Effective Mechanical Properties Research Articles

Isogeometric 3D optimal designs of functionally graded triply periodic minimal surface plates

Recent research attention has been drawn to the interdisciplinary engineering applications of functionally graded triply periodic minimal surface (FG-TPMS) lattice structures due to their lightweight yet high mechanical properties. These features are especially important in the dynamic structural behaviors yet the TPMS gradation has not been studied in multi-dimensions. This paper presents the establishment of the optimization problem finding the 3D optimal designs of FG-TPMS plates under free vibration by assigning the relative density to each control point and applying the concept of NURBS-based interpolation for the continuous effective mechanical properties. The general 3D case of the constraint on total material volume is derived from the existing 1D case, which is required for the 3D optimization problem. Isogeometric analysis and generalized shear deformation theory are utilized to analyze the free vibration behavior of the FG-TPMS plates. Verification with the 1D case and a parametric study of the 3D FG-TPMS plate are conducted. Optimization examples include both basic and complex geometries. Unseen-before optimal 3D FG-TPMS designs with significantly elevated natural frequencies are obtained. The physical meaning of the optimal solutions can be explained by the similarity to porous structures in nature: less dense in the center or at free end, and more dense at the constrained boundaries and surfaces.

Preparation of low‐rolling resistance natural rubber composites from pyrolysis carbon black by plasma treatment

AbstractIn this study, the surface of pyrolysis carbon black (CBp) is modified by integrating the ball milling process with plasma treatment. High‐energy mechanical ball milling enabled more uniform contact and sufficient reaction temperature for the silane coupling agent and CBp. In addition, the impact of plasma activated the ash and surface deposits of CBp, reducing its inertness. Herein, the filler dispersion grade, Payne effect, vulcanization characteristics, and mechanical and dynamic mechanical properties are investigated by considering modified CBp/natural rubber (NR) composites. The ball milling plasma process can reduce the polarity of CBp. Compared with untreated CBp/NR composites, the plasma‐treated SCA‐CBp/NR composites exhibited increased CBp dispersion grades, higher processing safety, better processing fluidity, and improved mechanical properties. The reduced Payne effect ensured more filler‐rubber network structure, resulting in a reduction in rolling resistance.HighlightsThe coupling agent and CBp are treated by low‐temperature plasma and ball milling.The process promotes the formation of the filler‐rubber network.The dispersion grade of composites increased by 26.29%.The tensile strength increased by 5.57%, and the rolling resistance decreased by 19.44%.

On the data-driven description of lattice materials mechanics

In the emerging field of mechanical metamaterials, using periodic lattice structures as a primary ingredient is relatively frequent. However, the choice of aperiodic lattices in these structures presents unique advantages regarding failure, e.g., buckling or fracture, because avoiding repeated patterns prevents global failures, with local failures occurring in turn that can beneficially delay structural collapse. Therefore, it is expedient to develop models for computing efficiently the effective mechanical properties in lattices from different general features while addressing the challenge of presenting topologies (or graphs) of different sizes. In this paper, we develop a deep learning model to predict energetically-equivalent mechanical properties of linear elastic lattices effectively. Considering the lattice as a graph and defining material and geometrical features on such, we show that Graph Neural Networks provide more accurate predictions than a dense, fully connected strategy, thanks to the geometrically induced bias through graph representation, closer to the underlying equilibrium laws from mechanics solved in the direct problem. Leveraging the efficient forward-evaluation of a vast number of lattices using this surrogate enables the inverse problem, i.e., to obtain a structure having prescribed specific behavior, which is ultimately suitable for multiscale structural optimization problems.

On the Design and Mechanical Properties of a Novel Tubular Auxetic Anti-Tri-Missing Rib Structure

In a previous work, the authors proposed a novel planar isotropic anti-tri-missing rib structure exhibiting excellent negative Poisson’s ratio (NPR) performance within extremely large strain range. Building upon this foundation, a novel tubular auxetic anti-tri-missing rib structure is further proposed in this work. By utilizing the Castigliano’s theorem, the theoretical formulae of the effective mechanical properties of the proposed auxetic tubular structure were then established to facilitate the understanding of the underlying microstructural mechanisms. Discussions of the analytical solutions were presented to elucidate different roles of the microstructural geometry on the effective mechanical properties of the proposed design. Results indicate that desired mechanical properties will be obtained by adjusting the geometrical parameters. The analytical solutions were also validated by systematic finite element (FE) analyses, which align well with theoretical values, confirming the feasibility of the developed theoretical formulae. The research findings presented herein provide theoretical foundations and design insights for the practical application of the auxetic tubular meta-structures.

