Elastic Properties Of Composites Research Articles

Objective Function Distortion Reduction in Identification Technique of Composite Material Elastic Properties

In studies of structural mechanics, modal analysis, presented in this paper, is an important tool for analyzing the vibration of an object and its frequencies. In modal analysis, different modes of vibration and the frequencies that generate them are considered. The study covers the nondestructive identification of the elastic characteristics of materials, which involves stochastic algorithms and the application of reverse engineering (i.e., the comparison of reference eigenfrequencies with the results of mathematical models). Identification is achieved by minimizing the objective function—the smaller the value of the objective function, the higher the identification accuracy obtained. By changing the parameters of a material’s mathematical model during identification, certain (usually higher order) modes can change places in a natural frequency spectrum. This leads to the comparison of different order eigenfrequencies, slow convergence and poor accuracy of the identification process. The technique involved in this work is the mode-shape recognition of a specimen of material with an “incorrect” set of elastic properties. The results prove that the identification accuracy of a material’s elastic properties can be increased if an “incorrect” set of elastic properties is removed from the identification process. The research covers only numerical research, with a physical experiment simulation.

Correlation between surface-to-volume ratio of the particle shape and elastic properties of the particulate composites

This work is motivated by real-world particle shapes, observed using a scanning electron microscopy. The focus of the presented studies was to understand the influence of the particle shapes on the effective elastic properties of the two-phase composites. For this, particles with polyhedral, undulated and other shapes were numerically modeled using analytical functions. Creation of some shapes, like polyhedral, are known from the literature but Laplace’s spherical harmonics, as well as the Goursat’s surface and some others, were used for the first time to create novel particle shapes. Elastic properties of the composites with different particle shapes were calculated using the finite element analysis. The obtained results show good agreement with mean-field homogenization methods such like Mori-Tanaka and Lielens as well as other numerical results available in the literature. Further, the dependence of the effective Young’s moduli of the composite on the shape and the corresponding surface-to-volume ratio of the particles was studied. It was observed that the effective Young’s moduli increase with the surface-to-volume ratio of the particles in the case where particles are stiffer in comparison to the matrix. It was also remarked that, in the case of particles of similar shapes, the particle surface-to-volume ratio and the effective Young’s moduli differ significantly with the surface curvature and the edge sharpness of the particles.

Effect of tapered natural fiber on elastic properties of sisal fiber-reinforced composite: An experimental and micromechanics approach

In the characterization of natural fiber-reinforced composites, it is crucial to consider the nonuniform cross-section of fibers extracted from plants or leaves, which results from the inherent variation in fiber diameter. This variation is a key aspect of the actual reinforcement behavior, and disregarding it by assuming a uniform cross-section can violate the physical understanding of the composite’s mechanics. This study focuses on characterizing the elastic properties of a natural tapered sisal fiber-reinforced epoxy composite, taking into account the variation in fiber diameter along its length. To achieve this, both experimental, analytical, and micromechanics methods are employed. The experimental approach involves conducting tests to measure the mechanical properties of the composite, while the micromechanics analysis provides a framework to understand the reinforcement behavior and predict the composite’s mechanical response. The study aims to identify and present various elastic properties of the composite, including the longitudinal modulus, transverse modulus, in-plane and out-of-plane shear modulus, and major and minor Poisson’s ratios. The fiber taper angle has a significant effect on longitudinal and transverse modulus and interfacial stresses. The longitudinal modulus experiences a reduction of 25.9% when increasing the taper angle from [Formula: see text] to [Formula: see text] at a higher fiber volume fraction (40%). However, at a lower volume fraction of the same fiber (10%), the reduction in modulus is limited to 5.74%. Similarly, the transverse modulus is also affected by the taper angle. At the higher fiber volume fraction, there is a decrease of 24.52%, whereas at the lower volume fraction and higher taper angle of the fiber, the decrement is 4.94%.

