In recent years, the proportion of composite materials used in aircraft structures has exceeded 5... more In recent years, the proportion of composite materials used in aircraft structures has exceeded 50% and continues to grow over time. The substitution of metal materials by composites in aeronautics is no longer reserved for secondary structures, but it was extended to some primary structures, such as the fuselage and wings of the Airbus A350 and Boeing 787. This progress is considered as a major step towards the aim of building a whole aircraft structure from composite materials. However, during this development, the thickness of the composite laminates used in this area has greatly increased and led to several questions about the mechanical and damage behavior of these materials which are little studied in the literature. The industrial research has already made great strides in this sense, nevertheless, the state of the non-academic art is inaccessible. In this context, this thesis deals with the characterization and understanding of the mechanical behavior and damage mechanisms o...
The results of investigation of light-duty gas engine running on natural gas and hydrogen mixture... more The results of investigation of light-duty gas engine running on natural gas and hydrogen mixture has been given. The mathematical model of combustion process with variable Vibe combus-tion factor for this engine type has been specified.
Abstract: A study was undertaken to examine the life dispersion of 15 specimens made of near-alph... more Abstract: A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium alloy (IMI 834) tested in dwell-fatigue loading conditions. Nucleation and propagation features were examined and results were discussed in relation with results obtained from experiments and simulations undertaken by the various authors of the present paper. Micromechanical mechanisms seem to play critical roles in the nucleation and propagation of cracks and the presence of strong local textures are thought to intensify and explain the dramatic scatter of dwell fatigue lifes.
The objective of this study is modeling by finite elements of the kinetics of the damage by tired... more The objective of this study is modeling by finite elements of the kinetics of the damage by tiredness of a laminated composite with carbon fibers and epoxy matrix, solicited in fatigue (corrugated traction), used in the clothes industry of the structures in the aeronautical field. From the results of tiredness on flat test-tubes in has pus to determine the kinetics of the damage of material on a macroscopic scale and to identify the parameters of a model of damage which is based on work of Mao and Mahadevan [1] for established in a code of calculates finite elements. The finite elements results obtained show a good correlation with the experimental results, this without taking into account the final rupture of material. Mots-cles : materiaux composites, fatigue, endommagement, methode des elements finis.
Objective To understand the influencing factors of the breastfeeding start time of premature newb... more Objective To understand the influencing factors of the breastfeeding start time of premature newborns after being discharged from the hospital, and to provide the theoretical basis for the effective promotion of breastfeeding for premature infants after discharge. Methods Using the convenient sampling method, the mothers of premature infants who were hospitalized in Affiliated Children's Hospital of Zhengzhou University from October to December 2017 were selected as the research subjects. A self-designed questionnaire that included general demographic information, breastfeeding knowledge and breastfeeding burden was used in telephone follow-ups, in order to analyze the influencing factors of breastfeeding start time of premature newborns after discharge. SPSS 17.0 was used for data entry and statistical analysis. Among the 100 families that were initially chosen, 2 calls could not be completed, 5 calls were not answered by the parents or too much information was lost, which resu...
In addition to be recyclable, natural fiber composi tes (NFC) have interesting mechanical propert... more In addition to be recyclable, natural fiber composi tes (NFC) have interesting mechanical properties and compete with non-degradable materials in several fields of application. Indeed they present low density, good mechanical properties, low cost, and ease of machining. However the disparity of their properties, which results in variability of their behavior, prevents the growth of their use, unlike synthetic fiber composites. To assess their sustainability and promote the use of these materials in the industry, their mechanical behavior must be carefully studied. Prediction models use several parameters that are often measured with uncertainty. Furthermore, these parameters differ depending on the various tools an d / or standards used. Lord and Morelle [1] conducted a study to identify the sources of uncertainty in the calculation of th e modulus of elasticity. They demonstrated that the uncertainties in Young’s modulus values can vary from 1% to 6%. The objectives in this work ar...
