Orthotropic Mechanical Properties Research Articles

Determination of the mechanical properties of 3d-printed polymer products by methods of structural mechanics

Mathematical models of stress-strain state (SSS) for modeling tests of polymer composite samples obtained by fused deposition modeling (FDM) in approximations of isotropic and orthotropic media are formulated. An algorithm for solving the inverse SSS problem to determine the effective mechanical properties in the orthotropic approximation of composite products printed by the FDM method has been developed. Numerical models have been developed to solve inverse SSS problems to determine the effective orthotropic mechanical properties of composite products with different degrees of reinforcement, obtained using additive technologies based on the FDM method. The grid convergence of the developed numerical models by the method of double recalculation is investigated. It is established that the used mesh of geometric models of product samples leads to errors in determining the vector of the modulus of elasticity in the range of 0–3.19%, and the vector of the shear modulus does not exceed 0.05–0.2%. Numerical experiments to determine the effective mechanical properties of samples of composite polymeric materials in the approximation of orthotropic homogeneous medium were performed. The obtained results are compared with the data of calculations by analytical dependences to determine the effective mechanical properties of composite materials. It is shown that the results of numerical studies agree satisfactorily with the corresponding data obtained from analytical dependences in the range of 0.081–5.696%. It is established that all three components of the vectors of modulus of elasticity and shear increase with the degree of reinforcement. The largest increase is observed for the components of vectors and , which is due to the reinforcement in the direction , and the difference between the values ​​of the components of vectors and and and is due to the cross-sectional asymmetry of the strand. Dependences for operative prediction of effective orthotropic mechanical properties of composites based on PLA + KEVLAR 29 within the limits of change in the volume fraction of reinforcing fibers up to 5% are obtained. To develop new composite materials with predetermined properties, it is not necessary to perform multivariate, rather complex and cumbersome numerical experiments in solving the inverse SSS problem.

К РАСЧЕТУ МЕХАНИЧЕСКИХ ХАРАКТЕРИСТИК СОТОВЫХ ЗАПОЛНИТЕЛЕЙ, ИЗГОТОВЛЕННЫХ АДДИТИВНЫМИ ТЕХНОЛОГИЯМИ FDM

Honeycomb is described by orthotropic homogeneous media. The mechanical properties of the media are described by the simulation of the stress state honeycomb in commercial software ANSYS. The classical hexagonal honeycomb is analyzed numerically. The other types of the honeycomb are not considered in this paper. The media, which is obtained as a result of homogenization, has orthotropic mechanical properties. The honeycomb is produced from polycarbonate, which is orthotropic material. The suggested approach can be applied to other materials, which are used for 3D printing. The mechanical properties of this honeycomb material are determined experimentally for specimens, which are produced by FDM manufacturing. The matrix of the Hooke law is obtained in the result of six finite element calculations of the cell part of the honeycomb. To determine the different elements of this matrix, the cell part of the honeycomb undergoes different boundary conditions and different stressing. The fourth part of one cell is considered to calculate honeycomb mechanical properties. The software ANSYS is used to calculate the fourth part of the cell. The area near the cell part is filled up to cube using elastic air. The elastic air is isotropic material with a small Young modulus. The cube sides undergo constant displacements to perform numerical analysis. Such different displacements are equal to six. As a result of the numerical simulations, the elements of the stress tensor are determined by the stress averaging on the volume of the finite element. As a result of calculations, the set of nine engineering constants of orthotropic homogeneous media is obtained. Analysis of the convergence of the numerical simulation results is carried out for numerical simulations of the stress state by the concentration of the finite element mesh. As follows from the convergence analysis, 1745481 3D finite elements are enough for the discretization of the cube area.

