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Every year hundreds of serious accidents and catastrophic are accompanied by mining sector services as disaster, flooding, and demolition. To reduce the severity of the results such as high death numbers, lost communication inner and out mining, we have to find an easy way to improve communication means during that problems. In this paper, we reach out to fabricate durable, flexible, and wearable chaps, in addition to an easier carrier with highly efficient receiving and sending a signal at 2.4 GHz broad wide band. By doping a bunch of unique conductive metals (silver, copper, and gallium indium alloy) assembled on Graphene, its integration inside Polydimethylsiloxane to be future applicable antenna. Furthermore, we studied the physical and electric properties of a composite including Electrochemical Impedance properties (EIS), cyclic voltammetry (CV), and its thermal stability chip (DSC), as well as, using Transmission electron microscopy (TEM), and, scanning electron microscopy (SEM) techniques to clarify the surface morphology of fabricated materials. In addition to various measurements had been carried out such as Ultraviolet-visible, inductively coupled plasma (ICP) spectroscopy, and Energy-dispersive X-ray spectroscopy (EDX) to reinforce and elucidate the solid-state of ions inside fabricated Antenna. On the other hand, throughout stress-strain for the stretchability of fabricated is expanded to 30% of its original length, in addition to thermal stability reached to 485°C compared to pure PDMS substrate, with enhancing electric conductivity of composite ship.

Our work aims to make a unique polymer to be used as a conductive and flexible chip antenna. Its properties are robustness, rigidity, stretchability, and good conduction. The fabricated composite is composed of two copolymers, Polydimethylsiloxane (PDMS) and Polyethylenimine (PEI), assembled with nano metals (Copper, Silver ), and graphene nanoparticles as a matrix. Nano metals fill out the inter-layer space, and polymer voids reinforce the cross linker. Graphene/metal nanoparticles help make chelating complexes using metallic bonds, enhancing the polymer’s conductivity from 1.87 × 10− 4 to 5.64 ×10− 6 σ Scm− 1. We analyze the conductivity, self-healing, and surface morphology of fabricated composite using different spectroscopic techniques, such as electrochemical impedance (EIS), Scanning Electronic Microscopy ( SEM), Transition Electronic Microscopy (TEM), Infrared spectroscopy ( IR), UV-Visible spectroscopy (UV), and a particle size analyzer.

Purpose Reliability plays an important role in the execution of the maintenance improvement and the understanding of its concepts is essential to predict the type of maintenance according to the equipment state. Thereby, a computational tool was developed and programming with VBA in Excel® for reliability and failure analysis in a mining context. The paper aims to discuss these issues. Design/methodology/approach The developed approach use the modeling of stochastic processes, such as the renewal process, the non-homogeneous Poisson process and less conventional method as the Bayesian approach, by considering Jeffreys non-informative prior. The resolution gives the best associated model, the parameters estimation, the mean time between failure and the reliability estimate. This approach is validated with the reliability analysis of inter-failure times from underground rock bolters subsystems, over a two-year period. Findings Results show that Weibull and lognormal probability distribution fit to the most subsystems inter-failure times. The study revealed that the bolting head, the rock drill, the screen handler, the electric/electronic system, the hydraulic system, the drilling feeder and the structural consume the most repair frequency. The hydraulic and electric/electronic subsystems represent the lowest reliability after 50 operation hours. Originality/value For the first time, this case study defines practical failures and reliability information for rock bolter subsystems based on real operation data. This paper is useful to the comparative evaluation of rock bolter by detecting the weakest elements and understanding failure patterns in the individual observation subsystems on the overall machine performance.

The anisotropic problem of thermal conduction in a solid is generally treated in a reference coordinate system, which adequately describes its thermal conductivity tensor (Cartesian, cylindrical or spherical). For this problem, numerical treatment is difficult, especially if the thermophysical properties are non-linear or if the anisotropic medium undergoes a phase change. In this paper, we propose an approach using a Cartesian reference system to treat the anisotropic thermal conduction of problems for which the solid medium is characterized by a set of tensors of thermal conductivity of different natures (Cartesian and/or cylindrical and/or spherical), with or without phase change. For this purpose, we the anisotropic thermal conductivity tensor, with respect to a cylindrical or spherical coordinate system, is transformed by an equivalent tensor into global Cartesian coordinates. The nonlinear heat conduction problem involving phase changes, such as wood freezing, is solved using hybrid three-dimensional volumetric specific enthalpy based on finite-element analysis. The proposed approach is validated with analytical testing for two anisotropic media and with two experimental tests related to the heating of frozen woods. As an application, we have numerically quantified, on the one hand, the minimum time required for the thaw and, on the other hand, the freezing of a log of wood, such as white pine, according to the length of its radius (7.5, 10, 15, 20 and 25 cm). The thermophysical properties are a function of temperature, moisture content and structural orientation.

