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This study is focused on the application of 3D-printed elements and conventional elements to create a prototype of a custom-made exoskeleton for lower limb rehabilitation. The 3D-printed elements were produced by using Fused Deposition Modeling technology and acrylonitrile butadiene styrene (ABS) material. The scope of this work involved the design and construction of an exoskeleton, experimental testing of the ABS material and numerical research by using the finite element method. On the basis of the obtained results, it was possible to deduce whether the load-bearing 3D-printed elements can be used in the proposed mechanical construction. The work contains full data of the material models used in FEM modeling, taking into account the orthotropic properties of the ABS material. Various types of finite elements were used in the presented FE models. The work is a comprehensive combination of material testing issues with the possibility of implementing the obtained results in numerical strength models of machine parts. [ABSTRACT FROM AUTHOR]

A meshfree orthotropic laminated shell model for geometrically nonlinear static and dynamic analysis based on the reproducing kernel particle method (RKPM) and the Mindlin-Reissner shell theory is proposed for the first time, suitable for dealing with the finite deformation of composite shell structures of arbitrary geometry in engineering. The Mindlin-Reissner shell theory is adopted to describe the geometric configuration of the laminated shells via a single-layer particle. Then, the Galerkin weak form governing equations are established explicitly and discretized using RKPM and linear transformation in the thickness direction. Furthermore, a laminate stacking sequence that can eliminate the coupling terms of linear and angular acceleration is proposed for simplification. For considering the orthotropic materials, the stress–strain transformation between local and material coordinates is introduced. A stiffened laminated shell model is also presented for simulating complex composited structures. The accuracy and convergence of the proposed laminated shell model are verified through several static and dynamic benchmarks, demonstrating the ability of the presented model to solve the nonlinear response of composite structures. [ABSTRACT FROM AUTHOR]

To investigate the crack growth behavior in a cladded structure, a numerical simulation method based on the extended finite element method (XFEM) was developed. This method employs 8-node hexahedral continuum elements enriched only with the Heaviside step function, which can model planar crack independently of finite elements. For a crack across the interface of dissimilar materials in cladded structures, stress intensity factors along the crack front are evaluated by the domain integral method. Crack front shapes are updated by using Paris’ law and then smoothed by cubic Bézier curves in each region. In addition, fatigue crack propagation analyses for cladded compact tension [C(T)] specimens were performed. The relationships between crack length and load cycles as well as the transition of propagating crack front shapes were compared with experimental results and validated. Furthermore, sensitivity analyses were performed to explore the influence on the crack propagation behaviors of analysis parameters and conditions. The developed method was shown to provide an appropriate approximation of fatigue crack growth behaviors in cladded C(T) specimens.

Nowadays, the interaction of additive technologies and methods for designing or optimizing porous structures has yielded good results. Construction with complex microarchitectures can be created using this approach. Varying the microarchitecture leads to changes in weight and mechanical properties. However, there are problems with geometry reconstruction when dealing with complex microarchitecture. One approach is to use Voronoi cells for geometry reconstruction. In this article, an extension of the Voronoi diagram algorithm to orthotropic space for material structural design is presented. The inputs for the method include porosity, ellipticity, and ellipticity direction fields. As an example, a beam with fixed end faces and center kinematic loading was used. To estimate robust results for different numbers of clusters, 50, 75, and 100 clusters are presented. The porosity for smoothed structures ranged from 21.5% up to 22.8%. The stress–strain state was determined for the resulting structures. The stiffness for the initial and smoothed structures was the same. However, in the case of 75 and 100 clusters, local stress factors appeared in the smoothed structure. The maximum von Mises stress decreased by 20% for all smoothed structures in the area of kinematic loading and increased by 20% for all smoothed structures in the area of end faces. [ABSTRACT FROM AUTHOR]

The present research is concerned with the reflection phenomenon of plane waves in an orthotropic micropolar thermoelastic medium with diffusion and two-temperature. The governing equations of the present investigation are formulated in the context of dual-phase lag theory. The plane wave solutions of the governing equations imply the emergence of five plane waves, namely quasi longitudinal displacement wave, quasi thermal wave, quasi mass diffusion wave, quasi transverse micro-rotational wave and quasi transverse displacement wave. Using the relevant boundary conditions, the amplitude ratios and energy ratios for various reflected waves are calculated. The phase speeds, reflection coefficients and energy ratios are computed numerically with the help of MATLAB programming and are depicted graphically to show the effect of diffusion parameter and anisotropy. It is found that there is no dissipation of energy at the boundary surface during reflection. On the other hand, some attempts have also been made to explore the three-dimensional responses of the thermoelastic medium. Some particular cases of interest have been inferred from the present problem. [ABSTRACT FROM AUTHOR]