Fabrication of carbon nanotubes/Cu composites with orthotropic mechanical and tribological properties

In this work, Multi-Walled Carbon Nanotubes reinforced copper matrix composites were prepared through a series of preparation processes including ultrasonic and nitrogen-assisted mixing, electroless Nickel–Copper bilayers plating, hot extrusion and cold drawing. The mechanical and tribological properties of the composites were enhanced with the increase of MWCNTs. The Cu matrix composites enhanced with 10 vol% MWCNTs showed significant improvements in the mechanical and tribological properties. Compared with the pure Cu sample prepared by the same method, the tensile strength and yield strength of the composite increased by 52.15% and 56.67%, while the friction coefficient and wear rate decreased by 66.8% and 62.3%, respectively. Better than most of the reported data. The 3 vol% MWCNTs in the composites exhibited the highest strengthening efficiency. Due to the directional arrangement of the MWCNTs in the Cu matrix, the composites showed obvious orthogonal anisotropy, and the properties in the parallel drawing direction were much better than those in the vertical drawing direction. Dislocation and load transfer effect are considered as the main mechanism of mechanical properties enhancement. The formation of self-lubricating layer, load transfer, efficient derivation of friction heat and orientation arrangement of MWCNTs were the reasons which lead to the friction performance enhancement.

Design of a small-scale wind turbine blade of glass fibre/epoxy composite for electrification of rural villages in Ethiopia: a case study

This paper targeted the design and stress comparison of a small-scale wind turbine blade which was constructed for the specific environmental conditions of the small rural village in Ethiopia. Firstly, the blade was designed from the characteristic of aerodynamic performance. Secondly, modelling and stress analysis of the windmills was conducted which is very significant for the further design and application of wind turbines. The material was epoxy-GFRP composite. The orthotropic mechanical properties of woven fibre epoxy polymer composite were created (ASTM D1683) with help of Autodesk Helius Composite V.16 software. The tensile and flexural testing specimens were fabricated by D3039M-17 and D7264M-15, respectively. Load, displacement, and modulus were investigated using UTM. Based on the parameters of the airfoil, the three-dimension and the assembly models of blades were mounted with the SOLIDWORK-V.16. Then the models were imported into ANSYS-V.15 WORKBENCH software for analysis. The displacement, Von Misses, and principal stress effects were determined.

Superior Mechanical and Magnetic Performance of Highly Anisotropic Sendust‐Flake Composites Freeze Cast in a Uniform Magnetic Field

AbstractDespite extensive research, the manufacture in the bulk of high‐performance flake‐based magnetic composites with a highly aligned, nacre‐like structure remains challenging. Many challenges can be overcome by freeze casting in an externally applied, uniform magnetic field, which causes both the flakes and the composite walls of the cellular solid to align parallel to the B‐field lines. When appropriately sized, the flakes experience a second alignment parallel to the freezing direction because of a shear flow that occurs due to both the volumetric expansion of the ice phase and mold contraction during the directional solidification. The resulting orthotropic structure of the freeze‐cast magnetic composite is reflected in orthotropic mechanical and magnetic properties of the material. The magnetic composites manufactured by magnetic‐field assisted freeze casting outperform by a factor of 2–4 in terms of stiffness, strength, and toughness materials that are processed in the absence of a magnetic field and do not exhibit a monodomain architecture. Because of the highly aligned microstructure, it is possible to compact the initially lamellar composite with 90% porosity to at least 80% strain. The results presented in this study illustrate the tremendous potential for magnetic freeze casting of magnetic composites for use in power conversion.

On incorporating scanning strategy effects into the modified inherent strain modeling framework for laser powder bed fusion

Laser powder bed fusion ( L -PBF) has been the most popular metal additive manufacturing (AM) process thus far. However, residual deformation of the metal builds has been a significant issue. Laser scanning strategies adopted in the laser-assisted fabricating process have proved to have important influence on the residual stress and deformation. As the main contribution of this paper, the effects of different laser scanning strategies are incorporated into the modified inherent strain modeling (MISM) framework for the first time to enable accurate simulation for residual deformation of the L -PBF metal parts. Anisotropy in mechanical property of the fabricated components caused by the laser scanning strategies is also fully considered. For the rotational laser scanning strategies, only a small-scale representative volume element (RVE) is modeled by employing both the inherent strains and asymptotic homogenization. By employing the homogenized inherent strains, residual deformation can be predicted for the L -PBF manufactured components using different rotational scanning strategies accurately. Regarding the unidirectional parallel line scanning strategy, the directional inherent strain vector and orthotropic mechanical properties are used in the MISM-based layer-wise simulation. Good accuracy of the proposed framework is fully validated through comparing the simulated residual deformations with the experimental results for Inconel 718 parts produced by different laser scanning strategies. Thus, it is demonstrated that the effects of both parallel line and rotational laser scanning strategies have been successfully integrated into the MISM framework for predicting residual deformations of the L -PBF builds.

