Isotropic Behavior Research Articles

Thermotropic reentrant isotropy and induced smectic antiferroelectricity in the ferroelectric nematic realm: comparing RM734 and DIO.

The current intense study of ferroelectric nematic liquid crystals was initiated by the observation of the same ferroelectric nematic phase in two independently discovered organic, rod-shaped, mesogenic compounds, RM734 and DIO. We recently reported that the compound RM734 also exhibits a monotropic, low-temperature, apolar phase having reentrant isotropic symmetry (the IR phase), the formation of which is facilitated to a remarkable degree by doping with small (below 1%) amounts of the ionic liquid BMIM-PF6. Here we report similar phenomenology in DIO, showing that this reentrant isotropic behavior is not only a property of RM734 but is rather a more general, material-independent feature of ferroelectric nematic mesogens. We find that the reentrant isotropic phases observed in RM734 and DIO are similar but not identical, adding two new phases to the ferroelectric nematic realm. These phases exhibit similar, strongly peaked, diffuse X-ray scattering in the WAXS range (1 < q < 2 Å-1) indicative of a distinctive mode of short-ranged, side-by-side molecular packing. The scattering at small q is, however, quite different in the two materials, with RM734 exhibiting a strong, single, diffuse peak at q ∼ 0.08 Å-1 indicating mesoscale modulation with ∼80 Å periodicity, and DIO a sharper diffuse peak at q ∼ 0.27 Å-1 ∼ (2π/molecular length), with second and third harmonics, indicating that in the reentrant isotropic phase of DIO (which we denote IRlam), short-ranged molecular positional correlation is smectic layer-like. Both reentrant isotropic phases are metastable, eventually generating birefringent crystals.

Dark matter influences on wormhole stability in de Rham–Gabadadze–Tolley like massive gravity

The characteristics of wormhole models in the context of the de Rham–Gabadadze–Tolley-like massive gravity theory are examined in this article. Dark matter density profiles of Thomas Fermi and Einasto spike are used to find the wormhole shape functions. By exploiting these formed shape functions, we create a wormhole geometry that connects asymptotically flat regions of spacetime while fulfilling all necessary requirements. Through a comprehensive analytical and graphical investigation, we explore the characteristics of exotic matter in these wormhole structures and examine their material composition within the context of energy conditions. The volume integral quantifier is used to quantify the exotic matter. We also discuss the phenomena of the complexity factor for all wormhole models and conclude that it approaches zero for increasing values of the radial coordinate, indicating the homogeneity of the energy density and the isotropic behavior of the pressure. Moreover, the repulsive nature of these wormhole solutions, a critical characteristic for their possible traversability is revealed by our analysis of the anisotropy parameter.

Bioinspired Design of Isotropic Lattices with Tunable and Controllable Anisotropy

This study presents novel nested isotropic lattices, drawing inspiration from bio‐architectures found in cortical bone osteons, golden spirals, and fractals. These lattices provide tunable anisotropy by integrating architectural elements like “nesting orders (NOs)” and corresponding “nesting orientations (NORs),” along with repetitive self‐similar X‐cross struts and three fourfold axes of symmetry, resulting in a wide spectrum of novel lattice designs. Nine mon‐onest and 20 multinest lattices, along with 252 parametric variations, are realized. Employing finite element‐based numerical homogenization, elastic stiffness tensors are estimated to evaluate the anisotropic measure—Zener ratio and elastic modulus. The mono‐nest lattices generated considering higher NOs and respective NORs exhibit a transition from shear dominant to tensile‐compression dominant (TCD) anisotropic behavior and their strut size variations show a strong influence on performances. In contrast, multinest lattices exhibit isotropic and neo‐isotropic characteristics, with strut size mismatch exerting more influence on the Zener ratio. Increasing NOs and NORs result in isotropic or TCD behavior for most multinest lattices, with strut size mismatch leading to many isotropic lattices. These bioinspired nested lattices, coupled with advancements in additive manufacturing, hold potential for diverse applications.

