Advances in Applied Mechanics

This paper aims to study the elastic properties of glass fibers reinforced acrylic thermoplastic resin-based Nanostrength® M53. The acrylic resin was filled with three weight fractions (\({5}\), \({10}\) and 15 wt %\(\text{)}\) of the Nanostrength® M53. The effect of Nanostrength® M53 on the elastic properties was studied using tensile tests and finite element method-based RVEs by means of Digimat-FE. For this purpose, platelet inclusions and three aspect ratios (AR) were considered for microstructures reconstruction. A multi-scales homogenization scheme was used for the determination of the effective elastic properties using Digimat-FE solver. From the experimental and numerical results, the elastic properties decreased slightly while the weight fraction (wt %) of the Nanostrength® M53 increased in the composites. The loss in Young modulus was estimated at about \(\text{9.5}\) to 10% according to the Nanostrength weight fractions of 10 wt % and the comparison of the elastic properties was consistent. The use of the Nanostrength® M53 would then be a source of a slight loss of elastic properties, however, the Nanostrengths® M53 were suitable for many applications that needed an increase in resistance to crack propagation, and in the literature, the laminate composites filled with 10 wt % of Nanostrength® M53 depicted better low-velocity impact resistance.

Due to the large applications field of Unmanned Aerial Vehicles (UAV) in civil, military, and scientific activities, with the associated missions’ specific operating points requirements, there is a need for a large amount of experimental and numerical testing for new concepts development. In aerodynamic studies, aeromodelling or more specifically; small scale models, are often used in wind tunnel testing or numerical simulations thanks to Reynolds number similarity. On another hand, the possible uses of additive manufacturing (AM) have significantly increased in recent years, due to the freedom it offers for the manufacture of complex parts and the reduced cycle time to manufacturing, in contrast to conventional processes. For rapid aero-models manufacturing, we focus in this work on the filament deposition modelling (FDM), which is the most affordable, compared to other AM technics. But, before going from CAD to physical model, some preliminary assessments of the process fidelity have to be introduced. In this context, the aim of our present paper is the manufacture of a small scale UAV Blended Wing Body (BWB) using FDM for subsonic wind tunnel testing. The results of the models in the wind tunnel are compared to numerical results obtained from XFLR5, and then the process fidelity is discussed.

Graphite-epoxy composites are widely used in the space industry. They have the advantage of being resistant to thermal distortion with high structural rigidity and minimal weight. However, the non-complete adhesion between fiber and matrix and the defects resulting from the manufacturing processes can affect these structures. It seems therefore necessary to control these materials. The non-destructive testing by ultrasonic guided waves presents an interesting alternative for the detection of these imperfections. For a proper ultrasonic non-destructive testing by guided waves, the knowledge of dispersion curves is an essential step to determine the modes susceptible to propagate in our material during the control.

In this paper, we present analytical matrix methods for plotting the dispersion curves of a graphite-epoxy laminate composite material. The formulations and limitations of these methods have been presented. We have modeled the propagation of ultrasonic guided waves in two- and four-layer anisotropic laminates for different fiber orientations. The accuracy of the obtained results has been checked with the help of the software DISPERSION CALCULATOR.

This work aims to examine combined heat transfers through concrete hollow bricks. The thermal behavior of hollow bricks is simulated using a mathematical model based on the conservation of mass, momentum and energy. The effect of internal surfaces emissivity, aspect ratio of inner holes and solid wall thermal conductivity on global heat transfer is investigated using practical values of the thermal excitations. The results show that the contribution of radiation to the overall heat transfer through hollow bricks increases progressively with higher values of the thermal emissivity. The results reveal also that the overall heat flux through the concrete bricks is greatly influenced by the solid walls’ thermal conductivity. Since thermal conductivity cannot be adjusted after construction, this finding emphasizes the importance of careful material selection in designing energy-efficient structures, especially in regions characterized by hot and arid climates. Based on these results, we propose a practical recommendation to opt for concrete with low thermal conductivity in such climates. By adopting this approach, construction practices can be tailored to enhance the overall energy efficiency and thermal performance of buildings, providing sustainable solutions for the challenges posed by extreme environmental conditions.

During the last decades, manufacturers have opted for the miniaturization of electronic devices as an answer to high-performance equipment demand. However, Downscaling the Integrated Circuit (IC) technology has several side effects on the device’s performance. Considered one of the IC problems in the design, the skin effect impacts the IC design. In addition, high clock frequency can lead to severe Electromagnetic Compatibility (EMC) issues. The present work has used an efficient numerical method for transient analysis based on the Finite Difference Time Domain (FDTD) Method to investigate the previous phenomenon. It is used to examine the skin and incident electromagnetic field effect on the signals applied in non-uniform submicron CMOS interconnects. We have selected two research situations of non-uniform interconnects loaded by linear terminals, either in the absence or presence of an incident field. The MATLAB tool is used to implement the proposed algorithms. The outcomes are contrasted with PSPICE’s results. A close match was obtained between the two results.

