Uniaxial Material Research Articles

Anisotropy in carbon fiber reinforced polymer (CFRP) and its effect on induction thermography

Lock-in induction thermography was carried out on uniaxial, biaxial, and multi-ply woven carbon fiber reinforced polymers (CFRPs) at an induction frequency of approximately 300 kHz and at modulation frequencies of 0.4–36 Hz to detect defects in them. The measurements were performed in reflection and transmission modes. In the uniaxial material, heating occurred far away from the excitation coil. Lines of minimal heating were observed. The modulation frequency dependence of the amplitude showed an inverse proportionality, indicating volume heating. The multi-ply woven CFRP plates with impacts of 3 and 5 J showed distinct contrast because of cracked fibers. The results were compared with those obtained using optically excited thermography and X-ray tomography.

Elastic-plastic analysis of functionally graded bars under torsional loading

In this paper a new integral equation solution to the elastic-plastic problem of functionally graded bars under torsional loading is presented. The formulation is general in the sense that it can be applied to an arbitrary cross-section made of any type of elastoplastic material. In material science the Functionally Graded Material (FGM) is a non-homogeneous composite which performs as a single-phase material, by unifying the best properties of its constituent phase material. The nonlinear elastic-plastic behavior is mathematically described by the deformation theory of plasticity. According to this theory, the material constants are assumed variable within the cross section, and are updated through an iterative process so as the equivalent stress and strain at each point coincide with the uniaxial material curve. In this investigation a new straightforward nonlinear procedure is introduced in the deformation theory of plasticity which simplifies the solution method. At each iteration step, the warping function is obtained by solving the torsion problem of a non-homogeneous isotropic bar using the Boundary Element Method (BEM) in conjunction with the Analog Equation Method (AEM). Without restricting the generality, the FGM material is comprised of a ceramic phase and a metal phase. The ceramic is assumed to behave linearly elastic, whereas the metal is modeled as an elastic – linear hardening material. Furthermore, the TTO homogenization scheme for estimating the effective properties of the two-phase FGM was adopted. Several bars with various cross-sections and material types are analyzed, in order to validate the proposed model and exemplify its salient features. Moreover, useful conclusion are drawn from the elastic-plastic behavior of functionally graded bars under torsional loading.

Abstract 105: Association of Viscoelastic Material Properties and Extracellular Matrix Remodeling in Human Abdominal Aortic Aneurysmal Tissue

Objectives: Predicting rupture of abdominal aortic aneurysm (AAA) requires knowledge of both the rate of extracellular matrix (ECM) degradation and the pulsatile stress on the aortic tissue. The activity of matrix metallopeptidase 9 (MMP9) and its inhibitor, TIMP1, are associated with alterations in aortic ECM but it is unknown if these changes effect the dynamic viscoelastic properties. We hypothesize that increased levels of MMP9 within AAA tissue will be associated with a greater dynamic modulus (E*), as a surrogate of increased aortic wall stress. Methods: Human aneurysmal aortic tissue was obtained at the time of open AAA repair (n=11) and age-matched non-aneurysmal cadavers (n=10). Uniaxial viscoelastic material properties were measured in the circumferential orientation under physiologic preload (110 mmHg) and cyclic strain (± 5%@1Hz). Quantitative histologic and immunohistochemistry were preformed using Fiji imaging software. Aortic MMP9 and TIMP1 content and activity were quantified using western blot and zymography. Results: E* was greater (1862±464 vs 1362±405 kPa, p=0.02) in the AAA tissue as compared to non-aneurysmal tissue. AAA tissue contained less elastin (6.7±6.7 vs 23.4±8.7%, p=0.01) and a greater collagen/elastin ratio (19.9±20.6 vs 2.3±2.5%, p=0.05). Immunohistochemistry revealed 200% greater MMP9 content in the AAA tissue (Figure A & B, 0.61 vs 0.03%, p=0.03). Increased MMP9 content was confirmed using a western blot (0.43 vs 0.06 AU, p<0.01). No difference in relative MMP9 activity (4307 vs 2324 AU, p=0.25) or level of TIMP1 (0.03 vs 0.02, p=0.6) were observed. There was a positive linear correlation (Figure C, r 2 =0.47) between E* and MMP9 as determined by quantitative immunohistochemistry. Conclusions: Our data suggests a positive relationship between E* and MMP9 content. Increased tissue stiffness may trigger MMP9 production resulting in a positive-feedback loop, progressively increasing aortic wall stress and rupture risk.