Anisotropic in-plane field angle dependence of critical current in commercial REBCO tapes and its impact on toroidal field magnet for compact tokamak fusion device

Abstract The critical current (I c) of commercial rare-earth barium copper oxide (REBCO) tapes is generally assumed to exhibit isotropic behavior with respect to the magnetic field angle applied within the tape’s basal plane (in-plane). This paper investigates the field angle dependence of critical current, both in-plane and out-of-plane, for commercial REBCO tapes manufactured by SuperOX, under fields ranging from 0 T to 8 T at 20 K. Remarkably, the in-plane field angle dependence of I c shows significant anisotropy, with the minimum I c no longer occurring at the traditional 90° (parallel to the ab-plane), but instead shifting to approximately 130°, a phenomenon reported for the first time. This novel anisotropic in-plane field angle dependence of I c can substantially affect the performance of toroidal field magnets for compact tokamak fusion devices. Simulations indicate that considering versus neglecting the anisotropic in-plane field angle dependence of I c can lead to I c variations of up to 19.58% within the D-shaped coils of the toroidal field magnets. The locations of maximum deviation vary across different double-pancake coils within the D-shaped winding packs. This study highlights the complexity of I c distribution in toroidal field magnets for compact fusion applications, urging further consideration of anisotropic in-plane field angle dependence of I c of commercial REBCO tapes in fusion magnet design.

A strain rate-dependent distortional hardening model for nonlinear strain paths

In this paper, a strain rate-dependent distortional hardening model is firstly proposed to describe strain rate-dependent material behaviors under linear and nonlinear strain paths changes in 0≤θpathchange≤180∘. The proposed model is formulated based on the simplified strain rate-independent distortional hardening model (Choi and Yoon, 2023). Any yield function could be used for the strain rate-dependent isotropic and anisotropic yielding. For the linear strain path, the strain rate-dependent isotropic hardening behavior could be explained by two state variables representing rate-dependent yielding and convergence rate of flow stress under monotonically increasing loading condition, respectively. For the nonlinear strain paths, the strain rate-dependent material behaviors such as Bauschinger effect, yield surface contraction, permanent softening, and nonlinear transient behavior could be described by modifying the evolution equations of the simplified strain rate-independent distortional hardening model with a logarithmic term of strain rate. For the verification purpose, it was used the strain-rate dependent tension-compression experiments of TRIP980 and TWIP980 (Joo et al., 2019). In addition, a high speed U-draw bending test was conducted with original and pre-strained specimens. The springback prediction in high speed U-draw bending test was performed by using strain rate-independent isotropic, strain rate-dependent isotropic-kinematic and distortional hardening models. It is identified that the proposed model showed the most accurate prediction for the pre-strained specimen where the possible bilinear and trilinear path change in 0≤θpathchange≤180∘ is observed while it showed the same accuracy for the original specimen where main strain path change occur in forward-reverse manner (θpathchange=180∘).

Magnetic properties and I‐V characteristics of DC magnetron sputtered [Co (0.2 nm)/Ni (0.4 nm)]10 thin films

AbstractA set of [Co(0.2 nm)/Ni(0.4 nm)]10 multilayers (MLs) thin films were fabricated on silicon and glass substrate under various distinct conditions (i) as‐prepared films without an under‐layer, (ii) films with a copper [Cu(2 nm)] underlayer (UL), (iii) films with an in situ annealed Ta/Cu UL during sputtering, and (iv) films with post‐annealing treatment, by using a DC magnetron sputtering machine. The [Co/Ni] MLs thin films prepared under various conditions exhibit in‐plane magnetic anisotropic behavior except as‐prepared films which show isotropic behavior. The maximum saturation magnetization was observed in the as‐prepared films prepared on both silicon and glass substrate. The Ta/Cu UL in situ annealing followed by post‐annealing films exhibit highest coercivity, moderate saturation magnetization but lowest squareness in contrast to the films deposited under other conditions. The I‐V curves of the films show diode like behavior with breakdown voltage of 42, 58, 14, and 21 V for [Co/Ni] MLs under four different conditions.