A deep understanding of the material parameters and the behavior of sandwich panels, which are used in the construction industry as roof and façade cladding, is important for the design of these construction components. Due to the constant changes in the polyurethane (PU) foams used as a core material, the experimental database for the current foams is small. Nowadays, there is an increasing number of failures of façade and roof panels after installation. This article presents a variety of experimental investigations on sandwich panels from two manufacturers with a core of polyisocyanurate (PIR) rigid foam (density: 40 kg/m3). As part of this study, compression, tension, shear, and bending tests were performed in several spatial directions and over the range required by the standard. The results of the tests showed the orthotropy of the core material and the dependence of the material on the direction and type of load. The stress-strain curves showed linear and non-linear areas. Using the data from this experimental study, a numerical model was implemented which utilized the Hill yield criterion to represent the orthotropy of the core material. The present investigation suggests that the classical von Mises failure criterion, used in many studies, is not suitable for the foam system applied in these sandwich panels. Instead, the Tsai–Wu criterion is more appropriate for defining the failure stresses. [ABSTRACT FROM AUTHOR]

A comprehensive study has been conducted on the thermo-elastic behavior of a polar orthotropic rotating functionally graded disk, focusing on the effects of grading indices and thermal field on various stress and displacement parameters. The normalized radial stress, tangential stress, and normalized displacement of a hollow annular disk rotating at a constant angular speed were examined under different thermal conditions and grading indices. The study posed a significant challenge in determining the stress fields in a rotating disk, which required solving a specific second-order differential equation. After validation of the proposed methodology, the problem was solved for a rotating disk under a thermal field, and the results were obtained for both free-free and fixed-free boundary conditions. The objective of this research was to investigate how the material gradation and thermal loading impact the deformation and stresses of an annular disk, which was accomplished through the use of the point collocation method—a numerical technique used to compute the normalized stress, strain, and displacement components in the radial direction. This research provides insights into the behavior of annular disks under different conditions and has practical implications for designing and analyzing various engineering applications such as rotating machinery, aerospace components, and energy systems. [ABSTRACT FROM AUTHOR]

This paper presents a new method to model the nonlinear behavior of double-curvature masonry structures, possibly reinforced by composite materials, by means of conventional elasto-plastic analyses. The method is meant to be used in professional design, especially for assessment and retrofitting purposes, based on the exploitation of the simplest nonlinear finite elements available in commercial software, namely, trusses with elasto-fragile and elasto-ductile behavior (Cutoff Bars, according for instance to the definition provided by Strand7 R3.1.3a). Numerical static nonlinear analyses are carried out by considering elastic hexahedral elements for bricks and by lumping nonlinearities on joints. These are assumed, in turn, to be elastic–brittle and elastic–plastic by using 1D elements, namely, Point Contacts, under the No-Tension Material hypothesis, and Cutoff Bars, respectively, assigning a small tensile resistance to the material. The reinforcement, realized with FRP hooping strips, is successfully modeled in a similar fashion, i.e., by applying perfectly bonded elastic–plastic Cutoff Bars at the extrados of the dome, where debonding is accounted for in a conventional way, limiting the tensile strength according to Italian Standards' indications. The procedure is validated against benchmark models with the same geometry, using experimental data and more refined structural model results for comparison. After an in-depth analysis of the obtained results, in terms of capacity curves, the robustness and accuracy of the proposed approach are assessed. [ABSTRACT FROM AUTHOR]

This study is focused on the application of 3D-printed elements and conventional elements to create a prototype of a custom-made exoskeleton for lower limb rehabilitation. The 3D-printed elements were produced by using Fused Deposition Modeling technology and acrylonitrile butadiene styrene (ABS) material. The scope of this work involved the design and construction of an exoskeleton, experimental testing of the ABS material and numerical research by using the finite element method. On the basis of the obtained results, it was possible to deduce whether the load-bearing 3D-printed elements can be used in the proposed mechanical construction. The work contains full data of the material models used in FEM modeling, taking into account the orthotropic properties of the ABS material. Various types of finite elements were used in the presented FE models. The work is a comprehensive combination of material testing issues with the possibility of implementing the obtained results in numerical strength models of machine parts.

