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Open Journal of Applied Sciences 2020年第10期10卷 592-612页

作者： Frank Ferry Kamgue Tiam Raïdandi Danwe Noël Konaï lucien meva’a Laboratory of Civil and Mechanical Engineering National Advanced School of Engineering Yaoundé 1 University Yaoundé Cameroon School of Geology and Mining Engineering Ngaoundéré University Meiganga Cameroon National Advanced School of Engineering of Maroua Maroua Cameroon

The Non-explosive expansion material (NEEM) is a method more environmentally friendly than the harmful conventional rock fracturing techniques. However, it is slower and very costly. Thus, any means of economizing their use is very desirable. This paper investigates the crack growth between two neighboring holes of a gneiss rock internally pressurized by NEEM mixed with water with the aim to evaluate the influence of holes spacing (center-to-center distance), on the initiation and growth of cracks. Field experimental results reveal that crack starts earlier and grows faster with increasing ambient temperature. But when the ambient temperature is above 28°C, the NEEM is “blown out” of the holes. At these ambient temperatures, the surrounding rocks are hot and cannot dissipate efficiently the heat generated by the hydration reaction. The best filling time was found to be in the evening when the daily hot temperature has drooped. The time to first crack increases as hole diameter decreases. The 3D numerical modeling and simulation of crack growth between two neighboring holes internally pressurized by NEEM using ABAQUS (XFEM/CZM) software shows a good agreement with the theoretical and experimental results.

关键词： Crack Growth XFEM Gneiss Holes Spacing

Mechanical Characterization of Rhecktophyllum Camerunense (RC) Fiber Reinforced Concrete

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Journal of Modern Physics 2023年第8期14卷 20-32页

作者： Jean Calvin Bidoung Nicolas Stéphane Nyobe Mey Mahamat Imar lucien meva’a National Advanced School of Engineering Yaounde Cameroon Local Materials Promotion Authority Yaounde Cameroon

This work presents the development and mechanical characterization of a concrete reinforced with plant fiber extracted from Rhecktophyllum Camerunense (RC), a plant found in the regions of Center and South Cameroon. A comparative study between ordinary concrete and concrete reinforced with RC fiber at different percentages (0.1%, 0.2% and 0.3%) was carried out. The mechanical characterization of the material consisted in studying the flexural, compressive and splitting tensile strength by using cylindrical specimens of dimensions 160 × 320 in accordance with standards EN 12390-3 and EN 12390-6. The study of the mechanical properties was completed by the three-point bending test using prismatic test specimens of dimension 40 × 40 × 160 made according to the EN 196 standard. It emerges from this work that the addition of RC fiber improves the mechanical properties of concrete up to 0.2% with a peak at 0.1% of fiber corresponding to respective increases of 9%, 16% and 6% of the values of mechanical resistance to compression, flexion and tension after 28 days. From 0.3% of fiber, the values of the mechanical characteristics of the composite drop to values lower than those of ordinary concrete. The density reduction rate at 28 days is about 10% compared to the mass of ordinary concrete. These results allow us to conclude that the RC fiber could be valorized for the production of lightweight concrete.

关键词： Reinforced Concrete RC Fiber Mechanical Properties Lightweight Concrete

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Characteristics and Mechanicals Potentials of Wood Adhesives Manufactured with Grasses’ Lignins

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Journal of Materials Science and Chemical Engineering 2019年第1期7卷 35-47页

作者： Lionel Tapsia Karga Danwe Raidandi Noel Konai Antonio Pizzi lucien meva’a Laboratory of Mechanics and Civil Engineering National Advanced School of Engineering University of Yaoundé 1 Yaoundé Cameroon Department of Mechanical Engineering Petroleum and Gas Faculty of Mines and Petroleum Industries University of Maroua Kaélé Cameroon Departement of Mechanical Engineering and Materials National Advanced School of Engineering University of Maroua Maroua Cameroon ENSTIB-LERMAB University of Lorraine Epinal France