The influence of the drilling parameters and the stacking sequence of flax/epoxy composite lamina... more The influence of the drilling parameters and the stacking sequence of flax/epoxy composite laminate on the cutting force and the damage induced were studied experimentally and numerically. Drilling tests were carried out based on full experimental design and the delamination at the entry and exit of the hole were quantified using an optical microscopy. Moreover, the damages at the wall of the hole were analyzed using scanning electron microscopy. Based on the experimental results, it was observed that the drilling forces and the machining quality are influenced on the one side by the spindle speed and feed and on the other side by the stacking sequence composite plate. In fact, the cutting forces recorded when drilling a composite plate with [90/0/90/0]2s is 30% higher to the one recorded when drilling a composite made with quasi-isotropic stacking sequence. A numerical model was developed in ABAQUS/Explicit using Hashin’s failure criteria in order to predict the cutting forces and ...
A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium... more A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium alloy (IMI 834) tested in dwell-fatigue loading conditions. Nucleation and propagation features were examined and results were discussed in relation with results obtained from experiments and simulations undertaken by the various authors of the present paper. Micromechanical mechanisms seem to play critical roles in the nucleation and propagation of cracks and the presence of strong local textures are thought to intensify and explain the dramatic scatter of dwell fatigue lifes.
ABSTRACT The kinetic of isothermal water absorption of injected polypropylene reinforced short he... more ABSTRACT The kinetic of isothermal water absorption of injected polypropylene reinforced short hemp fibers specimens is studied for four immersion temperatures (20, 40, 60, 80°C). The experimental results do not obey the Fick model based on a constant coefficient of diffusion and the time to reach the saturation level of water absorption decreases significantly with temperature. Thus, a new analytical model is proposed, using a variable coefficient of diffusion, which is used in analytical and FEA simulations. The results obtained show a very good correlation between experimental, analytical and FEA absorption curves.
In addition to being recyclable, wood fiber composites (biocomposites) have interesting mechanica... more In addition to being recyclable, wood fiber composites (biocomposites) have interesting mechanical properties and compete with petroleum based materials in several fields of application (in our paper, we will deal with gearing systems). For this purpose, we will study the behavior of these materials and their modes of damage. This step is required for reliable and safe use of biocomposites. In this work, we developed a biocomposite material with paper industry natural fibers (Birch) mixed with a thermoplastic matrix (polyethylene). Monotonic and cyclic tensile tests were conducted to measure the mechanical properties of the material. The instrumentation of our specimen with acoustic emission sensors was used to assess the damage to our material. For each type of specimen, we conducted five tests. We notice an improvement in both, the elastic modulus and maximum stress by increasing the rate of the fibers. The evolution of damage for the specimens happens in four phases. Therefore, w...
Wood fiber composites (biocomposites) have interesting mechanical properties that can compete wit... more Wood fiber composites (biocomposites) have interesting mechanical properties that can compete with non-degradable materials in several fields of applications. Therefore, it is important to improve the mechanical properties of these environmentally friendly materials. In this work, a biocomposite of polyethylene reinforced with birch tree fibers (the main raw material in the paper industry) is developed and tested both with and without a coupling agent. The mechanical properties of the biocomposite material are measured and some of its properties including its damage modes are investigated. This work is a required step for the reliable and safe use of biocomposites.
The aim of this paper is to analyze the influence of two machining processes on the mechanical be... more The aim of this paper is to analyze the influence of two machining processes on the mechanical behaviour of composite plates under cyclic loading. For this purpose, an experimental study using several CFRP plates drilled with conventional machining and non-conventional machining (abrasive water jet) was carried out. Digital image correlation and static tests using an Instron 4206 tester were performed. In addition, infrared thermography (IR) and fatigue tests were also performed to assess temperature and damage evolutions and also the stiffness degradation. Fatigue results have shown that the damage accumulation in specimens drilled with conventional machining was higher than the abrasive water jet ones. Furthermore, the endurance limit for plates drilled conventionally was approximately 10% higher than those drilled with abrasive water jet. This difference was related to the initial surface integrity after machining induced by the difference in the mechanism of material's remov...