Micro-CT image-based computation of effective thermal and mechanical properties of fibrous porous materials

Fibrous porous materials are extensively employed as heat shielding material for space vehicles and capsules. To predict the performance of these materials using computational modeling at the vehicle/capsule scale, the effective material properties are needed. In this work, the effective thermal conductivity and elastic constants of a carbon fibrous porous material called FiberForm (precursor of PICA) were calculated using a direct image-based approach. In this image-based approach, the microstructures obtained using X-ray computed tomography technique are represented as binary voxel data. Nonlocal interactions are introduced between neighboring voxels. Integro-differential equations, with respect to spatial and temporal dimensions respectively, are developed to govern material thermal and mechanical behaviors. Using this approach, energy-based computational procedures were developed to calculate the effective material properties of fibrous and porous materials irrespective of the periodicity of underlying microstructures. The size of representative volume element was determined by convergence of effective properties with respect to microstructure size.

A reconfigurable metamaterial using trapeziums and triangles with alternative connectivity

A category of metamaterial that can manifest a wide range of Poisson's ratio from positive to negative is presented herein. This metamaterial consists of rigid units in the shapes of right trapeziums and right triangles that are connected at their corners in the form of necks, which supply elastic restraint during relative rotation of the rigid units. The on-axes Poisson's ratio of the metamaterial was formulated by geometrical analysis. By assigning a rotational spring constant to the connecting necks, the total spring potential energy for a specific enclosure was obtained. This energy was then matched against the strain energy of deformation for the homogenized continuum of the metamaterial for the same enclosure to give the on-axes Young's moduli. Results reveal a configuration that enables the metamaterial to display sign-programmable Poisson's ratio. In addition to being able to adjust the on-axes Young's moduli relative to each other, two specific configurations have been identified that permit both on-axes Young's moduli to be equal. The ease of reconfiguration, the wide range of effective mechanical properties and the capability of the Poisson's ratio sign to be programmed, therefore, avail the metamaterial as a viable material for applications that require frequent in situ adjustment of effective properties.

Theoretical and Numerical Investigation of the Effective Mechanical Properties of an Arc Star-Shaped Auxetic Honeycomb

Background: Auxetic honeycombs have attracted a lot of attention due to their excellent properties, including lightweight, and outstanding impact resistance and energy absorption. Methods: This study focuses on a new type of arc star-shaped honeycomb (ASSH) by replacing the tip angles of the classical star-shaped honeycomb (SSH) with curved edges. The theoretical expressions of the effective Poisson’s ratio and Young’s modulus are deduced by using the Timoshenko beam theory and energy method. Furthermore, the numerical model is also established through the Finite Element Method (FEM); then, both the analytical and computational approaches are adopted to conduct parametric analysis. Results: It was found that the effective mechanical properties obtained by theoretical analysis and the FEM are consistent with each other, and ASSH bears tunable effective Poisson’s ratio and Young’s modulus under varying geometric configurations. Conclusion: The present work may provide some guidance for the design and analysis of future auxetic honeycombs.

Simulating squirt flow in realistic rock models using graphical processing units (GPUs)