This work presents an experimental evaluation into the effect of the temperature upon the thermal properties and the mechanical properties of jute fabric/epoxy composite heated at different temperatures. The jute fabric/epoxy was prepared at the ambient temperature and fixed volume fraction of jute (four fabric layers) using infusion method. To examine the effect of the temperature, the composite was heated at different temperatures. The mechanical properties of the jute fabric/epoxy heated at different temperatures were carefully investigated. The results shows that the composites exposed to the high temperature are prone to the lower mechanical properties. At the temperature (80 ℃), the composite shows a high ability to deformation due to the matrix softening which reduces the cohesion between the epoxy and the jute fabric, which is the reason for the decrease of the tensile stress. Moreover, the matrix softening increase with an increase of heating temperature. The lowest tensile stress (reduce by more than 58%) was determined in the case of the composite heated at the temperature 80 ℃. The results in this research confirm the limitation of the composite use in different applications, especially at high temperature.

The field of non-destructive evaluations (NDE) using ultrasonic waves is widely used in industry to guarantee the safety and proper functioning of materials. Thus, mastering the dispersion curves of propagation waves in a material is an essential first step. This paper presents a numerical approach used for plotting the dispersion curves of cross-section ultrasonic guided waves. The spectral collocation method (SCM) described here can turn the set of partial differential equations for sound waves into an eigenvalue problem. In order to evaluate the efficiency of this method for an isotropic aluminum plate, we have established algorithm executed with Matlab program. The results were compared with a classical bisection zero-finding method, the stiffness matrix method, and SAFE method. The results found confirm that the SCM remains conceptually simpler and depends on the differentiation matrices used. Finally, the method proves its accuracy, its calculation speed and its capacity to compute the phase velocity and wavenumber curves as well as the complete three-dimensional dispersion spectrum which includes both propagative (real wavenumber) and non-propagative modes (complex wave number).

In this study, thermal radiation and mixed convection in a ventilated horizontal channel are analyzed. The channel contains five cylindrical blocks that produce different volumetric heat rates. The channel is ventilated by two openings; the inlet is located on the left wall, and the outflow is on the top one. All the channel walls are adiabatic, except for the upper wall, which is held at a constant low temperature of T_C = 20 ℃. To numerically solve the differential equations governing the current problem, a numerical code based on the finite volume approach and the SIMPLE algorithm is utilized. The discrete ordinate method is used to discretize the radiative transfer equation. The impacts of the Reynolds number and the emissivity of the surfaces on the heat transfer and fluid flow are analyzed. The numerical simulations indicate that increasing the Reynolds number or the emissivity considerably decreases the maximum temperature in the cavity and improves the performance of the considered system.

Water absorption and vibration issues are major concerns for manufacturers and researchers using bio-based composites. In light of this, this work examines how water aging affects the dynamic characteristics of a sandwich with a reentrant auxetic core. The material considered to manufacture the specimens is polylactic acid (PLA) reinforced with flax fibers. It is manufactured using 3D printing which proceeds by adding layers successively. For various immersion times, the impact of water absorption on the dynamic characteristics is examined. Water aging obviously affects equivalent stiffness and damping. We therefore observe a decrease in rigidity and an increase in damping. These results could be explained by the plasticizing effect of water on bio-based composites, stimulated by water absorption as well as by the architecture of the core of the sandwich. Finally, a numerical strategy based on the finite element technique is developed. It made it possible to evaluate the equivalent rigidity and the damping for different immersion times. The results of this approach are in close agreement with those obtained experimentally.

In this work we propose a microstructurally motivated hyperelastic model to describe the behavior of elastomer materials. At the scale of the Representative Volume Element (RVE), composed of randomly oriented macromolecular chains, we assume that the segments of the chains are deformable and that there is a bending energy between two consecutive segments. We propose to model each macromolecular chain using micromechanical elements: linear elastic bars to represent the segments between the cross-linking points and non linear elastic spires to represent the flexibility of rotations around the cross-linking points. Numerical simulations, on different structured RVEs composed of 3, 4, and 8 chains in the case of three boundary conditions: uniaxial compressible tension, uniaxial incompressible tension, and shear, show that this modeling allows to find the classical response curves of hyperelastic elastomeric. In the proposed model, we have to identify only three parameters: a, \( M_0 \) and K. From numerical simulations, we show that the first parameter, a, control the first phase of activation of rotations between chain segments, the second parameter, \( M_0 \), control the unfolding phase, and that the third parameter K control the stiffening phase at large deformations.

