Orthotropic Nature Research Articles

Miniaturized Shear Testing: In-Plane and Through-Thickness Characterization of Plywood.

This study addresses the challenges associated with conventional plywood shear testing by introducing a novel miniaturized shear test method. This approach utilizes a controlled router toolpath for precise sample fabrication, enabling efficient material use and data acquisition. Miniaturized samples, designed with double shear zones, were tested for τxy, τxz, and τyz configurations using a universal testing machine. Results revealed a mean ultimate shear strength ranging from 5.6 MPa to 7.3 MPa and a mean shear modulus ranging from 0.039 GPa to 0.095 GPa, confirming the orthotropic nature of plywood. The resulting shear behavior was determined with stress-strain curves correlated with failure patterns. The miniaturized tests effectively captured the material's heterogeneous behavior, particularly at smaller scales, and demonstrated consistent load-bearing capacity even after substantial stress reduction, suggesting suitability for bracing applications. This method allows for increased sample sizes, facilitating robust data collection for developing and validating finite element models. Future work will focus on evaluating the scalability of the observed orthotropic behavior and data scatter at larger scales and assessing the potential for this method to replace conventional full-scale plywood shear testing.

3D Printed Concrete: Fresh and Hardened Properties

3D concrete printing (3D CP) is an advanced form of additive manufacturing (AM), that allows for the creation of complex geometrical structures using concrete. This technology has the potential to reduce construction time and labour costs while minimizing material waste. However, there are also challenges related to material properties, structural integrity, and standardization of construction practices. The primary challenge in developing 3D printable cementitious materials lies in engineering specific fresh properties that enable extrusion-based printing. Unlike cast concrete, where formwork provides dimensional stability during the printing process, the absence of formwork in 3D printing necessitates fresh mixtures with low-slump and high-thixotropy to be suitable for concrete 3D printing. Additionally, the orthotropic nature of the resulting 3D printed object due to the extrusion process impacts its mechanical properties. Therefore, this research aims to study the effect of water content and loading directions on 3D printed concrete. A pre-mix material from Sika was used in this study. Three mixes were prepared by using three different water to dry material (w/d) ratios, 0.140 l/kg, 0.145 l/kg and 0.150 l/kg. The experiments focused on analysing flowability, green strength, mechanical properties (compressive strength, flexural strength, and modulus of elasticity), water absorption, porosity, and chemical transformations at high temperatures through thermoanalytical measurement. The results showed that the mixture containing 0.145 l/kg (w/d) exhibited satisfactory 3D printability, optimal mechanical performance, lower porosities compared with mixtures 0.140 and 0.150, and same total porosity compared with cast specimen.

Multiscale homogenization of aluminum honeycomb structures: Thermal analysis with orthotropic representative volume element and finite element method

This study develops a thermal homogenization model for an aluminum honeycomb panel using the representative volume element (RVE) concept, considering the orthotropic nature of the structure. The RVE thermal homogenization method is a numerical approach for analyzing heterogeneous materials. It employs a constitutive model based on RVE performance to represent thermal behavior. Effective parameters are determined through averaging techniques, and the finite element method solves the thermal problem, accounting for structure topology and material behavior. The resulting heat conduction problem is solved using the finite element method (FEM) to evaluate the effective thermal characteristics. A 3D RVE is generated based on the honeycomb panel's geometry, evaluating thermal conductivity tensor and describing the medium's thermal performance. Numerical tests validate the model by comparing it with the real honeycomb structure under sinusoidal heat flux. Results show good correlation, with maximum temperatures of 1101.9 °C in the real structure and 1096.4 °C in the medium. The homogeneous medium is further used to investigate thermal performance under convective conditions with varying panel thicknesses, achieving over 77 °C temperature reduction with the thickest panel. Natural vibration behavior is considered, demonstrating strong correlation between modal responses and natural frequencies. This modeling approach efficiently analyzes thermal behavior in large honeycomb structures, reducing computational time significantly.