Interplay of liquid particles and interphases on the macroscopic elastic response of Liquid-filled composites

This paper deals with providing the effective elastic response of three-phase composites consist of a matrix filled with a random suspension of liquid-filled capsules firmly bonded to the matrix in the realm of small deformation theory. The capsules shell (interphases) and the matrix are considered to be elastic solids and the liquid is considered ideal. For this purpose, the solution for dilute concentrations of the interphases and the liquid particles are derived analytically. Then, the dilute solution is passed to an iterative technique to generate the non-dilute version of the solution. The non-dilute response is available in terms of a system of two nonlinear-coupled-ODE-initial-value problems. The results are confronted with the results of a 3D full-field FE analysis and experimental data and a good agreement is observed. The solution, provided here for polydisperse microstructures, allows for considering different thicknesses for the interphases and in turn can possibly account for different physical phenomena like the size and the surface tension effects. A comprehensive study on the effects of interphases (capsules shell) thickness and mechanical properties as well as the volume concentration of the capsules and the liquid particles on the overall elastic properties of three-phase liquid-filled composites are carried out. We show that although the addition of liquid particles to the matrix has deteriorating effects on the overall elastic properties of the composites, proper selection of the interphases can compensate for these negative effects.

Predict Elastic Properties of Fiber Composites by an Artificial Neural Network

Predict Elastic Properties of Fiber Composites by an Artificial Neural Network

A particular manner to observe free-edge effects in hybrid elastomer/composites plates

Hybrid elastomer/composite sandwich plate structures are typically used where simultaneously both lateral stiffness and shear flexibility are required. In these hybrid structures, however infinitesimal strains take place in laminated composite layers, but elastomer layer is under hyper-elastic strains. The present work aims to adapt an individual two-step technique to examine three-dimensional stress field in this plate to observe free-edge effects in composite layers. For this purpose, at the first step, employing elastic equivalent properties for the composite layers and nonlinear elastic properties for elastomer layer, large deformation finite element analysis is performed for the hybrid structure by ameliorate an available open source code named FLagSHyp. This analysis provides the load distribution at elastomer-composite interface. Next, using this external load distribution on composite layers, based on Kantorovich technique a detail analysis is proposed to study free edge effect in composite layer. The results are verified numerically and/or experimentally and vital observations involving free-edge effects are reported.

An analysis of composites with two-dimensional decagonal quasicrystal matrix and spheroidal inclusions

Eshelby tensors in elasticity are obtained for two-dimensional (2D) decagonal quasicrystal containing an ellipsoidal inclusion. Based on the intrinsic strain formula and Mori–Tanaka theory, the effective elastic properties of 2D decagonal composites are obtained. The effects of inclusion volume fraction and inclusion aspect ratio on elastic properties of composites with 2D decagonal quasicrystal are discussed.

Effect of interphase thickness and fiber diameter on elastic properties of composites using multi-scale modelling

Composite materials are the largely used engineering materials in aerospace and automobile industries due to their high specific strength and high specific stiffness. The composites’ properties are essential for the design and development of the machine parts. They vary with fiber content, fiber properties, matrix properties, and type of manufacturing process. More experiments are required to obtain the properties and the best combination of fibers and matrices. However, several analytical methods are available to find the properties of the composite to avoid the number of experiments. In the present study, the properties of CFRP, GFRP, Amino-functional multi-walled carbon nano-tubes (CNT) added CFRP, CNT added GFRP composites have been calculated using the properties of fiber, interphase between fiber and matrix, matrix, and CNT. The properties of CNT added epoxy are obtained using the Halpin-Tsai equation in the first stage. In the second stage, the properties of interphase are calculated using the properties of CNT added epoxy and fiber properties. In the third stage, the properties of CFRP and GFRP are calculated using three phase constitutive model by considering the properties of fiber, interphase, and CNT added matrix. The properties are calculated at fiber diameters: 8 μm and 14 μm while varying the fiber volume fraction (%): 0 to 70%, interphase thickness: 50 nm to 500 nm, the weight fraction of CNT (%) added in epoxy: 0 to 5%. The addition of CNT has improved the elastic properties of CFRP and GFRP. The elastic properties of the composites are improved significantly with an increase in the interphase thickness.

