Effective Mechanical Properties Research Articles

Novel modified triply periodic minimal surfaces (MTPMS) developed using genetic algorithm

The desirable properties of natural porous materials have inspired humans to design cellular materials with remarkable properties such as high energy absorption, acoustic and thermal insulation, and high specific strength structures. Triply Periodic Minimal Surface (TPMS) structures are particularly important among the architected materials. In this research, we have developed a novel approach based on a genetic algorithm for geometry modification of TPMS structures. The approach is exploited to enhance the effective thermal and mechanical properties of TPMS structures, namely Primitive, IWP, Gyroid, and GPrime. New modified TMPS structures (MTPMS) have much higher Young's modulus and thermal conductivity than their base structures, and some of them have properties very close to the upper Hashin-Shtrikman bounds. Unlike previous studies conducted to improve the properties of TPMS structures, MTPMS can be expressed by simple equations. Although MTPMS are not generally considered minimal surfaces, they nonetheless possess the desirable geometric qualities of TPMS structures, such as being smooth and splitting space into two non-intersecting and continuous domains, etc.

Simulative Determination of Effective Mechanical Properties for Digitally Generated Foam Geometries

Metal foams constitute a promising and emerging material class in the context of lightweight construction. There exists a variety of different foam topologies, on which resulting mechanical properties depend. To maximize the potential of foams in material use under mechanical load, the present work addresses the question how different geometrical parameters influence the material behaviour. Therefore, an algorithm for digital generation and design of open pore foam structures is presented, that allows to regulate the geometry precisely. A method for retrieving effective mechanical properties from numerical simulations of compression tests in the elastic regime is introduced. Additionally, the representativeness of foam volumes considered for simulations is investigated. This yields a fully digital workflow, which enables the investigation of geometry influence on mechanical properties. This approach is used to conduct simulation studies on generated foam structures with a systematic variation of geometrical parameters. Herein, a range of effective Young's moduli varying by up to a factor of 1.3 for different foam structures at the same porosity is found. This shows a significant impact of the foam geometry on the elastic properties of metal foams. The presented methodology yields insights, which can guide design and optimization of materials for specific applications.

The asymptotic homogenization evaluation of effective mechanical property of the C/C-ZrC composite by the reconstruction technique

In this framework, we formulate a procedure to reconstruct the structure of general random 3D braid heterogeneous media based on transformation of Gaussian random fields, where the correlation of the underlying Gaussian field is determined explicitly rather than through iterative methods. The reconstructed media can meet the key microstructural information contained in the micrographs and two-point correlation function of the reference media. A robust and efficient algorithm is the operation for accurate determination the effective physical properties from a local heterogeneous material based on the methods of asymptotic homogenization and the finite element. Comparison of the present result to the experimental data from the literature shows a good agreement. The correlation length, Gaussian complexity, representative volume element size and mesh size are investigated and selected to highlight the importance of morphologically realistic microstructures. The effective properties of 3D braid composites are evaluated numerically and the respective effect of the volume fraction and relative material parameters of the reinforcement is assessed numerically. This breakthrough is the possibility to design, predict properties, and even manufacture materials not only with the help of experiments but also with computer science.

Effect of low‐temperature plasma modified pyrolysis carbon black on the properties of rubber composites prepared by wet process

AbstractPyrolysis carbon black is the pyrolysis product of waste tires. The high‐value utilization of pyrolysis carbon black can reduce black pollution of the environment, achieve sustainable development, and solve the problem of energy supply and consumption in the world. This paper mainly studies the modification and excitation of low‐temperature plasma on pyrolysis carbon black. It proposes a micro flocculation wet process (DMLI process) for preparing master rubber by wet mixing. Combined with DMLI process, the vulcanization performance, physical and mechanical properties, Payne effect, and dynamic mechanical properties were also analyzed and characterized. The results showed that the properties of the rubber compound prepared by low‐temperature plasma modification of pyrolytic carbon black were significantly improved. The modified pyrolytic carbon black had the characteristics of less ash, higher activity, and stronger affinity with rubber, and the wettability was significantly improved. In wet mixing, the new DMLI process can effectively improve the degree of combination and dispersion of carbon black and natural rubber latex. Therefore, the modified pyrolytic carbon black can completely replace the industrial carbon black N330, thereby preparing high‐performance rubber composites, realizing the high‐value utilization of pyrolytic carbon black and sustainable green development.