SUMMARY Understanding the underlying mechanisms of seismic attenuation and moduli dispersion in fluid-saturated cracked porous rocks is of great importance for the development of non-invasive methods to characterize the subsurface. Wave-induced fluid flow at the pore scale, so-called squirt flow, is responsible for seismic attenuation and moduli dispersion at sonic and ultra-sonic frequencies and may be relevant at seismic frequencies. The squirt flow associated attenuation is usually quantified using analytical models. However, numerical experiments suggest that the squirt flow related dissipation is sensitive to fine details of the pore geometry, which can only be modelled numerically. Most of the existing numerical studies explore this phenomenon using simplified models, and there is a lack of numerical studies that model the physics in realistic pore geometries with sufficient numerical resolution. As a result, the impact of wave-induced fluid flow on the effective static and time-dependent mechanical characteristics in realistic settings is still poorly understood. I address these issues by developing a numerical method to model the effective mechanical properties of a hydromechanically coupled system at the pore scale suitable for graphical processing units. A numerical evaluation of attenuation and modulus dispersion due to squirt flow in models based on 3-D microtomography images of cracked Carrara marble is presented. It is shown that the local hydraulic conductivity can be quantitatively estimated from the numerically evaluated effective properties. The accuracy of the numerical results is carefully analysed. This study improves the understanding of the underlying mechanisms of attenuation and moduli dispersion in fluid-saturated cracked rocks. The new method can be applied to model squirt flow for entire laboratory samples in the centimetre scale which was not possible a decade ago.

Effect of degradation in polymer scaffolds on mechanical properties: Surface vs. bulk erosion

Porous polymeric scaffolds are used in tissue engineering to maintain or replace damaged biological tissues. Once embedded in body, they are involved into different physical and biological processes, among which their degradation and dissolution of their material can be singled out as one of the most important ones. Degradation parameters depend mostly on the properties of both the material and surrounding native tissues, which can substantially alter the original mechanical parameters of the scaffolds. The aim of this study is to examine the change in the effective mechanical properties of functionally graded additively manufactured polylactide scaffolds with a linear porosity gradient and morphology based on triply periodic minimal surfaces during simultaneous degradation and compressive loading. Two main types of scaffold-degradation processes, bulk and surface erosions are simulated with two suggested modelling methods. The fundamental differences in the proposed approaches are identified and the influence of different types of scaffold morphology on the change in effective elastic properties is evaluated. The results of this study can be useful for design of optimal scaffolds taking into account the effect of the degradation process on their structural integrity.

Coupling μ-computed tomography and multi-scale modelling to assess the mechanical performance of material extrusion metal components

The porosity defects arising in objects produced by metal Material Extrusion (MEX) additive manufacturing affect the macroscopic mechanical behaviour. This paper presents a new approach integrating μ-computed tomography (μXCT) and multi-scale finite element analysis to evaluate the mechanical performance of components fabricated by metal MEX. The porosity information from μXCT is mapped into the finite element model, allowing to define the volume fraction of porosity to each finite mesh element. Then, the Mori-Tanaka homogenization technique is used to estimate the effective mechanical properties in each integration point, assuming a representative volume element composed by a metal matrix with a void. The reliability of the proposed approach was assessed using tensile specimens of stainless steel 316L produced by metal MEX. The numerical predictions were compared with experimental measurements, namely the strain field evolution measured by digital image correlation (DIC). The results highlight the detrimental influence of the porosity distribution, evaluated in the specimen using μXCT, on the strain distribution during the loading stage. The numerical predictions are in agreement with the experimental measurements, i.e. the difference is lower than 11%. Therefore, the proposed approach offers valuable insights for evaluating the mechanical performance of components produced by metal MEX, focusing on the detrimental effects of porosity defects.

Multifunctional 58S Bioactive Glass/Silver/Cerium Oxide-Based Biocomposites with Effective Antibacterial, Cytocompatibility, and Mechanical Properties.

58S bioactive glass (BG) has effective biocompatibility and bioresorbable properties for bone tissue engineering; however, it has limitations regarding antibacterial, antioxidant, and mechanical properties. Therefore, we have developed BGAC biocomposites by reinforcing 58S BG with silver and ceria nanoparticles, which showed effective bactericidal properties by forming inhibited zones of 2.13 mm (against Escherichia coli) and 1.96 mm (against Staphylococcus aureus; evidenced by disc diffusion assay) and an increment in the antioxidant properties by 39.9%. Moreover, the elastic modulus, hardness, and fracture toughness were observed to be increased by ∼84.7% (∼51.9 GPa), ∼54.5% (∼3.4 GPa), and ∼160% (∼1.3 MPam1/2), whereas the specific wear rate was decreased by ∼55.2% (∼1.9 × 10-11 m3/Nm). X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy confirmed the fabrication of biocomposites and the uniform distribution of the nanomaterials in the BG matrix. The addition of silver nanoparticles in the 58S BG matrix (in BGA) increased mechanical properties by composite strengthening and bactericidal properties by damaging the cytoplasmic membrane of bacterial cells. The addition of nanoceria in 58S BG (BGC) increased the antioxidant properties by 44.5% (as evidenced by the 2,2-diphenyl-1-picrylhydrazyl assay). The resazurin reduction assay and MTT assay confirmed the effective cytocompatibility for BGAC biocomposites against mouse embryonic fibroblast cells (NIH3T3) and mouse bone marrow stromal cells. Overall, BGAC resulted in mechanical properties comparable to those of cancellous bone, and its effective antibacterial and cytocompatibility properties make it a good candidate for bone healing.