Cylindrical Anisotropic Dielectric Resonator Antenna With Improved Gain

Uniaxial anisotropic material obtained by parallel layers of two different dielectrics is used to obtain a cylindrical dielectric resonator antenna (CDRA). As a consequence of the anisotropy, the boresight gain of the antenna is increased. The effect of the height-to-radius ratio on the boresight gain variation is also investigated. It is shown that by increasing this ratio, the directivity of the antenna in the boresight direction can be increased. A prototype of the anisotropic CDRA is fabricated and measured. A reasonable agreement between the simulated and measured results is attained.

Exceptional points in anisotropic planar microcavities

Planar microcavities allow the control and manipulation of spin-polarization, manifested in phenomena like the optical spin Hall effect due to the intrinsic polarization mode splitting. Here, we study a transparent microcavity with broken rotational symmetry, realized by aligning the optical axis of a uniaxial cavity material in the cavity plane. We demonstrate that the in-plane optical anisotropy gives rise to exceptional points in the dispersion relation, which occur pair-wise, are circularly polarized, and are cores of polarization vortices. These exceptional points are a result of the non-Hermitian character of the system, and are in close relationship to singular optical axes in absorptive biaxial systems.

Light propagation in two-dimensional photonic crystals based on uniaxial polar materials: results on polaritonic spectrum

The dispersion relations of two-dimensional photonic crystals made of uniaxial polaritonic cylinders arranged in triangular lattice are calculated. The particular case of the transverse magnetic polarization is taken into account. Three different uniaxial materials showing transverse phonon-polariton excitations are considered: aluminum nitride, gallium nitride, and indium nitride. The study is carried out by means of the finite-difference time-domain technique for the solution of Maxwell equations, together with the method of the auxiliary differential equation. It is shown that changing the filling fraction can result in the modification of both the photonic and polaritonic bandgaps in the optical dispersion relations. Wider gaps appear for smaller filling fraction values, whereas a larger number of photonic bandgaps will occur within the frequency range considered when a larger filling fraction is used. The effect of including the distinct wurtzite III–V nitride semiconductors as core materials in the cylinders embedded in the air on the photonic properties is discussed as well, highlighting the effect of the dielectric anisotropy on the properties of the polaritonic part of the photonic spectrum.

Sensitivity and optimisation of the Chaboche plasticity model parameters in strain-life fatigue predictions

The aerospace industry is widely employing strain-life methodologies for structural fatigue predictions. Under spectrum loading, overloads significantly affect the fatigue, therefore it is very important to accurately account for the cyclic transient deformation phenomena. Describing these phenomena requires advanced plasticity models that involve a set of material parameters. Even for the well-known Chaboche model, there is lack of understanding of each parameter's sensitivity in strain-life fatigue calculation among engineering practitioners. A parameter optimisation technique using a multi-objective genetic algorithm is applied for the Chaboche model parameters by employing varying strain and stress controlled uniaxial data from tests on Aluminium Alloy 7075-T6. The parameters obtained from each of the optimisations and for various workflows, are then used in strain-life fatigue calculations with a Defence Science and Technology Group in-house software. Fatigue life predictions for P-3C aircraft load spectra are compared against experimental lives obtained from the Masing model to ascertain the parameters offering the most accurate results. The optimum uniaxial material dataset for strain-life predictions employing the Chaboche model is determined. The results of this study offer new insights of the model parameters' function and their sensitivity in fatigue predictions.

High Gain Rectangular Dielectric Resonator Antenna Using Uniaxial Material at Fundamental Mode

The use of uniaxial anisotropic materials in rectangular dielectric resonator antennas (DRAs) increases the radiation from their side walls compared to their top walls due to the fundamental radiating mode, which leads to the improvement of boresight directivity. The different boundary conditions on the walls of DRA are also investigated. The main phenomenon of gain enhancement is also theoretically explained. The proposed method is validated by comparing the simulation results for the cases of isotropic DRAs and anisotropic DRAs (ADRAs). The measured results for an aperture-coupled uniaxial ADRA show an impedance bandwidth of 20.65% between 3.17 and 3.9 GHz and a peak broadside gain of 8.4 dB.