Our work aims to make a unique polymer to be used as a conductive and flexible chip antenna. Its properties are robustness, rigidity, stretchability, and good conduction. The fabricated composite is composed of two copolymers, PDMS and PEI, assembled with nano metals (Cu, Ag), and graphene nanoparticles as a matrix. Nano metals fill out the inter-layer space, and polymer voids reinforce the crosslinker. Graphene/metal nanoparticles help make chelating complexes using metallic bonds, enhancing the polymer’s conductivity from 1.87* 10− 4 to 5.64*10− 6 σ Scm− 1. We analyze the conductivity, self-healing, and surface morphology of fabricated composite using different spectroscopic techniques, such as electrochemical impedance (EIS), SEM, TEM, IR, UV, and a particle size analyzer.

Numerical modeling of the thermoforming process of polymeric sheets requires precise knowledge of the viscoelastic behavior under conjugate effect pressure and temperature. Using two different experiments, bubble inflation and dynamic mechanical testing on a high-density polyethylene (HDPE) nanocomposite reinforced with polymethylsilsesquioxane HDPE (PMSQ&ndash, HDPE) nanoparticles, material constants for Christensen&rsquo, s model were determined by the least squares optimization. The viscoelastic identification relative to the inflation test seemed to be the most appropriate for the numerical study of thermoforming of a thin PMSQ&ndash, HDPE part. For this purpose, the finite element method was considered.

In many applications, metal gears have been replaced by plastic gears because of their functionality and cost advantages. Despite their many benefits, the intensive use of plastics and composites raises sustainability issues because of the depletion of non-renewable petroleum resources and the pollution that is generated. Thus, alternative ecological solutions for plastic gears are necessary; however, little is known regarding ecologically designed gears. In this study, we propose two types of innovative gear materials. The first is a semi-ecological polyethylene bio-composite gear reinforced with birch fibers, and the second is a fully bio-sourced natural polyethylene gear with birch fibers. This study is the first time such fully ecological composite-plastic gears have been tested. The tests record the evolution of the fatigue and temperature over time under various operating conditions. Furthermore, acoustic emission is used to assess the evolution of fatigue cracks. The results indicate that the fully ecological gears are feasible and offer an alternative to traditional materials, such as engineering plastics, likely at a lower cost.

In this work, laminated polyester thermoset composites based on palm tree fibers extracted from palms leaflets and glass mats fibers were manufactured to develop hybrid compositions with good mechanical properties; the mixture of fibers was elaborated to not exceed 25 vol.%. Samples were prepared with a resin transfer molding (RTM) method and mechanically characterized using tensile and flexural, hardness, and impact tests, and ultrasonic waves as a non-destructive technique. The water sorption of these composite materials was carried out in addition to solar irradiation aging for approximately 300 days to predict the applicability and the long-term performance of the manufactured composites. Results have shown that the use of glass fibers significantly increased all properties; however, an optimum combination of the mixture could be interesting and could be developed with less glass sheet and more natural fibers, which is the goal of this study. On the other hand, exposure to natural sunlight deteriorated the mechanical resistance of the neat resin after only 60 days, while the composites kept high mechanical resistance for 365 days of exposure.

For non-linear problems, the solution of the heat equation in terms of the Kirchhoff transformation, θ(T), is very limited. This restriction is due to the practical disadvantage of the inverse temperature shift from the Kirchhoff transform T(θ). In order to get around the difficulties associated with the representation of θ(T) and its inverse T(θ) for solids with strongly non-linear conductivities, a strategy based on a reverse engineering method is considered. It consists in identifying the number of knots and their respective locations on the curve T(θ) at the most efficient computational cost. In order to obtain the location of the knots, the curve is fitted by B-spline functions and the data is partitioned by an application of the bisectional method with a predetermined error. These knots are further optimized using the non-linear least squares method. The proposed approach can be combined with a numerical method such as the FEM, BEM, and FEV to provide the non-linear solution of the heat equation in terms of θ. However, in this work we have limited ourselves to the FEM. The validation of the proposed approach is achieved through several cases ranging from constant to strongly non-linear thermal conductivities with or without convection. As an application, the 3D finite element method is applied to determine the non-linear temperature distribution in a copper block with an imposed temperature.