Stochastic reconstruction and performance prediction of cathode microstructures based on deep learning

The effective properties of lithium-ion battery (LIB) cathode are determined by both the volume fractions of constituents and the morphological features of microstructure. However, it is difficult to establish an accurate quantitative relationship between the macroscopic effective properties and microstructural features. Deep learning techniques, due to their exceptional nonlinear fitting capabilities, have been widely applied in various complex fields. Our study presents a generation scheme of numerous three-dimensional (3D) digital microstructures of cathode, using a deep convolutional neural network (CNN)-based stochastic reconstruction algorithm combining with the scanning electron microscope (SEM) images. The reconstructed samples are substituted with the corresponding finite element (FE) models, and the effective mechanical and electrochemical properties are assessed through the FE-based homogenization theory. Finally, the generated cathode samples and their effective properties are used to train the 3D CNN for performance prediction. This study demonstrates that the deep learning approaches can accurately and rapidly reconstruct the microstructure of cathode and predict their effective properties. Furthermore, the established framework can be extended to other heterogeneous materials.

Stiffness, strength, anisotropy, and buckling of lattices derived from TPMS and Platonic and Archimedean solids

Lattice metamaterials have gained considerable attention due to their distinctive topological structures and multifunctional properties. In this work, the effect of topology, loading conditions, and relative density on the effective mechanical properties of various novel lattice architectures is investigated numerically and experimentally. Thirteen strut-based lattices derived from triply periodic minimal surfaces (five lattices) as well as Platonic (three lattices) and Archimedean (five lattices) solids are considered for the first time, and their anisotropic mechanical properties, including uniaxial, shear, and bulk moduli and strengths as well as their total stiffness, buckling strengths, Poisson’s ratio, and anisotropy are investigated as a function of a wide range of relative densities (0.1% to 37%). Finite element analysis is employed to capture the full effective behavior of these lattices using periodic boundary conditions. Bifurcation analysis is performed to predict the threshold relative density governing their buckling vs yielding deformation behavior. Selected lattice structures of various relative densities are 3D printed using polymer selective laser sintering additive manufacturing technique and tested under quasi-static uniaxial compression where the experimental and numerical results are compared. The numerical results indicate that the deformation behavior can be altered between stretching and bending dominated mode of deformation as function of loading. Archimedean lattices are shown to outperform a wide range of strut-based lattices. This work opens the doors for more investigations of the multifunctional properties of these novel types of lattices and their engineering applications. Furthermore, the generated comprehensive data are useful in optimizing latticed structures using topology optimization techniques.

A zinc-embedded multicomponent copolymer customized for polypropylene and its synergistic flame-retardant effect and outstanding mechanical properties

The poor compatibility between the common polar intumescent flame-retardant system (IFR) and the nonpolar polypropylene (PP), as well as the high additive amount, seriously impacts the mechanical properties of the composites. This study introduced collaborative flame-retardant technology to construct block copolymer flame retardants and prepared a zinc-embedded multicomponent copolymer (PM-Zn2+) customized for PP composites. In the PM-Zn2+ system, zinc oxide was embedded into the copolymer composed of piperazine phosphate oligomer and melamine phosphate. PM-Zn2+ exhibited an amorphous structure with extremely low crystallinity and demonstrated specific morphological adaptability. The PM-Zn2+ were well dispersed in the PP matrix and changed their morphology during processing. When applied to PP, excellent flame retardancy and mechanical properties were obtained by using a minimal amount of flame retardants (20 %). PM-2 %Zn2+ gave PP an LOI value of 31.5 %, and achieved a UL94 V-0 rating (1.6 mm thick), exhibiting a lower heat release rate and smoke release. The flame-retardant mechanisms of PM-Zn2+ mainly involved the synergistic and aggregative effects. Transition metal zinc synergistically interacted with polyphosphate groups to create a charring barrier effect and enhance synergistic smoke suppression, leading to a significant reduction in combustion intensity. In comparison to the Mix-Zn/PP composites, the mechanical properties of PM-Zn2+/PP were significantly enhanced due to the specific morphological adaptability and improved compatibility. The elongation at break increased significantly from 15.6 % to 627.9 %, marking a remarkable improvement of 40-fold improvement, while the impact strength rose from 23.7 kJ/m2 to 54.3 kJ/m2, representing a 129 % enhancement. Finally, the zinc-embedded multicomponent block copolymer offers a promising approach to developing high-performance flame-retardant polypropylene materials.