Analysis of Magnetization Curves and Magnetocrystalline Anisotropy of Uniaxial Ferromagnets

Theoretical analysis of the processes of magnetization of uniaxial ferromagnetic materials is performed within the Neel theory of magnetic phases. Relations are obtained for the constants of magnetic crystal anisotropy K 1, K 2, the form factor N, and the saturation magnetization I s , at which the magnetization curves exhibit jumps (FOMP). Formulas for computing the saturation fields H s and the jump fields H FOMP are derived for crystals with different types of magnetocrystalline anisotropy MCA. It is shown that the Sucksmith–Thompson method is applicable for computing the first too MCAconstants of uniaxial ferromagnets with any type of MCA. Constants K 1 and K 2 are computed with allowance for the form factor of the specimen. Model magnetization curves are plotted for uniaxial ferromagnets with different types of MCA along and perpendicularly to crystallographic axis c. The analytical results match the model curves well.

Characterization of Hardening Behavior at Ultra-High Strain Rate, Large Strain, and High Temperature

This paper is concerned with the characterization of the OFHC copper flow stress at strain rates ranging from 10−3 s−1 to 106 s−1 considering the large strain and high temperature effects. Several uniaxial material tests with OFHC copper are performed at a wide range of strain rates from 10−3 s−1 to 103 s−1 by using a INSTRON 5583, a High Speed Material Testing Machine (HSMTM), and a tension split Hopkinson pressure bar. In order to consider the thermal softening effect, tensile tests at 25°C and 200°C are performed at strain rates of 10−3 s−1,101 s−1, and 102 s−1. A modified thermal softening model is considered for the accurate application of the thermal softening effect at high strain rates. The large strain behavior is challenged by using the swift power law model. The high strain rates behavior is fitted with the Lim–Huh model. The hardening curves are evaluated by comparing the final shape of the projectile from numerical simulation results with the Taylor impact tests.

Enhanced the tunable omnidirectional photonic band gaps in the two-dimensional plasma photonic crystals

In this paper, the features of omnidirectional band gap (OBG) in the two-dimensional (2D) plasma photonic crystals (PPCs) with triangular lattices are theoretically studied in detail by the modified plane wave expansion method as the off-plane incidence wave vector is considered, which are composed of the non-magnetized plasma cylinders inserted into the homogeneous and isotropic dielectric background. The simulated results demonstrate that a flatband region and the OBG can be obtained in the proposed PPCs. The influences of the radius of inserted cylinder and plasma frequency on the OBG are investigated. The calculated results illustrate that not only the tunable OBG can be obtained but also the achieved OBG also can be enlarged by optimizing those parameters. To enhance the OBGs, two novel configurations of PPCs are present. The computed results reveal that the proposed two configurations have the advantages of obtaining the larger OBGs compared to the conventional 2D PPCs since the symmetry of 2D PPCs is broken, and the OBGs also can be manipulated obviously by changing the geometric parameters of such two PCs structures. Introducing the anisotropic dielectric (uniaxial material) into the proposed 2D PPCs to enlarge the OBGs also is studied. The effects of ordinary-refractive and extraordinary-refractive indices of uniaxial material on the properties of OBGs also are investigated in theory, respectively. The computed results show that the OBGs can be enlarged by introducing the uniaxial material, and the OBGs also can be tuned by changing the parameters of uniaxial material.

Reflection formulae for ray tracing in uniaxial anisotropic media using Huygens's principle.

Ray tracing in uniaxial anisotropic materials is important because they are widely used for instrumentation, liquid-crystal displays, laser cavities, and quantum experiments. There are previous works regarding ray tracing refraction and reflection formulae using the common electromagnetic theory approach, but only the refraction formulae have been deduced using Huygens's principle. In this paper we obtain the reflection expressions using this unconventional approach with a specific coordinate system in which both refraction and reflection formulae are simplified as well as their deduction. We compute some numerical examples to compare them with the common expressions obtained using electromagnetic theory.

