Anisotropic Composite Materials Research Articles

Non-contact detection of delamination in layered anisotropic composite materials with ultrasonic waves generated and detected by lasers

This paper presents the non-contact detection of internal delamination in layered anisotropic composite material with ultrasonic waves generated by a pulse laser and received by a two-wave mixing laser interferometer. Three-dimensional finite element method is used to simulate the propagation of laser generated ultrasonic waves in carbon fiber reinforced plastics and the interaction with internal delamination. A composite laminate with simulated internal delamination is made as specimen, and a laser ultrasonic system for experiments is set up. The reflection and attenuation characteristics of laser ultrasonic induced by the internal delamination are analyzed theoretically and experimentally. The effects of measuring position and wave frequency on the detection of internal delamination are discussed, and suitable choices of the parameters of laser ultrasonic are suggested. The C-scan images of the composite specimen are obtained using the laser ultrasonic system. The results show that it is possible to decrease the influences of the layered anisotropic feature of composite materials on the detection of internal delamination by controlling the laser parameters.

Polarization tensors of planar domains as functions of the admittivity contrast

(Electric) polarization tensors describe part of the leading order term of asymptotic voltage perturbations caused by low volume fraction inhomogeneities of the electrical properties of a medium. They depend on the geometry of the support of the inhomogeneities and on their admittivity contrast. Corresponding asymptotic formulas are of particular interest in the design of reconstruction algorithms for determining the locations and the material properties of inhomogeneities inside a body from measurements of current flows and associated voltage potentials on the body’s surface. In this work, we consider the two-dimensional case only and provide an analytic representation of the polarization tensor in terms of spectral properties of the double layer integral operator associated with the support of simply connected conductivity inhomogeneities. Furthermore, we establish that an (infinitesimal) simply connected inhomogeneity has the shape of an ellipse, if and only if the polarization tensor is a rational function of the admittivity contrast with at most two poles whose residues satisfy a certain algebraic constraint. We also use the analytic representation to provide a proof of the so-called Hashin–Shtrikman bounds for polarization tensors; a similar approach has been taken previously by Golden and Papanicolaou and Kohn and Milton in the context of anisotropic composite materials.

A study of high-order grid-characteristic methods on unstructured grids

In this paper, grid-characteristic methods for solving hyperbolic systems using approximation with high-order interpolation on unstructured tetrahedral and triangular grids are studied. Interpolation methods of order from 1 through 5 inclusive are considered. One-dimensional finite difference schemes for these methods are presented. The stability of these schemes is investigated. The grid-characteristic methods on unstructured triangular and tetrahedral grids are successfully used in seismic prospecting, specifically under the Arctic shelf and permafrost conditions. They are also used to solve problems of seismics, dynamic deformation and destruction, and to study anisotropic composite materials.

Performance Enhancement of Tilt-Body Micro Air Vehicle by Use of Orthotropic Laminated Proprotors

A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles (MAV). In this paper, adaptation of the proprotor geometry in accordance to flight configurations is achieved by induced twist generated by the inherent structural coupling effect in anisotropic composite material and centrifugal force emanating from the tip load. Beam Finite Element Model based on Rotating Timoshenko Theory is used to predict structural loads, while Blade Element Momentum Theory is employed to predict the aerodynamic performance of adaptive proprotor as applied on Micro Air Vehicles (MAV). The iterative process of combination of aerodynamic model and structural model is used to compute the steady-state deformation of the flexible laminated proprotor blade due aerodynamic loads. Finally, the optimal design of lamina blade material is carried out to investigate the potential of flexible blade in the proprotorperformance enhancement.

Anisotropic n-Type Bi2Te3–In2Te3 Thermoelectric Material Produced by Seeding Zone Melting and Solid State Transformation

Seeding zone melting is applied to produce bulk Bi1.625In0.375Te3 with 7.5 atom % In in solid solution. The concentration distribution is markedly homogeneous and exhibits pronounced anisotropic electrical and thermal conductivity. Subsequent precipitation from the solid solution leads to the formation of a highly anisotropic composite thermoelectric material consisting of aligned microscaled Bi2Te3 and extended micro- to nanoscaled In2Te3 plates. By the precipitation, an increase of zT by a factor of 6 compared with the parent supersaturated solid solution crystal is achieved. This is attributed to the combination of a decrease of In concentration from 7.5 to 3 atom % in the Bi2Te3 layer and an increasing interface density due to the precipitation of In2Te3. The Bi2Te3/In2Te3 interface is determined as coherent, and the crystallographic orientation between the two phases is determined as ⟨211⟩In2Te3//⟨1100⟩Bi2Te3, {111}In2Te3//{0001}Bi2Te3.

