Nonhomogeneous Materials Research Articles

Numerical investigation of pre-flawed FGM tubes repaired with different composite jackets under sequential gaseous detonation loading

Investigation on the structural response of pre-flawed functionally graded material (FGM) cylindrical tubes submitted to sequential detonation loading is the main contribution of this study. Analyses are made for repaired and unrepaired tubes using three different composite patch (CP) geometric shapes: full cylindrical, semi-cylindrical, and circular. The effect of non-homogeneous FGM materials (ceramic-to-aluminum, aluminum-to-ceramic, and steel-to-ceramic) and CPs on the stress field in the tube is studied using three-dimensional finite element (FE) models. The FE analyses are conducted for two distinct categories of detonation loading: low- and high-pressure detonations. This approach helps to enhance the understanding of how material gradation influences stress distribution and damage assessment in tubes subjected to these specific loading conditions. The FE analyses revealed that both forward and reflective waves coming from detonation load significantly contribute to crack propagation by elevating stresses near crack tips. The application of CPs, made of boron/epoxy material, effectively mitigated stress concentrations across all FGMs, with full cylindrical CPs providing the best results. Delamination was observed in CPs with two composite layers under high-pressure loading, particularly in aluminum-to-ceramic FGM.

Modeling and Parameter Selection of the Corn Straw–Soil Composite Model Based on the DEM

During corn harvesting operations, machine–straw–soil contact often occurs, but there is a lack of research related to the role of straw–soil contact. Therefore, in this study, a composite contact model of corn straw‒soil particles was established based on the discrete element method (DEM). First, the discrete element Hertz‒Mindlin method with bonding particle contact was used to establish a numerical model of the double-bonded bimodal distribution of corn straw, and bonding particle models of the outer skin‒outer skin, inner pulp‒inner pulp, and outer skin‒inner pulp were developed. The nonhomogeneous and deformable material properties were accurately expressed. The straw compression test combined with simulation calibration was used to determine some of the bonding contact parameters by means of the PB (Plackett–Burman) test, the steepest ascent test, and the BB (Box–Behnken) test. Additionally, Additionally, the Hertz-Mindlin with JKR (Johnson-Kendall-Roberts) + bonding key model was used to establish the numerical model of the soil particles, which was used to describe the irregularity and adhesion properties of the soil particles. The geometric model of the soil particles was established using the multisphere filling method. Finally, a composite contact model of corn straw‒soil particles was established, the contact parameters between straw and soil were calibrated via collision tests, inclined tests and inclined rolling tests, and the established composite contact model was further verified through direct shear tests between straw and soil. A theoretical foundation for the optimal design of equipment linked to maize harvesting is provided by this work.

Applying heterogeneous building materials for the protection of people against electromagnetic radiation

The object of this study is the processes of shielding electromagnetic radiation by building and facing materials. The research is aimed at solving the problem of ensuring the electromagnetic safety of people by improving the composition and structures of building and facing materials. Means for improving the electromagnetic safety of people under industrial and domestic conditions using non-homogeneous building materials have been determined. The shielding properties of reinforced concrete structures were studied. A methodology for increasing their efficiency depending on the amplitude-frequency characteristics of the radiation that needs shielding has been devised. The efficiency of electromagnetic radiation shielding by heterogeneous dielectric building materials based on cement concrete and basalt fibers was determined. It was established that shielding through the refraction of electromagnetic waves on inhomogeneities does not give an acceptable effect. The expediency of covering basalt fibers with a conductive substance to increase the protective properties of materials was substantiated. The protective properties of flat facing material with carbonyl iron content were studied. It has been shown that the properties of materials can be effectively controlled by adjusting the filler. The material's transmission coefficient of ultra-high frequency electromagnetic radiation does not exceed 0.40, and the reflection coefficient – 0.25 with a filler content in the base of 14–15 % by volume. This makes it possible to simultaneously ensure the electromagnetic safety of people and the stable functioning of wireless communication devices. The advantage of the material is the low coefficients of reflection of electromagnetic waves, which does not lead to deterioration of the electromagnetic situation in other areas where people stay. It has been established that the addition of boron nitride to the facing material significantly increases the thermal insulation characteristics of the coating and contributes to the solution of energy saving problems. Adding a layer containing boron nitride to the material provides thermal conductivity coefficients of 0.030–0.031 W/m·K, which is better than known analogs