In order to manufacture environmentally friendly particle boards and enhance local resources, the lignins of Sorghum bicolor and Andropogon gayanus characterized using RMN 13C and MALDI TOF have the same structures. They contents Guaiacyl (G), Syringyl (S), p-hydroxyphenylpropane (H) and functional groups of phenols, flavonoids and secondary alcohols. The total phenol content determinated using Folin-Ciocalteu reagent is respectively 20.97 and 15.42 mg eqgallic acid/g of extract. The power of their adhesives is different. The Internal Bond (IB) of particleboards manufactured with these adhesives are respectively 0.37 MPa and 0.41 MPa. These lignins can be used as antioxydants.

关键词： Lignins Sorghum bicolor and Andropogon gayanus Structures Adhesives Internal Bond Antioxydants

Experimental and Numerical Study of Mechanical Behaviour of Fired Clay Bricks after Exposure to High Temperatures

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Journal of Minerals and Materials Characterization and Engineering 2023年第5期11卷 143-160页

作者： Jean Calvin Bidoung Léon Arnaud Mpoung Jean Aimé Mbey Jean Raymond lucien meva’a Laboratory of Civil Engineering and Mechanics National Advanced School of Engineering of Yaoundé University of Yaoundé 1 Yaoundé Cameroon Laboratory of Applied Inorganic Chemistry Department of Inorganic Chemistry University of Yaoundé 1 Yaoundé Cameroon

This paper reports the modeling of residual compressive strength of fired clay bricks submitted to elevated temperature. Five formulations were used and the explored temperatures were 95˚C, 200˚C, 550˚C, 700˚C and 950˚C. The stress–strain relationships and the mechanical properties (including Young’s modulus and compressive strength) were assessed using a uniaxial compressive strength machine. A proposed model equation was established and found satisfying. The elastic modulus was evaluated and tested with one existing model together with two proposed models. The proposed model was both satisfying and even more precise than the existing one. The overall results show that the effect of temperature on the mechanical properties of clays can be accurately described through the definition of thermal damage using elastic modulus.

关键词： Clay Bricks Modeling Stress-Strain Equations Compressive Strength Young’s Modulus

Micro Hydro Power Plant for Sustainable Energy in Rural Electrification: A Case Study in Cameroon

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Journal of Power and Energy Engineering 2023年第6期11卷 34-43页

作者： Elie Bertrand Kengne Signe Lyse Vanessa Ngansop Tchatchouang Pierre Pokem Paule Alexandrine Ekoube lucien meva’a Jean Nganhou Center of Research on Renewable Energy Institute for Geological and Mining Research Yaoundé Cameroon National Advanced School of Engineering University of Yaoundé 1 Yaoundé Cameroon

The state of Cameroon, faced with the situation the electricity deficits, is promoting the development of renewable energies in general and to meet rural electrification needs in particular. The purpose of this work is to study the feasibility of the MHP of Batcheu, to show its contribution to sustainable development in this locality and to prove that it is a profitable project. After study, it appears that the waterfall of Batcheu is favourable to the establishment of a MHP with an installed power of 260 kW with an operating diagram corresponding to a Francis turbine. Given that it is a renewable energy that can supply more than 800 households in rural areas, its contribution to sustainable development is obvious. Its investment cost is estimated at 171,465,396 FCFA. It is a profitable project with a payback time of 7 years and 2 months.

关键词： Micro Hydro Power Sustainable Development Rural Electrification

Performance Improvement in Manufacturing Shop Floor Operations of Developing Countries Based on Three Characteristics of Information Flow

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Journal of Computer and Communications 2022年第3期10卷 46-65页

作者： Joseph Voufo André Marie Mbakop Florent Biyeme Rolland Djomi Pélagie Flore Nanfack Temgoua Jean Raymond lucien meva’a National Advanced School of Engineering of Yaoundé (NASEY) Yaoundé Cameroon Laboratory of Civil and Mechanical Engineering Yaoundé Cameroon Department of Mechanical and Industrial Engineering Yaoundé Cameroon Ministry of Scientific Research and Innovation National Committee for Development of Technologies Yaoundé Cameroon

