Elastic Properties Of Composite Materials Research Articles

Investigation on the torsional property of hybrid composite/metal shafts at different service temperatures: Experimental and analytical study

AbstractTorsional tests were conducted to investigate the influence of service temperature on torsional property of composite/steel hybrid structures. In the experiment, two types of lightweight hybrid composite‐metal shafts were tested at both room temperature and various elevated temperatures up to 150°C, including hybrid shafts with and without a metal core. Consequently, the torsional stiffness of the two hybrid shafts at different temperatures was calculated based on the recorded angular deformation‐torque curves. The experimental results revealed a significant decrease in the torsional stiffness of the hybrid shaft without metal core as the increase of service temperature, while the torsional stiffness of the one with metal core remained almost unchanged, especially at high temperatures. In addition, a finite element model was proposed to predict the torsional behavior of the hybrid shafts at different service temperatures. In the model, an empirical equation was introduced, and micromechanical method was adopted to determine the temperature‐dependant elastic properties of composite material and adhesive layer in the hybrid structure. Then, the predicted torsional property was compared to the experimental results for model verification.Highlights Two types of hybrid composite‐metal shafts are designed and manufactured. Torsional tests are conducted at both room and elevated temperatures up to 150°C. A finite element model applicable to shaft at various temperatures is proposed. The temperature‐dependant property is characterized by an efficient equation.

Exploring elastic properties of fly ash recycled aggregate concrete: Insights from multiscale modeling and machine learning

The primary focus of this study is to analyze the impact of different components of fly ash recycled aggregate concrete (FARAC) on its elastic properties, aiming to suggest it as a potential alternative to traditional concrete. For this study, a variety of techniques were employed, such as multiscale modeling, finite element methods, and Mori-Tanaka theory. The study employed supervised machine learning methods to conduct classification and regression analyses, with the goal of investigating the impact of mix proportion on elastic properties. The results obtained from the machine learning models suggest that the XGBoost and K-Nearest Neighbors algorithms have shown exceptional precision when compared to the other algorithms, achieving an accuracy of over 0.9. The current investigation reveals that the elastic characteristics of FARAC are primarily affected by fly ash and calcium silicate hydrate (C-S-H) in comparison to other components. According to the research findings, incorporating recycled aggregate content in the range of 0–100% resulted in a 25% decrease in Young's modulus and an 8% increase in Poisson's ratio of FARAC. In addition, two web-based applications have been developed to calculate the elastic properties of composite materials with spherical inclusions using the Mori-Tanaka theory, and to predict the elastic properties of FARAC through machine learning.

Allowing for the Nonlinear Elastic Properties of Composite Materials in Designing Shell Elements with Holes of Rockets

Allowing for the Nonlinear Elastic Properties of Composite Materials in Designing Shell Elements with Holes of Rockets

Nanomechanical study of aqueous-processed h-BN reinforced PVA composites

Hexagonal boron nitride (h-BN) as a filler has significantly improved the mechanical properties of various polymers composites. Among them, polyvinyl alcohol (PVA) is particularly important for its wide range of industrial applications and biocompatibility nature. However, preparing a homogenous composite of h-BN and PVA in water is troublesome as the aqueous processing of h-BN without any additives is challenging. In this context, a pre-processing technique is used to produce an additive-free aqueous dispersion of h-BN. The uniformly dispersed composites are then prepared with different concentrations of h-BN. Free-standing thin films are fabricated using the doctor blade technique, and nanoindentation is employed to understand their deformation behaviour at smaller length scale for better understanding of micro-mechanism involved. Reduced elastic modulus and hardness of 10 wt% h-BN/PVA composite film are enhanced by ∼93% and ∼159%, respectively, compared to pristine PVA. Frequency sweep dynamic mechanical analysis is performed between 1 and 50 Hz, and the elastic properties of composite materials are found to improve significantly upon addition of h-BN nanosheets. Besides, the impact of h-BN incorporation in stress relaxation behaviour and hardness depth profiling are also investigated. The observed improvement in mechanical properties of the composites may be attributed to the uniform distribution of the nanosheets and the strong interfacial interaction between h-BN and PVA, which ensures efficient mechanical stress transfer at the interface.

