Experimental investigation on mean crushing stress characterization of carbon–epoxy plies under compressive crushing mode

A challenge in numerical simulation of crashworthiness study is to be able to predict the crush damage modes, their evolution during crushing and the energy absorption in any composite structure from elementary material characterisation data. Therefore, it is important to know the behavior of one ply subjected to crushing load, and especially to determine the mean crushing stress that could be used for simulation. For that purpose, quasi-static crushing tests are performed for different configurations of two CFRP materials, UD and fabrics to determine the mean crushing stress of plies alone and inside a laminate. This study shows there is a linear relationship between crushing load and the contact surface of the plies being crushed on a metallic base which enables actually to define a mean crushing stress for a ply. The method to calculate this value is presented in this paper, based on image analysis of specific crushing tests. Experimental results show that for the UD material, the mean crushing stresses in 0° and 90° plies are very close. The value for a balanced fabric is also similar, approximately 270 MPa

Effect of fiber misalignment on tensile response of unidirectional cfrp composite lamina

Mechanical responses and failure of fiber-reinforced polymer (FRP) composite laminates could be predicted using the validated finite element (FE) simulation. The material constitutive and damage models employed in the simulation are developed based on the properties of the unidirectional lamina, including those obtained through tension tests. Such computational model assumes perfectly aligned fibers in the lamina. In this respect, this paper examined the effect of fabrication-inherited fiber misalignment on the tensile response of the unidirectional lamina. For this purpose, a series of tension tests are performed on unidirectional carbon fiber-reinforced polymer (CFRP) composite lamina specimens with different gage lengths ranging from 50 to 150 mm. Fiber misalignment is quantified to be 7o and represents the nominal deviation of the fibers from the reference longitudinal axis direction. Load-displacement responses of the specimens are compared. Results show that the nominal tensile strength of the lamina is 1089±33 MPa. The elastic modulus, however, increases from 36.96 to 55.93 GPa as the gage lengths vary from 50 to 150 mm, respectively. This is due to the induced bending effects on the reinforcing fibers that is greater for longer gage lengths. Multiple fiber fracture events, each is depicted in a noticeable load drop, are recorded throughout the tensile loading of long lamina specimens. Although the load at fracture is accurately reproduced by the FE simulation using the damage-based mesoscale model, the effect of fiber misalignment could not be captured

Etude expérimentale et numérique de l'écrasement de stratifiés composites à base de fibres de carbone

L un des défis de la simulation numérique de la résistance au crash des structures composites est de pouvoir prédire les endommagements, leur évolution au cours de l écrasement et l'énergie absorbée, à partir d'un nombre limité de propriétés matériau. Le but de cette étude est d'améliorer la compréhension des mécanismes élémentaires impliqués dans l'écrasement de stratifiés de plis unidirectionnels à base de fibres de carbone et de développer un modèle numérique. Des essais sont réalisés à différentes échelles (macro, micro), et conduisent à la définition d'une nouvelle propriété matériau, essentielle : la contrainte moyenne d'écrasement que peuvent soutenir les plis à 0 ou 90, et la méthode de caractérisation associée. L analyse des tests montre également que pour représenter correctement le comportement du matériau pendant le crash (évasement, fragmentation...), il est nécessaire de choisir un modèle à l échelle méso. Le modèle éléments finis développé repose sur cinq idées principales : 1-mailler chaque pli; 2-utiliser des éléments cohésifs pour représenter le délaminage et l évasement des plis; 3-pouvoir représenter la rupture des plis en gros fragments; 4-représenter l'écrasement localisé des plis, à leurs extrémités, par l'introduction d'un concept de free-face-crushing , associé à un critère spécifique basé sur la contrainte moyenne d'écrasement; 5-représenter les contacts entre plis, plis etsocle, plis et débris. Ce modèle phénoménologique est ensuite appliqué à la simulation du crash de plaques stratifiées. A partir des propriétés matérielles élémentaires du pli, il permet de prédire la force, les principaux mécanismes de rupture et la phénoménologie observée lors des expériences.A challenge in numerical simulation of crashworthiness is to be able to predict the crush damage modes, their evolution during crushing and the energy absorbed in any composite structure from a limited number of material properties. The aim of this study is to improve the understanding of the elementary mechanisms involved in the crushing of CFRP laminates made of unidirectional plies and to develop a numerical model. Crushing tests are performed at different scales (macro, micro), and lead to the definition of a new essential material property: the mean crushing stress that a 0 or 90 ply can support, and its associated characterization method. Tests analyses also show that to correctly represent the material behavior during crushing (splaying, fragmentation ) it is necessary to choose a mesoscale model. The Finite Element model developed in this thesis is based on five main ideas: 1-Meshing of each ply of the laminate; 2-Use of cohesive elements to represent delamination and plies splaying; 3-Possibility to represent failure of pliesinto big-sized fragments; 4-Representation of the localized crushing of plies, at their extremities, with the introduction of a free-face-crushing concept associated to a specific criterion based on the mean crushing stress; 5-Representation ofcontacts between plies, plies and impacted base, plies and debris.This physically based model is then applied to the simulation of the crushing of laminated plates. From elementary material properties of the ply, it allows to predict the force, the main failure mechanisms and the phenomenology observedduring crushing experiments.TOULOUSE-ISAE (315552318) / SudocSudocFranceF