Effective Mechanical Properties of Auxetic Materials: Numerical Predictions Using Variational Asymptotic Method Based Homogenization

Abstract In this work, the variational asymptotic method (VAM) based homogenization framework is used for the first time to determine the equivalent elastic stiffness tensor of auxetic materials. The proposed method allows the structural elements of the auxetic unit cell to naturally incorporate rotational degrees-of-freedom, without any ad-hoc assumptions. The overall macroscale homogenized response of the unit cells is considered to be fully anisotropic; specific possible responses, representative of orthotropy or transverse isotropy naturally emerge from the VAM-based homogenization, due to the arrangements of the structural elements making up the unit cell. For all the auxetic unit cell geometries considered in this study, the predictions obtained from the in-house python-based implementation of the VAM-based homogenization framework are validated using commercial finite element software (abaqus) and open literature. The results demonstrate the versatility and the computational efficiency of the VAM-based homogenization framework to describe auxetic metamaterials.

Grid octet truss lattice materials for energy absorption

Octet truss lattice material, the most well-known stretching-dominated lattice material, is attracting attention in lightweight material engineering. Low resistance to buckling loading limits its use in lightweight energy absorbers. Here, we propose a new strategy to construct octet truss lattice materials with high mechanical properties and stable nonlinear compression response at low relative densities. The effective mechanical properties of the generated grid octet lattice materials have been investigated both numerically and experimentally. Results show that the relative elastic modulus, yield strength and specific energy absorption will increase with either the relative density or the number of the grid structure. At a relative density of 0.5 and compared to the truss lattice, the gain in Young’s modulus, yield strength, and SEA is 26%, 26% and 25%. Respectively. Additional compression test on the 316l stainless steel samples demonstrates introducing triangular grid structures suppresses the post-buckling behavior of the octet lattice. The generated grid octet lattice materials possess a nearly constant plateau stress between initial yield and densification, even at a relative density of about 0.2. The designed lattice material is thus a noteworthy alternative for load bearing and energy absorption.

Topology optimization of fibre reinforced polymer lattice structures for additive manufacturing

The material anisotropy induced by the related additive manufacturing (AM) extrusion process and the geometric errors introduced into the unit lattices by the stair-stepping artifacts were coupled in the topology optimization model to ensure the accuracy and reliability of the optimal design for the fibre reinforced polymer lattice structures. The material properties of the 3D printed carbon fibre reinforced polymers (CFRP) were firstly systematically investigated by extensive tensile tests aided by the digital image correlation (DIC) system, through which the microscale material anisotropy was clarified. Moreover, the accurate orthotropic material models were introduced into the as-fabricated mesoscale unit lattices with geometric errors to obtain the effective mechanical properties. Finally, mechanical performance of the macroscale structures was optimized by the integration of the ideal and as-fabricated unit lattices with the homogenization-based topology optimization method. The AM process-induced material anisotropy and geometric errors result in significant deviations of the mechanical property of the topologically optimized macrostructures and more accurate topology optimization results can be achieved considering the microscale material anisotropy and the geometric error in the mesoscale unit lattice. The results obtained in this investigation indicate that it is essential to comprehensively consider the AM process-induced microscale material anisotropy and mesoscale geometric errors in the topology optimization of fibre reinforced polymer lattice structures to improve the accuracy and reliability of the optimal design.