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.

Prediction of elastic properties of unidirectional carbon/carbon composites using analytical and numerical homogenisation methods

ABSTRACT Carbon/carbon composites are being used increasingly in the field of Space, Aviation; Air craft breaks discs, High temperature applications. They can withstand a very high temperature up to 3315°C. They have distinct advantage of strength over graphite fibre. They are lighter to graphite fibres. Elastic properties of the carbon/carbon composites are important for design considerations. They can be evaluated through analytical, numerical or experimental methods. Experimental methods are expensive and are not feasible to be performed at the design stage. Analytical methods are complex and difficult to implement. Numerical methods through Finite Element Modelling (FEM) are useful tools for evaluation of elastic properties of composite materials. The present work is aimed at review and comparison of various analytical models and numerical finite model for evaluation of elastic properties. The elastic properties of unidirectional carbon/carbon composites are evaluated using analytical models and numerical finite element model using ABAQUS with EasyPBC plugin. Elastic modulus in longitudinal and transverse direction show good agreement in all methods. Major Poisson’s ratio and transverse Young’s modulus are also in agreement. Longitudinal shear modulus obtained by rule of mixtures is on lower side while that obtained by other models are on higher side when compared to numerical model.

Numerical micromechanics model of carbon fiber-reinforced composite using various periodical fiber arrangement

A numerical model of unidirectional carbon fiber-reinforced polymer composite material at the micro-level has been introduced to complement the experiment and analytical model in estimating the elastic properties of composite material. Idealization was performed in the model by using a periodically distributed fiber following square and hexagonal packing arrangement. The determination of the unit cell configuration was made by considering the periodic boundary condition associated with the selected configuration. The idealization using periodic fiber arrangement was proved to adequately estimate the elastic properties of composite material. The hexagonal model was proved to solve the drawbacks of the square model in estimating the shear properties with error reduction up to 50 % in comparison to the square model.

Nondestructive determination of local material properties of laminated composites with the impulse excitation technique

An innovative experimental methodology for the nondestructive assessment of local elastic properties of composite materials is proposed in this paper. A local region of rectangular shape is isolated on the investigated laminate with a proper clamping system. The first resonant frequency of the retained region with clamped boundaries is determined through the Impulse Excitation Technique. In order to take into account the anisotropy of the composite laminate, values of the resonant frequency are measured after rotating the clamping system with respect to the composite plate. The material constants are finally obtained from the measured frequencies through an inverse optimization algorithm based on Finite Element analysis.The proposed methodology is validated on a unidirectional composite plate with known elastic properties. Boundaries of the investigated region are clamped by pressing two rectangular frames to the plate through a testing machine, thus localizing the measure of the resonant frequencies. The first resonant frequency is measured at different angles (0°, 30°, 60° and 90°) between fibers direction and main axis of the rectangular region. Dynamic elastic properties are finally assessed through the proposed inverse optimization algorithm. The small differences between the nominal and the estimated mechanical properties prove the effectiveness of the proposed methodology.

Prediction of Elastic Properties of Short Fibers Reinforced Composites (Dept.T)

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Investigation of elastic properties of composite materials with use of ESPI

This paper addresses various methodological aspects of testing of composite laminates to determine elastic constants of materials. Electronic speckle pattern interferometry is used to measure deformation of specimens in the form of beams loaded with a bending moment. The optical compensation method allows determining directly of principal curvatures of deformed surface. To calculate the elastic constants of a material from the experimental data, the corresponding dependences of the theory of elasticity of an anisotropic body are used. Data are shown on the effect of moisture absorption on elastic properties of glass–epoxy laminate.