In recent years, significant improvements in the design of leg blade prosthetics have been carried out. After several advances in material and topological optimisations, sport-purpose feet prosthetics have reached high-level performances, allowing athletes with limb loss to participate in various sport activities at a competitive level. Since the knowledge of prosthetic mechanical behaviour is crucial for its optimal design, specific studies are required to meet the anthropometric characteristics of the athlete. This research work is focused on investigating the dynamic behaviour of a running blade prosthetic and developing a validated prosthetic model, placing particular emphasis on the definition of suitable material properties. An experimental modal analysis is performed on the Cheetah Xcel, Össur lower limb prosthetic. In contrast with what has already been presented in the literature, a roving hummer test under free–free conditions is proposed here to avoid the uncertainties due to constraint conditions. For the first time, blade prosthetic dynamic characteristics in free–free conditions are presented. Additionally, a novel Finite Element model of the prosthetic is developed and tuned on the basis of the experimental results. The modal assurance criterion index is exploited to compare experimental and numerical mode shapes. Starting from frequency response functions, the first six mode shapes are experimentally identified in the frequency range up to 750 Hz, including both bending and torsion. As expected, the bending in the vertical plane constitutes the primary mode shape: this kind of flexion enhances energy storage, enabling athletes to achieve an optimal running gait. This study shows the dynamic modal behaviour of a lower limb prosthetic in free–free conditions and demonstrates that a traditional isotropic material is not suitable in describing its dynamic features. The development of a model that exploits orthotropic material properties improves the alignment between experimental and numerical outcomes. This result is in agreement with the material composition of the prosthetic, which consists of carbon fibre layers. [ABSTRACT FROM AUTHOR]

Most refined bending models of medium-thick plates, which consider transverse shear and partial compression deformations, differ little. However, despite a significant increase in the order of the governing differential equations, the results obtained from their equations give mainly a small increase in accuracy compared to the existing theories. On the other hand, such an increase in the order of the constructed systems of differential equations requires a significant increase in the effort required to solve them, complicates their physical interpretation, and narrows the range of people who can use them, primarily engineers and designers. Therefore, developing a plate-bending model that incorporates all the above factors and is on par with previously applied theories regarding the complexity of the calculation equations remains relevant. For example, most of the applied theories that do not consider transverse compression cannot be used to solve problems of contact interaction with rigid and elastic dies and bases because it is impossible to satisfy the conditions at the contact boundary of the outer surface of the plate, as well as the boundary conditions at the edges of the plate. Therefore, to provide guaranteed accuracy of the results, some researchers of these problems have introduced such a concept as “energy consistency” between the functions of representation of the displacement vector components, their number, the order of equations, and the number of boundary conditions. The authors, based on the developed version of the model of orthotropic plates of medium thickness, investigate the problem of taking into account the so-called “energy consistency” effect of the bending model, depending on the order of the design equations and the number of boundary conditions, as well as its usefulness and disadvantages in practical calculations. The equations of equilibrium in displacements and expressions for stresses in terms of force and moment forces are recorded. For rectangular and circular plates of medium thickness, test problems are solved, and the numerical data are compared with those obtained using spatial problems of elasticity theory, as well as the refined Timoshenko and Reissner theories. An analysis of the obtained results is provided.

Long-span shell structures are widely used in various industries. To ensure safe modes of operation, it becomes necessary to develop calculation methods and study shell structures for buckling under the applied load. Traditionally, these data are obtained using analytical and semi-analytical methods. This paper presents a description of the process of determining the critical buckling loads and obtaining the “load-deflection” dependences, taking into account large deformations. For this purpose, a method for analyzing the buckling of orthotropic shell structures based on the functionality of finite element software systems is proposed. The computational model of a cylindrical shell structure is presented based on the finite element method in the ANSYS Mechanical APDL 2020 software package. Computational experiments and a comparison of the buckling of structures made of various materials were carried out: steel S345, plexiglass (PMMA), CFRP M60J/Epoxy, GFRP T-10/UPE22-27. It is shown that the ANSYS Mechanical APDL 2020 software package makes it possible to obtain the necessary data for obtaining the “load-deflection” dependencies. For the analysis of large deformations, it can be used only with a sufficiently detailed description of the calculation parameters and the assumptions made for different materials. The values of the critical uniformly distributed load are obtained. Graphs of the dependence of the deflection on the load are presented. The process of deformation is studied, taking into account the geometric nonlinearity and the self-weight of shell structures. The calculation results can be used to automate the calculations of shell structures as an alternative to analytical methods.

