In-plane Mechanical Properties Research Articles

Out-of-plane compressive properties of a butterfly-shaped auxetic metamaterial

Abstract Inspired by butterfly, a bio butterfly-shaped auxetic metamaterial (BSAM) was recently proposed in which the unite cell of BSAM was designed based on silhouette of a butterfly. The distinguished in-plane mechanical properties made the BSAM a potential absorber to be used in a broad range of applications. The aim of this study is to examine the out-of-plane mechanical properties under quasi-static compression. Using the validated FE models, a comparison was carried out between BSAM and two popular auxetic honeycombs, namely, re-entrant (RE) and modified re-entrant (MRE). Results showed that the nominal stress-strain curves of the BSAM were significantly higher than those of auxetic honeycombs (RE and MRE). However, the MRE revealed the highest Young’s modulus. The plateau stresses were 10.5 MPa, 7.5 MPa and 3.3 MPa for the compressed BSAM, MRE and RE, respectively. Furthermore, the calculated values of the specific energy absorption per volume (Wv) of the three structures indicated that the percentage of the absorbed energy by the BSAM was 182% and 456% higher than those absorbed by the MRE and RE, respectively. Based on the determined values of ideal Wv (11.4 J/cm3 “BSAM”, 5.2 J/cm3 “MRE” and 2.3 J/cm3 “RE”) , the energy efficiency of the three structures was 64%, 79% and 69% of the total energy in the case BSAM, MRE and RE, respectively. Moreover, the influence of the in-plane thickness (t1) and the thickness of cylinders (t2) on the mechanical performance of the BSAM were examined through a parametric study. Findings of the parametric study indicated that the mechanical properties as a function of t1 were considerably affected, while moderate influence was resulted as a function of t2.

A novel cellular structure with center-symmetric cell walls for morphing applications

Cellular structures are potential candidates for the supporting framework of flexible morphing skins. Unlike traditional zero Poisson’s ratio (ZPR) cellular structures with axisymmetric cell walls, this paper proposes a novel cellular structure with center-symmetric cell walls. The in-plane mechanical properties of this novel structure are explored through theoretical analysis and substantiated by both finite element simulations and experimental tests. Compared to the classic accordion honeycomb structure, the elastic modulus in the x-direction of the novel structure is reduced by an average of 58%, the strain amplification rate is increased by 122%, and the in-plane stiffness anisotropy is improved by 200%. These findings suggest that the proposed structure offers far superior stiffness anisotropy and large deformation potential, making it more suitable for morphing applications than the traditional ZPR cellular structures.

In-plane properties of an in-situ consolidated automated fiber placement thermoplastic composite

Automated fiber placement (AFP) has been employed to manufacture aerospace structures for decades, with a recent focus on thermoplastic composites (TPCs). The in-situ consolidation AFP of TPCs is pursued as an energy-efficient additive manufacturing (AM) approach for fabricating composite structures. This work compares the in-plane mechanical properties of in-situ consolidated coupons with those of compression molded counterparts to provide new insights into their failure mechanics and processing-structure relationships. Tensile and compressive properties along the fiber and transverse directions, in-plane shear properties, and short beam strength were measured for all samples. Failure modes and mechanics in tested coupons were related to AFP defects and processing, i.e., resultant crystallinities, fiber misalignment, matrix mechanical properties, porosity, and fiber–matrix interfacial strength. The findings of this study can be used to guide the manufacturing of future TPC structures and potentially open new avenues for applications where post-processing is not feasible or reduced mechanical performance is acceptable.