Investigation of the equivalent material properties and failure stress of the re-entrant composite lattice structures using an analytical model

In the present study, a novel theoretical model is developed, based on classical laminate theory, to predict the equivalent mechanical properties of the re-entrant lattice structures, which composed of continuous fiber reinforced composite struts. Three main mechanism of stretching, flexing and hinging are considered and a general closed-form formulation is derived to estimate the auxetic honeycomb’s elastic and shear modulus as well as Poisson’s ratios. In spite of previous studies in which the response of honeycomb structures is modeled using beam theory, here, each strut of unit cell is expressed as a composite laminate with orthotropic mechanical properties and classical laminate theory is implemented to calculate the mechanical constants. In addition, using the available relations, the elastic buckling stress and failure load of the auxetic unit cell is evaluated. The proposed model is validated using experimental results, which are available from the previous studies as well as FE simulations. A parametric study is also conducted on the model to study the effects of cell angle and honeycomb’s density on the mechanical properties and failure stresses of the re-entrant structure. The results show that, the proposed analytical model can finely predict the equivalent and failure properties of the auxetic honeycomb structures. Furthermore, it is observed that, for the considered re-entrant composite structures with the cell angles between −25 to 25, the vertical strut fails due to the damage evolution and for the unit cells with other cell angles, the buckling failure is determinative.

Vibration Analysis of Carbon Fiber-Graphene-Reinforced Hybrid Polymer Composites Using Finite Element Techniques.

In this study, a computational procedure for the investigation of the vibration behavior of laminated composite structures, including graphene inclusions in the matrix, is developed. Concerning the size-dependent behavior of graphene, its mechanical properties are derived using nanoscopic empiric equations. Using the appropriate Halpin-Tsai models, the equivalent elastic constants of the graphene reinforced matrix are obtained. Then, the orthotropic mechanical properties of a composite lamina of carbon fibers and hybrid matrix can be evaluated. Considering a specific stacking sequence and various geometric configurations, carbon fiber-graphene-reinforced hybrid composite plates are modeled using conventional finite element techniques. Applying simply support or clamped boundary conditions, the vibrational behavior of the composite structures are finally extracted. Specifically, the modes of vibration for every configuration are derived, as well as the effect of graphene inclusions in the natural frequencies, is calculated. The higher the volume fraction of graphene in the matrix, the higher the natural frequency for every mode. Comparisons with other methods, where it is possible, are performed for the validation of the proposed method.

Fracture toughness characterisation of a glass fibre‐reinforced plastic composite

AbstractBy examining the state of the art, it can be realised that few research works have been done on the fracture behaviour of plastic composites reinforced with continuous glass fibres. Therefore, the present paper deals with the fracture toughness of a unidirectional glass fibre‐reinforced plastic (GFRP), such a parameter being analytically determined by means of the modified two‐parameter model (MTPM). The input data of the MTPM are obtained from an experimental campaign related to three‐point bending tests on single edge‐notched specimens characterised by different sizes. The novelty of this research work is that the MTPM, originally proposed for isotropic materials, is here employed to estimate the fracture toughness of GFRPs characterised by orthotropic mechanical properties.

Orthotropic properties of cement-filled polyamide 12 manufactured by selective laser sintering