The mechanical and structural properties of five formulations of a novel melt processed poly-ethylene terephthalate (PET)-hemp fibers composite were determined, followed by a numerical investigation of their thermoformability using the ThermoForm® code. The composites' linear viscoelastic properties were determined by small amplitude oscillatory shear tests and their viscoelastic behavior characterized by the Christensen's model. The forming pressure load required by the numerical analysis was derived from the Redlich–Kwong's real gas equation of state. The air flow's influence on the thickness of the thermoformed part, as well as the stress and the energy required for the process were analyzed. Our observations indicate little influence of the constitutive equations of the investigated formulations on the final thickness distribution of the thermoformed part; moreover, the time and energy required for the process showed no clear variation with the fiber load. POLYM. ENG. SCI. 56:1021–1030, 2016. © 2016 Society of Plastics Engineers

In the last decades, research on atmospheric icing of structures such as power transmission lines has attracted much interest. Accumulation and the shedding of atmospheric ice from overhead transmission lines and ground wires may cause their rupture and tower collapses, leading to power outages. The present work concerns a study of the compressive strength of atmospheric ice, under different experimental conditions such as strain rate, temperature, and porosity. For this reason, ice was accumulated in the closed loop wind tunnel at CIGELE (Industrial Chair on Atmospheric Icing of Power Network Equipment), under three temperatures (− 20, − 15 and − 5 °C). The wind speed inside the tunnel was set at 20 m/s in order to obtain a mean volume droplet diameter (MVD) of 40 μm and a liquid water content (LWC) of 2.5 g/m 3 . Each type of ice was tested at the same temperature at which it had been accumulated. A tomographic analysis was carried out on a small specimen (cylinder of 1 cm diameter × 2 cm length) for each temperature in order to quantify the porosity and determine the grain size and their distribution. The obtained results show a strong dependence of the compressive strength on temperature, strain rate and porosity. The ductile–brittle transition was identified within a strain rate ranging between 10 − 4 s − 1 and 10 − 3 s − 1 . It was found that compressive strength increases with decreasing temperature for deaerated ice. However, for atmospheric porous ice, compressive strength increases until − 15 °C, then decreases for lower temperatures. Compressive strength of atmospheric ice is highly dependent on porosity, which is related to the amount, size and distribution of pores inside the ice.

International audience; Wood polymer composites (WPC) have well proven their applicability in several fields of the plasturgy sector, due to their aesthetics and low maintenance costs. However, for plasturgy applications, the characterization of viscoelastic behavior and thermomechanical and thermophysical properties of WPC with the temperature and wood filler contents is essential. Therefore, the processability of polymer composites made up with different percentage of wood particles needs a better understanding of materials behaviors in accordance with temperature and wood particles contents. To this end, a numerical analysis of the viscoelastic, mechanical, and thermophysical properties of composite composed of high density polyethylene (HDPE) reinforced with soft wood particles is evaluated.

There is a need to correctly dimension gears for an application with an understanding of how the gear will deteriorate until final failure. However, this task has been difficult because engineers must consider the complexity of gear meshing phenomena combined with the gear material-specific properties and application particularities to determine the critical failure and maintenance points. This article provides a review of the multiple damage modes of plastic gears, including both general and plastic gear-exclusive modes. This article reviews the different branches of the damage problem, performs a combined solution of finite element analysis (FEA) and validated analytical equations for plastic gears. With this knowledge, a unique system of analysis of gear utilization perspectives that evaluates all possible damaging processes is built. By applying a range of normal loads on a plastic gear, it was verified that the damage mode depends highly on the applied load. The identification of the proper damage mode allows preventive actions to be taken because the limits of plastic gears and the optimal usage are identified. With this damage modeling strategy, the designer can skip several steps in reaching a decision regarding plastic gear applicability. This synthesis represents significant progress for plastic gear damage modeling because the major factors of plastic gear functioning and the damage factors are observed.