In-Plane Mechanical Properties Test of Prefabricated Composite Wall with Light Steel and Tailings Microcrystalline Foamed Plate

The tailings microcrystalline foamed plate (TMF plate), produced from industrial waste tailings, has limited research regarding its use in high-performance building walls. Its brittleness under stress poses challenges. To improve its mechanical properties, a prefabricated light steel-tailings microcrystalline foamed plate composite wall (LS-TMF composite wall) has been proposed. This LS-TMF composite wall system integrates assembly, sustainability, insulation, and decorative functions, making it a promising market option. To study the in-plane performance of the composite wall, compression and seismic performance tests were conducted. The findings indicate that the light steel keel, steel bar, and TMF plate in the composite wall demonstrated good working performance. Strengthening the TMF plate enhanced the restraint on the light steel keel and improved the composite wall’s compressive performance. Increasing the thickness of the light steel keel further improved the compressive stability. Under horizontal cyclic loading, failure occurred at the light steel keel embedding location. Increasing the strength of the TMF plate was beneficial for the seismic performance of the composite wall. This structural configuration—incorporating light steel keels, TMF plates, and fly ash blocks—enhanced thermal insulation and significantly improved in-plane stress performance. However, the splicing plate structure adversely affected the seismic performance of the composite wall.

In-plane mechanical behavior design of triangular gradient rib honeycombs

Two types of triangular gradient rib honeycombs (Triangular gradient rib honeycomb-Type Z-AXBYs) were designed and proposed in this paper. A finite element numerical model was constructed using Abaqus/Explicit, with model accuracy verified, and a series of studies were conducted. Firstly, the mechanical properties of TCH, TGH, and two types of TGRH-Type Z-AXBYs under axial impact were analyzed. Results showed that the specific energy absorption (SEA) of TGH improved by 101.27 % compared to TCH; TGRH-Type I-170°-AXBYs SEA improved by up to 77.21 % compared to TGH; TGRH-Type II-180°-AXBYs SEA improved by up to 63.84 % compared to TGH. Adding a layer with a larger angle at the bottom of the honeycomb effectively improved the impact resistance and energy absorption of the structure. The mechanical properties of two types of TGRH-Type Z-θ-AXBYs with different layers were studied, showing that TGRH-Type I-θ-AXBYs had the best mechanical properties. TGRH-Type I-θ-AXBYs SEA improved by a maximum of 23.57 % compared to TGRH-Type II-θ-AXBYs and by a minimum of 13.71 %. TGRH-Type I-θ-AXBYs SEA improved by a maximum of 74.95 % and a minimum of 12.88 % compared to TGRH-Type I-θ-6X. Finally, the effects of wall thickness and velocity on the two types of TGRH-Type Z-AXBYs were analyzed. Properly increasing the wall thickness effectively improved the impact resistance of the structure. This paper provides a feasible reference for introducing a gradient ribbed plate design into triangular honeycombs to enhance their in-plane mechanical properties.

An optimized hybrid finite element analyses - Artificial neural networks technique for estimating in-plane orthotropic mechanical properties of printed circuit boards

Explicitly modeling Printed Circuit Boards (PCBs) in Finite Element Analysis (FEA) is not practical due to the complex multi-component structure of PCBs. To overcome this complication, a PCB can be simplified and modeled as an orthotropic plate with equivalent mechanical properties that result in the same natural frequencies as the actual PCB. This research introduces an optimized hybrid technique combining FEA and Artificial Neural Networks (ANNs) to accurately estimate the equivalent in-plane orthotropic mechanical properties of PCBs. This study presents a systematic approach where natural frequencies obtained from FEA are used to train ANNs for predicting the equivalent representative mechanical properties. The research employs a rigorous optimization procedure involving various ANN configurations (i.e., different learning algorithms, activation functions, and number of hidden neurons) and training dataset sizes. To further ensure the reliability of the results, 10 cross-validation are carried out for each ANN configuration by employing dynamic data-splitting strategy, and all measures used for assessing the accuracy of the ANN predictions are based on averaged results for the 10 cross-validations. The accuracy of the ANN predictions is tested against both simulated and experimental data. The Mean Absolute Percentage Error (MAPE) is found to be about 4 % based on material properties against the simulated data, and about 1.2 % based on natural frequencies against the experimental data point. The results demonstrate superior predictive accuracy and efficiency compared to existing models, highlighting the potential of the proposed approach in advancing the reliability and performance of PCB mechanical property estimations.