The management of information flow for production improvement has always been a target in the research. In this paper, the focus is on the analysis model of the characteristics of information flow in shop floor operations based on the influence that dimension (support or medium), direction and the quality information flow have on the value of information flow using machine learning classification algorithms. The obtained results of classification algorithms used to analyze the value of information flow are Decision Trees (DT) and Random Forest (RF) with a score of 0.99% and the mean absolute error of 0.005. The results also show that the management of information flow using DT or RF shows that, the dimension of information such as digital information has the greatest value of information flow in shop floor operations when the shop floor is totally digitalized. Direction of information flow does not have any great influence on shop floor operations processes when the operations processes are digitalized or done by operators as machines.

关键词： Developing Countries Information Flow Characteristics Machine Learning Shop Floor Operations Value of Information Flow

Physico-Chemical and Thermal Characterization of a Lignocellulosic Fiber, Extracted from the Bast of <i>Cola lepidota</i>Stem

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Journal of Minerals and Materials Characterization and Engineering 2020年第5期8卷 377-392页

作者： Ndoumou Belinga Rémy Legrand meva’a lucien Ouagne Pierre Betene Ebanda Fabien Noah Pierre Marcel Atangana Ateba Jean Laboratoire de Mécanique (LME) UFD SI Université de Douala Douala Cameroun Laboratoire d’Ingénierie Civile et Mécanique Université de Yaoundé I Yaoundé Cameroun Laboratoire Génie de Production (LGP) ENI de Tarbes Tarbes France

In this research work, fiber extracted from the bark of Cola lepidota (CL) plant, grown in the flora of Southern part of Cameroon, was investigated for composites reinforcement. The investigation was carried via evaluation of water absorption capacity, moisture content, real density, porosity, chemical composition, chemical structure and thermal behaviour. It was discovered that the new fiber has relatively low moisture content and water absorption capacity similar to those of other investigated natural fibers such as flax, sisal, coconut, hemp and jute. Its porosity was found appropriate for composite production and the fiber was found to be thermally stable up to 230°C, with maximum degradation temperature of 325°C. The main constituents of the fibre include cellulose, hemicellulose and lignin. In conclusion, based on the properties investigated, this fiber is considered suitable for composite manufacture.

关键词： Cola lepidota Fiber Thermal Stability Physico-Chemical Characteristics FTIR-ATR Liber Stem

Physicochemical and Thermal Characterization of Dura Palm Kernel Powder as a Load for Polymers: Case of Polyvinyl Chloride

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Journal of Materials Science and Chemical Engineering 2018年第6期6卷 1-18页

作者： Rolland Djomi lucien Jean Raymond meva’a Jean Nganhou Gérard Mbobda Abel Emmanuel Njom Yves Didier Modtegue Bampel Jean-Bosco Saha Tchinda Civil and Mechanical Engineering Laboratory National Advanced School of Engineering University of Yaounde I Yaounde Cameroon Research Unit for Macromolecular Chemistry Applied Inorganic Chemistry Laboratory Faculty of Science University of Yaounde I Yaounde Cameroon

This work presents the physical and thermal characterization of the dura palm kernel powder of Cameroon for their use as fillers for polymers composites. The powders of palm kernel were obtained using a percussion grinder mill with an industrial microniser which allowed obtaining a powder less than 50 μm with an apparent density between 0,505 ≤ ρ ≤ 0,680 g/cm3 at 1.56 of relative humidity. The infrared of the powder of palm kernel shows the presence of phenols groups with a large band around 3341 cm-1, -C-H at 2917.02 cm-1 and -C-O at 1040 cm-1 as the main peaks. The polyvinyl chloride of infrared obtained shows the presence of -C-Cl, -CH2 and CH as the mains peaks. The infrared of 12.5% of palm kernel powder with polyvinyl chloride shows an increase of the CH2 and CH bonds and a decrease of the -OH bonds. Thermogravimetric analysis and differential scanning calorimetric analysis of powders, polyvinyl chloride and mixture showed that the mixing powders are intermediate between the polyvinyl chloride and palm kernel powder. The powder decreased the phase temperatures of the mixture from 98.58℃ to 95℃ for the glass transition temperature and from 515℃ to 459℃ for the crystallization temperature. The thermogravimetric curves of palm kernel powder and polyvinyl chloride have showed that these materials lose their different masses in three different phases, and the one of composite (mixture of polyvinyl chloride with 12.5% of palm kernel powder) in two different phases.