Cutting Mechanism of Drilling CFRP Laminates—Effect of Ultrasonic Torsional Mode Vibration Cutting

Cutting mechanism of drilling CFRP laminates and effects of ultrasonic torsional mode vibration cutting are investigated. CFRP laminates are made of carbon fiber reinforced/epoxy-resin matrix composite ply. Challenges in drilling CFRP laminates arise because of anisotropy due to carbon fiber orientation and heterogeneousness between carbon fiber and epoxy-resin. Experimental works are performed to characterize major hole quality parameters and cutting mechanism encountered when conventional drilling CFRP laminates. Some craters of about 100 μm depth are found at the particular position on inner surface of drilled hole and the mechanism for the crater to be generated is revealed based on cutting mechanism of both anisotropic and hheterogeneous composite material. In order to improve hole quality and tool life, the specific drilling assisted by ultrasonic torsional mode vibration of 27 kHz is examined. The ultrasonic torsional mode vibration cutting is considerably effective to restrain the generation of crater and also to elongate tool life about five times.

Piezoelectric performance — composition relations in anisotropic materials based on Pb0.85Ca0.15-xCdxTi0.9Zr0.1O3 phases

The effect of processing methods and a composition of ferroelectric (FE) (piezoelectric) phases on forming a microstructure of a ceramic framework during poling is studied in a ceramic material of the composition Pb 0.85 Ca 0.15-x Cd x Ti 0.9 Zr 0.1 O 3. A transition from using the solid-phase method for the synthesis of powder of a particular phase to a method of bulk "chemical assembly" leads to a change in the mechanical strength of the bulk granular medium and intergranular boundaries therein. Depending on a relationship between mechanical strength parameters of the studied materials, on poling the samples with a particular composition, anisotropic piezo-active composite materials with various connectivities of Pb 0.85 Ca 0.15-x Cd x Ti 0.9 Zr 0.1 O 3 phases can be obtained. These materials are characterized by various combinations of electrophysical properties and demonstrate advantages over the known anisotropic Pb Ti O 3-type ceramics. The fracture of ceramic grains during the poling process can be intensified by introducing FE phases with the composition comprising Cd 2+ ions with a smaller radius and a most deformability in comparison to the Ca 2+ ion.

Theoretical Considerations on Fibre Reinforced Composites Thermal Conductivity Uncertainties

Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin facilitates to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. The increasing use of composites, for various applications, emphasizes its importance/significance in the thermal property analysis of an engineering system. Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. Various theoretical approaches are used to yield the thermal conductivity of a composite material so that the heat flow in anisotropic composite material in any direction can be estimated. In this paper few models will be considered and a theoretical study on thermal conductivity uncertainties will be conducted and discussed. The results identified the need and importance of carrying out further investigations on thermal behavior of composites materials.

Flexible barrier materials for protection against electromagnetic fields and their characterization

Composite materials for electromagnetic shielding can be manufactured as textiles using conductive yarns and textiles with conductivity obtained by various finishing processes on textile surfaces. The EM shielding effectiveness of fabrics are improved by lowering its conductivity using different methods and materials. An alternative is the usage of new light shielding materials in the form of metallized nonwoven fabrics or textiles. Their advantages are: a general availability on the market, a low price, good mechanical properties (strength, elasticity) and resistance to the environmental conditions. The composite anisotropic materials with a sandwich structure constituting of materials with different spatial orientations of fibers allow one to achieve relatively high and constant values of the shielding effectiveness which, together with the materials’ mechanical properties, leads to a wide range of applicability in various disciplines of modern technology. This article is devoted to innovative flexible materials shielding electromagnetic field. The results of the PEM shielding effectiveness obtained for the polypropylene (PP) nonwoven fabrics metallized by pulsed magnetron sputtering are presented.

Anisotropy in thermal conductivity of graphite flakes–SiCp/matrix composites: Implications in heat sinking design for thermal management applications

Within the frame of heat dissipation for electronics, a very interesting family of anisotropic composite materials, fabricated by liquid infiltration of a matrix into preforms of oriented graphite flakes and SiC particles, has been recently proposed. Aiming to investigate the implications of the inherent anisotropy of these composites on their thermal conductivity, and hence on their potential applications, materials with matrices of Al–12wt.% Si alloy and epoxy polymer have been fabricated. Samples have been cut at a variable angle with respect to the flakes plane and thermal conductivity has been measured by means of two standard techniques, namely, steady state technique and laser flash method. Experimental results are presented and discussed in terms of current models, from which important technological implications for heat sinking design can be derived.

