In-plane Properties Research Articles

Statistical Homogenization of Elastic and Fracture Properties of a Sample Selective Laser Melting Material

Selective laser melting (SLM) is an additive manufacturing technique commonly used in the rapid prototyping of components. The complexity of the SLM microstructure poses a unique challenge to deriving effective mechanical properties at different length scales. Representative volume elements (RVEs) are often used to homogenize the material properties of composites. Instead of RVEs, we use statistical volume elements (SVEs) to homogenize the elastic and fracture properties of the material. This relates the inherent variation of a material’s microstructure to the variation in its mechanical properties at different observation scales. The convergence to the RVE limit is examined from two perspectives: the stability of the mean value as the SVE size increases for the mean-based approach, and the tendency of the normalized variation in homogenized properties to zero as the SVE size increases for the variation-based approach. Fracture properties tend to make the RVE limit slower than do elastic properties from both perspectives. There are also differences between vertical (normal to printing plane) and horizontal (in-plane) properties. While the elastic properties tend to make the RVE limit faster for the horizontal direction, i.e., having a smaller variation and more stable mean value, the fracture properties exhibit the opposite effect. We attributed these differences to the geometry of the melt pools.

An infill-based approach towards stiffer auxetic lattices: Design and study of enhanced in-plane elastic properties

Mechanical metamaterials have tunable material properties, and the architecture of such materials can be tuned to impart Negative Poisson's Ratio (NPR). However, architected lattices typically have low stiffness. In the current study, the filler-based and infill-based strategies for creating auxetic lattices with enhanced stiffness are proposed and demonstrated. Analytic expressions for different in-plane elastic properties of the sinusoidal re-entrant honeycomb (SRH) lattice are developed. Finite element models are validated using data from published literature and analytic models. Using validated FE modelling, parametric studies involving infill patterns and filler materials in the SRH lattices are undertaken to find combinations leading to enhanced stiffness with minor loss in auxeticity. The possibility of attaining a massive increment in stiffness than that of the empty lattices, while retaining significant auxeticity (Poisson's ratio < −1), is demonstrated, which is a key outcome of this work. Using the proposed approach, high stiffness has been achieved in case of both non-auxetic infill-based (NAIB) and auxetic infill-based (AIB) while retaining NPR is established. Further studies have confirmed that the AIB lattices exhibit much higher stiffness compared to all the other lattices. Finally, the proposed approach is benchmarked against four published approaches towards generating stiff lattices with NPR. When compared with existing approaches, it is found that the strategies proposed in this paper perform better; for the same NPR, the proposed approaches lead to lattices with higher stiffness, and conversely, for the same normalised stiffness higher auxeticity is achieved. Implementation of the proposed approaches can be realized using in-built infill capabilities of prevalent additive manufacturing 3D printing technologies. New opportunities to enhance the capabilities of the existing technology are also indicated.

The Method of Multi-Angle Remote Sensing Observation Based on Unmanned Aerial Vehicles and the Validation of BRDF

The measurement of bidirectional reflectivity for ground-based objects is a highly intricate task, with significant limitations in the capabilities of both ground-based and satellite-based observations from multiple viewpoints. In recent years, unmanned aerial vehicles (UAVs) have emerged as a novel remote sensing method, offering convenience and cost-effectiveness while enabling multi-view observations. This study devised a polygonal flight path along the hemisphere to achieve bidirectional reflectance distribution function (BRDF) measurements for large zenith angles and all azimuth angles. By employing photogrammetry’s principle of aerial triangulation, accurate observation angles were restored, and the geometric structure of “sun-object-view” was constructed. Furthermore, three BRDF models (M_Walthall, RPV, RTLSR) were compared and evaluated at the UAV scale in terms of fitting quality, shape structure, and reflectance errors to assess their inversion performance. The results demonstrated that the RPV model exhibited superior inversion performance followed, by M_Walthall; however, RTLST performed comparatively poorly. Notably, the M_Walthall model excelled in capturing smooth terrain object characteristics while RPV proved applicable to various types of rough terrain objects with multi-scale applicability for both UAVs and satellites. These methods and findings are crucial for an extensive exploration into the bidirectional reflectivity properties of ground-based objects, and provide an essential technical procedure for studying various ground-based objects’ in-plane reflection properties.

