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Wood is a versatile material extensively utilized across industries due to its low density, favorable mechanical properties, and environmental benefits. However, despite considerable research, the diversity in species with varying compositions and properties remains insufficiently explored, particularly for native woods. A deeper understanding of these differences is crucial for optimizing their industrial applications. This study investigated the composition, tensile strength, flexural strength, Young's modulus, bending stiffness and elongation at break, thermal behavior, and viscoelastic properties of three Brazilian native wood species: Araucaria angustifolia (ARA), Dipterix odorata (DOD), and Tabeuia ochracea (TOC). The density of these woods showed a linear correlation with mechanical properties such as Young's modulus (0.9) and flexural modulus (0.9). The research revealed a linear correlation between the woods' density and mechanical properties, with lignin content emerging as a key determinant of thermal stability. This study highlights the importance of understanding wood species' composition and physical properties, and provides valuable insights into their behavior. [ABSTRACT FROM AUTHOR]

In polymer composites, the porosity acts mainly as a stress concentrator, which has detrimental effects depending on the shape and position of the voids. Also, the presence of voids is detrimental to the mechanical properties, which results in the need for an accurate method for their characterization in terms of morphology, position, and volume fraction. The aim of this study was to establish an appropriate procedure for the measurement of voids in a polymer composite using the mercury porosimetry technique. Data were also collected using the Taguchi approach. Subsequently, the feasibility of applying the Hg porosimetry methodology was confirmed through a comparison with standard techniques. Statistical analysis was used to determine the best Hg porosimetry parameters and pressures between 203 and 231 MPa was found to generate reliable results for the maximum porosity measurement, with no dependence on other parameters. Since the Hg porosimetry, acid digestion, and optical microscopy methods provided porosity results with a statistically significant similarity, it can be concluded that all these methods are feasible for the analysis of voids. Finally, potential benefits of the proposed porosity analysis methodology were highlighted through the characterization of the void volume, position, and morphology., INTRODUCTION The control of pore formation in a polymer composite is dependent on a successful infusion process, particularly in the case of materials for primary structural applications [1, 2], Void [...]

The mechanical properties of composite structures depend on the preform impregnation and a successful impregnation can be achieved using the permeability relation in the case of an infusion process. The objective of this study is to develop an analytical model to predict the permeability K of carbon and glass fabrics through hybrid laminate using different stacking sequence, applying an average-permeability model. Preforms permeabilities were evaluated through tortuosity and void-volume fraction. The model allows the analysis of different stacking sequence combinations (interleaved and in block), measuring the contribution of each material type. As a result, hybrid average-permeability model was validated through experimental permeability tests, dimensionless permeability, and tortuosity results, besides enabling predictions of the flow front behavior with, INTRODUCTION Resin transfer molding (RTM) is an attractive manufacturing process for composites. It provides many advantages for industrial processes: relatively low costs, reduced processing time, and ability to produce complex [...]

The industry of composite materials has grown in the last decade due to the requirements of light and high strength materials. The increasing demands of materials have to comply with low greenhouse gases emissions (GHG) as stated by international agreements, and reusing and recycling is a path to minimize the environmental impacts. This research aims to analyze the variables that influence the tensile strength of discontinuous laminate composites of short fibers from cutting operation process which is in the context of reusing. These variables were part of the equation of force equilibrium that involves shear strength failure criterium approach. In addition, the failure analysis and the results were compared with the literature data. Composites of glass fiber fabric wastes with varied fiber length (defined as short fiber) was designed and tested using polyethylene terephthalate (PET) as a matrix. A total of three different laminates with different fabric lengths were evaluated, totaling of seven interruptions/discontinuities along the thickness of each laminate. An image analysis of the failure sequence aided to assess the laminate behavior by comparing the stress–strain curve shape and they were in agreement with the results provided by the developed equation. The results show that this equation enables to identify the variables that influence the laminate strength: yielding stress; interface strength; stress concentration; and peel stress. In this particular research, the weak interface contributed to the low tensile strength of the laminates, and showed less influence of the "critical length," limiting the micromechanical approach that considered a fiber filament. [ABSTRACT FROM AUTHOR]

The environmental and social concerns regarding environmental‐friendly materials lead to alternatives in replacing synthetic fibers for natural ones on polymeric composites. This study focused on modeling dynamic mechanical curves of kenaf/polyester composites using response surface methodology (RSM). Composites with three different reinforcement contents (13.5, 22.33, and 36.27 vol%) were produced and subjected to the dynamic mechanical analysis (DMTA). From the experimental DMTA curves, a 3D surface plot using RSM was done. The results showed that the fiber dynamic mechanical behavior and fiber/matrix interface had a low influence on the glass transition temperature but significantly changed the tan δ peak height. On the other hand, the kenaf fibers presented an enormous difference in the elastomeric region. The constrained region (calculated using the tan delta height) increased ~4 times for the composite reinforced with 36.27 vol% when compared to the composite reinforced with 13.5 vol%. The RSM enabled the viscoelastic modeling using different fiber volumes with high reliability and low error (R2 > 0.99). The RSM approach proved to be an intelligent and reliable technique to access a higher range of results, reducing experimental time and cost and keeping statistical significance. Also, the present methodology can be extended to model other properties and/or optimize parameters. [ABSTRACT FROM AUTHOR]

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This work has been developed for a comparative purpose concerning the processing and respective mechanical performance of CFRP composites processed by resin transfer molding (RTM) and compression molding (CM) techniques. Thermal and viscosimetric tests before processing certified the optimal parameter procedure. Both composites were submitted to short-beam shear tests and through microscopy to determine failure mechanisms. CM specimens presented a decrease of 27% in shear strength caused by the presence of macro porosity that induced crack initiation and connection of different delamination plies, causing the speeding up of crack propagation and jump of the interlaminar layer. The low capillary effect and higher viscous force were responsible for macro porosity, inducing heterogeneous impregnation in CM and to the direction reduce in mechanical behavior. On the other hand, more homogeneous impregnation in RTM specimens was responsible for the absence of macro porosity, ensuring higher values of shear strength and lower void volume fraction. [ABSTRACT FROM AUTHOR]