Effect of Chain Orientation on Coupling of Optical and Mechanical Anisotropies of Polymer Films

Polymer films have broad applications in different industries with specific requirements for their optical and mechanical properties. In mass production, processing conditions during film formation that apply forces and motions in various directions to the film tend to manifest preferred molecular chain orientation in the film microstructure, which unavoidably produces optical and mechanical anisotropies. In this paper, we investigate the effect of such macromolecular orientations on the optical and mechanical anisotropies of several polymer films, including polystyrene, poly(methyl methacrylate), poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ether ether ketone), poly(ether sulfones), poly(ethylene chlorotrifluoroethylene), poly(phenylsulfone), and polycarbonate, at temperatures well below their respective glass transitions (Tg). The film mechanical responses, including elasticity, yielding, and post-yield behaviors, were obtained for the in- and out-of-plane directions utilizing tensile and nanoindentation testing methods, respectively. In addition, the net chain orientation within the films was evaluated by birefringence through analyzing the film optical refractive indices, which were verified and complemented by wide-angle X-ray scattering (WAXS) measurements. The results reveal a considerable quantitative correlation between the birefringence and the degree of elastic anisotropy and a qualitative correlation between the chain orientation and the film post-yield tensile instability (necking). These observations corroborate the interrelationship between the microstructure of polymer films and their optical and mechanical properties. In addition, they emphasize that process conditions can be selected to tune the optical and mechanical anisotropies to best serve the material performance in specific devices. We also propose an empirical equation to approximate the out-of-plane film stiffness based upon the optical and in-plane mechanical properties.

In-plane shear failure behavior and mechanical properties of SiC/SiC Composites

Fiber-reinforced ceramic matrix composites, especially SiC/SiC composites, have the characteristics of lightweight, high strength, high-temperature resistance, etc., which are ideal structural candidates for aerospace vehicle components, in-plane shear performance is one of the important indicators to characterize the mechanical properties of materials and component assessment, this paper designs and processes the in-plane shear test pieces and test devices and methods to study the shear mechanical behavior under the mechanical properties and failure behavior of SiC/SiC ceramic-based fiber bundle composites are studied under shear mechanical behavior. The results show that matrix cracking and fiber fracture are the main failure modes, and there are two obvious phases in the specimen shear force-displacement curves, and fiber fracture is the main cause of strain in the specimen.

In-plane mechanical properties of a re-entrant hexagonal and chiral hybrid unit-cell metamaterials

Negative Poisson's ratio (NPR) lattice metamaterials have considerable potential for aerospace, medical treatment, and piezoelectricity applications. However, a metamaterial with a high tensile stiffness in the vertical direction and can achieve substantial displacement in its horizontal direction is lacking. In this work, a novel hybrid unit cell comprising a re-entrant hexagonal cell and a tetra-chiral cell connected in parallel is designed. NPR and tunable stiffness are achieved in such a geometry, which can produce significant deformation in the x-direction and has good tensile stiffness in the y-direction. Based on the Eulerian–Bernoulli beam theory, the mechanical properties of the unit cell are derived. Poisson’s ratio in the xy plane and elastic modulus in the x and y directions are established. Using the finite element (FE) method, we analyzed this hybrid unite cell. Samples with identical geometric variables to those of theoretical models are fabricated by 3D printing. Their Poisson’s ratios and elastic modulus in the x and y directions are tested to verify the theoretical and FE results. Results indicate that the Poisson's ratio of metamaterial is negative. The cell-wall thickness has more influence on elastic properties than the aspect ratio of the cell wall. This study can provide new ideas for the engineering applications of metamaterials.

An artificial intelligence-based approach for identifying the in-plane orthotropic mechanical properties of electronic circuit boards

The finite element modeling of electronic boards is a challenging task due to the complexity of the multi-component board structure. Hence, it is acceptable to attain equivalent orthotropic in-plane mechanical properties and use them throughout the finite element analysis (FEA) simulations. This paper aims to present an artificial intelligence-based methodology, using the artificial neural networks (ANNs), to estimate the in-plane mechanical properties of the printed circuit boards (PCB). In this methodology, the ANN technique used FEA data to find the relationship between the first 10 natural frequencies and the mechanical properties, that is, modulus of elasticity, Poisson’s ratio and the shear modulus, of the test board. Subsequently, the experimentally derived natural frequency data is then imported to the ANN model to identify the equivalent orthotropic properties. The ANN-predicted properties are plugged back into FEA and provided natural frequencies and mode shapes that are in great match with experimental results.

