Triaxial variation of the modulus of elasticity in the thermos-elastic field of six species of tropical woods

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Short Communication: Statistical determination of the rigidity in flexion of some Cameroonian hardwoods.

This study dealt with the statistical study of the rigidity in flexion of some Cameroonian hardwoods. It was based on the statistical determination of the rigidity of the concerned woods from a series of bending measurements. Two Cameroonian hardwoods were used in the study, namely Moabi (Chlorophora excelsa) and Iroko (Milicia excelsa). Twenty-two samples of each wood were selected. The samples had the following dimensions 340 cm x 2 cm x 2 cm as recommended by the norm NF B51 008. They were tested under bending. From the graph of load against displacement, the rigidity in flexion at different moisture levels was determined from which the Young modulus was calculated. Linear regression models were fitted to the data and the results showed significant correlation coefficients between the Young modulus and moisture content for each wood. Résumé Le présent travail repose sur la détermination statistique de la rigidité en flexion de deux essences camerounaises dont : Moabi (Chlorophora excelsa) et Iroko (Milicia excelsa).. A cet effet, 22 éprouvettes de chaque essence ont été testées en flexion. Chaque éprouvette avait pour dimension 34 cm x 2 cm x 2 cm, conformément à la norme NF B51 008. A partir du graphe de la charge en fonction du déplacement, nous avons, à chaque taux d'humidité, déterminé la rigidité en flexion correspondante. La méthode des moindres carrés est ensuite utilisée pour déterminer la relation entre la rigidité en flexion et le taux d'humidité. Utilisant la relation donnant la rigidité en flexion en fonction du module d'Young, nous avons établi une relation entre le module d'Young et le taux d'humidité. Les coefficients de determination linear montrent qu'il existe une corrélation forte entre le module d'Young et le taux d'humidité pour les deux essences concernées. Key words: Moabi (Chlorophora excelsa); Iroko (Milicia excelsa); Bending; Rigidity in flexion; Guitard law on the rigidity in flexion Moor Journal of Agricultural Research Vol.4(2) 2003: 296-30

Approche par calculs fractionnaires du fluage viscoélastique non linéaire du bois d'Entandrophragma cylindricum (Sapelli)

International audienceWood is is emerging as a modern building material, and is becoming increasingly popular for structural use, not least because of its renewable nature, durability and ease of shaping. durability and ease of shaping. However, once it is in service, at room temperature and under low stresses, it warps and thus faces the problem of creep. problem of creep. In fact, the third phase of creep of creep can lead to the failure of the structural element, which can result in the ruin of the entire building. The first step in checking for this anomaly is to measuring the creep deformation. At the same time, it is essential to develop appropriate solutions, such as modelling and prediction, to deal with this potentially this potentially harmful phenomenon. Conventional rheological models for predicting prediction of creep have been the subject of several studies, some of which require a large number of parameters (Tagne, 2018). With a view to design prediction models with a reduced number of parameters and which, at the same time better represent the hereditary character of wood, fractional rheological models were developed (Krasnobrizha, 2016). The aim of this work is to model and predict predict the deformations of wood from Entandrophragma cylindricum (Sapelli) used in structures. For this purpose, Thomson's fractional fractional Thomson model is proposed.Le bois apparait aujourd’hui comme un matériau de construction moderne et s’impose davantage en structure notamment à cause de son caractère renouvelable, de sa durabilité et de sa mise en forme aisée. Cependant, une fois en service il flue à température ambiante et sous de faibles contraintes, se déforme et fait ainsi face au problème de fluage. De fait, la troisième phase du fluage peut conduire à la rupture de l’élément de structure, ce qui peut induire la ruine de tout l’édifice. Le premier stade du contrôle de cette anomalie est la mesure de la déformation de fluage. Parallèlement, Il est impératif de développer des solutions adéquates telles que la modélisation et la prédiction adressées à ce phénomène qui peut devenir nocif. Les modèles rhéologiques classiques de prédiction du fluage ont fait l’objet de plusieurs travaux qui pour certains requiert un grand nombre de paramètres (Tagne, 2018). Dans l’optique de concevoir des modèles de prédictions ayant un nombre réduit de paramètres et qui par la même occasion représentent mieux le caractère héréditaire du bois, les modèles rhéologiques fractionnaires ont vus le jour (Krasnobrizha, 2016). L’objectif de ce travail est de modéliser et de prédire les déformations du bois d’Entandrophragma cylindricum (Sapelli) utilisé en structure. Pour ce fait le modèle fractionnaire de Thomson est proposé