Electromagnetic surface waves guided by the interface of a metal and a tightly interlaced matched ambidextrous bilayer

The existence and characteristics of electromagnetic surface waves (ESWs) whose propagation is guided by the planar interface of metal and a tightly interlaced matched ambidextrous bilayer (TIMAB) were theoretically investigated, a TIMAB being a periodic unidirectionally nonhomogeneous material whose unit cell consists of one period each of two structurally chiral materials that are identical except in structural handedness. Thus, the structural handedness flips in the center of the unit cell. A canonical boundary-value problem was formulated and a dispersion equation was solved, the ESWs being classified as surface-plasmon-polariton (SPP) waves. Flipping the structural handedness once in the unit cell can greatly enhance the number of possible SPP waves, one or more of which may be superluminal.

Stability of arches with internal hinge

The in-plane stability of internally hinged, end-fixed shallow arches is in the spotlight. The non-linear model accounts for the coupled effect of the bending moment and axial force on the membrane strain. The model itself can handle homogeneous or non-homogeneous material distributions along the thickness of the uniform arch. Analytical findings reveal how the typical geometrical data, like arch length, radius of gyration, and arch angle, affect the lowest buckling loads. The typical non-linear behaviour of arches is also assessed including the equilibrium path and the internal force system.

Application of Femtosecond Laser Processing Method in the Sustainable Conservation of Stone Cultural Relics: An Example of Green Schist in Wudang Mountain, China

The ancient building complex in Wudang Mountain, China, is known as the “Museum of Ancient Chinese Architectural Accomplishments”. However, the valuable stone components are preserved in open or semi-open environments and environmental factors such as rain seriously threaten its sustainable conservation. In this context, a femtosecond laser processing method has been demonstrated to be able to prepare hierarchical micro-nano structures on the stone surface to regulate its wettability, achieving the purpose of sustainable conservation. In this paper, the processing mechanism and performance of the femtosecond laser on green schist, a local stone material in the Wudang Mountain, are systematically investigated. It is found that green schist, as a typical non-homogeneous material, exhibits significant differences in its absorption of femtosecond laser with different compositions. Among them, quartz, chlorite, and muscovite are the three main compositions, and they are mainly characterized by cold ablation, thermal melting, and expansion under the irradiation of the femtosecond laser (238 fs, 100 kHz, 40 μJ, 33 μm, 500–40,000 pulses), respectively, and it is difficult to achieve a uniform and stable surface structure. Based on this, we prepared grooves with a spacing of 100–400 μm by scanning the femtosecond laser. Through the characterization of surface morphology, elemental composition, and three-dimensional structure, the processing mechanism of the hierarchical micro-nano structures of green schist under the irradiation of the femtosecond laser is comprehensively revealed. Finally, the wettability modulation result of water contact angle up to 147° is achieved by processing the grooves with an optimal spacing of 400 μm. The results of this research are of guiding significance for the sustainable conservation of ancient buildings and cultural relics.

Analysis of an interfacial crack between two nonhomogeneous piezoelectric materials using a new domain-independent interaction integral

Considering the difficulties introduced by piezoelectric material non-homogeneity and discontinuities to interfacial crack analysis, a domain-independent interaction integral (DII-integral) is proposed to derive the stress intensity factors (SIFs) and electric displacement intensity factor (EDIF) of an interfacial crack between nonhomogeneous piezoelectrics. For continuously varying material properties, traditional interaction integral (I-integral) needs to compute the derivatives of material parameters with respect to the x1 direction of the local coordinate system, while the proposed DII-integral is demonstrated to be unrelated to any derivatives of material parameters. Furthermore, a significant improvement is achieved that the new formulation of I-integral remains valid even when the integration domains include intricate and multiple interfaces, as long as the material interfaces are perfectly bonded. Firstly, the intensity factors (IFs) calculated by the combination of the DII-integral and the extended finite element method are compared with the analytical solutions, and it is found that the relative errors of the IFs are all less than 1.79 % with various crack lengths, which verifies the accuracy of the proposed method. For the piezoelectric bi-material model with continuously nonhomogeneous properties, the calculated IFs match each other well (relative deviation < 1.3 %) for different sizes of integration domains. In addition, for the perfectly bonded interface with discontinuous electromechanical properties, the IFs are almost identical (relative deviation < 0.85 %) whether or not the integration domain contains the material interface, which further numerically verifies the good domain-independence of the established DII-integral. For an interfacial crack near extra interfaces, the differences in elastic stiffness and piezoelectric coefficient between interface sides have an obvious influence on mode-I SIF, but mode-II SIF and EDIF are affected mainly by piezoelectric coefficient and dielectric permittivity.