Mechanical Tester Driven by Surface Tension.

The measurement of in-plane mechanical properties, such as Young's modulus and strength, of thin and stretchable materials has long been a challenge. Existing measurements, including wrinkle instability and nano indentation, are either indirect or destructive, and are inapplicable to meshes or porous materials, while the conventional tension test fails to measure the mechanical properties of nanoscale films. Here, we report a technique to test thin and stretchable films by loading a thin film afloat via differential surface tension and recording its deformation. We have demonstrated the method by measuring the Young's moduli of homogeneous films of soft materials including polydimethylsiloxane and Ecoflex and verified the results with known values. We further measured the strain distributions of meshes, both isotropic and anisotropic, which were otherwise nearly impossible to measure. The method proposed herein is expected to be generally applicable to many material systems that are thin, stretchable, and water-insoluble.

In-plane dynamic impact mechanical properties of novel bi-directional hierarchical honeycomb

A novel bi-directional hierarchical honeycomb is proposed. A finite element numerical model was constructed using Abaqus/Explicit, the model's accuracy was verified, and a series of in-plane impact studies were carried out. Firstly, the mechanical properties of axial impact were analyzed for different bi-directional hierarchical honeycombs. The results show that the mechanical properties of NBHH-h1h22h3-III and NBHH-h1h2h3h4-IV are the best and almost identical. Subsequently, the mechanical properties of NBHH-XhxYhy-IIs with different layers were analyzed. Research results show that NBHH-h33h4-II has a 77.96 % increase in specific energy absorption (SEA) compared to NBHH-h13h2-II, and NBHH-h13h2-II has a 116.02 % increase in SEA compared to NBHH-3h1h2-II. A parametric study of NBHHs was conducted. The mechanical properties of NBHHs with different layer ratio coefficients were analyzed, and it was found that the mechanical properties of NBHHs with l2 = 12 and k = 0.2 are the best. Finally, the effects of wall thickness and velocity on NBHHs were analyzed. Increasing the wall thickness appropriately can effectively improve the impact resistance of the structure. Bi-directional hierarchical design provides a practical reference for enhancing the in-plane mechanical properties of honeycombs.

Analysis of In-Plane Impact Mechanical Properties of Centre-Symmetric Chiral Honeycomb

In this paper, two center-symmetric chiral honeycombs (CSCH-1 and CSCH-2) were designed through a center-symmetric approach. Corresponding samples were prepared using 3D printing technology, and in-plane impacts were carried out under quasi-static experiments with the conventional chiral honeycomb (CH). The experimental results show that CSCH-1 and CSCH-2 have better load-bearing capacity and energy-absorbing properties than CH. The mean stress of the two increased by 40% and 60%, and the energy absorption (EA) increased by 92.10% and 101.90%, respectively, compared to CH. Furthermore, the design of CSCH-2 effectively controls the expansion and deformation of the structure, and shows better negative Poisson’s ratio effect. Subsequent finite element modeling was performed using the finite element software Abaqus/Explicit, and the accuracy of the finite element model was verified. Furthermore, the in-plane impact mechanical behavior of CH, CSCH-1, and CSCH-2 was investigated at different impact velocities, various nodal circle radii, and different orthogonal array ratios.

A single carbon nanotube-entangled high-performance buckypaper with tunable fracture mode.