Anisotropic infrared absorption in monolayer black phosphorus metasurface with/without local oxidative effect

As one kind of anisotropic two-dimensional (2-D) layered material, the monolayer black phosphorus (BP) has ability to excite the surface plasmon resonance in the infrared spectrum, thus providing sufficient conditions for the strong light-matter interaction, so that some potential applications can be shown in the field of optoelectronics. Based on those physical properties, we design the patterned monolayer BP to achieve extremely high infrared absorption, and meanwhile use the finite element method to model the effects of factors such as n-type doping concentration, dielectric thickness, and angle of incidence light. Moreover, due to the strong anisotropic in-plane properties of monolayer BP, we analyze detailedly the absorption spectra in both the armchair and zigzag directions separately, and then understand that low-angle narrow-band absorption in the zigzag direction could be captured in that structure. The structure could achieve perfect absorption in the zigzag direction at an incidence angle of 89.3° with n-type doping concentration n = 3 × 1013 cm−2 and medium thickness d = 4.6 μm, and the maximum absorption can reach 99.98% with the full width at half peak (FWHM) of only 0.57 μm. Considering the case on surface oxidation, it may occur some possible effects for the perfect absorption, but with our structure, the proposed narrow-band absorption still have wide applications in the sensing and light body monitoring.

Investigation of single and multicell honeycomb reinforced shape memory polymer composites: Shape optimization and experimental characterization

Honeycomb materials as reinforcements for shape memory polymers have been considered for their commercial availability, ease of geometric tailoring, and high in-plane stiffnesses. The design optimization of these honeycomb cells remains an open field of research, with many approaches taken in formulating the structural optimization problems. This investigation focuses on implementing a shape variable parametrization of the honeycomb to study the possible value of both cell asymmetry and spatially varying cell geometries in multicell networks. A unit cell finite element model framework was developed to predict the in-plane elastic properties of these composites, and two design objectives were selected to be optimized. Pareto fronts were estimated for multiple loading cases and cell wall material models, and experimental results were collected for model validation. The optimization results find that these composites can achieve a large range of performances, with maximum moduli as high as 17.2 GPa. Large asymmetry is found in the optimized cell geometries, and relationships are identified between loading cases and for different wall materials. Furthermore, the experimental results validate the finite element model predictions, with relative errors as low as 20% for the predicted maximum modulus and 2% for the modulus ratio.

Experimental and numerical investigation of the intra-ply shear behaviour of unidirectional prepreg forming through picture-frame test

Intra-ply shear behaviour of uncured composite plies strongly influences component quality in advanced manufacturing processes such as prepreg compression moulding (PCM) and double diaphragm forming (DDF). This study investigates a straightforward method to characterise the intra-ply shear behaviour of a carbon fibre/epoxy UD prepreg using a specially designed picture-frame rig, by which specimens can be tested without involving inter-ply shear as would normally be observed in cross-plied UD prepreg stacks. Applying the proposed method, it is seen that specimens tend to suffer transverse buckling/wrinkling and local fibre-splitting at large shear strains. 3D digital image correlation (DIC) and a non-contacting video extensometer were utilised to determine the shear strain distribution throughout the test and particularly to determine the onset of out-of-plane deformations such that the trellis shear deformation portion of the test can be identified. The obtained shear stress-strain results show a temperature- and rate-dependent viscoelastic response, with the greatest influence from the temperature. The obtained in-plane shear properties were applied in the numerical simulation of the picture frame test based on a hypoelastic law. Although the predicted reaction forces are greater than experimental results at high strains due several factors including local fibre-splitting, a good agreement overall between physical test data and simulation results is seen for all test conditions. Finally, it is demonstrated that major advantages of the proposed test with respect to the conventional picture-frame test are that only load-extension data are required from the trellis shear experiment to calculate accurately the intra-ply shear stress-strain relationship and that the deformation rate can be easily controlled.