Improved Voigt and Reuss Formulas with the Poisson Effect

The Poisson effect, measured by the Poisson’s ratio, plays an important role in the regulation of the elastic properties of composite materials, but it is not considered in the conventional Voigt (iso-strain) and Reuss (iso-stress) formulas, which explains why the formulas are inaccurate even if the iso-strain or the iso-stress conditions are satisfied. To consider the Poisson effect, we derived a set of new formulas based on the governing equations of elasticity. The obtained formulas show greater mathematical complexity. To further understand how the Poisson effect influences composite elastic properties, two types of finite element models (FEM) were constructed to simulate the situations where the Poisson effect does or does not have an influence. The results show that the conventional Voigt and Reuss formulas are special cases of the newly derived ones. The Poisson effect induces secondary strains and stresses into the phase materials, which demands more strain energy to achieve the same deformation in the primary (loading) direction, and thus increases composite stiffness; the magnitude of the increase is dependent on the contrast of phase properties. The findings may have significant impact on the study of the emerging nanocomposites and functionally graded materials, where the conventional Voigt and Reuss formulas have wide applications.

X-ray CT based multi-layer unit cell modeling of carbon fiber-reinforced textile composites: Segmentation, meshing and elastic property homogenization

Generation of realistic finite element method (FEM) geometry of a textile composite material at tow scale remains a challenging stage of material modeling. In this paper, a FE model generation approach is introduced, based on micro-Computed Tomography (µ-CT) images of a carbon fiber reinforced textile composite with multiple layer orientations. For the specified laminate layup made of plain weave fabric layers, a tow instance segmentation method based on deep learning was proposed. The fiber local orientation field was extracted from the tow centerlines approximation. For the image-based finite element meshing, a material interface reconstruction algorithm was proposed. The algorithm leads to a conformal and smooth finite element (FE) mesh with high-quality elements. FE models with voxel and tetrahedral meshes considering different approximations of the material orientation field were generated and used for numerical homogenization of the composite material's elastic properties.

Nonlinear Thermoelastic Numerical Frequency Analysis and Experimental Verification of Cutout Abided Laminated Shallow Shell Structure

Abstract The cutout and temperature loading influences on the nonlinear frequencies of the laminated shell structures are predicted numerically using two different types of geometrical nonlinear strain-displacement relationships to count the large deformation. The displacement of any generic point on the structural panel is derived using the third-order shear deformation theory (TSDT). Moreover, the direct iterative method has been adopted to obtain the nonlinear eigenvalues in conjunction with the isoparametric finite element (FE) steps. The present analysis includes the effect of temperature and the temperature-dependent composite elastic properties on the thermoelastic frequencies. This study intends to establish the Green-Lagrange type of nonlinear strain's efficacy in computing the nonlinear frequency of layered structure with and without cutout instead of von-Karman strain kinematics. The numerical model's validity has been established by comparing the results to previously published results. In addition, experimentally obtained fundamental frequency values of a few modes are compared to numerical proposed numerical results under the thermal loading. Finally, the effects of cutout (shape and size) and the associated structural geometrical parameters on the nonlinear thermal frequency responses of the laminated structure are expressed in the final output form.

A functional triboelectric nanogenerator based on the LiCl/PVA hydrogel for cheerleading training

ABSTRACT Triboelectric nanogenerators (TENGs) are a novel energy harvesting, sensing system, and information systems device. This work describes the construction of the lithium chloride (LiCl)/polyvinyl alcohol (PVA) hydrogel triboelectric nanogenerator (LP-TENG) with easy manufacturing, excellent electrical output, and a wide range of sensing applications. The addition of LiCl powder enhances the PVA hydrogel crosslinking and increases the composite hydrogel's elastic properties. Additionally, the LiCl powder generates microchannels on the hydrogel's surfaces, which enhances ion transport and adds triboelectric outputs through a streaming vibration possible mechanism. Following the single-electrode mode, the LP-TENG's open-circuit voltage reaches up to 276 V. Due to good tensile properties, the LP-TENG shows a monotonically increasing relationship between extensible length and output voltage. Therefore, the remarkable stretchability and ultrahigh sensitivity to mechanical stimulation of the LP-TENG are used to illustrate applications in cheerleading monitoring and human mechanical energy obtaining.