Purpose The cement-filled PA12 manufactured by selective laser sintering (SLS) offers desirable mechanical properties; however, these properties are dependent on several fabrication parameters. As a result, SLS prototypes may exhibit orthotropic mechanical properties unless properly oriented in build chamber. This paper aims to evaluate the effects of part build orientation, laser energy and cement content on mechanical properties of cement-filled PA12. Design/methodology/approach The test specimens were fabricated by SLS using the “DTM Sinterstation 2000” system at which the specimens were aligned along six different orientations. The scanning speed was 914mm/s, scan spacing was 0.15mm, layer thickness was 0.1mm and laser power was 4.5–8Watt. A total of 270 tensile specimens, 270 flexural specimens and 135 compression specimens were manufactured and the tensile, compression and flexural properties of fabricated specimens were evaluated. Findings The experiments revealed orientation-dependent (orthotropic) mechanical properties of SLS cement-filled PA12 and confirmed that the parts with shorter scan vectors have enhanced flexural strength as compared with longer scan vectors. The maximum deviations of ultimate tensile strength, compressive strength and flexural modulus along the six orientations were 32%, 26% and 36%, respectively. Originality/value Although part build orientation is a key fabrication parameter, very little was found in open literature with contradictory findings about its effect on mechanical properties of fabricated parts. In this work, the effects of build orientation when combined with other fabrication parameters on the properties of SLS parts were evaluated along six different orientations.

Orthotropic elastic behaviors and yield strength of fused deposition modeling materials: Theory and experiments

This work is devoted to study the mechanical behaviors of polylactic acid (PLA) materials from additive manufacturing, and an orthotropic model is established to predict the mechanical properties under arbitrary printing orientation. Firstly, the morphology of PLA material is analyzed by using scanning electron microscopy, from which the orthotropic behavior of PLA material is obtained. Three printing planes are adopted, and on each printing plane different printing angles may be selected. The mechanical parameters, including Young's modulus, yielding stress, and Poisson's ratio, for material under different printing directions are determined via quasi-static experiments. Secondly, the orthotropic constitutive model of PLA materials under different printing angles is thus obtained, and the prediction method of orthotropic mechanical properties is built based on the coordinate transformation matrix, where the orthotropic coordinate transformation matrix is acquired by attitude angles (i.e., Euler angle, the rotation angle of the local coordinate system relative to the global coordinate system). Finally, the theoretical prediction method was verified, and high-quality printing methods were recommended. In addition, the obtained results of the model show that: for PLA material, the orthotropic hypothesis model is superior to the transverse isotropic hypothesis one. This present method is not only suitable for predicting the constitutive model of printed specimens in any direction but also for other materials of fused deposition modeling.

A new design method for a novel FRP strengthening technique against shear buckling of steel plate girders

Abstract This paper presents the theoretical part of an experimental study aimed for proposing a novel FRP strengthening technique to strengthen the webs of steel plate girders against breathing fatigue reducing the critical stresses and consequently increasing the life expectancy of the bridge. The proposed technique is economic, easy to install and is also designed for increasing the ultimate capacity of the strengthened specimens by up to 88% while maintaining the typical ductile shear failure of the steel plate girders, which is something not common with other strengthening techniques. A non-linear finite element model is developed and an extensive parametric study has been performed to propose a new design method for shear buckling of the new composite section including a simplified approach to determine the orthotropic mechanical properties of the proposed FRP section.

Numerical investigation of the mechanical properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets

This paper presents a numerical investigation of the elastic properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets. A finite element computational model was developed to analyze the mechanical properties of a new polymer hybrid composite reinforced with MXene and graphene taking into account the properties of the 2D nanosheets, different aspect ratios, placement options and volume fractions of nanoreinforcements, as well as the interaction effects between the nanofillers and the surrounding polymer matrix. Using the developed numerical model, the influences of the interface layer properties, MXene and graphene aspect ratio, alignment and volume fraction on the orthotropic mechanical properties of the proposed novel hybrid polymer nanocomposites were determined. The results suggest that MXenes along with graphene nanosheets show considerable promise in the development of novel nanoengineered high-strength multifunctional composite materials, as well as provides insight for future design of such materials.