In contrast to numerical methods, which are generally poorly adapted to thermal conduction treatments in solid media containing different materials with different types of orientations of thermal conductivity tensors (Cartesian and/or cylindrical and/or spherical), the proposed new approach, 3D hybrid finite elements, is easier to implement numerically and, in particular, for the finite element method. To improve the efficiency and accuracy of the solution by FEM, we consider the implicit method using the prediction/correction strategy. The proposed approach is validated in the following cases: (i) two analytical tests for cylindrical and spherical anisotropic thermal conduction; (ii) numerical orthotropic thermal conduction in the case where the local axes of the material are not aligned with the global Cartesian axes (case of a square plate made of two different materials: one isotropic and the other orthotropic) and (iii) experimental temperature obtained on the heating of a cylindrical log. As applications, two multi-material and multi-orientation situations of the thermal conductivity tensor were considered: one related to an ignition pipe made of multiple anisotropic materials and the other to a heated chair-seat made of multiple anisotropic materials.

This work deals with a numerical study of the potential use of microwave radiation as a heating mode for the thermoforming of wood-plastic composites (WPC). It also shows the comparison between the infrared and microwave heating modes for polypropylene (PP) and PP-based bio-composite sheets. The latter contain PP with 30% wood-based reinforcements. The differentiating parameters between the investigated bio-composite sheets were their thicknesses and the size of their reinforcements. Their thicknesses were 1, 2, 5 and 10 mm, and the size of their reinforcements were 100, 200 and 500 μm. The target heating temperature is 140 °C on the outer surfaces of the sheets. The results indicate that the microwaves generate a closely uniform temperature distribution in the sheets. Meanwhile, the minimum heating time is found for the bio-composites, which is 1 mm thick for the infrared mode, and the bio-composites whose reinforcements are 200 μm for the microwave mode.

A new green composite made of natural polyethylene (NPE) has never been produced using short birch fibers and compared with others biocomposites with matrices of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE). Versions with and without a coupling agent (CA) in fiber ratios of 10, 20, 30 and 40 wt% were produced. Tensile and 3-point flexural tests were conducted to measure the mechanical properties of the composites, and acoustic-emission testing was used to measure the evolution of damage caused by irreversible changes in the materials in correlation with an analysis of the damage modes. It was concluded that the extent of the damage and the contribution of each damage mode depend on the material, the test performed and, especially the presence of a CA. The results prove that the choice of composite for a particular application must be a judicious one and should consider not only the mechanical properties but also the damage processes of the composite, which may be crucial for long-term applications.

This paper addresses issues in the microwave phytosanitary treatment of frozen wood. Four eastern Canadian wood species are used: trembling aspen, yellow birch, white birch, and sugar maple. The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a volumetric specific enthalpy-based finite element method. Dielectric and thermophysical properties are functions of temperature and moisture content. As an application, we studied the dielectric heating of four wood species as a function of moisture content and microwave properties.

Designing and optimizing the performance of a piezoresistive pressure microsensor involves not only studying the piezoresistive properties of polysilicon but also analyse the thermomechanical behaviour of its most sensitive internal part. This work focuses on an analytical, numerical and experimental study of a silicon wafer used in a pressure sensor. A thermomechanical study was conducted to assess the effects of temperature and material orientation on the deflexion and failure mode of Silicon membrane. The chosen analytical approach is based on Kirchhoff theory in which a square Silicon membrane is subjected to a distributed pressure over all its surface. Thermomechanical simulations and fracture analysis are carried out using Abaqus software. An experimental thermomechanical technique to determine maximum wafer deflexion and its effect on crack initiation and fracture mode was implemented. Deflexions tests were carried out on a bending machine using specimens of p-Si doped wafers. Deflexion values are measured for each applied temperature. Some preliminary tests were performed to determine the impact of temperature and Silicon wafers orientation on maximum deflexion when fracture occurs. The test’s results confirmed that the failure mode is highly brittle and follow each time crystal orientations 0° and 45°. Furthermore, at room temperature, fracture occur at 389 μm of displacement, and grows by 5.2 % when temperature is increased over 40°C. Consequently, Silicon sensitivity will be increased by 4%.

The heating process of frozen wood exposed to plane microwaves is numerically investigated. The nonlinear heat conduction problem involving phase change such as wood freezing is solved by a specific 3D volumetric enthalpy-based finite element method. Dielectric and thermal properties are a function of temperature and moisture content. The numerical model is validated by experimental and analytical means. As an application, we studied the effect of moisture content and frequency on microwave heating of trembling aspen wood.