Mechanical Behavior of Pericopsis elata Relative to Age during Growth

The assamela (afrormosia) whose scientific name is “Pericopsis elata” (Harms), a large tree of great commercial value, is an exploited species. It is considered “endangered” by the IUCN.” Trees ready for harvesting are scarce because the logging diameter, which has been set at 100 cm, is very big. The studies recommended by the Cameroonian government as part of the ITTO/CITES project activities should be carried out to determine a new minimum logging diameter as the diameter increases with age. No credible solution is provided in the scientific literature to compensate for its scarcity of exploitation. Moreover, little or no information is available for describing the variation of its mechanical properties over time in order to determine the age at which its wood mechanical properties are good enough to be marketable. It is in this context that this work was undertaken. In this study, we adopted an experimental approach to evaluate the mechanical properties of this species exploited in southeast Cameroon. We then studied the variations in these properties as a function of tree age in order to propose leads for their exploitation. Thus, the compression and bending tests allowed us to estimate the relationship between the mechanical properties in three main directions of the log (MOE in compression and bending, failure stress in compression and bending, and creep in compression) and age (or diameter). We also used the 10-hour creep under low axial compressive loading data to implement the theoretical fractional Maxwell (MF) model, which was compared to the experimental data. For this purpose, after three months of natural drying in the laboratory, we evaluated the above mechanical properties according to age. This study shows that the mechanical properties change as the diameter increases and change very quickly from 70 cm diameter upwards. From the analysis of the experimental data, we deduced that the minimum diameter of exploitable trees should be equal to 80 cm corresponding to the age of about 200 years

M-THETA METHOD ON MODE I AND II FAILURE OF TWO CAMEROONIAN HARDWOODS IN BENDING

International audienceThis work deals with the numerical simulation on bending test to characterize two Cameroonian hardwoods under mode I and II loading for different crack lengths. The finite element analysis for fracture in orthotropic medium is developed. The algorithm of fracture is introduced in a finite element software Cast3M. According to the Mtheta method, the calculation of the stress intensity factors and the energy release rate for pure mode I and II fracture are deduced using a SENB (Single Edge Notch Bending) specimen. The path independence of Mθ-method on the specimen is confirmed

STUDY OF THE TEMPERATURE OF CEREBRAL ARTERIAL BLOOD FLOW, FOR THE CHARACTERIZATION OF THE DEGREE OF STENOSIS: APPLICATION TO STROKE

International audienceBased on the biological heat transfer equation of Penne, the internal temperature distribution of the biological tissue was studied, taking into account the evolution of stenosis and hematocrit. The one-dimensional simplifying cylindrical heat equation of the biological living tissues in permanent regime was solved by the finite difference method and analytically, to assess the temperature change under the variation of stenosis, hematocrit, thermal conductivity, kinematic viscosity, generation of metabolic heat and the heat transfer coefficient. The main results show that the temperature increases as the stenosis and hematocrit increase in size; and the secondary results show that the heat transfer coefficient and the thermal conductivity lower the body temperature while metabolic heat generation increases body temperature. This is in accordance with the literature

Automating the clinical stools exam using image processing integrated in an expert system

International audienceBackground and objective: The diagnosis of intestinal parasitosis disease relies on physiological symptoms and stool examination. Often, few specialists are available, and manual stool exam is slow, prone to error, and can cause eye fatigue. Our aim was to design and implement a medical expert system that would be automated and helpful for diagnosis of human intestinal parasitosis.Methods: The system was developed based on a decision algorithm. A knowledge base was constructed through information gleaned from books and physicians with information pertaining to the disease. The user interacts with the system by answering questions. The symptoms information collected led to a microscopic examination of stools, which was run on the system to detect parasites. The paradigm for automated microscopic examination of stools consisted of a combined distance regularized level set evolution, automatically initialized by a circular Hough transform, and a trained neuro-fuzzy classifier. The neuro-fuzzy classifier was trained for analysis of twenty human intestinal parasites.Results: We combined the reasoning scheme of diagnosis and the automated clinical exam of stools in the same system. The parasites found in microscopic imagery confirmed the suspicious disease. The final recommendation of diagnosis was then completed, with appropriate proposed therapy. The system was evaluated with sixty cases of infection, and compared to the diagnosis of two expert doctors; we obtained fifty eight correct diagnoses, corresponding to a 96.6% accuracy.Conclusions: The proposed system is automated, since the parameters of segmentation, feature extraction and classification are set to be computationally guided by the type of suspicious parasite. The system is potentially an important contribution for medical healthcare assistance