The objective of this paper is to evaluate the reliability of a system in its different states (absence of failures, partial failure and total failure) and to propose actions to improve this reliability by an approach...The objective of this paper is to evaluate the reliability of a system in its different states (absence of failures, partial failure and total failure) and to propose actions to improve this reliability by an approach based on Monte Carlo simulation. It consists of a probabilistic evaluation based on Markov Chains. In order to achieve this goal, the functionalities of Markov Chains and Monte Carlo simulation steps are deployed. The application is made on a production system. .展开更多
This work aims at characterizing the evolution of the damage of two tropical hardwoods. Two species from Cameroon, the Entandrophragma Cylindricum and the Chlorora Exelcia were used for the purpose. Repeated compressi...This work aims at characterizing the evolution of the damage of two tropical hardwoods. Two species from Cameroon, the Entandrophragma Cylindricum and the Chlorora Exelcia were used for the purpose. Repeated compressive loading has been made on specimens strictly selected along with longitudinal and radial directions of each species. Each cycle was made of one phase of monotonic loading and a phase of elastic release. From data obtained, we determined the variation of Young modulus and plastic deformation during each cycle of loading, and we had deduced the damage of the material. Results show that the damage appears only after a certain threshold of the plastic deformation;that damage then grows exponentially to reach a threshold after which the failure of the material occurs. As well, we noticed that the growth of damage is accompanied by the progressive decrease of the Young modulus;this confirms the deteriorating effect of the damage on the mechanical properties. Elsewhere, the damage failure threshold is less than the theoretical value, and differs from one direction to another. Finally, we noticed that the damage failure threshold of sapelli is greater than that of iroko that allows concluding that iroko gets damaged and fails more rapidly than sapelli.展开更多
The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more val...The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more valorization of biomaterials following the example material wood arouses for a few years a?private interest on behalf of the populations. The experimental characterization?makes it possible to consider the mechanical properties local of Pericopsis elata (Assamela) according to various parameters (the wood turpentine, the orientation of wood fibers, water the content, the type of test …). From the?results, we evaluate the mechanical characteristics of Pericopsis elata (Assamela)?according to the three directions of Orthotropy. Then from the tests of load-discharge we measured the evolution of the damage using the variation of the Young modulus, which enabled us to note the reduction in the modulus of elasticity because of the damage following the three directions. Finally we noted a progressive and irreversible degradation of mechanical properties induced by the development of the microscopic cracks within material.展开更多
In the realization of mechanical structures, achieving stability and balance is a problem commonly encountered by engineers in the field of civil engineering, mechanics, aeronautics, biomechanics and many others. The ...In the realization of mechanical structures, achieving stability and balance is a problem commonly encountered by engineers in the field of civil engineering, mechanics, aeronautics, biomechanics and many others. The study of plate behavior is a very sensitive subject because it is part of the structural elements. The study of the dynamic behavior of free vibration structures is done by modal analysis in order to calculate natural frequencies and modal deformations. In this paper, we present the modal analysis of a thin rectangular plate simply supported. The analytical solution of the differential equation is obtained by applying the method of separating the variables. We are talking about the exact solution of the problem to the limit values. However, numerical methods such as the finite element method allow us to approximate these functions with greater accuracy. It is one of the most powerful computational methods for predicting dynamic response in a complex structure subject to arbitrary boundary conditions. The results obtained by MEF through Ansys 15.0 are then compared with those obtained by the analytical method.展开更多
Due to their interesting properties, bamboo fibers are more and more used as reinforcements in polymer matrices as a substitute for synthetic fibers. For their future service life, it is important to understand their ...Due to their interesting properties, bamboo fibers are more and more used as reinforcements in polymer matrices as a substitute for synthetic fibers. For their future service life, it is important to understand their physical and mechanical behavior over time in order to control the aging phenomenon within this fiber. The paper analyzed the influence of the age of the bamboo thatch and the vertical position of the Bambusa vulgaris species cultivated in Cameroon on the physicomechanical properties of the fibers extracted from the thatch. Fibers were mechanically extracted from three bamboo culms aged respectively 3 years (BV3), 4 years (BV4) and 5 years (BV5). The culms were thus identified according to their number of ramifications, and were felled no abated for a total of three culms. A section of about one meter on each of the parts (lower part, middle part, upper part) of these three culms was made for the opposite technological studies. Each age was therefore represented by three portions of thatch, one from the upper part, one from the middle part and the last from the lower part of the thatch, all giving a total number of nine samples taken and marked BV3inf, BV3moy, BV3sup, BV4inf, BV4moy, BV4sup, BV5inf, BV5moy, BV5sup before handling in the laboratory. Physical (density, moisture absorption rate) and mechanical (tensile tests according to DIN EN ISO 13934-1, natural durability) characterizations were used to better understand the mechanisms of this influence. In view of all the results obtained, the fiber from the upper part of the 3-year-old thatch (BV3sup) is the one with the best characteristics and is recommended for a better elaboration of bamboo fiber composites: (Density: 0.83;Absorption rate 11.7%;Young’s modulus: 7.4 GPa;Maximal stress: 64.3 MPa;Elongation at rupture: 1.1;Loss of mass natural durability: 7.63%).展开更多
文摘The objective of this paper is to evaluate the reliability of a system in its different states (absence of failures, partial failure and total failure) and to propose actions to improve this reliability by an approach based on Monte Carlo simulation. It consists of a probabilistic evaluation based on Markov Chains. In order to achieve this goal, the functionalities of Markov Chains and Monte Carlo simulation steps are deployed. The application is made on a production system. .