Arctic temperature effects on the mechanical properties and failure modes of photopolymer resin for sandwich composite core' materials

The increased marine activity in the Arctic Circle presents significant challenges for naval structures operating in extreme conditions, such as temperatures as low as -60°C (Arctic temperature, AT). This study uniquely investigates the potential of Formlabs' “Durable resin” as a core material for sandwich composites. It focuses explicitly on its mechanical response under these extreme Arctic conditions, a largely unexplored area in current materials research. Durable resin's quasi-static tensile, flexural, and compressive behaviors were tested at both room temperature (RT) and AT. Finite element models were developed to explain observed failure mechanisms. At AT, the resin showed isotropic behavior with notable improvements, including a 318% increase in tensile modulus, 322% rise in ultimate tensile strength, 450% increase in flexural modulus, and 460% improvement in compressive modulus, though strain at failure decreased. Failure modes varied by temperature: tensile and flexural fractures consistently occurred at the midsection, while compressive samples at AT failed via axial splitting, compared to barreling at RT. This study's findings contribute to the foundational understanding needed to develop materials that endure extreme Arctic environments, underscoring the promise of Durable resin for Arctic exploration despite its reduced ductility under AT conditions.

Extrusion‐Based Additive Manufacturing of Cranial Implants Using High‐Performance Polymers: A Comparative Study on Mechanical Performance and Dimensional Accuracy

Fused filament fabrication (FFF) offers great potential to fabricate patient‐specific implants to treat large size defects resulting from craniectomy. Such cranial implants impose critical requirements on material and design. So far, the field has focused on printing cranial implants from polyetheretherketone (PEEK), which is semicrystalline in nature and, therefore, not ideal for FFF because of warping and nonhomogeneous crystallization. Consequently, this work aims at exploring alternative amorphous high‐performance polymers. The tensile and flexural mechanical properties of printed samples from PEEK, polyetherketoneketone (PEKK), and polyphenylsulfone (PPSU) according to ISO standards are compared. Testing of specimens obtained from three orthogonal build directions reveals nearly isotropic mechanical behavior (e.g. ultimate tensile strength differed no more than 8% between print orientations). This enables printing of patient‐specific cranial implants in vertical orientation with minimal support structures, which result in dimensional accuracies in the clinically acceptable range for craniofacial reconstructions. Mechanical assessment via an in‐house designed indentation set‐up shows that both PEKK and PPSU should be considered valid alternatives to PEEK for cranial implants. This work showcases the maturity of FFF for high‐performance polymers and leverages it for complex patient‐specific geometries such as a cranial implant.

Lattice Structures-Mechanical Description with Respect to Additive Manufacturing.

Lattice structures, characterized by their repetitive, interlocking patterns, provide an efficient balance of strength, flexibility, and reduced weight, making them essential in fields such as aerospace and automotive engineering. These structures use minimal material while effectively distributing stress, providing high resilience, energy absorption, and impact resistance. Composed of unit cells, lattice structures are highly customizable, from simple 2D honeycomb designs to complex 3D TPMS forms, and they adapt well to additive manufacturing, which minimizes material waste and production costs. In compression tests, lattice structures maintain stiffness even when filled with powder, suggesting minimal effect from the filler material. This paper shows the principles of creating finite element simulations with 3D-printed specimens and with usage of the lattice structure. The comparing of simulation and real testing is also shown in this research. The efficiency in material and energy use underscores the ecological and economic benefits of lattice-based designs, positioning them as a sustainable choice across multiple industries. This research analyzes three selected structures-solid material, pure latices structure, and boxed lattice structure with internal powder. The experimental findings reveal that the simulation error is less than 8% compared to the real measurement. This error is caused by the simplified material model, which is considering the isotropic behavior of the used material PA12GB (not the anisotropic model). The used and analyzed production method was multi jet fusion.