A novel computational approach presented in this work to improve the accuracy and efficiency of fracture modeling in an orthotropic material medium. Extended finite element method (XFEM) with higher-order enrichment functions was employed at the different scale mesh topology. The approach combined variable node element concepts for different scale mesh connections and higher-order XFEM for accuracy and completeness of discontinuity domain. The proposed computational methodology was employed with in-house developed MATLAB code. Further, stochastic fracture studies were discussed for reliability of the cracked structures. Few numerical examples with multiple geometrical discontinuities were simulated to check the computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

The focus of this study is the experimental assessment of the mechanical behaviour of balsa wood and its sandwich structures, where balsa serves as the core, supported by carbon fibre-epoxy skin layers. A comprehensive characterisation is conducted on the mechanical behaviour of balsa wood and carbon fibre-epoxy balsa core sandwich structures subjected to a range of low strain rates. Initially, the study undertakes a consistent procedure for sample preparation. Subsequently, the characterisation of the manufactured composite structures is performed experimentally. A stereo microscope is employed for a detailed visual inspection of the internal structure of the balsa wood and the sandwich structures. Furthermore, the mechanical characterisation is carried out with three-point bending tests at a range of strain rates from 0.1 % to 6 % strain per minute. This research reveals key findings about balsa wood and its sandwich structures, highlighting their performance and their sensitivity even under low strain rates.

Nowadays, the interaction of additive technologies and methods for designing or optimizing porous structures has yielded good results. Construction with complex microarchitectures can be created using this approach. Varying the microarchitecture leads to changes in weight and mechanical properties. However, there are problems with geometry reconstruction when dealing with complex microarchitecture. One approach is to use Voronoi cells for geometry reconstruction. In this article, an extension of the Voronoi diagram algorithm to orthotropic space for material structural design is presented. The inputs for the method include porosity, ellipticity, and ellipticity direction fields. As an example, a beam with fixed end faces and center kinematic loading was used. To estimate robust results for different numbers of clusters, 50, 75, and 100 clusters are presented. The porosity for smoothed structures ranged from 21.5% up to 22.8%. The stress–strain state was determined for the resulting structures. The stiffness for the initial and smoothed structures was the same. However, in the case of 75 and 100 clusters, local stress factors appeared in the smoothed structure. The maximum von Mises stress decreased by 20% for all smoothed structures in the area of kinematic loading and increased by 20% for all smoothed structures in the area of end faces.

A deep understanding of the material parameters and the behavior of sandwich panels, which are used in the construction industry as roof and façade cladding, is important for the design of these construction components. Due to the constant changes in the polyurethane (PU) foams used as a core material, the experimental database for the current foams is small. Nowadays, there is an increasing number of failures of façade and roof panels after installation. This article presents a variety of experimental investigations on sandwich panels from two manufacturers with a core of polyisocyanurate (PIR) rigid foam (density: 40 kg/m3). As part of this study, compression, tension, shear, and bending tests were performed in several spatial directions and over the range required by the standard. The results of the tests showed the orthotropy of the core material and the dependence of the material on the direction and type of load. The stress-strain curves showed linear and non-linear areas. Using the data from this experimental study, a numerical model was implemented which utilized the Hill yield criterion to represent the orthotropy of the core material. The present investigation suggests that the classical von Mises failure criterion, used in many studies, is not suitable for the foam system applied in these sandwich panels. Instead, the Tsai–Wu criterion is more appropriate for defining the failure stresses.

This paper presents a new method to model the nonlinear behavior of double-curvature masonry structures, possibly reinforced by composite materials, by means of conventional elasto-plastic analyses. The method is meant to be used in professional design, especially for assessment and retrofitting purposes, based on the exploitation of the simplest nonlinear finite elements available in commercial software, namely, trusses with elasto-fragile and elasto-ductile behavior (Cutoff Bars, according for instance to the definition provided by Strand7 R3.1.3a). Numerical static nonlinear analyses are carried out by considering elastic hexahedral elements for bricks and by lumping nonlinearities on joints. These are assumed, in turn, to be elastic–brittle and elastic–plastic by using 1D elements, namely, Point Contacts, under the No-Tension Material hypothesis, and Cutoff Bars, respectively, assigning a small tensile resistance to the material. The reinforcement, realized with FRP hooping strips, is successfully modeled in a similar fashion, i.e., by applying perfectly bonded elastic–plastic Cutoff Bars at the extrados of the dome, where debonding is accounted for in a conventional way, limiting the tensile strength according to Italian Standards’ indications. The procedure is validated against benchmark models with the same geometry, using experimental data and more refined structural model results for comparison. After an in-depth analysis of the obtained results, in terms of capacity curves, the robustness and accuracy of the proposed approach are assessed.