Free vibration analysis of FG‐GPL and FG‐CNT hybrid laminated nano composite truncated conical shells using systematic differential quadrature method

AbstractIn the present study, the free vibration of functionally graded graphene platelet‐reinforced (FG‐GPLs) and functionally graded carbon nanotube‐reinforced (FG‐CNTs) hybrid laminated nanocomposite truncated conical shells and panels are analyzed. Multi‐layers truncated conical shell and panel of pure FG‐CNTs, pure FG‐GPLs and hybrid CNTs‐GPLs reinforcement were evaluated. In light of its high accuracy in the calculation of thin and thick shells, a third‐order shear deformation theory is adopted. The governing equations and boundary conditions is derived using Hamilton's principle and is solved numerically using the systematic differential quadrature method (DQM) which uses Kronecker delta function. The effective mechanical properties of the CNT‐reinforced nanocomposite layers are estimated using the rule of mixtures, whereas those of the GPL‐reinforced nanocomposite layers is calculated using the Halpin‐Tsai micromechanical model. Convergence and accuracy evaluation of the presented study are confirmed and a number of parameters, including the CNTS volume fraction, GPLs mass fraction, distribution patterns (i.e., Uniform distribution (UD), Functionally graded O‐distribution (FG‐O), Functionally graded X‐distribution (FG‐X), Functionally graded V‐distribution (FG‐V) and FG‐A), different boundary conditions and the vertex angle of the cone, are investigated. The results obtained in this article for the combination of two different materials, GPLs and CNTs, showed that in controlling the natural frequency of the system, without changing the percentage of fiber and only by changing the arrangement, very wonderful results can be achieved.

Micromechanical homogenization of a hydrogel-filled electrospun scaffold for tissue-engineered epicardial patching of the infarcted heart: a feasibility study

AbstractFor tissue engineering applications, accurate prediction of the effective mechanical properties of tissue scaffolds is critical. Open and closed cell modelling, mean-field homogenization theory, and finite element (FE) methods are theories and techniques currently used in conventional homogenization methods to estimate the equivalent mechanical properties of tissue-engineering scaffolds. This study aimed at developing a formulation to link the microscopic structure and macroscopic mechanics of a fibrous electrospun scaffold filled with a hydrogel for use as an epicardial patch for local support of the infarcted heart. The macroscopic elastic modulus of the scaffold was predicted to be 0.287 MPa with the FE method and 0.290 MPa with the closed-cell model for the realistic fibre structure of the scaffold, and 0.108 MPa and 0.540 MPa with mean-field homogenization for randomly oriented and completely aligned fibres. The homogenized constitutive description of the scaffold was implemented for an epicardial patch in a FE model of a human cardiac left ventricle to assess the effects of patching on myocardial mechanics and ventricular function in the presence of an infarct. Epicardial patching was predicted to reduce maximum myocardial stress in the infarcted LV from 19 kPa (no patch) to 9.5 kPa (patch) and to marginally improve the ventricular ejection fraction from 40% (no patch) to 43% (patch). This study demonstrates the feasibility of homogenization techniques to represent complex multiscale structural features in a simplified but meaningful and effective manner.

Could Effective Mechanical Properties of Soft Tissues and Biomaterials at Mesoscale be Obtained by Modal Analysis?

Could Effective Mechanical Properties of Soft Tissues and Biomaterials at Mesoscale be Obtained by Modal Analysis?

Investigation into effective mechanical properties of porous material produced by the additive manufacturing method

Porous materials are defined as materials that contain holes, voids, or spaces in their structures, which can be interconnected or isolated. In the most complex forms of these materials, the holes can have irregular shapes with a random distribution in size, location, and direction, making studying their properties a challenging problem. Additive manufacturing techniques offer opportunities to create complex structures, and in this paper, we investigate the effective mechanical properties of porous material produced by the Fused Displacement Modeling (FDM) technique. We also propose an algorithm for generating a porous body containing irregularly shaped holes with arbitrary distributions in size and location while maintaining specific porosity. Due to the orthotropic properties of bodies created by the FDM technique, Reinforced Isotropic Solid Modeling (RISM) is combined with existing theories that calculate the effective properties of isotropic materials. For the experiments, some modified standard specimen with a porosity of 0.05 to 0.40 has been fabricated, and the elastic modulus and ultimate stress have been calculated using the tensile test. Finally, the results are compared with experimental data.