An experimental investigation of three-dimensional mechanical characteristics of gas diffusion layers in proton electrolyte membrane fuel cells

In this study, three-dimensional (3D) orthotropic mechanical properties of a commercial gas diffusion layer (GDL) are experimentally investigated. Although GDL is an important 3D structural membrane in proton electrolyte membrane fuel cells (PEMFCs), most papers have merely considered its in-plane linear isotropic characteristics due to the lack of 3D anisotropic mechanical performance investigation. In real operating PEMFCs, GDL is nonlinear orthotropic composite and its mechanical characteristics affect the overall performance of PEMFCs, seriously and directly. In this research, as considering GDL’s valid configuration in PEMFCs, mechanical tests such as compression test, tension test, and shear test are conducted to study its 3D mechanical behavior. Test results present that the GDL behaves in an orthotropic and nonlinear manner. In addition, microstructures of the GDL are observed through scanning electron microscope (SEM) images, to explain its different kinds of mechanical failure performance.

Modeling size-dependent thermoelastic energy dissipation of graphene nanoresonators using nonlocal elasticity theory

Recent developments in nanostructured materials have led to the use of graphene sheets as resonators in advanced micro- and nanoelectromechanical systems. An important feature of micro- and nanoresonators is their ability to function with low power dissipation. The main intrinsic mechanism of energy loss in these advanced devices is thermoelastic damping (TED). In this article, we study TED effects in orthotropic graphene sheets of varied lengths operating at different temperatures using nonlocal elasticity theory. For this purpose, the fundamental thermoelastic relations are used to develop a system of coupled partial differential equations to describe the behavior of graphene nanoresonators. The orthotropic mechanical and thermal properties of graphene were taken into account in our model for zigzag and armchair chiralities operating at different temperatures. The free in-plane vibration of the graphene nanoresonator is analyzed using Galerkin method. Decidedly, we show that the developed system of equations is capable of describing the TED behavior of graphene nanoresonators along the two considered chiralities during thermoelastic vibration. Specifically, we examined the influence of size, chirality, and temperature upon thermoelastic damping, as measured by the so-called quality factor, of the graphene nanoresonator. Our results reveal that the nanoresonator experiences higher energy dissipation with increased temperature. They also reveal the dependence of the energy dissipation upon the size and chirality of the graphene sheet.

Intraluminal Ultrasonic Palpation Imaging Technique Revisited for Anisotropic Characterization of Healthy and Atherosclerotic Coronary Arteries: A Feasibility Study

Accurate mechanical characterization of coronary atherosclerotic lesions remains essential for the in vivo detection of vulnerable plaques. Using intravascular ultrasound strain measurements and based on the mechanical response of a circular and concentric vascular model, E. I. Céspedes, C. L. de Korte and A. F. van der Steen developed an elasticity-palpography technique in 2000 to estimate the apparent stress–strain modulus palpogram of the thick subendoluminal arterial wall layer. More recently, this approach was improved by our group to consider the real anatomic shape of the vulnerable plaque. Even though these two studies highlighted original and promising approaches for improving the detection of vulnerable plaques, they did not overcome a main limitation related to the anisotropic mechanical behavior of the vascular tissue. The present study was therefore designed to extend these previous approaches by considering the orthotropic mechanical properties of the arterial wall and lesion constituents. Based on the continuum mechanics theory prescribing the strain field, an elastic anisotropy index was defined. This new anisotropic elasticity-palpography technique was successfully applied to characterize ten coronary plaque and one healthy vessel geometries of patients imaged in vivo with intravascular ultrasound. The results revealed that the anisotropy index-palpograms were estimated with a good accuracy (with a mean relative error of 26.8 ± 48.8%) compared with ground true solutions.

Numerical investigation of natural frequencies and mode shapes of air-supported structures

Natural frequencies and mode shapes are important properties of engineering structures and buildings. Modal analysis of the prestressed membrane structures made of orthotropic material is described in this paper. The equation of motion of the system with finite number of degrees of freedom was given in the matrix form. Features of the modal analysis of prestressed system are described. To validate our technique, we have found in the literature and repeated the modal analysis of cylindrical membrane structure (inflated beam). In the source paper the analytical solutions for the natural frequencies were obtained for the one-dimensional (beam) model with taking into account orthotropic mechanical properties and prestress. In this paper the test case was solved for the spatial shell model using finite element analysis, realized in program software “ANSYS Mechanical”. Comparison between authors’ results and results described in reference is carried out. The possible reasons of results divergence are explained. The validated technique has been applied to modal analysis of an air-supported structure based on the rectangular plan of 20×50 m. Models with different mesh sizes were used to achieve the mesh convergence of results. Almost linear dependence between internal pressure and squares of natural frequencies has been received. This result is in the accordance with known solutions, described in the literature for isotropic membranes.