Magnetic effects on surface waves in a rotating non-homogeneous half-space with grooved and impedance boundary characteristics

Investigation on the Mathematical modeling of waves in a rotating grooved and impedance boundary of a non-homogeneous fibre-reinforced solid half‐space under the influence of magnetic field and mechanical force is envisaged. We derived analytically, the dynamical equations for the rotating grooved and impedance boundary of the non-homogeneous fibre-reinforced solid under the influence of magnetic fields and mechanical force. Harmonic solution method of wave analysis is utilized. This is such that the component of displacements and stresses are developed and studied after employing dimensionless parameters in the equations of motion. Numerical computations are presented in graphical form by using Mathematica Software for a particular chosen material. We observed that the combined grooved, magnetic fields, impedance boundary etc. physical parameters, have remarkable effects on the material. A decrease in horizontal impedance yielded maximum amplitudes of displacements and stresses of the waves on the fibre-reinforced medium. The mechanical force and rotation of the medium induced increased behaviors to the amplitudes of displacement and stress components of the wave on the solid medium. Thus, this work should be of great importance in studies involving seismology and seismic Mechatronics solution for stress-wave generation in non-homogeneous materials.

FEATURES OF THE CONSTRUCTION OF THE STIFFNESS MATRIX OF THE SPATIAL HEXAGONAL FINITE ELEMENT FOR COMPOSITE MATERIAL WITH DISCRETE INCLUSIONS BASED ON THE MOMENT SCHEME

An approach to numerical modeling of the stress-strain state of composite structures with discrete inclusions is presented in the paper. The finite element method is used as the main method, namely its modification – the moment finite-element scheme. The moment scheme, in contrast to the classic scheme of finite elements, allows to avoid such negative properties as not taking in consideration the rigid rotation of the finite element and “false” shear. If both the material of the matrix and the material of the reinforcing inclusions are weakly compressible, then problems arise due to the fact that some elastic constants approach very large values. The Taylor series expansion of the components of the displacement vector, the components of the strain tensor, and the volume change function is used in order to eliminate the mentioned shortcomings, after that, according to the moment scheme, certain sums are removed from these expansions. Homogenization of the material with lamellar inclusions, a small proportion of spherical inclusions, and a large proportion of spherical inclusions is used for modeling the elastic properties of the composite. The chaotic nature of the location of inclusions after homogenization makes it possible to present a non-homogeneous composite material as a homogeneous quasi-isotropic one. The described approaches are used in the construction of the stiffness matrix of the spatial hexagonal finite element. The obtained expressions for the stiffness matrix are done in the software package for calculating structures from composite materials. The calculation of a thick-walled pipe under the action of internal pressure from a composite material with lamellar inclusions, a small proportion of spherical inclusions, and a large proportion of spherical inclusions was carried out using the software package. For different volume fractions of discrete inclusions, the numerical convergence of the results with different finite element meshes has been investigated, which shows great congruence with analytical solutions.

Investigation into compressive property, chloride ion permeability, and pore fractal characteristics of the cement mortar incorporated with zeolite powder

As a non-homogeneous porous material, the microstructure of cementitious composites critically affects the mechanical and durability properties. This paper aims to analyze the effect mechanism of cement replacement by zeolite powder on the microscopic pore structure characteristics, macroscopic mechanical behavior, and durability of mortar to reduce cement consumption and improve mortar performance. The compressive strength and chloride ion permeability of mortar incorporated with zeolite powder were experimentally determined, and the effects of zeolite powder content on the composition of cement hydration products and pore structure were further analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and mercury intrusion porosimetry (MIP). The pore structure characteristics were quantitatively analyzed by fractal theory. The results shows that incorporating zeolite powder in cement mortar fills the pores, promotes secondary hydrate formation, reduces the Ca/Si ratio, refines the pore size, and reduces the porosity of large pores. Thus, the internal pore structure of the matrix is significantly improved, reducing the pore fractal dimension and improving the compressive strength and chloride ion penetration resistance. 15% cement replacement zeolite powder has been found optimal in reducing the porosity and chloride ion permeability coefficient while enhancing the compressive strength. The pore structure fractal dimensions calculated by the Menger sponge fractal model can quantitatively describe the pore structure distribution characteristics, which can help ascertain the relationship between zeolite powder content, pore structure quantitative characteristics, and macroscopic mechanical behaviors.