A novel buckling-induced planner isotropic auxetic meta-structure and its application in BRB: A numerical study

Recently, anti-tetra-chiral-type bulking-induced auxetic meta-structure (generated by arraying periodic orthogonal elongated holes onto a sheet structure) was proved to exhibit superior aseismic performance. Anti-tetra-chiral-type auxetics, however, present strong anisotropic performance, which may limit their potential applications, as proper structural orientations are required during operations to utilize the beneficial auxetic effect. In analogy with anti-tetra-chiral-type bulking-induced auxetic meta-structure, an anti-tri-chiral-type bulking-induced auxetic meta-structure was therefore proposed by arraying periodic tri-dumbbell-shaped holes onto a sheet structure. Systematic finite element (FE) analyses were then conducted on a unit cell with periodic boundary conditions to elucidate the deformation mechanism and investigate the effective mechanical properties of the proposed auxetic meta-structure. Results show that the proposed design exhibits excellent auxeticity and planner isotropy. A novel auxetic buckling restrained brace (BRB) core brace was then designed based on the proposed auxetic meta-structure. Numerical calculations were then conducted to investigate the aseismic performance of the proposed auxetic BRB core. It is shown that the proposed auxetic BRB core brace demonstrates better energy dissipation capacity compared to a traditional BRB core brace with positive Poisson’s ratio and a recently reported auxetic BRB core brace with orthogonal elliptical holes. Practically, the aseismic performance of the proposed BRB core brace is independent of the orientation of the perforated holes and hence can allow uncertain fairly big manufacturing errors.

Impact response of negative stiffness curved-beam-architected metastructures

Mechanical metamaterials and metastructures exhibit superior effective mechanical properties, such as enhanced energy dissipation and resistance against impact loads, beyond those of natural materials. Metastructures with the ability to manipulate wave propagation are particularly desirable in numerous applications, such as actuators, dampers, and lightweight impact resistant systems with structural tunability and recoverability. Specifically, multi-stable structural forms have attracted considerable attention in the design of architected multi-materials, metamaterials, and morphing structures. To design such systems, a recently developed mechanical metamaterial/metastructure known as negative stiffness honeycomb, composed of arrays of curved double-beams (CDBs), is proposed. Here, we develop an analytical model to predict the dynamic response of the CDB metastructures, architected with a periodic array of the CDBs, and subjected to impact by a striker. The analytical model is developed using the Euler-Lagrange theorem and the snap-buckling phenomena in the honeycomb have been examined. The derived closed-form solutions were in good agreement with those of the numerical finite element model at different bistability ratios, defined as the ratio of beam apex height to its thickness. The findings demonstrated that the bistability ratio had a noticeable influence on the buckling response of the metastructure and the desired negativity in the stiffness matrix, while the snap-back buckling phenomena may be realised at high bistability ratios.

Adjustable indentation and vibration isolation performances of nacre-like metamaterial

ABSTRACT Along with the living environment, organisms have evolved structures that adapt to specific environments and have better mechanical properties. Bioinspired materials learn from nature and improve their mechanical properties by imitating the structure of living organisms. Based on the 4D printed shape memory polymer and the bioinspired design method, this research proposes a soft and hard phase hybrid bioinspired metamaterial with shape memory effect and programmable mechanical properties. Compared with traditional nacre-like materials, bioinspired materials have adjustable characteristics of mechanical properties, impact resistance, and low-frequency vibration isolation. First, based on the constitutive relation of SMP (Shape memory polymer) material and its numerical simulation, an intelligent bioinspired metamaterial is designed. Subsequently, the mechanical properties and vibration isolation behavior and adjustability performance of multi-scale bioinspired metamaterials are explained by experiments. Finally, the adjustable functional mechanism of the deformation and vibration isolation of the bioinspired metamaterial is described. The research of these bioinspired metamaterials has broad application prospects in the fields of impact protection and low-frequency vibration absorption.