Influencia de las Propiedades de un Tablero de Polímero Reforzado con Fibra de Vidrio en la Respuesta Dinámica de un Puente Carretero

The use of multicellular Glass Fiber Reinforced Polymer (GFRP) deck panels in the rehabilitation and construction of bridges has increased over the last 30 years due to several benefits, such as: low maintenance cost, fast installation, corrosion resistance, and high strength-to-weight ratio. Due to the orthotropic nature of GFRP decks and their complex cross-section geometry, expensive computational problems may be obtained when bridges that include these elements are analyzed under traffic loads. Therefore, this paper studies the dynamic response of a GFRP-steel road bridge modelling the multicellular GFRP deck as an orthotropic plate. For this purpose, a finite element model of the hybrid structure is developed, and a sensitivity analysis is carried out to investigate the influence of the mechanical properties of the orthotropic element on the bridge behavior. The roughness of the pavement, the degree of composite action between the deck and the stringers, the multibody dynamic model of a truck, and the vehicle-bridge interaction phenomenon are included in the analyses. Results indicate that the most relevant properties of the orthotropic plate on the response of the structure are the modulus of elasticity in the longitudinal direction, the modulus of elasticity in the transverse direction, and the shear modulus. Also, achieving a full composite action and avoiding deterioration of road are identified as key aspects to reduce the vibration levels on the hybrid bridge.

Topology optimization applied to the core of structural engineered wood product

Structural-engineered wood products are used in construction as a sustainable alternative to concrete and steel. The most commonly used engineered wood products are Glued-Laminated Timber (GLULAM) and Cross-Laminated Timber (CLT), which in most productions are made of layers of wood glued under pressure. In the GLULAM, the wood fiber directions are parallel stacked in layers, while in CLT, the layers have a typical rotation of 90°. This work develops a topology optimization method with an objective function in displacement and volume constraint applied to the core of engineered wood products such as GLULAM and CLT structures, seeking new product designs with reduced material consumption. The optimization considers the wood’s orthotropic nature and the layers’ stacking. Two numerical examples are performed, the first evaluating the core of a GLULAM structure with and without periodicity constraints and the second on the core of a CLT structure with periodicity constraints. The results show that the proposed procedure can be effectively applied to the core of the engineered wood products. In addition, applying periodic constraint result in optimized topologies that help the manufacturability of the new designs. Furthermore, the proposed procedure highlights the structural differences in layer importance.

Mechanical analysis and optimized performance of G-Code driven material extrusion components

In this work an end-to-end optimization procedure to maximize the mechanical performance of Additive Manufacturing (AM) components is presented. Material Extrusion (ME) is the selected demonstrative AM technology, but the approach is applicable to other AM processes where the manufacturing toolpaths of the geometry of the printed component are described in G-Code format. The proposed methodology is integrated into the AM workflow and drives a two-step optimization process in order to select the optimal printing orientation for a user defined case. The G-Code file containing the manufacturing toolpaths is used as input. This approach allows to operate as close as possible to the geometry of the actual component, avoiding the use of the STereoLithography (STL) geometry. A voxelized mesh is built from the G-Code by solving a modified 2.5D Shortest Path Problem (SPP) and high-fidelity Finite Element (FE) simulations are performed with the resulting mesh. A printing pattern-based material model that distinguishes three different zones of the printed component is used. Due to the orthotropic nature of the ME process, the Tsai–Wu failure criterion is applied to obtain the indicators of the mechanical performance of the component. These computed metrics are used to drive an optimization process where a robust criterion based on the Machine Learning (ML) algorithm Anomaly Detection (AD) is applied in order to select the optimal build direction from a prespecified span of orientations. Two test cases and one case study illustrate the performance of the proposed methodology. The results validate the approach against experiments, indicate that the selected optimization criterion is robust against factors alien to the actual physical problem and show that the accuracy of the voxelized method greatly improves the “traditional” STL-based simulations.

Experimental and Numerical Analysis of Chlorinated Polyethylene Honeycomb Mechanical Performance as Opposed to an Aluminum Alloy Design.