Transversely isotropic elastoplastic behaviour in a mechanically loaded rotating disk

This article deals with the study of transversely isotropic elastoplastic behaviour in a mechanical loaded rotating disk by using transition theory and generalised strain measure. Magnesium material disk requires higher value of angular speed to yield at the inner surface as compared to the disk made of beryl material. With the effect of mechanical loading, angular speed also increases at the inner surface of the disk made of magnesium/beryl. Upon the introduction of mechanical loading, the rotating disk made of beryl material requires maximum radial stress at the inner surface as compared to disk made of magnesium material. The beryl material disk is more convenient than that of magnesium material.

Structural Optimization of a Large-Scale 3D-Printed High-Altitude Propeller Blade with Experimental Validation

This paper presents a structural optimization of a 3D-printed thermoplastic-core propeller blade for high-altitude unmanned aerial vehicles using a genetic algorithm. It aims to minimize the weight of the blade by creating longitudinal holes and spars and to minimize the blade tip deflection during operation at an altitude of 16 km. The objective is to check the validity of a 3D-printed material modeling approach for large-scale and more complex 3D-printed parts, such as hollow twisted blades. The approach is based on attentively selecting the printing parameters that reduce the anisotropy of the 3D-printed parts. The linear isotropic behavior of 3D-printed Polylactic Acid and Acrylonitrile Butadiene Styrene M30 tensile samples, which have been tested at ambient and low temperatures (−60°C), is utilized to numerically predict the experimental deformation and natural frequencies of 3D-printed substitute and twisted full blades with good accuracy. The validated linear isotropic model of each material is then used to evaluate the objectives and the constraints of the two-objective optimization process using one-way fluid–structure interaction. Four optimized blades have been selected from the Pareto fronts as candidates, printed, and tested in bending and vibration. The numerical and experimental results of the candidate blades in terms of deformation and natural frequencies are in good agreement, proving the validity of the present macroscale approach for large-scale hollow twisted blades.

Variation of Gilbert damping constant via interface induced magnetic anisotropy in LSMO/PMN-PT heterostructures

The field of spintronics is emerging at blistering pace due to its promising room-temperature applications in low-power logic-based devices. In this work, we investigate the suitability of ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO) thin film/ferroelectric (FE) Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) heterostructures for spintronic device applications through characterizing the static and dynamic magnetic properties. Due to the magnetoelastic coupling at the interface, LSMO/PMN-PT(001) is found to exhibit a 4-fold symmetry of magnetic anisotropy, while LSMO/PMN-PT(111) shows isotropic behavior at room temperature. The direction dependent Gilbert damping constant (α) estimated for the LSMO/PMN-PT(001) sample clearly shows that its values are smaller along the magnetically hard axis than along the easy axis, while no significant variation is observed for the LSMO/PMN-PT(111) sample. The electric field induced variation of α also demonstrate that the Gilbert damping is closely related to the magnetic anisotropy. The present results clearly indicate that it will be possible to realize electric field controlled spin dynamics in FM/FEs to develop futuristic spintronic devices.

Enhancing wear resistance of aluminum 6061 composites with fly ash: A sustainable approach for industrial applications

This study investigated the benefits of adding fly ash as a reinforcement material. The benefits included cost-effectiveness, improved quality, isotropic behavior, and environmental advantages. To improve self-lubrication and wettability behavior, Al6061 alloy composites were fabricated with different amounts of fly ash (0%, 2%, 4%, 6%, and 8% by weight), along with a fixed amount of graphite (3wt.%) and magnesium (2wt.%). Wear tests were conducted using Taguchi’s Design of Experiment (DoE) approach on the composites. The optimized composition with 6% fly ash exhibited the least wear rate under the test conditions of load = 10 N, sliding velocity = 3 m/s, and sliding distance = 2 km. SEM images revealed a uniform distribution of fly ash and graphite reinforcement in the matrix, contributing to enhanced wear resistance. The composites exhibited fewer scratches and plastically deformed surfaces, indicating a decrease in wear rate and increased wear resistance with higher fly ash content. ANOVA were used, and four parameters were identified to be critical, Composition at 34%, Sliding Distance at 27%, load at 23%, and Sliding Velocity at 12% contribution with a statistical confidence of 95%. This research contributes to developing cost-effective and environmentally sustainable materials with improved mechanical properties. It makes them suitable for various industrial applications, such as the automotive industry, where wear resistance is essential.