Non-destructive characterization of fiber orientation in reinforced SMC as input for simulation based design

The macroscopic properties of materials are strongly influenced by their microstructure. This holds in particular for fiber reinforced composites where fiber distribution and orientation are crucial for the reinforcement to serve its purpose. This essential microstructural information can be obtained from high-resolution images using appropriate methods for quantitative image analysis. Sheet molding compounds feature a very dense layered system of reinforcing fibers and a particularly strong X-ray absorption. Therefore, in this case, state-of-the-art fiber orientation analysis based on 3D images obtained by X-ray microtomography faces problems. In this paper, we determine the local fiber orientation in each pixel by the orientation of the anisotropic Gaussian filter yielding the strongest filter response. Hence, the local fiber orientation can be computed without identifying individual fibers. From the thus determined area weighted orientation distribution, the degree of anisotropy and the main fiber orientation are derived. This extremely robust analysis method is applied to 2D slice images from scanning acoustic microscopy and high-resolution 3D microtomography. We show that the Gaussian filter based fiber orientation analysis method yields comparable results for both imaging techniques. Moreover, comparison with fatigue tests performed on the same specimens proves the image analytically determined fiber orientation and the failure behaviour to be strongly correlated. In particular, a critical degree of anisotropy could be identified. For degrees of anisotropy higher than this limit, the samples behave mechanically like a uniaxial material. The paper thus provides experimentally validated evidence for calibrating micro-mechanical models for subsequent simulation of macroscopic material properties using the combination of high-resolution imaging techniques and quantitative image analysis.

Effect of anisotropy on nonlinear surface plasmon polaritons in anisotropic/metal/nonlinear slab waveguides

The nonlinear surface plasmon polariton (SPP) supported by a linear/metal-nonlinear slab waveguide was studied analytically. The dispersion conditions were obtained from fundamental Maxwell’s equations to determine the propagation characteristics of the nonlinear SPPs supported by the waveguide. The mode profile of the nonlinear mode was studied to analyze the physics behind the observed propagation characteristics. After studying propagation characteristics of the mode, the linear layer was replaced with a layer containing a uniaxial material. The effect of optical anisotropy of the layer on the dispersion characteristics of the nonlinear SPPs was investigated to understand the possible tunability of the mode. It has been observed that the propagation characteristics of modes supported by the waveguide can be tuned with the help of an anisotropic medium. The guiding structure could find application in the tunable components in all-optical integrated chips.

Validation of the Hardening Behaviors for Metallic Materials at High Strain Rate and Temperature by Using the Taylor Impact Test

This paper is concerned with the validation of the dynamic hardening behaviors of metallic materials by comparing numerical and experimental results of the Taylor impact tests. Several uniaxial tensile tests are performed at different strain rates and temperatures by using three kinds of materials: 4130 steel (BCC); OFHC copper (FCC); and Ti6Al4V alloy (HCP). Uniaxial material tests are performed at a wide range of strain rates from 10−3 s−1 to 103 s−1. Moreover, tensile tests are performed at temperature of 25 °C and 200 °C at strain rates of 10−3 s−1, 10−1 s−1, and 102 s−1, respectively. A modified Johnson–Cook type thermal softening model is utilized for the accurate application of the thermal softening effect at different strain rates. The hardening behaviors of the three materials are characterized by comparing the seven sequentially deformed shapes of the projectile from numerical and experimental results of Taylor impact tests.

Micromechanical investigation into the effect of texture on the fatigue behaviour of superelastic nitinol

One material that has found particular favour for use in the manufacture of biomedical endovascular stents is the near equiatomic NiTi alloy, Nitinol. Stents are typically laser-cut from textured micro-tubing; texture is the distribution of crystallographic grain orientations in a polycrystalline material. Despite the well documented dependence of mechanical behaviour on crystallographic texture, the standard computational design practice for such stents simply calls for the use of uniaxial homogenous material properties which assumes continuum material behaviour. This study offers a computational examination into the effect of crystallographic texture on NiTi’s fatigue behaviour in order to highlight concerns with this current design practice. The computational methodology first developed by Bruzzi and McHugh (2002), and modified for use with superelastic NiTi by Weafer and Bruzzi (2016), is adapted to include crystallographic texture. This defect tolerant approach correlates local crack-tip driving force conditions of an initial small crack with an experimental long crack growth rate curve, using crack closure. Computationally derived predictions of fatigue life are compared for superelastic NiTi specimens considering the material as (1) a continuum material with homogenous behaviour, and (2) a textured material with anisotropic granular behaviour, presented using both realistic and idealised microstructural features. In this manner, further insight is achieved into the effect of crystallographic texture on the fatigue behaviour of superelastic NiTi and offers a quantitative explanation towards the observed scatter in experimental fatigue data.