Thermal and Mechanical Performance of 3-Phase Polymer Composite Panels for Structural Applications

The objective of this study is to establish a conceptual framework for fiber-reinforced polymer composite (FRPC) panels designed for structural purposes through the incorporation of a third phase (fillers). The present investigation was aimed to design and fabricate 3-phase polymer composite panels that offer enhanced thermal insulation and strength while maintaining low material and labor expenses. Two types of fibrous reinforcements (jute fabric and glass fabric) of different origins were used as reinforcement; polypropylene (PP) was used as the matrix, and microcrystalline cellulose (MCC) was used as particle reinforcement material. The composite materials were fabricated with different MCC concentrations (0, 2 wt%, and 4 wt%), using a hot compression molding technique. It was found that MCC helped to enhance the mechanical performance of the composite panels, while the thermal conductivity showed a slight reduction due to lower concentrations of MCC used. For polypropylene/glass (PPG) composites, thermal conductivity was reduced from 0.214 to 0.193 W/m·K by the addition of 4% MCC fillers. Similarly, for polypropylene/jute (PPJ) composites, it was reduced from 0.14 to 0.126 W/m·K by 4% MCC fillers. The Charpy impact strength of both PPG and PPJ composites was enhanced by the addition of fillers, and the effect was more significant in the case of PPG (increased from 24.83 to 43.98 kJ/m2 for 4% fillers). Cost analysis of the composite panels was also done, showing PPJ panels to be slightly cheaper as compared to PPG. The findings indicate that the developed composite panels have the potential to serve as partitioning as well as the outer shield of the building due to their effective thermal and mechanical properties.

Metal-ion-controlled hydrogel dressing with enhanced adhesive and antibacterial properties for accelerated wound healing

In order to improve the wound repair environment, this research has successfully developed a new multifunctional hydrogel dressing, which has strong adaptability and can accelerate wound healing. Pioneering the development of metal-ion-controlled hydrogel dressings, this research integrates dopamine and imidazole double crosslinked networks with metal-ion coordination. The resulting hydrogel dressing exhibits a notable antibacterial effect and exceptional mechanical properties, withstanding pressures of up to 12 kPa, tensions of 25 kPa, and maintaining skin adhesion at 6 kPa. Furthermore, the dressing can self-heal within only 7–8 s post-injection. Impressively, the hydrogel achieves complete biodegradation within a short timeframe (37 h). Notably, the use of various metal ions facilitates painless peeling during the degradation period, perfectly aligning with the requirements of an ideal wound dressing. This study has made significant progress in the fields of trauma repair and materials, providing strong solutions for dealing with harsh post-traumatic environments.

Multilayer modeling framework for analyzing thermo-mechanical properties and responses of twisted and coiled polymer actuators

The twisted and coiled polymer actuator (TCPA) has a complex multi-scale structure consisting of crystalline micro-fibrils and an amorphous matrix at the micro-scale, which are organized into a macro-scale fiber. When the polymer fiber undergoes twisting and coiling, its mechanical and thermal properties become variable. In this study, we developed a multi-layer modeling framework capable of accurately predicting the effective mechanical and thermal properties, as well as the thermo-mechanical responses of the TCPA. Our numerical results demonstrate that the effective mechanical and thermal properties of the TCPA are influenced by the radius and twisting angle of the polymer fiber. By analyzing the precise mechanical and thermal properties, the numerical calculated driving responses exhibit good agreement with experimental data. We also examined the influence of initial helical radius, helical pitch and fiber radius on the driving responses of the TCPA. The proposed numerical model can be further utilized to optimize the driving responses of the TCPA by adjusting geometric parameters and the twisting angle of the polymer fiber.