Research of Acoustic Emission Characteristics and Applicability of Artificial Intelligence for Source Localization

Within this research, the deployment of artificial intelligence for the localization of acoustic emissions (AE) is being investigated. In detail, series of experiments were conducted on a plate of granite with homogeneous and isotropic material behavior. Acoustic emissions could be generated by the breaking of pencil leads, as well as the impact of rice grains and steel balls on 81 specific positions with a distance of 50 mm in both horizontal axes to each other. The response of the system was recorded using 16 acoustic emission sensors, of which 8 sensors were positioned on each surface side of the plate. In further steps the data could be processed, so that the resulting characteristic signal features could be translated into spec-trograms and furthermore being used as input for the artificial intelligence. Additionally, the corresponding source locations appeared as labels. Both, the signal features as well as the labels, could be implemented in the process of supervised learning using a convolutional neural network (CNN). The results of this network indicated a validation accuracy of over 99% as well as a low loss value by classifying the inserted features to the right labels. Thus demonstrates the excellent applicability of artificial intelligence for the source localization of acoustic emission (AE).

Isotropic compression behavior of salinized unsaturated agricultural soil: An experimental and constitutive investigation

Salinity-induced soil degradation is a significant challenge in coastal reclamation areas, impacting agricultural productivity and infrastructure development. Variations in soil compression and deformation caused by changes in salinity warrant further investigation, particularly for agricultural applications. This study explores the relationship between soil pore water salinity and compressibility by conducting isotropic compression tests on salinized unsaturated agricultural soils treated with distilled water, 0.5 mol/L and 1 mol/L sodium chloride (NaCl) and calcium chloride (CaCl2) solutions. The results demonstrate that the type and concentration of salts significantly affect the compression behavior of these soils. The constitutive parameters were calibrated based on the experimental data. To account for osmotic suction, Barcelona Basic Model (BBM) was adjusted. The findings indicate that as pore water salinity increases, soil compressibility decreases, reflected by a compression index (Cc), and higher pre-consolidation stress (py). This modification aimed to quantify the impact of pore water salinity on soil compression. To validate the constitutive model, a numerical analysis of an isotropic compression test was carried out. This study contributes to our understanding of the isotropic compression behavior of coastal saline soil, proposes a constitutive framework for predicting soil responses under different salt conditions, and provides theoretical support for engineering construction in coastal reclamation areas.

Combined analytical and numerical modelling of the electrical conductivity of 3D printed carbon nanotube-cementitious nanocomposites

This study explores the electrical properties of 3D-printed carbon nanotube (CNT)-cementitious nanocomposites using a dual modelling approach that integrates micromechanics with finite element (FE) analysis for self-sensing applications. 3D-printed cementitious structures are prone to early crack formation, and incorporating CNTs enhances the material’s electrical conductivity, enabling a built-in health monitoring system. Given the critical impact of CNT dispersion, waviness, and orientation on the electrical conductivity, a theoretical model was developed to incorporate these factors. Experimental tests were conducted to evaluate the material’s conductivity and mechanical performance, and to validate the model. The results show that CNTs align with the printing direction at a 3D-printed layer’s surface, while maintaining isotropic behaviour at the core. Additionally, although the CNTs aggregate, they do not entangle with each other, instead creating conductive networks within the bundles. Moreover, the CNTs are not straight but wavy, which affects the material’s electrical conductivity. Based on the experimental results and the analytical model, a finite element model was developed to predict the conductivity of printed layers, accounting for varying CNT orientations throughout the layer. The results indicate that the model overestimates 3D-printed materials’ conductivity, suggesting that further studies are needed to account for interlayer effects on the measurements.