Manufacturing aircraft components through 3D printing has become a widespread concept with proven applicability for serial production of certain structural parts. The main objective of the research study is to determine whether a chlorinated polyethylene material reinforced with milled carbon fibers has the potential of replacing the current 5052 NIDA aluminum alloy core of the IAR330 helicopter tail rotor blade, under the form of a honeycomb structure with hexagonal cells. Achieving this purpose implied determining the tensile and compression mechanical properties of the material realized by fused deposition modeling. The tensile tests have been conducted on specimens manufactured on three printing directions, so that the orthotropic nature of the material may be taken into account. The bare compression tests were realized on specimens manufactured from both materials, with similar honeycomb characteristics. All the mechanical tests have been performed on the Instron 8872 servo hydraulic testing system and the results have been evaluated with the Dantec Q400 Digital Image Correlation system. The experimental tests have been reproduced as finite element analyses which have been validated by results comparison, in order to determine if the compression model is viable for more complex numerical analysis.

Stress Field Evaluation in Orthotropic Microstructured Composites with Holes as Cosserat Continuum.

It is known that the presence of microstructures in solids such as joints and interfaces has an essential influence on the studies of the development of advanced materials, rock mechanics, civil engineering, and so on. However, microstructures are often neglected in the classical local (Cauchy) continuum model, resulting in inaccurate descriptions of the behavior of microstructured materials. In this work, in order to show the impact of microstructures, an implicit ‘non-local’ model, i.e., micropolar continuum (Cosserat), is used to numerically investigate the effects of direction and scale of microstructures on the tension problem of a composite plate with a circular hole. The results show that distributions of field variables (such as displacements and stresses) have an obvious directionality with respect to the microstructures’ direction. As the scale of microstructures increases, such a direction effect becomes more evident. Unlike the isotropic material where stress concentration occurs at the vertex of the hole and the stress concentration factor is close to 3, for the microstructured composite, the stress concentration can be observed at any location depending on the microstructures’ directions, and the concentration factor can exceed 3 to a maximum close to 9 as the increasing scale of microstructures. In addition, differences in the mechanical behavior between Cosserat and Cauchy models can be also observed; such differences are more evident for the material showing a pronounced orthotropic nature.

Mechanical Characteristics Evaluation of a Single Ply and Multi-Ply Carbon Fiber-Reinforced Plastic Subjected to Tensile and Bending Loads.

Carbon fiber-reinforced composites represent a broadly utilized class of materials in aeronautical applications, due to their high-performance capability. The studied CFRP is manufactured from a 3K carbon biaxial fabric 0°/90° with high tensile resistance, reinforced with high-performance thermoset molding epoxy vinyl ester resin. The macroscale experimental characterization has constituted the subject of various studies, with the scope of assessing overall structural performance. This study, on the other hand, aims at evaluating the mesoscopic mechanical behavior of a single-ply CFRP, by utilizing tensile test specimens with an average experimental study area of only 3 cm2. The single-ply tensile testing was accomplished using a small scale custom-made uniaxial testing device, powered by a stepper motor, with measurements recorded by two 5-megapixel cameras of the DIC Q400 system, mounted on a Leica M125 digital stereo microscope. The single-ply testing results illustrated the orthotropic nature of the CFRP and turned out to be in close correlation with the multi-ply CFRP tensile and bending tests, resulting in a comprehensive material characterization. The results obtained for the multi-ply tensile and flexural characteristics are adequate in terms of CFRP expectations, having a satisfactory precision. The results have been evaluated using a broad experimental approach, consisting of the Dantec Q400 standard digital image correlation system, facilitating the determination of Poisson’s ratio, correlated with the measurements obtained from the INSTRON 8801 servo hydraulic testing system’s load cell, for a segment of the tensile and flexural characteristics determination. Finite element analyses were realized to reproduce the tensile and flexural test conditions, based on the experimentally determined stress–strain evolution of the material. The FEA results match very well with the experimental results, and thus will constitute the basis for further FEA analyses of aeronautic structures.