By the method of direct cutting-out, the problems of longitudinal shear of an orthotropic half space, a layer, and a wedge with thin elastic orthotropic inclusions are reduced to the basic problem of interaction of thin inhomogeneities in the orthotropic space. We establish the conditions of interaction of loaded elastic anisotropic inclusions with the matrix of the body. We study the influence of elastic moduli both of the inclusion and of the body, as well as of the geometric parameters of the problems on the generalized stress intensity factors. The level lines of stresses are plotted in the vicinity of the inclusion. [ABSTRACT FROM AUTHOR]

This article examines the free vibrations of spherical orthotropic within an elastic medium according to the one-dimensional (1D) elastic model. According to the linear elasticity model, rotation, magnetic field, and inhomogeneity effects on wave propagation in the orthotropic material are analyzed. The 1D magneto-elastodynamics equation is resolved concerning radial displacement. We consider three boundaries: free, fixed, and mixed orthotropic materials. Concerning harmonic vibrations, the eigenvalues of the natural frequency of the radial vibrations concerning various boundary settings are determined. For each case, the numerical results are provided, illustrated in graphs, and compared with those without rotation, magnetic field, and non-homogeneity. An increase in the rotation and non-homogeneity parameters is observed, similar to the findings of the classical sphere theory. The findings show that rotation, magnetic field, and non-homogeneity have a strong impact on wave propagation in orthotropic material. Increasing the rotation, magnetic field, and inhomogeneity parameters make the findings closer to the findings of the classical sphere model. Moreover, the present article applies to the design and optimal use of nanoplates and microplates. The findings show that the impacts of the magnetic field, rotation, and inhomogeneity parameter are very pronounced. [ABSTRACT FROM AUTHOR]

The current work is devoted to introduce a novel thermoelastic heat conduction model where the Moore-Gibson-Thompson (MGT) equation describes the heat equation. The constructed model is characterized by allowing limited velocities of heat wave propagation within the material, consistent with physical phenomena. The Green–Naghdi Type III model is improved by introducing the delay factor into the modified Fourier law. Also, from the presented model, some other models of thermoelasticity can be derived at specific states. Based on the suggested model, an infinite orthotropic material with a cylindrical hole exposed to time-dependent temperature variation was studied. It has also been considered that the coefficient of thermal conductivity varies with temperature, unlike in many other cases where this value is considered constant. The viscoelastic material of the investigated medium was assumed to be of the Kelvin–Voigt type. The Laplace transform method provides general solutions to the studied field variables equations. The effects of viscosity and thermal variability parameters on these fields are discussed and graphically presented. In addition, the numerical results were presented in tables, and a comparison with previous models was made to ensure the accuracy of the results of the proposed model.

Within the framework of plane elasticity, the equilibrium problem for an inhomogeneous orthotropic elastic strip under the action of a stamp with a smooth base is investigated. Based on the Fourier transform, a canonical system of differential equations with variable coefficients with respect to transformants of the displacement vector and stress tensor components is constructed. A connection between the vertical displacement and the normal boundary stress is constructed, with which an integral equation of the first kind with a difference kernel is formulated. Using the shooting method, the kernel symbol for the integral equation of the contact problem is constructed numerically. Based on the Vishik – Lyusternik method, an asymptotic analysis of the kernel symbol for large values of the transformation parameter is carried out. A computational scheme for solving an integral equation with an unknown contact area is~constructed. The solution of the contact problem for different laws of strip inhomogeneity is presented.