In recent years, the proportion of composite materials used in aircraft structures has exceeded 5... more In recent years, the proportion of composite materials used in aircraft structures has exceeded 50% and continues to grow over time. The substitution of metal materials by composites in aeronautics is no longer reserved for secondary structures, but it was extended to some primary structures, such as the fuselage and wings of the Airbus A350 and Boeing 787. This progress is considered as a major step towards the aim of building a whole aircraft structure from composite materials. However, during this development, the thickness of the composite laminates used in this area has greatly increased and led to several questions about the mechanical and damage behavior of these materials which are little studied in the literature. The industrial research has already made great strides in this sense, nevertheless, the state of the non-academic art is inaccessible. In this context, this thesis deals with the characterization and understanding of the mechanical behavior and damage mechanisms o...
The results of investigation of light-duty gas engine running on natural gas and hydrogen mixture... more The results of investigation of light-duty gas engine running on natural gas and hydrogen mixture has been given. The mathematical model of combustion process with variable Vibe combus-tion factor for this engine type has been specified.
Abstract: A study was undertaken to examine the life dispersion of 15 specimens made of near-alph... more Abstract: A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium alloy (IMI 834) tested in dwell-fatigue loading conditions. Nucleation and propagation features were examined and results were discussed in relation with results obtained from experiments and simulations undertaken by the various authors of the present paper. Micromechanical mechanisms seem to play critical roles in the nucleation and propagation of cracks and the presence of strong local textures are thought to intensify and explain the dramatic scatter of dwell fatigue lifes.
The objective of this study is modeling by finite elements of the kinetics of the damage by tired... more The objective of this study is modeling by finite elements of the kinetics of the damage by tiredness of a laminated composite with carbon fibers and epoxy matrix, solicited in fatigue (corrugated traction), used in the clothes industry of the structures in the aeronautical field. From the results of tiredness on flat test-tubes in has pus to determine the kinetics of the damage of material on a macroscopic scale and to identify the parameters of a model of damage which is based on work of Mao and Mahadevan [1] for established in a code of calculates finite elements. The finite elements results obtained show a good correlation with the experimental results, this without taking into account the final rupture of material. Mots-cles : materiaux composites, fatigue, endommagement, methode des elements finis.
Objective To understand the influencing factors of the breastfeeding start time of premature newb... more Objective To understand the influencing factors of the breastfeeding start time of premature newborns after being discharged from the hospital, and to provide the theoretical basis for the effective promotion of breastfeeding for premature infants after discharge. Methods Using the convenient sampling method, the mothers of premature infants who were hospitalized in Affiliated Children's Hospital of Zhengzhou University from October to December 2017 were selected as the research subjects. A self-designed questionnaire that included general demographic information, breastfeeding knowledge and breastfeeding burden was used in telephone follow-ups, in order to analyze the influencing factors of breastfeeding start time of premature newborns after discharge. SPSS 17.0 was used for data entry and statistical analysis. Among the 100 families that were initially chosen, 2 calls could not be completed, 5 calls were not answered by the parents or too much information was lost, which resu...
In addition to be recyclable, natural fiber composi tes (NFC) have interesting mechanical propert... more In addition to be recyclable, natural fiber composi tes (NFC) have interesting mechanical properties and compete with non-degradable materials in several fields of application. Indeed they present low density, good mechanical properties, low cost, and ease of machining. However the disparity of their properties, which results in variability of their behavior, prevents the growth of their use, unlike synthetic fiber composites. To assess their sustainability and promote the use of these materials in the industry, their mechanical behavior must be carefully studied. Prediction models use several parameters that are often measured with uncertainty. Furthermore, these parameters differ depending on the various tools an d / or standards used. Lord and Morelle [1] conducted a study to identify the sources of uncertainty in the calculation of th e modulus of elasticity. They demonstrated that the uncertainties in Young’s modulus values can vary from 1% to 6%. The objectives in this work ar...