Flexibility and anisotropy of MX3 (M = Zr, Hf; X = S, Se): New semiconductors with high photovoltaic performance

Optoelectronic functional materials with flexible and in-plane anisotropic properties has been a significant development direction of nanotechnology due to wearable and polarized optoelectronic applications. Herein, the elasticity, global band dispersion, optical dielectric properties of environmentally friendly IVB-VIA layered transition metal trichalcogenides (MX3, M = Zr, Hf; X = S, Se) are investigated systematically by density functional theory with different kinds of van der Waals correction and hybrid functional. The low elastic modulus suggests that they are appropriate for the design of flexible optoelectronic devices. Originating from the effect of d states of chalcogens and s states of transition metals, the dispersion of the valence band edge of monolayer MX3 shows that the effective mass of carriers along the wave vector kx is much heavier than that of carriers along the wave vector ky. This means that the mobility of carriers exhibits obvious in-plane anisotropy. Meanwhile, the optical dielectric properties of monolayer MX3 as well as absorbed photon flux (Jabs) of the related heterostructures display noteworthy in-plane anisotropy in the visible-IR region. The ratio of Jabs from different direction reaches up to 1.7. This work could not only promote understanding of rich photophyiscal properties of transition metal trichalcogenides, but also provide a theoretical reference for the invention of high-performance optoelectronic devices with high flexibility and anisotropy.

Structural phase transitions, mechanical properties, and electronic band structures of room-temperature ferromagnetic monolayers ScMP2 (M = Mn and Cr)

Two-dimensional (2D) auxetic properties and ferromagnetism are two major focuses of research for next-generation nanomechanical and spintronic devices. However, 2D materials with the two properties at the same time are rarely reported. Based on first-principles calculations, we propose the 2D bimetallic phosphide ScMP2 (M = Mn and Cr), including three stable tetragonal monolayers. The monolayer ScMnP2 exhibit the square structural phase while there is a structural phase transition between the square ScCrP2 and the rectangular ScCrP2, which originates from the mechanism of ferroelasticity and ferroelectricity. Both monolayers ScCrP2 exhibit in-plane auxetic properties, and the value of the negative Poisson’s ratio can reach –0.322. All the three monolayers show a ferromagnetic ground state with high Curie temperature, and are a Dirac half-metal without spin–orbit coupling (SOC). When considering SOC, a nontrivial bandgap can be found in the monolayer ScMnP2, which further becomes a half-Chern insulator. Importantly, the structural phase transitions from the square lattice to the rectangular lattice in the monolayers ScCrP2 will enable a significant improvement in the values of negative Poisson’s ratio and magnetic anisotropic energy simultaneously. Taking the multiferroic (ferroelastic, ferroelectric, and ferromagnetic), auxetic, and topological properties into consideration, the 2D system of ScMP2 provide promising applications for future multifunctional nanodevices.

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.

Electronic and optical properties of new Pentagonal Janus PtXY (X, Y=S, Se, Te; X [formula omitted] Y) monolayers: A DFT study

In this work, we investigate a new phase of two-dimensional Janus PtXY (X, Y = S, Se, Te; X ≠ Y) monolayers named pentagonal (Penta-PtXY) using the first-principles calculations. We found that Penta-PtXY monolayers are semiconductors with an indirect band gap of 1.69 eV, 1.52 eV, and 1.43 eV for Penta-PtSSe, Penta-PtSTe, and Penta-PtSeTe, respectively, that is reduced with the inclusion of spin–orbit coupling. These structures are dynamically stable as their phonon dispersions showed no soft phonon frequencies. The investigation of the optical properties revealed that monolayers Penta-PtXY have in-plane anisotropic optical properties with higher absorption spectra along the y-direction. Moreover, the maximum absorption occurs in the ultraviolet (UV) region, therefore, they can harvest UV and visible photons more effectively. This combination of properties makes these materials attractive for fundamental studies of anisotropic phenomena in 2D materials and may enable novel optoelectronic and nanotechnology applications.