Predicting the mechanical behaviour of structural supercapacitor composites

Multifunctional structural power composites may transform transport electrification, and other applications, but require performance and reliability improvements. Computational modelling has the potential to accelerate their development and deployment. This work addresses the lack of predictive models for the mechanical behaviour of structural supercapacitor composites exploiting carbon aerogel-modified carbon fabric electrodes. The elastic behaviour was investigated using finite element analysis of quasi-meso-scale periodic unit cell models, considering the effects of constituent properties, defects, stacking geometry, and boundary conditions. Nanoindentation was used to evaluate the Young’s modulus of carbon aerogel. Parametric modelling demonstrated a strong influence of the ply offset and matrix materials on the composite elastic properties. The initial numerical results overpredicted the actual performance measured from tensile and in-plane shear experiments in the literature. Optical, scanning electron and micro X-ray imaging revealed extensive pre-cracking and voidage in the physical laminates. Additional computational investigations showed that the pre-cracks were associated with a degradation of shear stiffness. The remaining performance gap was attributed to voidage. The present study highlights that challenges for mechanical performance and its prediction stem from the presence of processing defects and a lack of in-situ material data. Nevertheless, the models identify the potential of hierarchical laminates containing aerogels to generate sizable performance improvements, both in multifunctional and purely structural contexts.

Improving the mechanical and damping properties of polymer/memory alloy composite by introducing nanotubes covered with nano-scale Ni particles

Ni@CNT reinforced polymer/memory alloy damping composites were successfully fabricated by filling a porous CuAlMn shape memory alloy skeleton structure using polyurethane/epoxy interpenetrating network matrix. As 4 wt% Ni@CNT is dispersed in the polymer matrix, the loss factor (ratio of loss modulus to storage modulus) of the composite is above 0.09, and the maximum value can reach 0.156, at the whole test frequency (0.1 ∼ 200 Hz) and temperature (-10 ∼ 100 ℃) range. Meanwhile, its elastic modulus can reach 1137.9 MPa and the density is only 2.04 g/cm3. Compared with polymer/memory alloy composite, the average loss factor and elastic modulus of the prepared composite increased by 40.1% and 33.4%, respectively. A triphase damping model and a mechanical model were used to investigate the damping mechanism and elastic properties of composites, respectively. Calculation and simulation results indicated that the damping capacity of the Ni@CNT/polymer/memory alloy composite is basically related to interfacial dissipation, which is significantly enhanced via introducing nanotubes covered with nano-scale Ni particles. Due to the light weight, certain strength, good deformation resistance and excellent damping performance, this nanocomposite has potential applications in the damping field of aerospace.

Notch-type damage influence on the frequency of the principal mode of the composite cantilever beam flexural vibrations

The results of calculation investigations aimed at the determination of the influence mechanisms of the surface damage in the form of a rectangular notch and fibers’ orientation on the frequency of the principal mode of the composite cantilever beam flexural vibrations are presented. The three-dimensional finite element model of the beam made of the unidirectional carbon-fiber-reinforced plastic with the local surface rectangular notch-type damage has been developed using the effective modulus concept to determine the composite material elastic properties. Its adequacy is corroborated via the comparison of the determination results of the principal frequency of flexural vibrations of the intact beam as a function of the degree of anisotropy in composite material with the known experimental data. In this paper has been found the mechanisms of influence of the damage parameters (notch depth and its location along the beam length) and the degree of anisotropy of the elastic properties in composite material, which is defined by the angle of the fibers, on the variation of the frequency of the principal mode of flexural vibrations. It is established that there is such a notch location along the beam length for its specified depth and width, the so-called transition point, where the natural frequency of vibrations of the damaged and intact beams are equal independent of the angle of the fibers. This fact indicates that there is a simultaneous damage effect on both the variation of flexural stiffness of the beam and its inertia properties. The location of the transition point depends on the notch depth and fibers’ orientation. With the larger distance of the notch from the transition point to the free end, the principal frequency of vibrations of the damaged beam becomes larger as compared with that one for the intact beam.