The influence of the drilling parameters and the stacking sequence of flax/epoxy composite lamina... more The influence of the drilling parameters and the stacking sequence of flax/epoxy composite laminate on the cutting force and the damage induced were studied experimentally and numerically. Drilling tests were carried out based on full experimental design and the delamination at the entry and exit of the hole were quantified using an optical microscopy. Moreover, the damages at the wall of the hole were analyzed using scanning electron microscopy. Based on the experimental results, it was observed that the drilling forces and the machining quality are influenced on the one side by the spindle speed and feed and on the other side by the stacking sequence composite plate. In fact, the cutting forces recorded when drilling a composite plate with [90/0/90/0]2s is 30% higher to the one recorded when drilling a composite made with quasi-isotropic stacking sequence. A numerical model was developed in ABAQUS/Explicit using Hashin’s failure criteria in order to predict the cutting forces and ...
A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium... more A study was undertaken to examine the life dispersion of 15 specimens made of near-alpha titanium alloy (IMI 834) tested in dwell-fatigue loading conditions. Nucleation and propagation features were examined and results were discussed in relation with results obtained from experiments and simulations undertaken by the various authors of the present paper. Micromechanical mechanisms seem to play critical roles in the nucleation and propagation of cracks and the presence of strong local textures are thought to intensify and explain the dramatic scatter of dwell fatigue lifes.
ABSTRACT The kinetic of isothermal water absorption of injected polypropylene reinforced short he... more ABSTRACT The kinetic of isothermal water absorption of injected polypropylene reinforced short hemp fibers specimens is studied for four immersion temperatures (20, 40, 60, 80°C). The experimental results do not obey the Fick model based on a constant coefficient of diffusion and the time to reach the saturation level of water absorption decreases significantly with temperature. Thus, a new analytical model is proposed, using a variable coefficient of diffusion, which is used in analytical and FEA simulations. The results obtained show a very good correlation between experimental, analytical and FEA absorption curves.
In addition to being recyclable, wood fiber composites (biocomposites) have interesting mechanica... more In addition to being recyclable, wood fiber composites (biocomposites) have interesting mechanical properties and compete with petroleum based materials in several fields of application (in our paper, we will deal with gearing systems). For this purpose, we will study the behavior of these materials and their modes of damage. This step is required for reliable and safe use of biocomposites. In this work, we developed a biocomposite material with paper industry natural fibers (Birch) mixed with a thermoplastic matrix (polyethylene). Monotonic and cyclic tensile tests were conducted to measure the mechanical properties of the material. The instrumentation of our specimen with acoustic emission sensors was used to assess the damage to our material. For each type of specimen, we conducted five tests. We notice an improvement in both, the elastic modulus and maximum stress by increasing the rate of the fibers. The evolution of damage for the specimens happens in four phases. Therefore, w...
Wood fiber composites (biocomposites) have interesting mechanical properties that can compete wit... more Wood fiber composites (biocomposites) have interesting mechanical properties that can compete with non-degradable materials in several fields of applications. Therefore, it is important to improve the mechanical properties of these environmentally friendly materials. In this work, a biocomposite of polyethylene reinforced with birch tree fibers (the main raw material in the paper industry) is developed and tested both with and without a coupling agent. The mechanical properties of the biocomposite material are measured and some of its properties including its damage modes are investigated. This work is a required step for the reliable and safe use of biocomposites.
The aim of this paper is to analyze the influence of two machining processes on the mechanical be... more The aim of this paper is to analyze the influence of two machining processes on the mechanical behaviour of composite plates under cyclic loading. For this purpose, an experimental study using several CFRP plates drilled with conventional machining and non-conventional machining (abrasive water jet) was carried out. Digital image correlation and static tests using an Instron 4206 tester were performed. In addition, infrared thermography (IR) and fatigue tests were also performed to assess temperature and damage evolutions and also the stiffness degradation. Fatigue results have shown that the damage accumulation in specimens drilled with conventional machining was higher than the abrasive water jet ones. Furthermore, the endurance limit for plates drilled conventionally was approximately 10% higher than those drilled with abrasive water jet. This difference was related to the initial surface integrity after machining induced by the difference in the mechanism of material's remov...
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