Enhanced in-plane thermoelectric properties achieved through the vertical van der Waals stacking of black phosphorus and Ti2C

Vertical van der Waals heterostructures (vdWHs) exhibit considerable freedom in integrating two-dimensional layered materials for achieving excellent performance. In this study, we construct a double-layer Ti2C/BP vdWH by stacking pristine monolayer black phosphorus (BP) and Ti2C vertically. The in-plane thermoelectric properties of BP, Ti2C and Ti2C/BP vdWHs at different temperatures are investigated using density functional theory combined with the non-equilibrium Green's function method. Results showed that the thermoelectric figure of merit (ZT) of Ti2C/BP vdWHs at room temperature (300 K) was approximately 103 and 104 times that of Ti2C and BP, respectively. Because of the mutual compensation of the electronic energy bands and interfacial phonon scattering, Ti2C/BP vdWHs have higher electron conductance and lower phonon conductance than both BP and Ti2C, which significantly enhances the ZT value of these structures. More importantly, the prominent thermoelectric properties of Ti2C/BP vdWHs maintain greater stability as the temperature rises (300–900 K), which leads to a high thermoelectric power factor and ZT value without relying on high temperatures. These results provide a new idea for designing two-dimensional functionalised nanoscale devices with excellent thermoelectric performance.

Self-gated cine phase-contrast balanced SSFP flow quantification at 0.55 T.

To implement cine phase-contrast balanced SSFP (PC-bSSFP) for low-field 0.55T cardiac MRI by exploiting the intrinsic flow sensitivity of the bSSFP slice-select gradient and the in-plane phase-cancelation properties of radial trajectories, enabling self-gated and referenceless PC-bSSFP flow quantification at 0.55 T. A free-running, tiny golden-angle radial PC-bSSFP approach was implemented on 0.55T and 1.5T systems. Cardiac and respiratory self-gating was incorporated to enable electrocardiogram-free scanning during breath-hold and free-breathing. By exploiting the intrinsic in-plane phase-cancelation properties of radial acquisitions and background phase fitting, referenceless single-point PC-bSSFP was realized. In vivo data were acquired in the ascending aorta of healthy subjects at 0.55 T and 1.5 T during breath-hold and free-breathing. Flow data, SNR, and velocity-to-noise ratio were compared relative to data obtained with phase-contrast spoiled gradient-echo variants. Velocities acquired with PC-bSSFP compared well with data from phase-contrast spoiled gradient-echo (RMSEv = 5.8 cm/s). PC-bSSFP at 0.55 T resulted in high-quality cine magnitude images and phase maps with sufficient SNR and velocity-to-noise ratio. Breath-hold and free-breathing PC-bSSFP performed very similarly, with comparable flow quantification (RMSEv = 5.7 cm/s). Referenceless single-point PC-bSSFP results agreed well with two-point PC-bSSFP (-1.8 ± 5.2 cm/s) while reducing scan times 2-fold. PC-bSSFP is feasible on low-field 0.55T systems, producing high-quality cine images while permitting simultaneous aortic flow measurements during breath-hold and free-breathing and without the need for electrocardiogram gating.

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.

Impact of Aluminum Modification on the Dielectric Properties of Graphene Oxide Membrane: Different Al Source

The high dielectric constant and low dielectric loss of Graphene oxide (GO) membranes made them good dielectric separator membranes for both dielectric capacitors and planar micro-supercapacitors. A GO membrane, which is GO sheets laminated in the form of “brick-and-mortar” stacking configuration, is an orthotropic material. This means that GO will have different dielectric properties parallel to the GO sheets (in-plane) and perpendicular to the GO sheets (through-plane). Tailoring strategies applied to the membrane will impact its in-plane and through-plane dielectric property differently. Better understanding and ability to tailor the dielectric properties of the GO membrane is crucial for its dielectric applications. The Al3+ has the potential to interact with OFGs of GO sheets on the edge (carboxyl groups), which mainly impacts in-plane properties, or on the basal plane (hydroxyl, carbonyl, and carboxyl groups), which mainly impacts through-plane properties. The uneven interaction of Al3+ with the functional group on the edge and basal plane of GO sheets could lead to different modification effects of the in-plane and through-plane dielectric properties of the GO membrane. It was reported before that Al3+ from different sources will bond with the GO sheet differently, thus it has the potential to impact the through-plane and in-plane dielectric properties of the GO membrane differently. Here, the Al3+-modification to the GO membrane from three different Al source, Al metal foil, chloride salt, and alumina, were applied to tailor the through-plane and in-plane dielectric properties of as-fabricated GO membranes in the frequency range from 0.01 Hz to 105 Hz. Plane-to-plane and edge-to-edge coordination of Al3+ with the functional group on the basal plane or edge of the GO sheets were proposed to understand the different impact of Al3+ on the through-plane and in-plane dielectric properties of the GO membranes. This study provides a facile route to impact the dielectric property of GO membrane through interaction with the oxygenated functional group on the edge and basal plane of the GO sheet, and demonstrate the possibility of designing dielectric GO membrane with controllable dielectric performance.