Mechanical properties of bamboo and bamboo composites: a review

This article discuses on the studies that have been done by previous researchers on the mechanical properties of bamboo. Nowadays, natural fibre composites have gained the attentions of many industries as alternative materials due to their various advantages such as sustainable, abundant, low cost and good specific strength. With the current emphasis on environmental friendliness and sustainability, natural fibre composites are more preferred over conventional fibre which is normally non-biodegradable. Bamboo is a type of natural fibre composites that are widely used in many industries such as in construction and furnishing. Hence, it is crucial to study the mechanical properties of bamboo to make sure it is safe for certain applications. However, there are many factors that determine the mechanical properties of bamboo such as species, age and so on. This journal compiles and reviews on some of the researches on the mechanical properties of pure bamboo and bamboo composites such as their tensile properties, compressive properties, impact strength and fracture toughness. The reviews include how the researchers set up their experiments, the bamboo species used and the results obtained. Since bamboo are constantly exposed to harsh environment such as rain and river, the effect of moisture/ water content on the mechanical properties of bamboo are also reviewed and it exposed that moisture content has drastic effect on the mechanical properties of bamboo

Finite element simulation of 0°/90° CFRP laminated plates subjected to crushing using a free-face-crushing concept

This paper describes the development of a numerical model of (0°/90°) CFRP plates subjected to low velocity crushing, based on physical observations. The developed model is represented at the meso-scale and is based on five main ideas: 1 – meshing of each ply of the laminate; 2 – use of cohesive elements to represent delamination and plies splaying; 3 – simulation of macro-scale fragments; 4 – representation of the localized crushing of plies at their extremities with the introduction of a free-face-crushing concept; 5 – representation of contacts between plies, plies and impacted base, plies and debris. The results of the Abaqus/Explicit simulations show a good agreement with the experimental results, which demonstrates that the proposed methodology is able to predict the force, the main failure mechanisms and the phenomenology observed during experiments. Furthermore, an analysis of the repartition of absorbed energies is done, which shows that the most efficient mechanism is the localized crushing in the 0° plies

Displacement rate effects on the mode II shear delamination behavior of carbon fiber/epoxy composites

This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness GIIC increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher GIIC . Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment

The geoaccumulation index and enrichment factor of mercury in mangrove sediment of Port Klang, Selangor, Malaysia.

Mangrove areas are important to the ecosystem. One of its crucial functions is as a sink of pollutants, especially metal ions. However, the accumulation of metals in mangrove sediment can generate negative impacts on plant growth, microbial activity, and soil fertility. Apart from that, the severity of the impact is highly influenced by the type of metal found in the sediment and the quality of sediment itself. One of the metals that have adverse effects on the environment is mercury. The objectives of this study are to determine the concentration and distribution of mercury and to assess the enrichment of mercury in Port Klang mangrove sediment by using geoaccumulation index and enrichment factor. Sediment samples were collected from 30 sampling points that cover Langat River and Klang River estuaries, Lumut Straits, Pulau Klang, and Pulau Indah. During sampling, water parameters such as pH, salinity, electrical conductivity, and total dissolved solids were measured in situ, whereas the total mercury in sediment samples was determined at the laboratory using inductively coupled plasma mass spectrometry. In this study, mercury was found to be concentrated along Lumut Strait especially in the mixing zone near the confluence of Langat River and at the jetty to Pulau Ketam. The geoaccumulation index and enrichment factor (calculated using logarithmized data of the reference element) found that three stations were enriched with mercury. In addition, geoaccumulation index was also observed to be more objective compared to enrichment factor whose results were influenced by the concentration of reference element used

Experimental and Numerical Investigation of CFRP Composite Laminates under Crushing