It is well known that the traditional buckypaper (BP) is composed of a certain number of short carbon nanotubes (CNTs) intertwined with each other and sliding always happens when the BP is under tensile and impact loading, which results in inferior mechanical properties compared to single CNTs. In this work, a highly-entangled single-wire BP (SWBP) structure is constructed by a modified self-avoiding random walk approach. The in-plane mechanical properties and impacting behaviors of the SWBPs with different entanglement degrees and interface frictions are systematically investigated via newly developed coarse-grained molecular dynamics (CGMD) simulation. A coarse-grained method can effectively reflect the inter-tube van der Waals (vdW) interactions and the mechanical behaviors of CNTs, including tension, bending and adhesion. In this work, from the tensile simulations of the SWBP, the results showed that the self-locking mechanism between entangled CNTs could significantly enhance the tensile resistance of the film. Besides, the mechanical properties of the SWBP are highly dependent on the entanglement degree and the interface friction between CNTs. Furthermore, two distinct fracture modes, ductile fracture and brittle fracture, are revealed, which can be efficiently controlled by changing the related friction between CNTs. From the impacting simulations, it is found that the impacting performance can be effectively tuned by adjusting the entanglement degree of the film. In addition, the kinetic energy of the projectile could be rapidly dissipated through the stretching and bending of CNTs in the SWBP. This work provides an in-depth understanding of the effect of interface friction and entanglement degree on the mechanical properties of the buckypaper and provides a reference for the preparation of strong CNT-based micromaterials.

Composite curved hourglass cellular structures: Design optimization for stiffness response and crashworthiness performance

Auxetic lattice structures are known for their superior stiffness-to-density and strength-to-density ratios. Re-entrant hourglass exhibits an acceptable equivalent elastic modulus and remarkable energy absorption capacity among various auxetic configurations due to their flexibility and hinge deflecting during crushing loads. This study introduces a curved hourglass honeycomb which can be produced using 3D printing with pure or reinforced filaments incorporating continuous fibers. New closed-form formulations are analytically derived using an energy method by considering an extracted unit cell to predict the equivalent in-plane mechanical properties for the first time. The plateau stress of the proposed honeycomb is evaluated at the densification state of a unit cell using the energy conservation theory, equating external work with plastic energy dissipation. The accuracy of these extended relations is validated against experimental outcomes, demonstrating good agreement between analytical and experimental results. Additionally, robust linear and nonlinear finite element analyses are conducted to assess the accuracy of the obtained relations, including the equivalent stiffness and plateau stress for structures produced with reinforced filaments. The nonlinear finite element code employs appropriate subroutines to model plasticity/damage events. Based on the established analytical relations for stiffness and plateau stress, multi-objective optimization using Genetic Algorithm is applied to define optimum values for the Pareto front chart's objective functions of stiffness and plateau stress. The optimization process involves exploring the design space and defining the values of geometrical parameters to achieve the desired objectives. In conclusion, this study presents a novel approach to developing curved re-entrant honeycomb structures, with analytical formulations validated against experimental and numerical results. Optimization helps to identify optimal configurations concerning stiffness and plateau stress, offering potential applications in lightweight and high-strength materials design. According to the obtained results, for selection of the best value for curved strut angle which results in the optimum value of stiffness and plateau stress, a range between 10°-34° can be considered depending on the volume fraction of fibers.

A Novel Quasi-Planar Two-dimensional Carbon Sulfide with Negative Poisson's ratio and Dirac fermions.

In the present study, a novel and unconventional two-dimensional (2D) material with Dirac electronic features hasbeen designed using sulflower with the help of density functional theory methods and first principles calculations.This 2D material comprises of hetero atoms (C, S) and belongs to the tetragonal lattice with P4/nmm space group. Scrutiny of the results show that the 2D sheet exhibits a nanoporous wave-like geometrical structure. Quantummolecular dynamics simulations and phonon mode analysis emphasize the dynamical and thermal stability. Thenovel 2D sheet is an auxetic material with an anisotropy in the in-plane mechanical properties. Both compositionand geometrical features are completely different from the necessary conditions for the formation of Dirac conesin graphene. However, the presence of semi-metallic nature, linear band dispersion relation, massive fermions andmassless Dirac fermions are observed in the novel 2D sheet. The massless Dirac fermions exhibit highly isotropicFermi velocities (vf = 0.71 × 106 m/s) along all crystallographic directions. The zero-band gap semi metallic featuresof the novel 2D sheet are perturbative to the electric field and external strain.