Sine-based lattice plates: additive manufacturing and their mechanical properties when loaded out of plane

PurposeDemanding applications could benefit from the mathematical parametrization of lattice structures as this could lead not only to the characterization of structure–property relation but also facilitates the tailoring of the effective mechanical properties. This paper aims to characterize the mechanical performance of sine-based lattices. The characterization includes the results of in-plane Poisson’s ratio plates models, and the stiffness of additively manufactured lattice plates when loaded in the out-of-plane direction, with the objective of obtaining a relation with their geometrical parameters.Design/methodology/approachThe geometrical parameter–Poisson’s ratio relationship was characterized via finite element (FE) simulations. The stiffness was also measured on additively manufactured polylactic acid lattice plates and contrasted with FE computations.FindingsThe characterization of auxetic lattice plates performed using in-plane and out-of-plane loading leads to key properties when deciding the geometry specific for applications: relative density, auxetic behavior and stiffness. Approximately 26% reduction of stiffness was observed between the square lattice and sine-based lattices of the same volume fraction.Originality/valueAuxetic metamaterials are potential candidates for applications in biomedical engineering, smart sensors, sports and soft robotics. This paper aims to contribute to the existing gap in the study of auxetic metamaterials subjected to complex loading conditions, other than simple tension and compression, required for the mentioned applications.

Reinforced masonry homogenization by the finite-volume direct averaging micromechanics—FVDAM

The theory of finite-volume direct averaging micromechanics (FVDAM) has recently been used to analyze composite materials to obtain their effective properties. This technique has been continuously improved and applied to different problems and is promising in the heterogeneous materials research area with excellent results compared to other numerical approaches. As it is a relatively new technique, many applications have not been performed yet. This work applies the FVDAM for the first time to the numerical study of reinforced masonry, which presents complex behavior, often requiring structural reinforcement despite being an old material. Thus, the FVDAM theory is compared with results obtained by mechanics of structure genome (MSG), which has already been applied to the homogenization of unreinforced and FRP-reinforced masonry and by the finite element method (FEM). Lastly, FVDAM is applied to the solution of some examples involving different types of masonry unit cells, including the investigation of the effects of structural reinforcement, volume fraction, unit cell geometry, and the influence of block properties on effective mechanical properties. The results of such examples are compared with numerical methods such as MSG and FEM, demonstrating the good performance of FVDAM against the methods used in the comparison.

Numerical modeling of vibration and damping of higher-order magnetorheological elastomer polar orthotropic composite sectorial/annular plates

This study contributes to the modeling and analysis of damping and vibration in the innovative composite sector and annular plates composed of a magnetorheological elastomer (MRE) reinforced with glass fibers. These plates are formed of laminate construction. For the purpose of this investigation, polar orthotropic laminas are used. The generalized Maxwell constitutive law is employed in order to describe the tunable viscoelastic properties of the MR elastomer, including storage and modal loss factor. The application of a magnetic field enables one to exert control over the storage and loss moduli of these materials. In addition, the effective mechanical properties of the MRE composite (MREC) are determined through a modified version of the Voigt micromechanical rule and the Halpin–Tsai rule. In order to define the displacement field of the plate, a hyperbolic higher-order shear deformation approach is used. By adopting Hamilton’s principle, one may get the equations describing the motion as well as the relevant boundary and continuity conditions. In order to solve this system of highly coupled partial differential equations (PDEs), the 2D generalized differential quadrature (GDQ) approach is exploited. A comparison was made between the developed model and those available in the literature to validate the accuracy and convergence quality of the solution technique and formulation. A complete investigation is carried out into the influence of the magnetic field on the free-damped response of the MREC sector and annular plates. In addition, the effects of the composite and geometric properties of the structure on the natural frequencies and modal loss factors of the structure have been examined.