Modeling of the electromagnetic and elastic properties of composite materials

In this paper, we consider the solution of the problem of the theory of piezoelectricity. The effective elastic, piezoelectric, and dielectric characteristics are calculated for a two-layer composite with a volume concentration of layers of 50%. The corresponding characteristics are calculated for a two-layer material with an orthogonal-reinforced structure. For the numerical solution of the problem, the conjugate gradient method for solving systems of algebraic equations was used. The results were visualized using a software package developed at Bauman Moscow state technical University. The paper presents the distribution of the stress field σij and the vector in problems Lr and Lpq .

Effective Medium Theory for the Elastic Properties of Composite Materials with Various Percolation Thresholds.

It is discussed that the classical effective medium theory for the elastic properties of random heterogeneous materials is not congruous with the effective medium theory for the electrical conductivity. In particular, when describing the elastic and electro-conductive properties of a strongly inhomogeneous two-phase composite material, the steep rise of effective parameters occurs at different concentrations. To achieve the logical concordance between the cross-property relations, a modification of the effective medium theory of the elastic properties is introduced. It is shown that the qualitative conclusions of the theory do not change, while a possibility of describing a broader class of composite materials with various percolation thresholds arises. It is determined under what conditions there is an elasticity theory analogue of the Dykhne formula for the effective conductivity. The theoretical results are supported by known experiments and show improvement over the existing approach. The introduction of the theory with the variable percolation threshold paves the way for describing the magnetorheological properties of magnetoactive elastomers. A similar approach has been recently used for the description of magneto-dielectric and magnetic properties.

Surface Finite Element for Imperfect Interface Modeling in Elastic Properties Homogenization

The paper presents a mathematical model of a finite element for modeling imperfect interface conditions for two contacting surfaces. The element is used in the numerical implementation of the Asymptotic Averaging Method (AAM) for the determination of effective elastic properties of composite materials under investigation. Numerical experiments are carried out to calculate the elastic properties taking into account the adhesion layer using a displacements field jump condition at the phase boundary. Results are compared with adhesion modeling using an additional bulk phase.

Automated assessment of the low-rigid composite parts influence on the product assemblability in the GePARD system

Composite components tend to have higher deviations from the nominal dimension in conjunction with metal components. Composites production processes simulation methods have already been developed before long time ago. This article presents the possibility of integrating the technique of non-rigid dimensional chains, taking into account the elastic properties of composite materials to assess the products assemblage with machinery parts from composite materials, on the basis of three-dimensional GePARD system. The fundamental points of the dimensional chain calculating method with non-rigid parts, as well as methods of assessing the stiffness for some types of composite materials, which take into account some peculiarities of its structure, are also examined. The assemblability of an assembly unit is represented by the parameter of the functional assembly requirement depending on the critical accuracy characteristics.

Assessment of Residual Elastic Properties of a Damaged Composite Plate with Combined Damage Index and Finite Element Methods

In structural component applications the use of composite materials is increasing thanks to their optimal mechanical characteristics. However, the complexity of the damage evolution in composite materials significantly limits their widespread diffusion. Non-destructive tests are thus becoming ever more important. The detecting Damage Index ( D I d ) technique has been recently brought in the realm of the non-destructive characterization tests for components made of composite material. In contrast to other techniques, this methodology allows to quantitatively assess local residual properties. In this paper, the D I d technique is adopted in combination with the finite element method. The mechanical response of two composite plates (an 8-layer twill fabric carbon/epoxy) subjected to four-point bending test is firstly used to tune a finite element model of the laminate. Then, an undamaged laminate of the same composite material is progressively damaged through repeated four-point bending tests. Local residual elastic properties are mapped on the plate through the D I d technique. A continuous polynomial curve has been considered to account for the variation of the elastic modulus in the finite element model. The resulting force-displacement curve of the numerical analysis is compared to experimental data of damaged plate, resulting in very good agreement. The combination of the experimental activity and the numerical finite element analysis points out the accuracy of the D I d methodology in assessing local residual elastic properties of composite materials.