Soil resistivity plays a key role in designing grounding systems for high-voltage transmission lines and substations. The objectives of this paper are to determine the best estimated value of the apparent resistivity or electrode grounding resistance of N-layer soil and to use a new inversion method to precisely determine earth parameters. The inversion of electrical sounding data does not yield a unique solution, and a single model to interpret the observations is sought. This paper presents a new inversion method to statistically estimate soil parameters from Schlumberger and Wenner measurements. To validate the method and test the inversion scheme, four soundings were selected: two theoretical and two in the field. The procedure was applied using test data and a satisfactory soil model was obtained.

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.

Natural convection in an air-filled (Prandtl number = 0.7) porous cavity with profiled side cooling and constant bottom heating is investigated over the Rayleigh number range of 1 × 10 4 to 1 × 10 8 at two Darcy numbers: 1 × 10 - 4 and 1 × 10 - 6 . The aspect ratio based on cavity height was varied from 0.5 to 0.1 to investigate penetration length according to linear or sinusoidal temperature profile. The general non-Darcy model adopted in this work was validated against experimental and theoretical results in the literature and Nusselt number was predicted within less than 3% in the worst case. The effect of left wall imposed temperature profile was investigated in detail. Different convective regimes were observed depending on the imposed profile. An active region was found to take place with the linear temperature profile and with extent proportional to Rayleigh number as predicted by scale analysis.

Resume Dans cette etude, nous avons etabli par la methode des elements finis en trois dimensions une approche simplifiee pour analyser l'evolution de la temperature au sein d'une membrane semi-transparente de type polyethylene terephtalate (PET) amorphe, exposees a une source radiative. En se basant sur le comportement optique du PET, un transfert radiatif monodirectionnel, suivant l'epaisseur de la membrane est considere. Des simulations numeriques ont permis de confronter et de valider les resultats obtenus vis-a-vis des resultats analytiques et experimentaux. Comme application, nous avons etudie le chauffage d'une feuille thermoplastique en PET exposee a une source radiative infrarouge.

The aim of this study was to understand the roles of processing method and fiber size on the properties of wood–plastic composites (WPC). Composites were manufactured using extrusion or injection molding (IM) and fibers of different fiber length-to-diameter (L/D) ratio. IM resulted in better mechanical properties and lower water absorption and swelling than extrusion. These differences can be explained by the structure and surface quality of the composites. Fiber L/D ratio had a beneficial effect on mechanical properties but resulted in decreased water absorption characteristics. These results allow identifying a suitable forming process and/or fiber size according to application needs. This study provides a better understanding of the relationships between processing method, fiber characteristics, and composite behavior.

Fiber length and distribution play important roles in the processing and mechanical performance of fiber-based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length-to-diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high-density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Dans cet article nous nous interesserons, d'une part a la caracterisation biaxiale, en soufflage libre du comportement des membranes thermoplastiques circulaires en ABS et en HIPS et, d'autre part a la simulation numerique de la mise en forme d'une piece creuse en ABS et en HIPS. Les modeles de comportement hyperelastique de Mooney-Rivlin et d'Ogden sont consideres. Dans un premier temps nous utilisons la methode des differences finies a pas variables pour la resolution du probleme d'equilibre de la membrane et un algorithme modifie de Levenberg-Marquardt pour minimiser la difference entre la pression calculee et celle mesuree. Ceci permet l'identification des constantes materielles incorporees dans les modeles utilises. Pour la modelisation numerique par la methode dynamique des elements finis, nous considerons une formulation lagrangienne, l'hypothese de la theorie des membranes et une charge en pression, decoulant de la loi des gaz parfaits, pour etudier l'influence des lois de comportements sur la distribution finale des epaisseurs et des contraintes dans une piece thermoformee en ABS et en HIPS.

Resume Le probleme de transfert de chaleur radiative entre deux surfaces diffuses placees arbitrairement dans un milieu transparent se ramene au calcul de la valeur de la surface de radiation mutuelle. Dans le cas de deux surfaces arbitraires tres voisines, le calcul numerique de la valeur de la surface de radiation mutuelle conduit a des resultats divergents. Dans cet article, nous presentons, d'une part, une technique, basee sur la methode de contour, qui evite le probleme de singularite, tout en reduisant le nombre d'operations de calcul numerique et, d'autre part, une analyse comparative de cette technique avec d'autres methodes classiques.