Indentation of small format Lithium-ion pouch cells: Experiments and modeling

Lithium-ion pouch cells are widely used in applications such as cell phones and electric vehicle battery packs. Here, a series of indentation experiments is performed on 4Ah pouch cells. The experimental program includes hemispherical indentation with six different indenter tip radii as well as indentation with cylindrical indenters with three rod diameters. Aside from varying the shape and size of the indenters, the location and direction of loading is varied including out-of-plane and in-plane loading of the rectangular-prismatic pouch cells. It is found that the force–displacement curves obtained for hemispherical indenters scale linearly with the indenter tip radius, while a scaling with the square root of the radius is observed for the experiments with cylindrical indenters. Finite element simulations are performed of all experiments using an enhanced Deshpande-Fleck plasticity model with two stage hardening. Despite the orthotropic nature of the jelly-stack, it is found that the simulations with an isotropic plasticity model provide reasonable predictions of the force–displacement curves for all experimental configurations. This surprising result is explained through the exceptionally high slenderness of the metallic current collector foils comprised in a pouch cell that respond through early buckling failure instead of contributing to the in-plane compressive load carrying capacity.

An improved mean-field homogenization model for the three-dimensional elastic properties of masonry

Accurate assessment of the overall mechanical behavior of masonry, composed of bricks and mortar joints, remains challenging due to its inhomogeneous and orthotropic nature. In this study, the feasibility of various mean-field homogenization schemes for the three-dimensional orthotropic elastic properties of masonry is comprehensively investigated. Three kinds of masonry patterns are considered, including the stack bonded pattern, the running bonded pattern and the double-leaf Flemish bonded pattern that has received limited attention so far. Special attention is paid to the homogenization schemes which have not been applied to the masonry case, such as Lielens’ interpolative double inclusions (D-I) and the interaction direct derivative (IDD) schemes. After a comparison between the well-known mean-field homogenization schemes, an improved micro-mechanical model is proposed by combining the advantages of the IDD and D-I models. The validation of the proposed model is conducted through a comparison against experimental data from literature and numerical results obtained via finite element analyses (FEA). The results show that the proposed model can accurately evaluate the orthotropic elastic properties of the three masonry typologies for a wide range of stiffness ratios between brick and mortar, ranging from 1 to 1000. The proposed model also shows better performance than the classical schemes especially when the stiffness ratios between brick and mortar are higher than 10, which is of major importance for the application of mean-field homogenization based multiscale methods to the nonlinear analysis of masonry. Furthermore, the presented homogenization method can be of interest for other anisotropic materials, e.g., laminate materials.

Characterization of the Thermal Behavior of a Complex Composite (Clutch Facing) Combining Digital Image Stereo Correlation and Numerical Approach.

Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only exists in its final form as a non-planar annular disc, it is difficult to define an elementary representative volume. The objective of this work was to develop a method for identifying the CTE distributions on the entire part. A device allowing measuring the strain fields by digital image correlation (DIC) under homogeneous thermal loading (up to 300 °C) was developed. The experimental results highlight the heterogeneity and the orthotropic nature of the material behavior and the influence of the angle between the fibers on the CTE. To take into account that the measured strain fields are related to the CTE, but also to the shape of the part, different approaches to identify the CTE were considered: direct measurements, classical laminate theory (CLT) and finite element method updating (FEMU). Only the FEMU allows an accurate identification of the CTE distributions. Nevertheless, the CLT respects the orders of magnitude and remains a useful tool for the design of clutches.

Elastic Modulus, Thermal Expansion, and Pyrolysis Shrinkage of Norway Spruce Under High Temperature

The orthotropic and temperature-dependent nature of the mechanical properties of wood is well recognized. However, past studies of mechanical properties at elevated temperatures are either limited to temperatures below 200 °C or focus only on the direction parallel to grain. The effect of time-dependent pyrolysis during measurement is often neglected. This paper presents a novel method for determining elastic modulus at high temperatures and thermal expansion coefficient in different orthotropic directions via Dynamic Mechanical-Thermal Analyser (DMTA). The method allows for drying, drying verification, and measurement in one chamber, eliminating the possibility of moisture reabsorption from ambient air. The repeatable measurements can be carried out in temperatures up to 325°C, adequate for observing time-dependent pyrolysis during measurement. Results of the measurements of Norway Spruce provide data of its mechanical response at temperature range previously not explored widely, as well as in the orthotropic direction. Time-dependent behaviour was observed in the thermal expansion and shrinkage experiment, where above 250°C the amount of shrinkage depends on heating rate. At such temperature, elastic moduli measurement also shows time dependence, where longer heating at certain temperature slightly increases the measured elastic modulus. Additionally, bilinear regression of the relationship between elastic moduli and temperature shows quantitatively good fit. Numerical simulation of the DMTA temperature history and wood chemical components mass losses show the onset of shrinkage and onset of hemicellulose mass loss occurring at around the same time, while decomposition of cellulose correlate with the sudden loss of elastic moduli.