文摘This work aims at characterizing the evolution of the damage of two tropical hardwoods. Two species from Cameroon, the Entandrophragma Cylindricum and the Chlorora Exelcia were used for the purpose. Repeated compressive loading has been made on specimens strictly selected along with longitudinal and radial directions of each species. Each cycle was made of one phase of monotonic loading and a phase of elastic release. From data obtained, we determined the variation of Young modulus and plastic deformation during each cycle of loading, and we had deduced the damage of the material. Results show that the damage appears only after a certain threshold of the plastic deformation;that damage then grows exponentially to reach a threshold after which the failure of the material occurs. As well, we noticed that the growth of damage is accompanied by the progressive decrease of the Young modulus;this confirms the deteriorating effect of the damage on the mechanical properties. Elsewhere, the damage failure threshold is less than the theoretical value, and differs from one direction to another. Finally, we noticed that the damage failure threshold of sapelli is greater than that of iroko that allows concluding that iroko gets damaged and fails more rapidly than sapelli.
文摘The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more valorization of biomaterials following the example material wood arouses for a few years a?private interest on behalf of the populations. The experimental characterization?makes it possible to consider the mechanical properties local of Pericopsis elata (Assamela) according to various parameters (the wood turpentine, the orientation of wood fibers, water the content, the type of test …). From the?results, we evaluate the mechanical characteristics of Pericopsis elata (Assamela)?according to the three directions of Orthotropy. Then from the tests of load-discharge we measured the evolution of the damage using the variation of the Young modulus, which enabled us to note the reduction in the modulus of elasticity because of the damage following the three directions. Finally we noted a progressive and irreversible degradation of mechanical properties induced by the development of the microscopic cracks within material.
文摘In the realization of mechanical structures, achieving stability and balance is a problem commonly encountered by engineers in the field of civil engineering, mechanics, aeronautics, biomechanics and many others. The study of plate behavior is a very sensitive subject because it is part of the structural elements. The study of the dynamic behavior of free vibration structures is done by modal analysis in order to calculate natural frequencies and modal deformations. In this paper, we present the modal analysis of a thin rectangular plate simply supported. The analytical solution of the differential equation is obtained by applying the method of separating the variables. We are talking about the exact solution of the problem to the limit values. However, numerical methods such as the finite element method allow us to approximate these functions with greater accuracy. It is one of the most powerful computational methods for predicting dynamic response in a complex structure subject to arbitrary boundary conditions. The results obtained by MEF through Ansys 15.0 are then compared with those obtained by the analytical method.
文摘Due to their interesting properties, bamboo fibers are more and more used as reinforcements in polymer matrices as a substitute for synthetic fibers. For their future service life, it is important to understand their physical and mechanical behavior over time in order to control the aging phenomenon within this fiber. The paper analyzed the influence of the age of the bamboo thatch and the vertical position of the Bambusa vulgaris species cultivated in Cameroon on the physicomechanical properties of the fibers extracted from the thatch. Fibers were mechanically extracted from three bamboo culms aged respectively 3 years (BV3), 4 years (BV4) and 5 years (BV5). The culms were thus identified according to their number of ramifications, and were felled no abated for a total of three culms. A section of about one meter on each of the parts (lower part, middle part, upper part) of these three culms was made for the opposite technological studies. Each age was therefore represented by three portions of thatch, one from the upper part, one from the middle part and the last from the lower part of the thatch, all giving a total number of nine samples taken and marked BV3inf, BV3moy, BV3sup, BV4inf, BV4moy, BV4sup, BV5inf, BV5moy, BV5sup before handling in the laboratory. Physical (density, moisture absorption rate) and mechanical (tensile tests according to DIN EN ISO 13934-1, natural durability) characterizations were used to better understand the mechanisms of this influence. In view of all the results obtained, the fiber from the upper part of the 3-year-old thatch (BV3sup) is the one with the best characteristics and is recommended for a better elaboration of bamboo fiber composites: (Density: 0.83;Absorption rate 11.7%;Young’s modulus: 7.4 GPa;Maximal stress: 64.3 MPa;Elongation at rupture: 1.1;Loss of mass natural durability: 7.63%).