Characterization of Woven Composite Material Properties by Using an Inverse Technique Based on Vibration Tests

A mixed numerical-experimental technique based on vibration tests is modified and applied to determine the elastic material properties of woven composites. This non-destructive technique consists of physical experiments, numerical modelling and material identification procedure. For the purpose of characterization, two carbon fiber panels were prepared by manual layout technology. An evaluation of the accuracy of woven composite elastic properties is executed comparing the numerical and experimentally obtained resonant frequencies.

Effect of statistical scatter in the elastic properties on the predictability of first ply failure of a polymer composite pressure vessel

Statistical variations in the elastic properties of composites are unavoidable. This work is concerned with the assessment of the probabilistic first ply failure of pressure vessel in response to the variations of elastic properties of T700 carbon/epoxy composite among the published literature. Initially, deterministic failure pressure is estimated using Finite Element Analysis software ANSYS. The uncertainties with respect to elastic properties are quantified by using Statistical software MINITAB. Then, the probability design system platform in ANSYS software has been utilized to perform probabilistic failure analysis by Monte Carlo simulations. The statistical results in terms of the mean and standard deviation of first ply failure pressure are computed. The probabilistic first ply failure pressure range determined is within 3 limits with 99.997% confidence level. It is helpful to the designers to assess the factor of safety in the case of anticipated variations in properties.

Study of the structure and properties of cermets based on the NiAl–Al<sub>2</sub>O<sub>3</sub> system

The powder metallurgy method including mechanical activation of powders in a planetary mill and spark plasma sintering at 1470 °C in an inert atmosphere was used to obtain NiAl–45vol.%Al2O3 cermet samples with the addition of nanoparticles of magnesium aluminum spinel in an amount of 0.05 vol.%. The features of their microstructure were investigated. Spinel nanoparticles are located at the boundaries between the grains of composite components. The results of X-ray phase analysis at t = 25 and 800 °C were obtained. The main components of the material at t = 20 °C are α-Al2O3 and NiAl. The dependence of internal friction on temperature in the range of 20–900 °C was studied, and the influence of magnesium aluminum spinel nanoparticles on the nature of its change was established. The internal friction curve shows that vibration damping occurs up to 600 °C. Dependences of the ultimate bending strength of cermets at t = 20÷750 °C were determined. The positive effect of introducing a small amount of magnesium aluminum spinel on the elastic properties of composites was established. The best mechanical properties were demonstrated for NiAl–42vol.%Al2O3–0.05vol.%MgAl2O4 samples. On average, the ultimate bending strength of this material was 8–15 % higher compared to samples without nanoparticles. The materials obtained in this research had an ultimate bending strength under normal conditions of 460–490 MPa. A summarizing analysis of NiAl–Al2O3 cermet researches was carried out to determine the nature of the ultimate bending strength dependence on the ratio of components. It was found that it has an extreme nature: the maximum is observed when using the ratio of aluminum oxide to aluminum nickel equal to 0.5.

The elasticity of the polymeric composite material with orthotropic structure

The preparation of orthotropic polymeric composite is described. Method is based on curing the epoxy resin with nickel carbonyl nanoparticles (the content up to 35 vol.%) directly in the magnetic field B ≈ 0.2 T. The noticeable anisotropy of composite elastic properties is proved by the measurements of Yung's modulus of the disk and plate-shaped samples.

Modeling Elastic Properties of Composites using Asymptotic Averaging Method with Imperfect Interface

The paper presents a modification of the asymptotic averaging method for solving the homogenization problem of elastic properties for composite materials. The elasticity of the phase interface is taken into account. The conditions of a soft imperfect interface are considered, which account for a displacement jump on the phase boundary. A review of the interface-modeling methods in composite materials is presented. The finite element method is used for the numerical implementation of the averaging method. A model of a interface finite element is proposed. Elastic properties averaging is adapted to the presence of a discontinuity in the displacement field. Application limits of the soft imperfect interface are estimated in terms of interphase layer properties. The identification of the interface parameters using experimental data is considered. Computational experiments are conducted for dispersed-reinforced and unidirectional composite with isotropic inclusion.