Weight minimization of fiber laminated composite beam for aircraft wing construction using exhaustive enumeration algorithm and numerical modeling

PurposeThis paper aims to focus on calculating the number of layers of composite laminates required to take the applied load made up of graphite/epoxy (AS4/3501-6) which can be used in many industrial applications. Optimization for minimization of weight by variation in the mechanical properties is possible by using different combinations of fiber angle, number of plies and their stacking sequence.Design/methodology/approachLots of research studies have been put forth by aerospace industry experts to improve the performance of aircraft wings with weight constraints. The orthotropic nature of the laminated composites and their ability to characterize as per various performance requirements of aerospace industry make them the most suitable material. This leads to necessity of implementing most appropriate optimization technique for selecting appropriate parameter sets and material configurations.FindingsIn this work, exhaustive enumeration algorithm has been applied for weight minimization of fiber laminated composite beam subjected to two different loading conditions by computing overall possible stacking sequences and material properties using classical laminate theory. This combinatorial type optimization technique enumerates all possible solutions with an assurance of getting global optimum solution. Stacking sequences are filtered through Tsai-Wu failure criteria.Originality/valueFinally, through the outcome of this optimization framework, eight different combinations of stacking sequences and 24-ply symmetric layup have been obtained. Furthermore, this 24-ply layup weighing 0.468 kg has been validated using finite element solver for given boundary conditions. Interlaminar stresses at top and bottom of the optimized ply layup were validated with Autodesk’s Helius composites solver.

Investigating the Underlying Effect of Thermal Modification on Shrinkage Behavior of Bamboo Culm by Experimental and Numerical Methods.

This study probes into the root cause of split in thermally modified bamboo culm by investigating the underlying effect of thermal contraction with respect to its orthotropic nature by experimental and numerical methods while concurrently monitoring the chemical variation of its structure by Fourier transformed infrared spectroscopy (FTIR). In first part of this study, a non-linear increase in dimensional and weight changes of small clear bamboo specimens were observed with increasing temperature. The dimensional changes in the radial and tangential directions significantly exceeded that in the longitudinal direction. From FTIR results, shrinkage effect between 150 °C to 200 °C was associated with weight loss engendered by reduction in weakly bound water and increase in desorption of water content while alteration of its mechanical properties was attributed to changes in cellulose, hemicellulose, and lignin. From results of finite element method (FEM), the graded variation in thermal expansion coefficient, which showed the formation of a narrowed region of strain concentration corresponding to longitudinal crack propagation, was associated with the inducement of internal forces, namely tensile and compressive forces, at specific regions along the culm length. The results of this study can be useful to achieve optimized durability in modified bamboo for construction.

The Effect of Direction of Load on Bending Strength of <i>Melia compositae</i>

In this paper, empirical study of stiffness (modulus of elasticity-MoE) and Bending strength/flexural strength (modulus of rupture-MoR) in wood, mainly on radial and Tangential surface of <i>Melia compositae</i> wood were evaluated. Here loading in the radial direction means that load is applied to the tangential surface and loading in the tangential direction means that load is applied to the radial surface. The strength properties vary with species to species and also application of direction of load. Loading direction appreciably affects the bending properties remarkably due to the anisotropic /orthotropic nature of timber. It was observed that always MoE and MoR have greater value in Radial surface. The direction of application of load has an appreciable effect on strength properties of wood. While this is generally attributable to the presence of medullary rays in the radial direction. The bending strength of timber when loaded parallel to the direction of load is greater than that of timber loaded perpendicular to the direction of load. The ratio of flexural strength values varied from13% to 14% for <i>Melia composita</i>.