关键词： Dura Palm Kernel Shell Load for Polymers Thermogravimetric Analysis DSC

Degradation of AZ31 and AZ91 magnesium alloys in different physiological media:Effect of surface layer stability on electrochemical behaviour

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Journal of Magnesium and Alloys 2020年第3期8卷 667-675页

作者： Emmanuel Mena-Morcillo lucien Veleva Applied Physics Department Center for Investigation and Advanced StudyCINVESTAV-IPNCarr.Ant.a Progreso Km.697310 MeridaYucatanMexico

This work deals with the degradation of AZ31 and AZ91 magnesium alloys when they are exposed to three types of physiological media for seven days at 37°C:Ringer's,Hanks\and simulated body fluid(SBF)solutions.A combination of immersions tests and surface characterisation methods were employed to evaluate the attack on the surface,and the stability of the formed corrosion product layers for each alloy/electrolyte *** of the Mg-ion released into the electrolytes were also carried out in order to be correlated with the degradation of the *** impedance spectroscopy(EIS)and potentiodynamic polarisation(PDP)techniques were employed to compare the performance of the alloys in these different aggressive *** to the obtained results,the Mg-alloys exposed to Hanks'media were the less affected,which fact was attributed to a higher stability of the corrosion products layer formed in this medium,in comparison of those formed in Ringer's and SBF *** add让ion,the corrosion damage was lower for AZ91 than for AZ31 alloy in all environments due to its higher Al *** mass loss rates calculated from both immersion tests and electrochemical methods followed the same trend for comparative purposes between alloys.

关键词： Mg-alloys AZ-series Surface layer Physiological media Mass loss rate Degradation

Preliminary multiproxy surface air temperature field reconstruction for China over the past millennium

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Science China Earth Sciences 2012年第12期55卷 2058-2067页

作者： SHI Feng YANG Bao lucien Von GUNTEN Key Laboratory of Desert and Desertification Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of SciencesLanzhou 730000China State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Oeschger Centre for Climate Change Research&Institute of Geography University of BernBernSwitzerland

We present the first millennial-length gridded field reconstruction of annual temperature for China, and analyze the reconstruction for spatiotemporal changes and associated uncertainties, based on a network of 415 well-distributed and accurately dated climatic proxy *** new reconstruction method is a modified form of the point-by-point regression (PPR) *** main difference is the incorporation of the "composite plus scale" (CPS) and "Regularized errors-in-variables" (EIV) algorithms to allow for the assimilation of various types of the proxy ***, the search radius is restricted to a grid size; this restriction helps effectively exclude proxy data possibly correlated with temperature but belonging to a different climate *** results indicate that: 1) the past temperature record in China is spatially heterogenic, with variable correlations between cells in time; 2) the late 20th century warming in China probably exceeds mean temperature levels at any period of the past 1000 years, but the temperature anomalies of some grids in eastern China during the Medieval climate anomaly period are warmer than during the modern warming; 3) the climatic variability in the eastern and western regions of China was not synchronous during much of the last millennium, probably due to the influence of the Tibetan *** temperature reconstruction may serve as a reference to test simulation results over the past millennium, and help to finely analyze the spatial characteristics and the driving mechanism of the past temperature ***, the lower reconstruction skill scores for some grid points underline that the present set of available proxy data series is not yet sufficient to accurately reconstruct the heterogeneous climate of China in all regions, and that there is the need for more highly resolved temperature proxies, particularly in the Tibetan Plateau.

关键词： climate change global warming paleoclimatology temperature field reconstruction