Macroscopic constitutive relations for elastomers reinforced with short aligned fibers: Instabilities and post-bifurcation response

This paper is concerned with the characterization of the macroscopic response and possible development of instabilities in a certain class of anisotropic composite materials consisting of random distributions of aligned rigid fibers of elliptical cross section in a soft elastomeric matrix, which are subjected to general plane strain loading conditions. For this purpose, use is made of an estimate for the stored-energy function that was derived by Lopez-Pamies and Ponte Castañeda (2006b) for this class of reinforced elastomers by means of the second-order linear comparison homogenization method. This homogenization estimate has been shown to lose strong ellipticity by the development of shear localization bands, when the composite is loaded in compression along the (in-plane) long axes of the fibers. The instability is produced by the sudden, collective rotation of a band of fibers to partially release the high stresses that develop in the elastomer matrix when the composite is compressed along the stiff, long-fiber direction. Consistent with the mode of the impending instability, a lower-energy, post-bifurcation solution is constructed where “striped domain” microstructures consisting of layers with alternating fiber orientations develop in the composite. The volume fractions of the layers and the fiber orientations within the layers adjust themselves to satisfy equilibrium and compatibility across the layers, while remaining compatible with the imposed overall deformation. Mathematically, this construction is shown to correspond to the rank-one convex envelope of the original estimate for the energy, and is further shown to be polyconvex and therefore quasiconvex. Thus, it corresponds to the “relaxation” of the stored-energy function of the composite, and can in turn be viewed as a stress-driven “phase transition,” where the symmetry of the fiber microstructures changes from nematic to smectic.

Comparisons of Horizontal-Axis Wind Turbine Wake Interaction Models

In this study, Reynolds-averaged Navier–Stokes (RANS) simulations are performed using the k-ε and k-ω shear stress transport (SST) turbulence closure schemes to investigate the interactions of horizontal-axis wind turbine (HAWT) models in the neutrally stratified atmospheric boundary layer (ABL). A comparative study of actuator disk, actuator line, and full rotor models of the National Renewable Energy Laboratory (NREL) 5 MW reference turbine is presented. The open-source computational fluid dynamics (CFD) code openfoam 2.1.0 and the commercial software ansysfluent 13.0 are used for simulations. Single turbine models are analyzed for turbulent structures and wake resolution in the downstream region. To investigate the influence of the incident wind field on very large turbine blades, a high-resolution full rotor simulation is carried out for a single turbine to determine blade pressure distributions. Finally, simulations are performed for two inline turbines spaced 5 diameters (5D) apart. The research presented in this study provides an intercomparison of three dominant HAWT models operating at rated conditions in a neutral ABL using an RANS framework. Furthermore, the pressure distributions of the highly resolved full rotor model (FRM) will be useful for future aeroelastic structural analysis of anisotropic composite blade materials.

Modeling of constitutive behavior of anisotropic composite material using multi-scale approach

The paper is focused on determining the elastic-plastic behavior of anisotropic composite materials. One of the main goals of this study is to compute effective material properties by analyzing material behavior at microstructure level. The effective material properties were investigated with the use of homogenization procedure connected with volume averaging of stress and strain values in RVE (Representative Volume Element). Three dimensional RVE geometry that represents material microstructure is taken into consideration. The spatial distribution of the particles is determined with experimental data. A boundary value problem is solved by using the finite element method and enforcing periodic boundary conditions. In addition, another approaches based on two step homogenization method and orientation averaging procedure are proposed. Results obtained numerically by using different approaches are presented, compared and related to the experimental results.DOI: http://dx.doi.org/10.5755/j01.mech.21.2.10276

A general Bayesian framework for ellipse-based and hyperbola-based damage localization in anisotropic composite plates

This article focuses on Bayesian Lamb wave-based damage localization in structural health monitoring of anisotropic composite materials. A Bayesian framework is applied to take account of uncertainties from experimental time-of-flight measurements and angle-dependent group velocity within the composite material. An original parametric analytical expression of the direction dependence of group velocity is proposed and validated numerically and experimentally for anisotropic composite and sandwich plates. This expression is incorporated into time-of-arrival (ellipse-based) and time-difference-of-arrival (hyperbola-based) Bayesian damage localization algorithms. This way, the damage location and the group velocity profile are estimated jointly and a priori information is taken into consideration. The proposed algorithm is general as it allows us to take into account uncertainties within a Bayesian framework, and to model effects of anisotropy on group velocity. Numerical and experimental results obtained with different damage sizes or locations and for different degrees of anisotropy validate the ability of the proposed algorithm to estimate both the damage location and the group velocity profile as well as the associated confidence intervals. Results highlight the need to consider for anisotropy in order to increase localization accuracy, and to use Bayesian analysis to quantify uncertainties in damage localization.