Strain rate sensitivity of the in-plane mechanical properties of two UHMWPE thin ply composites

The mechanical characterisation of two recent grades of Ultra High Molecular Weight PolyEthylene (UHMWPE) fibres composite is proposed. Used in bulletproof vests, they share the same type of fibres, while composed of different matrices (respectively polyurethane and rubber). The in-plane characterisation is performed through tensile tests on thin layer samples at 0°of the fibres and in-plane shear, in both quasi-static and dynamic conditions. Digital Image Correlation is used for each test to accurately measure strains and evaluate its homogeneity. To study the strain rate effect, various experimental methods were adapted: universal press, drop tower, Split Hopkinson Tensile Bars (SHTB). A significant increase of stiffness with strain rate was observed for both materials At 0°, it transcribed into an increase of 60% for the Young’s modulus, and 40% on failure stress. The in-plane shear modulus was multiplied by two and even eight depending on the considered grade.

Analyzing in-plane mechanics of a novel honeycomb structure with zero Poisson's ratio

The superior performance of honeycomb structure has facilitated its extensive application in various fields. In this paper, a novel honeycomb structure is proposed, which exhibits zero Poisson's ratio behavior. Firstly, the in-plane mechanical properties are analyzed based on the classical Castigliano's theorem to obtain expressions connecting the three elastic constants of the structure and geometric parameters. Then, the theoretical expressions are verified by homogenized finite element methods and 3D-printed experimental models, which help to determine the relationship between the in-plane mechanical properties and the geometric parameters. The results show that the mechanical properties of the honeycomb structure can be tailored by changing the geometric parameters, while ensuring that the zero Poisson's ratio property is maintained within a relatively small fluctuation range. This study reveals that the mechanical properties of the novel honeycomb structure are tunable, which has outperformed some honeycomb structures on adjusting range.

Bio-inspired interleaved hybrids: Novel solutions for improving the high-velocity impact response of carbon fibre-reinforced polymers (CFRP)

We propose a novel design methodology consisting of bio-inspired (BI) and interleaved layups to develop hybrid carbon fibre-reinforced polymer (CFRP) composite structures for improved high-velocity impact (HVI) performance. Firstly, we apply a BI helicoidal design method consisting of various pitch angles (considering both thick- and thin-ply CFRP) to develop BI monolithic CFRP laminates. Secondly, we apply the interleaving design method to develop BI hybrid CFRP-based laminates interleaved with blocks of BI Zylon fibre-reinforced polymers through the thickness. We evaluate their response and compare it with traditional quasi-isotropic (QI) hybrid bulk layups. In addition to hybridising with Zylon, we apply titanium (Ti) foils to both the monolithic and hybrid CFRP-based laminates to investigate and compare their response. For all our hybrids, we kept the ratio of the hybridising material(s) to be less than 50% to ensure suitable in-plane mechanical properties and aimed at a target areal weight of 0.95 g/cm2. We also manufactured QI thick- and thin-ply monolithic CFRP laminates as baselines. We tested all laminates at 170 and 210 m/s and studied their response and failure modes. Our results show that the average energy dissipation of the QI monolithic thin-ply baseline improved by up to 22% by changing the layup from QI to BI, and by about 118% by changing the baseline QI layup to BI hybrid interleaved. Post-mortem analysis reveals that there are additional failure mechanisms activated in the BI hybrid interleaved layup with respect to the baseline.

In-plane anisotropic mechanical properties of two-dimensional NbOI2

Two-dimensional niobium oxide diiodide (NbOI2) has recently attracted extensive attention due to its highly anisotropic band structures and rich physical characteristics in electronics and optoelectronics. Nevertheless, mechanical properties of NbOI2 have not been systematically investigated, which are critical parameters for applications. Here, we determine the directional dependence of Young's modulus of thin NbOI2 flakes by using an atomic force microscopy-based nanoindentation technique. We find that Young's moduli along two perpendicular in-plane crystalline axis, the c-axis and the a-axis, were 97.27 ± 2.12 and 51.51 ± 8.21 GPa, respectively. The anisotropic ratio is up to 1.89, which is a high anisotropy value in two-dimensional materials reported so far.