The behavior of surface horizontally polarized shear waves (SH waves) in the composite multi-material structure with a periodic irregular surface and interface is investigated analytically in the present study. To unravel the enshrouded features of the SH-wave propagation in a multi-layer structure, we consider a model of three distinct composite materials. In the schematic of the problem, the guiding layer (M-I) contains fluid-saturated porous materials of finite thickness, the intermediate layer (M-II) contains fiber-reinforced composites, and the substrate contains the functionally graded orthotropic materials (M-III). The free surface of M-I and the upper interface of the medium are considered to be irregular on a periodic basis, but the interface of M-II and M-III is supposed to be regular. The dispersion relation is obtained analytically and demonstrated graphically for the phase velocity versus the wave number to analyze the propagation behavior of the SH-wave propagation in the proposed structure. The acquired results resemble the typical Love wave results, confirming the validity of the present work. The current work provides a comprehensive evaluation of the impact of regular and irregular boundaries of the composite materials on the phase velocity of the SH waves. It is notable that the behavior of the reinforced parameters, initial stress, and porosity on the phase velocity is consistent in both scenarios. More than the irregularity of the free surface, the periodic irregularity of the interface had an impact on the phase velocity. The obtained results are useful to understand the compositions of the materials on the mountain surface. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the mechanical behavior of microstructured materials, in particular porous media. We consider a detailed description of the material through a discrete model, considered as the benchmark of the problem. Two continuous models, one micropolar and one classic, obtained through a homogenization procedure of the material, are studied both in static and dynamic conditions. Furthermore, the internal characteristics of the material, such as the internal scale of the microstructure and the percentage of the voids, are made to vary in order to investigate the mechanical response and to have an exhaustive comparison among the models. [ABSTRACT FROM AUTHOR]

In recent years, significant improvements in the design of leg blade prosthetics have been carried out. After several advances in material and topological optimisations, sport-purpose feet prosthetics have reached high-level performances, allowing athletes with limb loss to participate in various sport activities at a competitive level. Since the knowledge of prosthetic mechanical behaviour is crucial for its optimal design, specific studies are required to meet the anthropometric characteristics of the athlete. This research work is focused on investigating the dynamic behaviour of a running blade prosthetic and developing a validated prosthetic model, placing particular emphasis on the definition of suitable material properties. An experimental modal analysis is performed on the Cheetah Xcel, Össur lower limb prosthetic. In contrast with what has already been presented in the literature, a roving hummer test under free–free conditions is proposed here to avoid the uncertainties due to constraint conditions. For the first time, blade prosthetic dynamic characteristics in free–free conditions are presented. Additionally, a novel Finite Element model of the prosthetic is developed and tuned on the basis of the experimental results. The modal assurance criterion index is exploited to compare experimental and numerical mode shapes. Starting from frequency response functions, the first six mode shapes are experimentally identified in the frequency range up to 750 Hz, including both bending and torsion. As expected, the bending in the vertical plane constitutes the primary mode shape: this kind of flexion enhances energy storage, enabling athletes to achieve an optimal running gait. This study shows the dynamic modal behaviour of a lower limb prosthetic in free–free conditions and demonstrates that a traditional isotropic material is not suitable in describing its dynamic features. The development of a model that exploits orthotropic material properties improves the alignment between experimental and numerical outcomes. This result is in agreement with the material composition of the prosthetic, which consists of carbon fibre layers.

An optimization strategy has been developed to determine the optimal surface-profile of a uniform thickness orthotropic shell for maximizing its ultimate load-carrying capacity. Ultimate load is obtained by considering both buckling and Tsai-Wu failure criteria. A parametric model of the laminated cylindrical shell is created in ANSYS to compute the ultimate load. Later, this finite element computation is coupled with MATLAB to obtain the optimal design parameters. It is shown that the optimal shapes, obtained for several loading conditions, can result in remarkable improvement in the ultimate strength in comparison to the base model of a circular cylindrical shell. [ABSTRACT FROM AUTHOR]

This article presents an attractive and straightforward computational strategy for estimating the anisotropic thermal conductivity in a wide range of materials. It results in a reliable and efficient approach with many potential applications. The proposed method is based on the mathematical model solution of a thermal process to generate some synthetic measurements simulating sensors located at the center of each face of a body under study. This work implements three optimization techniques for solving the formulated inverse thermal problem: Levenberg-Marquardt Algorithm, Particle Swarm Optimization, and Symbiotic Organism Search. Plus, we use an anisotropic cubic piece of solid material as a demonstrative case. Results show an excellent agreement between the estimated anisotropic thermal conductivities and the proposed solutions for the model. Furthermore, we notice a strong impact of the noise level on the measurement system, which affects the precision of the estimated conductivities. [ABSTRACT FROM AUTHOR]