L’un des défis de la simulation numérique de la résistance au crash des structures composites est de pouvoir prédire les endommagements, leur évolution au cours de l’écrasement et l'énergie absorbée, à partir d'un nombre limité de propriétés matériau. Le but de cette étude est d'améliorer la compréhension des mécanismes élémentaires impliqués dans l'écrasement de stratifiés de plis unidirectionnels à base de fibres de carbone et de développer un modèle numérique. Des essais sont réalisés à différentes échelles (macro, micro), et conduisent à la définition d'une nouvelle propriété matériau, essentielle : la contrainte moyenne d'écrasement que peuvent soutenir les plis à 0° ou 90°, et la méthode de caractérisation associée. L’analyse des tests montre également que pour représenter correctement le comportement du matériau pendant le crash (évasement, fragmentation...), il est nécessaire de choisir un modèle à l’échelle méso. Le modèle éléments finis développé repose sur cinq idées principales : 1-mailler chaque pli; 2-utiliser des éléments cohésifs pour représenter le délaminage et l’évasement des plis; 3-pouvoir représenter la rupture des plis en gros fragments; 4-représenter l'écrasement localisé des plis, à leurs extrémités, par l'introduction d'un concept de « free-face-crushing », associé à un critère spécifique basé sur la contrainte moyenne d'écrasement; 5-représenter les contacts entre plis, plis etsocle, plis et débris. Ce modèle phénoménologique est ensuite appliqué à la simulation du crash de plaques stratifiées. A partir des propriétés matérielles élémentaires du pli, il permet de prédire la force, les principaux mécanismes de rupture et la phénoménologie observée lors des expériences.A challenge in numerical simulation of crashworthiness is to be able to predict the crush damage modes, their evolution during crushing and the energy absorbed in any composite structure from a limited number of material properties. The aim of this study is to improve the understanding of the elementary mechanisms involved in the crushing of CFRP laminates made of unidirectional plies and to develop a numerical model. Crushing tests are performed at different scales (macro, micro), and lead to the definition of a new essential material property: the mean crushing stress that a 0° or 90° ply can support, and its associated characterization method. Tests analyses also show that to correctly represent the material behavior during crushing (splaying, fragmentation…) it is necessary to choose a mesoscale model. The Finite Element model developed in this thesis is based on five main ideas: 1-Meshing of each ply of the laminate; 2-Use of cohesive elements to represent delamination and plies splaying; 3-Possibility to represent failure of pliesinto big-sized fragments; 4-Representation of the localized crushing of plies, at their extremities, with the introduction of a free-face-crushing concept associated to a specific criterion based on the mean crushing stress; 5-Representation ofcontacts between plies, plies and impacted base, plies and debris.This physically based model is then applied to the simulation of the crushing of laminated plates. From elementary material properties of the ply, it allows to predict the force, the main failure mechanisms and the phenomenology observedduring crushing experiments

Numerical modelling strategies for composite structures crashworthiness: a review

The crashworthiness test programs used to validate the design variants through experimental works has caused the design costs increase drastically. In the meantime, the growth in computer performance resources and new explicit finite element codes has given the opportunity to use such tools to address the design issue and the crashworthiness problem by developing numerical modelling to minimize the experimental tests costs. As a result, extensive crushing simulations for composite structures had been conducted and reported in the open literature. In this paper, it distinguished the state of the art in composite crashworthiness numerical modelling studies. Different approaches and methodologies such as modelling scales, failure modelling and architecture of crushing simulation have been studied where these factors could affected the outcomes of the simulations result for the crash analysis significantly

Enhancement of electrical, mechanical and thermal properties of silicone based coating with aluminatrihydrate/silica for ceramic insulators

The present work explores durability enhancement in various properties of room temperature vulcanized silicone rubber (RTV-SiR) coating with the incorporation of alumina trihydrate (ATH) and silica (SiO2) fillers. Test samples i.e., neat RTV-SiR, RTV-SiR +10% μSiO2, and RTV-SiR filled with micro-ATH/SiO2 (10% each) were chosen for experimentation. Long-term (10,000 h) lab aging of composite coatings is performed under bipolar direct current (DC) voltage with simulated environmental stresses in a test chamber. The effect of fillers against stresses is quantified through characterization results comparison of filled composites with unfilled RTV-SiR samples. Moreover, the polarity effect on degradation is evaluated through the relative performance of each composite under the positive and negative polarity of the voltage. Findings revealed that samples filled with a mixture of additives bring enhanced improvement into the base matrix of RTV-SiR. Amongst unfilled and micro-silica filled specimens aged under positive DC, the samples S-3 with combined silica-ATH fillers offered superior hydrophobic behavior showing hydrophobicity class HC3 and demonstrated a minimum final leakage current of 6.13 μA. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) results showed relatively lower variations in the chemical and morphological structure of cross-filed specimens (S-3). Furthermore, results of mechanical properties (tensile strength, elasticity, and weight) show a significant loss, whereas the hardness of composite increased with aging. Hybrid samples (S-3) exhibited the minimum deviation of 29.77% and 43.12% in tensile strength and elongation-at-break (EAB), respectively under positive DC voltage. Similarly, it shows enhanced resistance against weight loss and change in hardness due to aging. Moreover, thermogravimetric analysis (TGA) confirmed that filled composite gets enabled to offers the least alteration in thermal properties. In the context of the polarity, positive DC voltage incurred more devaluation of desirable properties as compared to negative polarity