Advanced Thermoplastic Composite Manufacturing by In-Situ Consolidation: A Review

This article provides an overview of the evolution of the in-situ consolidation (ISC) process over time. This evolution is intimately linked with the advancements in each of the steps of the ISC manufacturing process, is additive in nature, and is limited by the orthotropic nature of composite materials and the physicochemical behavior of the thermoplastic matrix. This review covers four key topics: (a) Thermal models—simulation tools are critical to understand a process with such large spatial gradients and fast changes. Heating systems once marked a turning point in the development of industrial ISC systems. Today, lasers are the most recent trend, and there are three key issues being studied: The absorption of energy of light by the material, the laser profile, and the laser focusing. Several approaches have been proposed for the distributed temperature measurements, given the strong temperature gradients. (b) Adhesion—this refers to two subsequent mechanisms. In the first place, the process of intimate contact is one by which two surfaces of thermoplastic pre-impregnated composite materials are brought into contact under pressure and temperature. This enables closure of the existing gaps between the two microscopic irregular surfaces. This process is then followed by the healing or diffusion of polymer molecules across the interface. (c) Crystallinity—mostly influenced by the cooling rate, and strongly affects the mechanical properties. (d) Degradation—this refers to the potential irreversible changes in the polymer structure caused by the high temperatures required for the process. Degradation can be avoided through adequate control of the process parameters. The end goal of the ISC manufacturing process is to achieve a high product quality with a high deposition rate through an industrial process competitive with the current manufacturing process for thermoset composites.

Effect of bearing length on web crippling behavior of pultruded GFRP channel section

Pultrude glass fiber reinforced polymer (GFRP) sections have gained increasing acceptance in building and construction industries considering their promising physical and mechanical properties. However, they are prone to premature web crippling failure due to their orthotropic nature and relatively low interlaminar shear strength and modulus when subjected to transverse bearing load. This paper presents a study on the effect of bearing length on web crippling behavior of pultruded GFRP channel sections. Four channel sections with different sectional dimensions were selected for web crippling testing. Two loading conditions including end-two-flange (ETF) and interior-two-flange (ITF) were adopted. Transverse loading was applied through bearing plates with five different lengths of 20 mm, 50 mm, 100 mm, 150 mm and 200 mm. Failure modes, load–displacement curves and web crippling capacities were reported and discussed associated with the effect of bearing length. Mechanism based design equations which were able to consider effect of bearing length were proposed, and the predicted web crippling capacities agreed well with experimental results.

Analysis of a cured-in-place pressure pipe liner spanning circular voids

The performance of a commercially available cured-in-place pipe (CIPP) liner as it spans circular voids in its host pipe is examined using finite element analyses. A three dimensional model is presented and compared to an existing axisymmetric model. The effect of friction and the orthotropic nature of the liner’s material are also investigated. Lastly, the internal pressure at failure is estimated for a number of void sizes through simulated burst tests using a conditional equation from ASTM F1216-16 along with the interactive and maximum stress failure criteria from ASTM F2207-06. It is recommended that a multi-axial strength criterion be used for smaller void sizes that conform with the conditional equation, while the uniaxial strength criterion be used for larger void sizes that do not satisfy the conditional equation.

Strain energy density decompositions in phase-field fracture theories for orthotropy and anisotropy

In phase-field theories of fracture, decompositions of the strain energy density into tensile and compressive parts are often necessary to avoid interpenetration of cracked surfaces and to select physically trustworthy crack paths. General formulations accounting for orthotropy of the well-known spectral and hydrostatic-deviatoric decompositions of the strain tensor (often referred to as Miehe and Amor decompositions) are presented in this study. Additionally, a new principal energy decomposition based on spectral decomposition of the stiffness tensor is proposed for general anisotropic materials. The decompositions are evaluated numerically in a quadratic specimen with an initial stationary edge crack subject to both tensile and shear global remote loading. It is shown that when an isotropic case is considered, solutions agree well with results reported elsewhere for both the spectral and the hydrostatic-deviatoric approaches. The principal energy decomposition results in similar crack paths as the other approaches, with only subtle differences. When orthotropy is considered, however, significant differences in the resulting crack paths as well as global force-displacement behavior are obtained, especially when the crack is subjected to shear loading. For global tensile loading, the decompositions result in similar crack paths and force-displacement relations. The results provide a step forward when developing phase-field fracture theories for brittle materials with an orthotropic nature and highlight the importance of a proper decomposition of the strain energy density.