The present study addresses a multiscale and stochastic design approach for polycrystalline microstructures to achieve a zone of isotropic elastic properties to improve the predictability of the performance of aerospace components. The microstructures are modeled with Orientation Distribution Function (ODF), which is related to the volume densities of crystallographic orientations in a microstructure. The microstructures can have inherent uncertainty due to the variations arising from thermomechanical processing that can alter the component performance. Example design problems are solved for titanium (Ti), aluminum (Al), and galfenol, which are either widely used or have potential applications in the aerospace industry. The level of isotropy for the materials is measured using the available anisotropy index formulas. The optimum microstructure designs are found to provide equivalent stiffness and Young's modulus values in different directions. Next, property closures for stiffness parameters are generated to demonstrate the ranges of their anisotropy. The closures show that multiple microstructure designs can provide quasi-isotropic elastic properties and the range of material anisotropy is larger for galfenol compared to Ti and Al. Additionally, the stochastic analysis is performed using Gaussian process regression, which is validated with Monte Carlo Simulation. The results show that 10% uncertainty in the ODFs, due to variations in the thermomechanical processing steps, can cause 1.44, 0.44, and 1.02 GPa of standard deviations from the mean values of Young's modulus for Ti, Al, and galfenol, respectively. However, the effects of the uncertainty are found to be negligibly small for the anisotropy ratio. [ABSTRACT FROM AUTHOR]

While machining materials changes and deformation of grain structure take place. This deformation of the grains affects the thermal properties of the material leading to orthotropic thermo-physical property. Typical materials like Ti-6Al-4 V having high hardness which are extensively used in many critical applications especially medical implants, requires study of such properties for proper fitment, sustainability and longevity. As a large amount of heat is produced during machining hence, in depth idea of the distribution of temperature in the product is highly necessary to design an optimally cooling strategy, to control the thermo-physical property of the material. In this present work, 2D material domain has been modelled to numerically predict the distribution of temperature, aided with Finite Difference scheme using Python. The differential equation governing the heat conduction and the boundary conditions have been are discretized, which are solved using an iterative method. The effect of different orthotropic thermo-physical property on heat conduction for Ti-4Al-4 V alloy have been demonstrated using the temperature distribution plots. The results can be used for deciding both the machining parameters as well as post-machining operations like cooling strategies. [ABSTRACT FROM AUTHOR]

Alloys fabricated by wire-and-arc additive manufacturing (WAAM) exhibit a peculiar anisotropy in their elastic response. As shown by recent numerical investigations concerning the optimal design of WAAM-produced structural components, the printing direction remarkably affects the stiffness of the optimal layouts, as well as their shape. So far, single-plate specimens have been investigated. In this contribution, the optimal design of WAAM-produced I-beams is addressed assuming that a web plate and two flat flanges are printed and subsequently welded to assemble the structural component. A formulation of displacement-constrained topology optimization is implemented to design minimum weight specimens resorting to a simplified two-dimensional model of the I-beam. Comparisons are provided addressing solutions achieved by performing topology optimization with (i) conventional isotropic stainless steel and with (ii) WAAM-produced orthotropic stainless steel at prescribed printing orientations. Lightweight solutions arise whose specific shape depends on the selected material and the adopted printing direction. [ABSTRACT FROM AUTHOR]

• Evaluation of various mandible modeling approaches and their influence on stress field accuracy, including assessment of mechanical properties and modeling approaches. • Finite element model of intact mandible developed based on tomographic images and discussion on image processing of tomography-derived data for CAD reconstruction. • Discussion on strategies for achieving high precision in mandible modeling, thorough mesh quality verification process, and importance of good modeling practices and mesh metric study for precise representation. • Comparison between different mandible models lacking in existing literature, notable dispersion observed in stress field outcomes at symphysis region in models proposed by other authors, and importance of comprehensive examination of solid model behavior before contemplating damage and prosthesis insertion. This study assesses the various methodologies utilized in the literature for computational mandible modeling and their implications on research findings. Previous studies have explored diverse material properties for the mandible, whether modeled as a single entity, in pairs, or as multiple sub-regions. Within this framework, a finite element model of an intact mandible was created using sliced tomographic images to examine the dispersion of stress fields resulting from different sets of bone material properties sourced from specialized literature. This research introduces the methodology employed in mandible model development, strategies for achieving high precision, and the influence of mechanical properties. Through an evaluation of models proposed by different authors, significant dispersion was observed, leading to disparities ranging from 4.4% to 67.4% in stress field outcomes at the symphysis region. RMSE served as an estimator to assess the similarity between these models. The findings suggest that the Caraveo (2008) and Palka (2020) models exhibit notable convergence in predicting stress fields in the symphysis regions. By incorporating good modeling practices in the intact mandible model, a more reliable representation is ensured, laying the groundwork for future investigations involving nonlinear contact phenomena and topology optimization. [ABSTRACT FROM AUTHOR]

