José Daniel D. Melo

Viscoelastic Characterization of Transversely Isotropic Composite Laminae

Understanding and designing for damping in composite laminates has become a topic of great interest; unfortunately, only limited viscoelastic property data is presently available. Direct experimental measurement of the three-dimensional viscoelastic properties is not simple to implement and, thus, an approach leading to the complete 3-D viscoelastic characterization using a reduced number of measured parameters is desirable. To address the difficulties related to direct measurement of properties, this work proposes a reduced number of material coefficients, which allow the specification of the viscoelastic constitutive relationships for a transversely isotropic material, based on only five independent dynamic stiffness parameters and three independent damping loss factors. Further, using this model, a method is developed, based on energy equations, which allows the viscoelastic properties to be evaluated from experimental data, collected from three bend-beam oscillatory tests and two measured Poisson’s ratios. The approach is validated through the use of both published data and an experimental investigation conducted using a Dynamic Mechanical Analyzer.

Mechanical behavior of GRP pressure pipes with addition of quartz sand filler

In comparison with steel, concrete, and polymeric pipes, glass-reinforced plastic (GRP) pressure pipes use more expensive raw materials. Thus, despite of their attractive structural performance, mainly in terms of mechanical strength combined with low weight, the higher cost can be a limitation in many applications. In this scenario, an alternative to reduce the final price of GRP pipes is the addition of quartz sand filler. In this experimental and numerical study, filament-wound E-glass/polyester pipes with nominal inside diameter of 300 mm and wall thickness of 5.7 mm were produced with the incorporation of quartz sand as filler and tested to failure under internal pressure. The mechanical behavior of the composite pipes was evaluated experimentally, throughout short-time hydraulic failure pressure tests, as well as using finite element analysis (FEA). In the FEA simulations, the shell wall was modeled as an axisymmetric layered orthotropic material. A good agreement, varying from 96% to 98%, was obtai...In comparison with steel, concrete, and polymeric pipes, glass-reinforced plastic (GRP) pressure pipes use more expensive raw materials. Thus, despite of their attractive structural performance, mainly in terms of mechanical strength combined with low weight, the higher cost can be a limitation in many applications. In this scenario, an alternative to reduce the final price of GRP pipes is the addition of quartz sand filler. In this experimental and numerical study, filament-wound E-glass/polyester pipes with nominal inside diameter of 300 mm and wall thickness of 5.7 mm were produced with the incorporation of quartz sand as filler and tested to failure under internal pressure. The mechanical behavior of the composite pipes was evaluated experimentally, throughout short-time hydraulic failure pressure tests, as well as using finite element analysis (FEA). In the FEA simulations, the shell wall was modeled as an axisymmetric layered orthotropic material. A good agreement, varying from 96% to 98%, was obtained between the average hydraulic failure pressure measured and FEA predicted failure pressures, using Tsai—Hill and Hoffman failure criteria, respectively.

Determination of the Elastic Constants of a Transversely Isotropic Lamina Using Laminate Coefficients of Thermal Expansion

Three-dimensional elastic constants for a fiber-reinforced lamina are often difficult to obtain from traditional mechanical tests. The relationships developed in thiswork enable the determination of any three of the five independent elastic constants, of a transversely isotropic lamina, from measurements of the remaining two elastic constants and the coefficients of thermal expansion (CTE’s) of [(+θ/−θ)n]s and unidirectional laminates. The approach is used to predict the elastic propertiesof a carbon fiber reinforced epoxy material and the predicted properties are shown to be in good agreement with quoted values. Further, the developed relationships can be used to determine elastic constants over a range of temperatures and, potentially, to study the effects of manufacturing on elastic properties. Therefore, this technique constitutes an additional method for evaluating the elastic constants that characterize a transversely isotropic, fiber-reinforced lamina.

Encapsulation of solvent into halloysite nanotubes to promote self-healing ability in polymers

Microcracking during service is a critical problem, which can be particularly detrimental to the durability of polymers and polymer composite structures. Materials with self-healing ability are capable to partially or completely repair damages, thus increasing the life of the structural component. One of the self-healing approaches involves the use of solvents as healing agent, which reacts with the polymer healing microcracks. The objective of this research is to investigate a procedure to encapsulate solvents into halloysite nanotubes (HNT) to promote self-healing ability in epoxy. Autonomic healing would be triggered by crack propagation through the embedded nanotubes in the polymer, releasing the liquid solvent into the crack plane. Two solvents were considered in this work: dimethylsulfoxide (DMSO) and nitrobenzene. A procedure was developed to fill HNT with the solvents, which were then coated using the layer-by-layer technique of oppositely charged polyelectrolytes. Solvent encapsulation was verified by X-ray diffraction, Fourier transform infrared analysis, thermogravimetry, specific surface area (BET), and scanning electron microscopy. The results suggest that the procedure was successful to encapsulate DMSO into the nanotubes.