The Influence of GPL Reinforcements on the Post-Buckling Behavior of FG Porous Rings Subjected to an External Pressure

The work focuses on the post- buckling behavior of functionally graded graphene platelet (FG-GPL)-reinforced porous thick rings with open-cell internal cavities under a uniform external pressure. The generalized rule of mixture and the modified Halpin–Tsai model are here used to evaluate the effective mechanical properties of the ring. Three types of porosity patterns are assumed together with five different GPL distributions as reinforcement across the ring thickness. The theoretical formulation relies on a 2D-plane stress linear elasticity theory and Green strain field in conjunction a virtual work principle to derive the nonlinear governing equations of the post-buckling problem. Unlike the simple ring models, 2D elasticity considers the thickness stretching. The finite element model combined with an iterative Newton–Raphson algorithm is used to obtain the post-buckling path of the ring up to the collapse. A systematic investigation evaluates the effect of the weight fraction of nanofillers, the coefficient of porosity, porosity distribution, and the GPLs distribution on the deep post-buckling path of the ring. Based on the results, it is found that the buckling value and post-buckling strength increase considerably (by approximately 80%) by increasing the weight fraction of the nanofiller of about 1%.

Effect of SIS block copolymers on damping properties of natural rubber/AO-80 and the performance enhancement mechanism: experimental study and molecular dynamics simulation

Natural rubber/blocked phenol/styrene-isoprene block copolymer (NR/AO-80/SIS) composites were prepared by using hindered phenolic polar small molecules (AO-80) and styrene isoprene block copolymer (SIS) as damping performance-enhancing components and (NR) as rubber substrate to overcome the problems of narrow effective damping temperature range, unsatisfactory damping effect and subpar mechanical properties in NR/AO-80 rubber applications.The effects of SIS and AO-80 on the morphology, structure, mechanical properties, aging resistance, and damping properties of the NR/AO-80/SIS composite were investigated. Molecular dynamics simulations (MD) were employed to investigate the intermolecular forces, and interaction mechanisms of the rubber composites. SIS exhibited compatibility with the NR/AO-80 matrix and can significantly enhanced the mechanical, aging, and damping properties of the NR/AO-80 matrix. The effective damping temperature range can be extended to a maximum of 114.5 °C, demonstrating its notable improvement to the damping performance of NR/AO-80. The primary mechanisms of enhancing damping performance involve the more van der Waals forces, electrostatic interactions in NR/AO-80/SIS composites,which is beneficial for increasing the internal friction of rubber and improving the damping performance of NR/AO-80 /SIS.

Prediction of effective mechanical properties of 2D triaxially braided composites using a geometrical model incorporating flat portions of composite yarns

This study aims to predict the effective mechanical properties (EMPs) of a 2-D triaxially braided composite (TBC) using an analytical model and to investigate the effects of various geometric parameters on them. The 2-D TBC, a type of braided textile composite, consists of an axial yarn and two braider yarns that are oriented in different diagonal directions within a plane, alternating between running below and above each other. A geometrical model is built considering the flat portion of the composite yarn to adjust the fiber volume fraction of the 2-D TBC while keeping other parameters constant. The prediction method is verified by comparing it with experimental and predicted results reported in various references, demonstrating good agreement. A parametric study indicates that geometric parameters affect the undulation path of a braider yarn and the volume content or each composite yarn, resulting in significant impacts on EMPs. The proposed prediction method is competitive in terms of computing time compared to finite element-based methods and can contribute to the design and improvement of composite structures.