An anchoring element for prestressed FRP reinforcement: simplified design of the anchoring area

Today, fibre-reinforced polymers (FRP) are widely used construction materials. The use of non-metallic reinforcement as inner reinforcement has many advantages, as is well known, but there are some areas of application that need to be resolved in order to improve the usage of FRP reinforcement in real-world conditions. One of these is the design of a suitable anchorage for prestressed FRP applications. It is difficult to design a safe anchorage using conventional methods of anchoring (systems for the anchorage of steel tendons) due to the well-known low compressive strength perpendicular to the fibres, this being due to the anisotropy of composite materials. Most of the anchoring systems commonly used worldwide are based on the use of metal parts (steel tubes, wedges, etc.) in a system which is primarily designed to be non-metallic. It is in contradiction with the initial intention to use non-metallic reinforcement. The presented text describes the basic physical and mechanical properties of a developed non-metallic anchor element. The essential principles of an analytical solution of the developed anchoring element based on the stiffness parameters of the system’s individual components are also presented. The behaviour of each material used is described in terms of simplify form. The functionality of the anchoring system was verified by a number of load tests and the obtained results were compared with theoretically and numerically calculated values. The presented results show the high efficiency of the anchoring system as well as the suitability of the derived analytical solution for simplified design and evaluation of the anchoring area.

Hydro-Structure Analysis of Composite Marine Propeller under Pressure Hydrodynamic Loading

This paper aims to predict the hydrodynamic characteristics and structural analysis of the marine propeller under pressure hydrodynamic loading. Because of the loading on the propeller blade, it goes under significant deformation that may affect the hydrodynamic performance of the propeller. Thus, the blade deformation of a propeller due to fluid pressure should be analyzed, considering hydro-elastic analysis. The propeller was made of anisotropic composite materials, and the geometry of the propeller is for one skew angle. First, the hydrodynamic pressure loading is obtained by FVM and then the deformation of the blade due to this pressure was calculated. Next, the pressure load for deformed propeller is achieved; it is again repeated to obtain the new deformed propeller. This procedure is repeated to converge the thrust, torque and efficiency. We present all results of the pressure distribution, hydrodynamic characteristics, stress and deformation of the propeller.

Evaluation of Multiple Reflections in the Characterization of Anisotropic Materials by Through Transmission Ultrasonic Technique

Ultrasonic through-transmission techniques have been widely used along decades for determining the elastic constants of anisotropic composite materials. This work presents a new methodology that takes into account not only the transmitted waves but also the multiple reflections inside the sample. The superposition of different reflected waves are theoretically and experimentally identified and excluded, which avoids the distortion caused by pulse superposition. Additionally, the results of the Christoffel tensor optimization are evaluated in the reflected waves, improving the results validation. Experimental results using unidirectional carbon-matrix composite samples used in the aeronautical industry are presented.

Finite Element Model of Trimming CFRP Aerospace Composites

Carbon Fiber Reinforced Plastics (CFRP) exhibit superior characteristics such as high specific strength, high specific modulus, fatigue strength and endurance. During the manufacture of components from CFRP, it is usually necessary to carry out a post-machining step. Generally, after curing process, the parts will be trimmed in order to meet the required tolerances. Due to the heterogeneous composition and anisotropy of composite materials, machining procedures can damage the material in ways that directly affect its mechanical properties. Currently a costly try and error approach is employed to determine the optimal process conditions. Thus, this study focused on numerical modelling of machining CFRP composites using cross-nick router. A set of machining tests were performed in order to validate the accuracy of the model. Good agreement between simulation and experimental results show the validity of the model in handling real-field problems. The proposed numerical modeling technique can be used as an input in the process planning and decision making levels.

Modeling and analysis of water-hammer in coaxial pipes

The fluid-structure interaction is studied for a system composed of two coaxial pipes in an annular geometry, for both homogeneous isotropic metal pipes and fiber-reinforced (anisotropic) pipes. Multiple waves, traveling at different speeds and amplitudes, result when a projectile impacts on the water fillinhe annular space between the pipes. In the case of carbon fiber-reinforced plastic thin pipes we compute the wavespeeds, the fluid pressure and mechanical strains as functions of the fiber winding angle. This generalizes the single-pipe analysis of J. H. You, and K. Inaba, Fluid-structure interaction in water-filled pipes of anisotropic composite materials, J. Fl. Str. 36 (2013). Comparison with a set of experimental measurements seems to validate our models and predictions.

Prediction of attenuated guided waves propagation in carbon fiber composites using Rayleigh damping model

In this work, a predictive model of attenuated guided wave propagation in carbon fiber–reinforced polymer using Rayleigh damping is developed. After a brief introduction, this article reviews the theory of guided waves in anisotropic composite materials. It follows with a discussion of the piezoelectric wafer active sensors, which are lightweight and inexpensive transducers for structural health monitoring applications. Experiments were performed on a carbon fiber–reinforced polymer panel to measure the dispersion curves and the piezoelectric wafer active sensors tuning curves. Lamb wave damping coefficient was modeled using the multi-physics finite element method and compared with experimental results. A discussion about the capability to simulate, with multi-physics finite element method commercial software, guided wave in composite material using the Rayleigh damping is developed. This article ends with conclusion, and suggestions for further work are also presented.