In this work, we propose an explicit meshless approach based on the coupling of the Weighted Least Squares (WLS) method and the explicit Runge-Kutta (RK) scheme. This last scheme is used to approximate time derivatives while WLS approximation is used for spatial discretization. The proposed meshless approach offers several advantages over traditional methods. This approach provides a powerful tool for simulating compressible fluid flows, offering improved accuracy and computational efficiency compared to traditional methods. This approach is dedicated to the study of the flows of compressible isothermal fluids whose mathematical formulation is governed by the Navier-Stokes equations written in a strong formulation to avoid any difficulty in integration calculating. This meshless approach is tested on the classic example of a square cavity with a discussion on effects of the Mach number and the monomial basis order. The results are compared to those obtained using a traditional finite difference method.

In this paper, we focus on analyzing the linear stability of a Newtonian fluid layer whose upper surface is subjected to parametric thermal excitation that is periodic in time with zero mean. The fluid layer is considered of infinite extension in the horizontal directions. The Floquet theory and the Chebyshev spectral collocation method are used to solve the linear stability problem in the case of rigid-rigid boundary conditions. Although the unmodulated version of this configuration, where the fluid layer is heated from above, is known to be linearly stable, it turns out that destabilization is possible in the presence of modulation on the top surface. Parametric resonances appear at the onset of the instability, and the convection threshold is harmonic or sub-harmonic depending on the range of oscillation frequencies. The dynamics of this instability is characterized by the existence of a bifurcation point in codimension two, giving rise to a discontinuity in the evolution of the critical wavenumber at a specific frequency number.

In this study, we present a new high-order implicit algorithm to simulate cardiac electrophysiological waves. Several cardiac pathologies are due to a malfunction in the propagation of the wave causing the contraction of the heart: the cardiac action potential. Its dynamics are described by a system of nonlinear and nonstationary partial differential equations (EDP). However, these equations retain major challenges for numerical simulation. These challenges are mainly reflected in the coexistence of a slow dynamic and a rapid dynamic inducing abrupt changes in time and space and having a wavefront type behavior. Faced with these challenges, we propose in this work an algorithm belonging to the family of asymptotic numerical methods (ANM), which combines representations in whole series, implicit time schemes, a mesh-less approach to spatial discretization using radial base functions (RBF) and a continuation method. This combination improves accuracy and significantly reduces computation time. To demonstrate its effectiveness, we first apply the algorithm to a one-dimensional equation (1D) of Fisher flame propagation, then to a two-dimensional equation (2D) modeling cardiac electrical activity, especially the well-known FitzHugh-Nagumo.

The aim of this work is to examine the effect of a periodic vertical oscillation with two frequencies on the instability of a thin horizontal fluid layer in a Rayleigh Taylor configuration. The linear stability analysis leads to the periodic Mathieu equation, which describes the evolution of the interface amplitude. To solve the linear problem numerically, a combination of Floquet’s theory and the Runge-Kutta method is used. Numerical results show, as indicated in previous works for a single frequency, that the Rayleigh Taylor instability is not affected by the oscillation, while the resonances are. Moreover, the incorporation of two frequencies produces a richer dynamic, in terms of parametric resonances, than in the case of a single-frequency oscillation. The most unstable parametric resonances depend on the frequency ratio and can occur over a wide range of wavenumbers (large or small). Thus, the wavelength of the waves can be selected according to this ratio. It should also be noted that this ratio can have a stabilizing or destabilizing effect. The effect of fluid layer thickness on the threshold of parametric resonances is also discussed in this study.

This work aims to the introduction of a new micromechanical modeling of the elastic behavior of nanocomposite materials with coated nanoparticles. The model is developed taking into account the interphase and particle clustering effects. The model is used to explain the relationship between mechanical properties of nanocomposites and their complex microstructure. Here we consider that the micromechanical modeling of the complex microstructure of nanocomposites requires the combination of the four-phase model and the three-phase model and we assume that all phases are elastic, isotropic and perfectly bonded. In this way, the effective elastic properties are derived using the integral equation and interfacial operators. In the micromechanical study, it was observed that the elastic modulus increases with the increasing in the volume fraction of nanoparticles. The effect of interphase zone is studied and the performance of the present model is showing by comparing with numerical and experiment results and show a good agreement.

The goal of this work is to study the effect of number of engines and payload weight on the static stability of an unmanned aerial vehicle (uav) after the pre-sizing phase of its design. The aim is to answer the designer’s question, at this early stage, what will happen to the uav’s static stability if we increase these two parameters? After pre-sizing an uav that satisfies our requirements, we start by using the semi-empirical method known as Data Compendium to calculate and quantify their effect on static stability derivatives coefficients. In the next step, we develop a model using the vortex lattice method of the XFLR5 software to characterize these effects. Both methods give similar qualitative results. Using these results, we show that increasing the number of engines of this uav induces a non-monotonic change in its static stability with respect to the three axes. We also show that increasing the payload weight increases its static stability. However, this increase is non-monotonic with the increase of the number of engines. These conclusions show uav designers, focused on increasing static stability with respect to specific axis, how to choose the right number of engines and to manage payload’s weight during operations.