f is the frequency of microwave radiation; m and n are adjustment constants). The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a three-dimensional volumetric specific enthalpy-based finite element method. The dielectric and thermophysical properties are functions of temperature and moisture content. The specific volumetric enthalpy approach is validated by experimental testing. For instance, we studied the frequency effect on the thawing of frozen trembling aspen wood.

Formulation and tensile characterization of wood–plastic composites Polypropylene reinforced by birch and aspen fibers for gear applications

This study reports the effects of wood fibers and 3 wt% maleic anhydride-grafted polypropylene used as coupling agent on the tensile properties of polypropylene/wood composites. Compounding was done in a roller-based internal batch mixer followed by compression molding. Our findings show that both birch and aspen wood fibers improve the elastic modulus and the tensile strength of composites, and the chemical treatment improves the fiber–matrix interface. A comparison of experimental results’ elastic modulus with micromechanics theoretical models shows that the Lavengood–Goettler model is closer to experimental data. Also the results showed that the polypropylene/wood composites’ elastic modulus exceeds high-performance thermoplastics commonly used in gears manufacturing. Thus, the price of polypropylene/wood fibers makes it a viable alternative for similar application.

Impact of TEMPO-oxidization strength on the properties of cellulose nanofibril reinforced polyvinyl acetate nanocomposites

Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5min (5min of oxidation) and CNF-O-120min (120min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Youngs modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120min films. In addition, the water uptake is higher for PVAc/CNF-O-120min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5min). All these results are discussed in connection with the CNFs characteristics.

Optimized use of cooling holes to decrease the amount of thermal damage on a plastic gear tooth

The full potential of plastic gear usage is limited by not only poor mechanical properties but also equally poor temperature limits and poor heat conduction properties. Cooling holes were developed to decrease the amount of thermal damage on the contact surface. These cooling holes promote increased stress and tooth deflection, thus exerting a negative effect. This article compares various cooling holes for plastic gear configurations and proposes novel cooling holes. Thermal and mechanical simulations that consider specific aspects of plastic gear meshing were performed. The main objective of this article was to verify the best methods for reducing thermal damage through cooling holes. The results indicate the best compromise between the temperature reduction and the mechanical properties of the new tooth geometry. The results also indicate that the simple variations in the cooling holes proposed can improve tooth performance.

Analysis and Evaluation of Power Formulations for Wood and Hardboard Using Radio Frequency and Microwave Energy

This article analyzes the influence of frequency, temperature, moisture content, and structural orientation on the applicability of the Beer-Lambert law for various wood species using radio frequency and microwave radiation. To achieve this objective, the study compares the power dissipation computed from Maxwells equation and Lamberts power law. The wood species considered are white oak (Quercus alba), Douglas fir (Pseudotsuga menziesii), trembling aspen (Populus tremuloides), white birch (Betula paperyfera), yellow birch (Betula alleghaniensis), sugar maple (Acer saccharum), and four commercial hardboards. The dielectric constant and dielectric loss factor are examined as a function of moisture conditions, temperature, frequencies, and the three principal structural orientations. The study involved 3,000 complex dielectric constants. It was found that the radial critical thickness is somewhat smaller than the tangential critical thickness (0.95 times smaller) and the longitudinal critical thickness is significantly smaller than the radial (0.52 times). It was demonstrated that the critical thickness L crit above which the Beer-Lambert law is valid for all of the wood species studied under various conditions obeys the following conditions: log10(L crt) = 0.999 log10(β−1) + 0.4122, where β−1 is the penetration depth (cm). In the case of microwave radiation, the critical thickness can be estimated from L crt = 2.615 β−1 − 0.0626. Finally, a model is proposed to take into consideration the effect of moisture content with frequency (or with attenuation constant).

Investigation of Three Immiscible Fluids in a Microchannel Accounting for the Pressure Gradient and the Electroosmotic Flow.

This study deals with the investigation of three immiscible fluids in a microchannel consisting of two parallel plates. These fluids were composed of two electric conducting fluids and one electric nonconducting fluid. The concept of pumping a nonconducting fluid using interfacial viscous shear stress was applied accounting for the effect of the electroosmosis and pressure gradient. The electric potential and the flow parameters were found resolving the Poisson-Boltzmann equation and the modified Navier-Stokes equations for a hydraulic steady fully-developed laminar flow of an incompressible fluid. The results achieved revealed the influence of the wall and interfacial zeta potentials, the pressure difference, and the dynamic fluid viscosity ratio on the flow characteristics of the three immiscible fluids. The developed approach was compared with a model of two immiscible flows to highlight the relevance of this work.