Magnetic Properties of Amorphous Ta/CoFeB/MgO/Ta Thin Films on Deformable Substrates with Magnetic Field Angle and Tensile Strain.

Recently, the application of cobalt iron boron (CoFeB) thin films in magnetic sensors has been widely studied owing to their high magnetic moment, anisotropy, and stability. However, most of these studies were conducted on rigid silicon substrates. For diverse applications of magnetic and angle sensors, it is important to explore the properties of ferromagnetic thin films grown on nonrigid deformable substrates. In this study, representative deformable substrates (polyimide (PI), polyethylene naphthalate (PEN), and polydimethylsiloxane (PDMS)), which can be bent or stretched, were used to assess the in-plane magnetic field angle-dependent properties of amorphous Ta/CoFeB/MgO/Ta thin films grown on deformable substrates. The effects of substrate roughness, tensile stress, deformable substrate characteristics, and sputtering on magnetic properties, such as the coercive field (Hc), remanence over saturation magnetization (Mr/Ms), and biaxial characteristics, were investigated. This study presents an unconventional foundation for exploring deformable magnetic sensors capable of detecting magnetic field angles.

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.

Effect of carbon/tantalum hybrid film on the properties of carbon fiber and its composites based on magnetron sputtering

To simultaneously improve the strength and toughness of carbon fiber-reinforced polymer composites (CFRPs) using the hybrid effect, a multi-size film with carbon/tantalum (C/Ta) hybrid structure was constructed on the surface of carbon fibers (CFs) by magnetron sputtering using carbon and tantalum as the target materials. Carbon fiber epoxy composites (CFEPs) were prepared by injection molding. The effects of the C/Ta hybrid interface layer on the interfacial bonding and mechanical properties of the CFEPs were analyzed by testing their in-plane shear and bending properties. The results show that the C/Ta hybrid interface layer structure can effectively improve the interfacial bonding and mechanical properties of the CFEP. The in-plane shear and flexural strengths of CFEP modified by double C/Ta magnetron sputtering were 63.53% and 33.15% higher than those of unmodified CFEP, respectively, the in-plane shear modulus increased by 1.53 times, and the bending modulus by 63.26%.

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.

Nanofiber Interleaved Composites for Aerospace Applications

This paper extended the authors previous work of demonstrating the concept of polymer nanofiber interleaving to enhance the toughness of fiber reinforced carbon/epoxy composite laminates. In this study, in-plane tension, compression, interlaminar shear, and Mode I fracture and fatigue onset life properties were studied. Results demonstrated that by adding 1% weight of nanofibers in the form of interlayer in-plane tension and compression properties (strength, modulus, and Poisson’s ratio) of interleaved composites remained the same as base composites. Whereas polymer nanofiber interleaving increased interlaminar shear strength by 4%, fracture toughness by 150% and fatigue threshold energy release rate by 67%

Large-area WS2 Deposited on Sapphire and Its In-Plane Raman and PL Spectral Distributions

Large-area and high-quality WS2 monolayer has been fabricated on the Al2O3 substrate. Three typical WS2 configurations were adopted to examine the in-plane spectral properties. For the triangle WS2 monolayer, the PL light region exhibits a large peak wavelength and could be deduced to be the relaxation of the compressed strain of the WS2 monolayer and the low defect density. For triangle WS2 monolayer with multilayer WS2 on center, combining the peak intensity and position results of PL and Raman spectra, the line traces near the side of the center triangle can be demonstrated to be the defects or dislocations due to the exist of the central multilayer WS2. For large-area WS2 monolayer with crystal domain, PL area integrated mapping shows a uniform light region across the whole surface, except the existing dark crystal domain boundary. The dark line traces could be attributed to compressed strain in the WS2 monolayer due to the formation of the WS2/Al2O3 hybrid structure. The in-plane PL and Raman spectra and mapping exhibited in this work reveal the distribution of stress and defects in this system and further clarify the effects of stress and defects on the optoelectronic properties of WS2 monolayer on Al2O3.