The uniqueness of some singular Kirchhoff equations with non-homogeneous material

The uniqueness of some singular Kirchhoff equations with non-homogeneous material

Coupling homogeneous chains of damped harmonic oscillators

We study vibrational properties of non-homogeneous materials. We consider idealized materials composed of one dimensional chains of damped harmonic oscillators represented by a sequence of particles, springs and dampers. The system is linear, thus possesses exact explicit solutions, nevertheless the formulas can be very complicated. Homogeneous chains are used as basic building blocks for characterizing global dynamics of the system. In particular, we determine the solutions for a system composed of two distinct homogeneous chains in terms of the original solutions for these two homogeneous chains, and the original parameters, when uncoupled. Two types of coupling are considered, one with a gluing particle, the other with a gluing spring and damper.

Enhanced peroxymonosulfate activation by highly magnetic FeCo-CoFe2O4 biphasic fibers for norfloxacin degradation

Transition metal-based non-homogeneous materials have excellent activation properties for persulfates (peroxymonosulfate and peroxydisulfate, abbreviated as PMS and PDS). In this study, FeCo-CoFe2O4 (FC-CFO) biphasic fibers were prepared using the electrospinning technique and a stepwise heat-treatment. The prepared fibers possessed magnetic separation properties (Ms = 91.7 emu/g) and achieved a 93.8 % degradation efficiency of norfloxacin (NFX) in 10 min. Quenching experiment, ESR spectrum, and intermediate product revealed that radical •SO4− and non-radical 1O2 species made major contribution to the FC-CF-500/PMS/NFX system. XPS spectrum and ESR spectrum of oxygen vacancy suggested the abundant oxygen vacancies generated in FC-CFO-500 fibers which could trigger the generation of 1O2. Those findings may demonstrate a reference preparation method of electrospinning nanofibers with an improved PMS activation ability.

Development of a low-medium temperature T-history setup for the thermal storage characterization of non-homogeneous mixtures containing PCMs

More attention has been paid to thermal energy storage in recent years for its advantages in heating and cooling applications to foster the use of renewable energies. As part of the design of new thermal energy storage materials, the characterization of specific heat capacity and phase change enthalpy is required. One of the most widespread methods for evaluating specific heat capacity and phase change enthalpy is differential scanning calorimetry (DSC). However, the small amount of required material means that DSC is not the most suitable method for non-homogeneous materials. This paper presents the development and validation of a low-medium temperature (<100 °C) T-history system for measuring specific heat capacity and phase change enthalpy as an economical alternative. Validation was carried out with paraffins used as phase change material and two data processing methods were applied. Only one of the methods was able to measure the specific heat capacity in the liquid and solid phases, and the phase change enthalpy. Acceptable deviations calculated as the relative error in relation to DSC and manufacturer values were obtained with values lower than 18.50 % and 14.58 % respectively. The new system was used to evaluate the thermal properties of a pure paraffin/water emulsion and a hybrid carbon-paraffin/water emulsion by corroborating its suitability for measuring non-homogeneous samples.

Generalized dynamic domain-independent interaction integral in the transient fracture investigation of magneto-electro-elastic composites

The domain-independent interaction integral (DII-integral) is a powerful tool for dealing with crack issues of nonhomogeneous materials, due to its feature of being independent of the scale of integration domain, regardless of the nonhomogeneous properties and complex material interfaces. As an important part of the interaction integral (I-integral), the auxiliary field conditions required to establish the dynamic DII-integral have not been clearly clarified so far. For the first time, this work rigorously proves and gives the requirements of the auxiliary fields for building the dynamic DII-integral in anisotropic linear elastic, piezoelectric (PE), piezomagnetic (PM) and MEE materials, respectively, and a theoretical framework is derived for designing the dynamic DII-integral for new functional materials in the future. This proof guarantees the successful utilization of DII-integral to investigate the transient response in cracked composites without employing homogenized material parameters, while considering internal microstructure and complex interfaces. Using the extended finite element method (XFEM) as a pre-processing technique, the accuracy of the DII-integral is verified by comparing available references. Then, the domain-independence is confirmed with multiple integration domains, especially for those containing interfaces. Finally, the arrangements of PE/PM layers, locations and distributions of PE/PM particles affecting dynamic IFs are systematically investigated. Simultaneously, illustrations of elastic wave in cracked MEE composites are depicted to better understand the dynamic fracture response.