Multi-scale model updating of a timber footbridge using experimental vibration data

PurposeThe purpose of this paper is to capture the actual structural behavior of the longest timber footbridge in Spain by means of a multi-scale model updating approach in conjunction with ambient vibration tests.Design/methodology/approachIn a first stage, a numerical pre-test analysis of the full bridge is performed, using standard beam-type finite elements with isotropic material properties. This approach offers a first structural model in which optimal sensor placement (OSP) methodologies are applied to improve the system identification process. In particular, the effective independence (EFI) method is used to determine the optimal locations of a set of sensors. Ambient vibration tests are conducted to determine experimentally the modal characteristics of the structure. The identified modal parameters are compared with those values obtained from this preliminary model. To improve the accuracy of the numerical predictions, the material response is modeled by means of a homogenization-based multi-scale computational approach. In a second stage, the structure is modeled by means of three-dimensional solid elements with the above material definition, capturing realistically the full orthotropic mechanical properties of wood. A genetic algorithm (GA) technique is adopted to calibrate the micromechanical parameters which are either not well-known or susceptible to considerable variations when measured experimentally.FindingsAn overall good agreement is found between the results of the updated numerical simulations and the corresponding experimental measurements. The longitudinal and transverse Young's moduli, sliding and rolling shear moduli, density and natural frequencies are computed by the present approach. The obtained results reveal the potential predictive capabilities of the present GA/multi-scale/experimental approach to capture accurately the actual behavior of complex materials and structures.Originality/valueThe uniqueness and importance of this structure leads to an intensive study of its structural behavior. Ambient vibration tests are carried out under environmental excitation. Extraction of modal parameters is obtained from output-only experimental data. The EFI methodology is applied for the OSP on a large-scale structure. Information coming from several length scales, from sub-micrometer dimensions to macroscopic scales, is included in the material definition. The strong differences found between the stiffness along the longitudinal and transverse directions of wood lumbers are incorporated in the structural model. A multi-scale model updating approach is carried out by means of a GA technique to calibrate the micromechanical parameters which are either not well-known or susceptible to considerable variations when measured experimentally.

Analysis of stress distribution near a blunt surface notch tip in an orthotropic fiber under tension

The intrinsic strength of carbon fiber is determined from tensile tests of carbon fibers with a blunt surface notch using a point stress criterion. A stress distribution around the blunt surface notch tip is needed for the carbon fiber with cylindrical shape and orthotropic mechanical properties. In this study, the stress distribution around a blunt surface notch in a fiber with various orthotropy under tension were calculated using a finite element method. An effect of orthotropy on the stress distribution is investigate. To predict the stress distribution for various notch and various orthotropy, an approximate stress distribution equation was proposed.

A New Damage Model to Predict Orthotropic Nonlinear Behavior of Woven Glass-Epoxy Composite

In the present work a new damage model based on continuum damage mechanic was proposed to predict the nonlinear behavior of woven glass fiber composite under tensile test. The composite specimens were fabricated by hand lay-up method and they were put into a temperature and pressure controlled curing chamber. In order to perform the tensile test a universal Instron machine was used with the DIC method to measure the strain field during the tensile test. All orthotropic mechanical properties such as elasticity modulus, Poisson`s ratio and failure strain were calculated from experiment. After tensile test it was observed that the material behavior was brittle elastic however the stress-strain curve was exhibited a nonlinear fashion. The reason of nonlinearity assumed as irreversible damage effect during the test for instance initial void, fiber breakage, matrix cracking, delamination and fibers debonding. A new damage model with four physical meaning constants was proposed to predict the nonlinear behavior of the material. The model was implemented by a user subroutine in MSC MARC finite element software. Additionally the material damage constants were obtained from iterative numerical simulations. Moreover the damage parameters were optimized by Genetic Algorithm. In conclusion the damage model can predict the nonlinear behavior of composite in both warp and weft direction with reasonable agreement in comparing with experiment.