A general ordinary state-based peridynamic formulation to model anisotropic materials in 2D and 3D is proposed. The new peridynamic constitutive model introduces two bond stiffness functions depending on the bond orientations. These functions are defined such that the components of the elasticity tensor evaluated by using the new formulation exactly reproduce those of classical continuum mechanics in the case of homogeneous deformation. Several numerical examples in 2D and 3D illustrate the validity of the proposed formulation for fully anisotropic materials. This formulation is also suitable to model monoclinic, orthotropic, transversely isotropic, and isotropic materials. [ABSTRACT FROM AUTHOR]

The most popular additive manufacturing technique is the Fused Deposition Method (FDM), which is capable of producing components in a huge variety of geometries. For this reason, this technique is called the attention of engineers designing rotating machines, because it can be used to supply spare parts in a cheap and fast way. The adoption of the FDM is advantageous in the case of small and light rotors due to the reduced dynamic loads and the mechanical strength in the rotating parts during operation. If the rotor is manufactured by layers of a cylindrical material (filaments), one obtains a rotor with a cross-sectional area whose properties completely differ from those of a rotor composed of solid and homogeneous material. In this work, one presents the dynamic analysis of a rotor whose properties are those of a printed rotor using the FDM and ABS material. First, one shows the effect of the filament layers on the resultant second moment of the cross-sectional area of the shaft, which becomes orthotropic. This orthotropy leads to a time-varying system of equations, whose eigenvalues can be calculated by the Hill's infinite determinant in truncated form. Second, the numerical results show the presence of parametric resonances and instability regions in the unbalance response of the rotor. The vibration of the rotor in the parametric resonances is associated with backward motion caused by the super-synchronous 3 × Ω components. The instability regions increase in bandwidth as the orthotropy of the cross-sectional area increases. [ABSTRACT FROM AUTHOR]

This paper presents closed-form expressions for the energy release rate and mode partitioning of face/core debonds in sandwich composites with orthotropic faces and core, by use of an elastic foundation analysis. The elastic foundation analysis used here is comprehensive and includes the deformation of the substrate part (core and the bottom face) and is done for generally asymmetric sandwich construction. To capture the transverse shear effects, the Timoshenko beam theory is used, which introduces an additional degree of freedom. A finite length sandwich is treated as having a debonded section, where the debonded top face and the substrate are free, and a bonded section, where an elastic foundation is used between the face and the substrate. The interaction between the face and the substrate in the bonded section is modeled using both normal and shear spring distributions. A double-cantilever beam specimen with applied external moments and shearing forces is chosen to demonstrate the procedure. The energy release rate is obtained by use of the J-integral. A mode partitioning measure in terms of the crack flank opening and shearing displacements is used. The results are compared with finite element results and show very good agreement. [ABSTRACT FROM AUTHOR]

FDM 3D printed honeycombs are investigated. A honeycomb is composed of regular hexagonal cells. A honeycomb is 3D printed so that the fused filament runs along the walls of its cells. We emphasize that the thickness of these walls is one or two times the thickness of the fused filament. When calculating the mechanical properties of a honeycomb, its walls are considered as a Euler-Bernoulli beam bending in one plane. To describe honeycombs, a homogenization procedure is used, which reduces a honeycomb to a homogeneous orthotropic medium. An adequate analytical calculation of the mechanical properties of this medium is the subject of our research. Analytical formulae for calculating the mechanical properties of honeycombs are presented. To assess the adequacy of the calculation results, the analytical data are compared with the results of simulation in the commercial ANSYS package. For this, the mechanical properties of the honeycombs made of the ULTEM 9085 material are determined numerically. To assess these properties, from a large number of analytical formulae are selected those that predict them adequately. As a result of calculations, an analytical prediction of all mechanical properties is obtained, with the exception of the in-plane shear modulus of a honeycomb. This is due to the fact that to simulate such a shear modulus one has to use a three-dimensional theory that does not have an adequate analytical description. A thin aluminum honeycomb was considered. In the future, three-layer structures with such a honeycomb will be investigated. Analytical results for ULTEM 9085 and aluminum honeycombs are similar.