Application of plasma‐activated silanized cellulose nanofibers in natural rubber composites

AbstractCellulose nanofiber (CNF) is an advanced bio‐nanomaterial. However, the hydroxyl groups on the surface of CNFs are highly polar, leading to its weak interfacial compatibility with natural rubber (NR). Therefore, it is necessary to organically modify CNFs by silanization to improve the interfacial compatibility between CNFs and NR, which can then be used to prepare high‐performance CNF/NR composites. In this study, the effect of plasma‐activated pre‐silanization of CNFs on the vulcanization characteristics, mechanical properties, Payne effect, and dynamic mechanical properties of CNF/NR composites is investigated. The high‐energy impact of the plasma weakens the agglomeration of CNFs and increased the fiber surface roughness, providing a larger contact reaction area for the silanization reaction between the silane coupling agent and CNFs. The results show that the prepared CNF/NR composites have excellent physical and mechanical properties and processing safety. Compared with the unmodified CNF, its DIN wear increases by 4%, tensile strength increases by 23%, reinforcement factor increases by 7%, rolling resistance decreases by 6.3%, and Mooney viscosity decreases by 17.6%. Overall, this study presents a novel approach for the high‐value utilization of CNFs and the preparation of NR composites with exceptional properties, thereby establishing a solid foundation for the application of all‐steel treads.

Flutter analysis of laminated fiber-reinforced magnetorheological elastomer sandwich plate resting on an elastic foundation using an improved first-order shear deformation theory

Magnetorheological elastomers (MREs) are polymers with viscoelastic properties that can be adjusted by manipulating the magnetic field. When MREs are combined with reinforcing fabrics, a new category of materials known as MRE composites (MRECs) can be created, which not only possess the characteristics of MREs but also enhance their rigidity. This study focuses on investigating the supersonic aeroelastic instability of a rectangular sandwich plate with a laminated MREC core layer and functionally graded materials with porosities as face layers. Additionally, the sandwich plate is supported by an elastic foundation and subjected to supersonic airflow. This investigation presents an improved first-order shear deformation theory, postulating a parabolic distribution of shear stresses. Consequently, the transverse shear stresses are rendered as zero at the surface of every individual layer; thus, the requirement for shear correction in this theory is eliminated. In addition, 8-node elements are implemented to circumvent the necessity for distinct handling of shear-locking. The aeroelastic pressure acting on the structure is considered using first-order piston theory. Micromechanical approaches, such as Halpin‐Tsai and rule of mixture approaches, are employed to determine the effective mechanical properties of the core and face layers. The dynamic equations of the structure are derived using Hamilton’s principle and the finite element method. The study also examines the impact of different magnetic fields, fiber volume fraction, elastic foundation factors, layering angles, geometry, and boundary conditions on flutter frequency.

Biodegradable flexible conductive film based on sliver nanowires and PLA electrospun fibers

AbstractBiodegradable conductive films are crucial for the sustainable development of wearable electronics. In this work, a flexible and degradable conductive film was prepared based on a carefully designed interface of polylactic acid (PLA) electrospun fibers and silver nanowires (AgNWs). The amphiphilic triblock copolymer was added to PLA solution for electrospinning, followed by solvent posttreatment to induce the hydrophilic block of the amphiphilic triblock copolymer to migrate to the fiber surface. Dopamine can be uniformly polymerized on the surface of hydrophilic PLA fibers, and the prepared PLA@PDA fiber film can form a good interface combination with AgNWs. The electrical conductivity of AgNWs/PLA@PDA flexible film can reach 258.5 S cm−1, showing obvious Joule heating effect and good mechanical properties. Degradation experiments showed that in phosphate buffered saline, the PLA molecular chain showed a dynamic equilibrium due to the scission and rearrangement of the ester groups and degraded slowly, while AgNWs/PLA@PDA degraded rapidly under alkaline conditions. Our study provides a simple and controllable method to prepare flexible degradable electronic films, which is expected to be applied to flexible wearable bioelectrodes.