Phase velocity analysis by multi-parametric variations in a highly heterogeneous sandwich plate structure embedded in the Pasternak foundations with viscoelastic interlayer

This investigation explores the vibrational response of a sandwich plate with material parameter nonhomogeneity and a viscoelastic core, incorporating Pasternak foundations. The study views the equation of motion from an anti-plane shear perspective, presenting a generalized exact dispersion relation (GEDR). It analyzes the impact of parameters like material nonhomogeneity, viscoelasticity, and Pasternak foundation properties on the dimensionless phase velocity against wave number. Findings reveal decreasing phase velocity with increasing wave number, with nonhomogeneity and Pasternak parameters exerting substantial influence. The study offers valuable insights into composite material wave behavior, benefiting design methodologies for diverse applications.

Analyzing of continuous and discontinuous contact problems of a functionally graded layer: theory of elasticity and finite element method

Contact mechanics analysis is crucial because such problems often arise in engineering practice. When examining contact mechanics, the material property of the contacting components is a crucially significant aspect. It is more complex to solve the contact mechanics of systems that are composed of materials that do not have a homogenous structure compared to materials that have homogeneous qualities throughout. While many studies on contact problems with homogeneous materials exist, those involving non-homogeneous materials are scarce in the literature. As material technology improves fast, there will be a greater need to solve such problems. In this respect, analytical and finite element method (FEM) solutions of the continuous and discontinuous contact problems of a functionally graded (FG) layer are carried out in this article. The FG layer in the problem rests on a rigid foundation and is pressed with a rigid punch. From the solutions, the contact length, contact stress, initial separation distance, and beginning and ending points of separation were determined, and the results were compared. It has been concluded that the FEM findings are consistent with the analytical results to a satisfactory degree. This study analyzes contact problem using different approaches and accounts for the influence of body force in a contact geometry that has yet to be reported.

Grading bamboo through four-point bending tests. A report on six species of Italian bamboo

The adoption of natural construction materials can help mitigate the environmental impact of the construction industry by reducing the amount of energy required and emissions. Among the natural materials, bamboo is a remarkable option, combining high mechanical resistance with a low specific weight and a very high growth speed; however, its application is limited by the absence of a suitable grading method. This paper aims at filling this lack by providing a strength-based grading methodology relying on a four-point bending test. Experimental results were processed considering bamboo both as a homogeneous material and as a non-homogeneous material and using the ANOVA test. Results show that statistical groups can be defined which are not based on the bamboo species, but on the values of the mechanical properties, hence supporting the appropriateness of strength classes. The bending tests used in this paper could be a crucial test for bamboo grading: it is easier to perform than a tensile test and it gives complete information on the change of material properties along the culm wall thickness. The study focuses on six different species of bamboo grown in Italy, for which little data is present in the literature.

Analytical Approach for Sharp Corner Reconstruction in the Kernel Free Boundary Integral Method during Magnetostatic Analysis for Inductor Design

It is very important to perform magnetostatic analysis accurately and efficiently when it comes to multi-objective optimization of designs of electromagnetic devices, particularly for inductors, transformers, and electric motors. A kernel free boundary integral method (KFBIM) was studied for analyzing 2D magnetostatic problems. Although KFBIM is accurate and computationally efficient, sharp corners can be a major problem for KFBIM. In this paper, an inverse discrete Fourier transform (DFT) based geometry reconstruction is explored to overcome this challenge for smoothening sharp corners. A toroidal inductor core with an airgap (C-core) is used to show the effectiveness of the proposed approach for addressing the sharp corner problem. A numerical example demonstrates that the method works for the variable coefficient PDE. In addition, magnetostatic analysis for homogeneous and nonhomogeneous material is presented for the reconstructed geometry, and results carried out using KFBIM are compared with the results of FEM analysis for the original geometry to show the differences and the potential of the proposed method.

Transient heat transfer analysis of the porous nonhomogeneous material structure

Transient heat transfer analysis of the porous nonhomogeneous material structure