Mechanical behaviour of scaled-down unsupported tunnel walls in hard rock under high stress

A large number of scaled-down tunnel experiments were undertaken to investigate the response of unsupported walls to an increased stress field. The experiments were undertaken in 200mm diameter tunnels that were drilled into intact rock blocks of sandstone and granite ranging in strength from moderately strong to very strong. The tunnels were loaded by a servo-controlled, 450 tonne capacity INSTRON compression testing machine. As the ratio of intact rock strength to induced stress decreased, the unsupported tunnel walls became increasingly unstable. Critical ratios of compressive strength to induced stress were determined for critical instability stages such as tunnel spalling and also pillar crushing adjacent to the tunnels. The physical models have been simulated using three-dimensional finite element modelling. The values of the critical ratios correlate well with underground observations of full scale tunnels with similar Uniaxial Compressive Strength materials. Dynamic ejection velocities similar to those calculated from back analysis of actual failures have been determined. In addition, the seismic responses prior and during key failure stages have been established as a function of the increased loadings.

Yielding behaviors of polymeric scaffolds with implications to tissue engineering

Polymers are amongst the main candidate materials for load bearing tissue engineering scaffolds. Their effective and reliable clinical uses necessitate insightful analyses of the nonlinear characteristics, which has so far received little attention in literature. To better understand the failure characteristics of these porous structures, yielding behaviors of scaffolds made of a commercial photopolymer (RGD720) were studied using experiments and finite element method (FEM). The polymer exhibits substantial softening under uniaxial material test, but the extent of such softening behavior in a scaffold structure is compromised or even eliminated due to the internal non-uniformity of material yielding.

Analysis of magneto-optical properties for three-dimensional photonic crystals in high-symmetry arrangement doped by metamaterials and uniaxial materials

Abstract In this paper, we use a modified plane wave expansion (PWE) method to investigate the properties of photonic band gaps (PBGs) for the extraordinary mode in the three-dimensional (3D) photonic crystals (PCs) which are composed of the anisotropic dielectric (the uniaxial materials) spheres immersed in the homogeneous metamaterials (epsilon-negative materials) background with high-symmetry (body-centered-cubic) lattices, as the magneto-optical Voigt effects are considered. The equations for calculating the PBGs in the first irreducible Brillouin zone are theoretically derived. It is numerically illustrated that the anisotropic PBGs and two flattened band regions can be achieved. The influences of the ordinary-refractive index, extraordinary-refractive index, filling factor of dielectric spheres, electronic plasma frequency and cyclotron frequency on the magneto-optical properties of such 3D PCs also are studied in detail, respectively, and some corresponding physical explanations are given. The numerical results demonstrate that the anisotropy can open partial band gaps in the proposed PCs, and the complete PBGs can be obtained compared with the conventional PCs only containing the isotropic material with similar structures. The bandwidths of PBGs can be tuned by introducing the epsilon-negative materials into such PCs containing the uniaxial materials. The anisotropic PBGs can be manipulated by the parameters as mentioned above. As the proposed PCs with high-symmetry lattices, the complete PBGs can be obtained by introducing the uniaxial materials.

Constitutive Model for Reinforcing Steel under Cyclic Loading

AbstractThe hysteretic stress-strain response of steel reinforcement can significantly affect the performance of reinforced concrete (RC) structures. Additionally, the possibility of inelastic buckling and fracture of longitudinal bars can have a negative impact on the ductility of RC flexural members. This paper presents a uniaxial material model to describe the inelastic behavior of reinforcing steel under cyclic loading. As a starting point, an existing hysteretic law is employed, which is capable of capturing the material behavior in the absence of buckling and rupture. One issue with this existing law is the need for an iterative stress calculation. A series of enhancements to the hysteretic law are established, including the formulation and implementation of a noniterative stress update procedure and the capability to efficiently account for local inelastic buckling and rupture due to low-cycle fatigue. The proposed material model is validated using the results of experimental tests.