A Non-Destructive Method for Evaluation of the Out of Plane Elastic Modulus of Porous and Composite Materials

This paper presents an effective and reliable non-destructive method to measure the Young Modulus of porous and out of plane Young Modulus of composite materials using sound waves. First, a Finite Element Model based on Representative Volume Element (RVE) is developed to demonstrate how the elastic properties of composite material can be estimated by acoustic measurements using an impedance tube test rig. Second, the results of the experimental measurement campaign was carried out to validate the proposed method. In particular, two soft elastic foams with different density, an epoxy-carbon fibre composite and vynilester-glass fibre composite were tested. In the proposed method, a two-microphone impedance tube setup was used where the measured acoustic pressures at two upstream locations allowed the estimation of the reflection coefficient and the acoustic impedance of the tested materials. Since the acoustic impedance can be expressed as a function of the longitudinal speed of sound (assuming a plane standing wave excitation), the elastic modulus can be estimated which is associated with the speed of sound. The elastic modulus measured using the proposed method were in good agreement with the values obtained by the standard methods such as tensile tests and ultrasound time of flight measurements. The proposed method would allow in an accurate and fast manner the non-destructive evaluation of Young Modulus of porous materials and for the first time the proposed approach is applied successfully to the measurement of out of plane Young modulus of composite materials.

Mechanical Property Evaluation of Composites Based on n+1 Phase Model and Mori–Tanaka Theory

AbstractA new micromechanical model is developed for the prediction of the elastic properties of composite materials with embedded spherical multicoated inhomogeneities of various sizes and types. ...

Effect of elastic properties dependence of the stress state in composite materials

Buckling problem is quite important for the engineering practice, mostly in cases of lightweight structures. The use of composites reduces the weight of the structure but gives problems in choice of reliable methods to model buckling and postbuckling behavior of details, especially if they contain thin-walled components. One of the problems is the choice of correct elastic properties of composite material for analysis. Elastic characteristics of composite material depend on the type of loading and uniaxial tension/compression test results in some cases demonstrate an essential difference. The buckling analysis usually assumes compression of the structure and the choice of elastic constants obtained in compression tests leads to more accurate results, but does not guarantee a good correlation with experiments in case of postbuckling analysis due to ignoring some regions with tension stress state. A possible way of material stress-state sensitivity consideration is usage of material models that take into account stiffness susceptibility to different types of loading. Further development of nonlinear elastic model in problems related to buckling and postbuckling analysis for composite materials up to failure is the introduction of material progressive degradation model to consider material properties reduction due to damage in conjunction with nonlinear elasticity.

Micromechanical analysis of composites with fibers distributed randomly over the transverse cross-section

A new method to generate the random distribution of fibers in the transverse cross-section of fiber reinforced composites with high fiber volume fraction is presented in this paper. Based on the microscopy observation of the transverse cross-sections of unidirectional composite laminates, hexagon arrangement is set as the initial arrangement status, and the initial velocity of each fiber is arbitrary at an arbitrary direction, the micro-scale representative volume element (RVE) is established by simulating perfectly elastic collision. Combined with the proposed periodic boundary conditions which are suitable for multi-axial loading, the effective elastic properties of composite materials can be predicted. The predicted properties show reasonable agreement with experimental results. By comparing the stress field of RVE with fibers distributed randomly and RVE with fibers distributed periodically, the predicted elastic modulus of RVE with fibers distributed randomly is greater than RVE with fibers distributed periodically.

Stochastic Elastic Properties of Composite Matrix Material with Random Voids Based on Radial Basis Function Network

The stochastic characteristics of the voids result in the randomness of the equivalent elastic modulus. It is computationally expensive to quantify the stochastic characteristics of the equivalent elastic modulus using the representative volume element. This paper is focused on the stochastic elastic properties of composite material with random voids. The Karhunen–Loeve Transform is introduced to convert the random variables to a certain number of principal components; the approximate relationship is established between the principal components and the equivalent elastic modulus taking use of the radial basis function network to reduce the computational burden. The dispersion-based sampling is proposed to solve the overfitting problem. The cumulative distribution function (CDF) and probability density function (PDF) are obtained from the surrogate model, which has good agreement with the results from Monte Carlo simulations from the original model.