Time and Temperature Dependence of the Viscoelastic Properties of PEEK/IM7

Understanding viscoelastic properties of composite materials is essential for the design and analysis of many advanced structures. However, experimental viscoelastic characterization of anisotropic materials can be complicated because of the number of independent parameters to be evaluated. Recently, an approach leading to the 3-D viscoelastic characterization of transversely isotropic materials using a reduced number of measured parameters has been developed. The model reduces the number of independent parameters to describe the viscoelastic behavior of transversely isotropic materials, which greatly simplifies the experimental procedures. Based on this recently developed model, the present article evaluates time and temperature effects on the viscoelastic properties of a fiber reinforced lamina. The experimental investigation is conducted on sub-scale specimens loaded in flexure, using Dynamic Mechanical Analysis (DMA) equipment. Ultimately, the approach presented in this work will allow the construction of master curves for the independent viscoelastic parameters that characterize a transversely isotropic material. Therefore, the experimental technique presented in this work provides a means for the study of viscoelastic properties of fiber reinforced composites, and constitutes a valuable contribution to the understanding of time and temperature dependence of these mechanical properties.

Elastic properties of PEEK/IM7 related to temperature

An approach using laminate Coefficient of Thermal Expansion (CTE) measurements and two measured elastic constants is applied to predict the elastic properties of PEEK-IM7 prepreg laminae. This study assesses the feasibility of the use of this method to compute elastic properties over a range of temperatures. Three-dimensional elastic constants of PEEK/IM7 are determined for the temperature range of 20°Cto 120°C. The results indicate good agreement with quoted values measured by standard techniques, at room temperature. Moreover, the technique allows the study of the temperature dependence of the elastic properties over a range of temperatures. Thus, the technique demonstrates an ability to generate elastic properties data for a transversely isotropic material, over a wide temperature range, which ultimately can be used for improved performance prediction of structural composites.

Effect of Fiber Volume Fraction on the Energy Absorption Capacity of Composite Materials

In this investigation, the effect of fiber volume fraction on the energy absorption capacity of fiber-reinforced composite materials was studied using dynamic mechanical analysis measurements. Laminates were fabricated with and without vacuum bag using plain weave E-glass fabric and three types of polymer matrix: epoxy, polyester, and vinyl ester. The higher energy absorption displayed by samples processed under vacuum was related to the shorter distance between adjacent fibers which produces stresses of higher magnitude in the matrix, thus promoting higher energy dissipation. However, when the energy dissipation is divided by the material density, the higher material density of vacuum processed laminates offsets the effects of increased loss modulus at higher fiber volume fraction.

High Energy Mill Processing of Polymer Based Nanocomposites

Polymer matrix nanocomposites have attracted growing attention due to the potential for significantly improving the properties of the polymer by adding a very small amount of nanoparticles. However, the improvement in properties has been related to the degree of dispersion of the nanoparticles in the polymer matrix and, due to their enormous specific surface area, nanoparticles tend to agglomerate. Thus, processing techniques able to produce complete particle dispersion in polymer matrix are of great interest. The purpose of this work is to present a new processing technique for polymer matrix nanocomposites using a high energy mill as an effective approach to disperse ceramic nanoparticles in a polymer matrix. SiO2/epoxy nanocomposites were processed with various SiO2 contents using the proposed approach. Transmission electron microscopy (TEM) micrographs of the nanocomposites processed indicated good particle dispersion. In addition, agglomerates were not observed on the scanning electron microscopy (SEM) fractographs of the nanocomposites, up to 3wt% SiO2. The processed nanocomposites were also characterized by dynamic mechanical analysis (DMA) to investigate the effect of nanoparticles content on the viscoelastic properties and on the glass transition temperature. In summary, the technique was found promising in achieving good levels of particle dispersion in a thermoset polymer matrix.

Mechanical and Microstructural Evaluation of Polymer Matrix Composites Filled with Recycled Industrial Waste

In this study, the influence of the addition of industrial waste of polyester and EVA (ethylene vinyl acetate) on the mechanical properties of polyester resin was studied. Specimens were fabricated and tested for the evaluation of flexural properties and Charpy impact resistance. Properties of the filled materials were measured and compared to those of the plain resin. The effect of particle size and filler content was also investigated. Then, fracture surfaces were analyzed by scanning electron microscopy (SEM). The results indicate reductions in flexural strength and strain to failure with the addition of particulate fillers. However, an increase of about 6% in impact resistance was observed in composites with 12.5 wt% of EVA.In this study, the influence of the addition of industrial waste of polyester and EVA (ethylene vinyl acetate) on the mechanical properties of polyester resin was studied. Specimens were fabricated and tested for the evaluation of flexural properties and Charpy impact resistance. Properties of the filled materials were measured and compared to those of the plain resin. The effect of particle size and filler content was also investigated. Then, fracture surfaces were analyzed by scanning electron microscopy (SEM). The results indicate reductions in flexural strength and strain to failure with the addition of particulate fillers. However, an increase of about 6% in impact resistance was observed in composites with 12.5 wt% of EVA.

Elastic characterization of PEEK/IM7 using coefficients of thermal expansion

Abstract Three-dimensional elastic properties of a PEEK/IM7 unidirectional lamina are determined by an approach using laminate coefficient of thermal expansion (CTE) measurements and two known elastic constants. Specific relationships required to apply the technique and generate material elastic properties are derived from the general equations presented by the authors in a previous publication. The investigation emphasizes the feasibility and practical aspects of using CTE data to determine elastic properties. The room temperature elastic constants determined, based on measured CTEs, are compared with available data from the literature, obtained according to ASTM standard techniques. The approach, based on the CTE measurements, plus unidirectional tensile tests, allows the determination of all of the elastic constants, including the through-thickness Poissons ratio ν23, which is not commonly quoted.