Stress-strain curve estimation from micropillar compression with transverse contraction effect

The Focused Ion Beam (FIB) technique and the associated compression testing capabilities provide versatile access to understanding the microstructural behaviour of materials. Among many objectives, determining the stress-strain relationship from experimental or numerical force-displacement data remains a fundamental challenge. However, for micropillers under compression, the inside deformation constraint is complex like in components and the transformation of a measured force-displacement curve into an accurate uniaxial stress-strain curve is not straightforward. In this context, in a previous numerical based analysis for perfect volume constancy or incompressibility the determination of reliable and accurate stress-strain curves from nonlinear load-deformation curves of micropillers was already verified. In the case of transverse contractions, however, numerical simulations of micropillers provide unexpected force-displacement behaviour, i.e. their force-displacement curves are almost superimposing and are very close to the force-displacements for incompressibility. This effect implies, that transverse contraction would have no contributions in micropillar compression. In contrast, independent simulations using a single finite element accurately explore the true uniaxial stress-strain behaviour for the whole range of transverse contractions. These are considered as the reference behaviour and are also treated by an analytical expression. With the presented new stress-strain estimation approach, including transverse contraction, any force-displacement curve from a micropillar under compression can be stepwise corrected. The first step of the new stress-strain curve estimation method, including transverse contraction, is carried out in the same way as in the preceding analysis for incompressibility, followed by further steps to obtain the final true stress-strain curve. Although the presented numerical analysis is exemplarily performed for the behaviour of fused silica, but the stress-strain approach is in the same manner generally applicable for a material behaviour with other stress-strain curves. The assumption behind is isotropic and nonlinear material behaviour.

Investigation on the effects of deposition strategy on the mechanical characteristics and microstructure of austenitic stainless steel 308LSi manufactured via wire arc additive manufacturing

This study examines the impact of deposition strategy on ASS 308LSi thin-walled structure manufactured via the Wire Arc Additive Manufacturing (WAAM) technique on the microstructural characteristics, tensile strength, microhardness, Charpy impact testing, and fracture morphology of the WAAM 308LSi. The analysis of the microstructure reveals that the deposition strategy promotes transitioning from columnar to equiaxed fine grain structure. The tensile strength results show that specimens with a 45° deposition strategy exhibit lower anisotropy and higher tensile properties compared to those with a 0° deposition strategy, with improvements of 33.1% in the transverse direction and 26.7% in the longitudinal deposition directions, respectively. The microhardness in WAAM SS308LSi demonstrates variations in the bottom, middle, and top regions, with the highest average value observed at a 45° deposition strategy (213.3 ± 6.5 HV, 201.1 ± 10.7 HV, and 191.5 ± 5.2 HV) as well. The impact testing results indicate that the highest absorbed energy occurs at a 45° deposition strategy, with 75 ± 4.2 J and 74 ± 4.0 J for the transverse and longitudinal directions, respectively. The fractures observed during testing exhibit ductile characteristics, with the presence of dimples and particles. This study demonstrates the significant potential of the 45° deposition strategy with the implementation of double-sided substrate deposition, resulting in a refined microstructure, nearly isotropic behavior, and excellent mechanical performance.

Alternating current electrophoretic deposition of maleic anhydride modified chitosan on Ti implants to combat biofilm formation

Chitosan, a cationic biopolymer, holds promise for diverse applications, including dental implant surface modification, due to its biocompatibility, non-toxicity, and antimicrobial properties. However, its limited water solubility at neutral pH complicates its use in alternating current electrophoretic deposition (AC-EPD). This study explores the novel use of water-soluble maleic anhydride modified chitosan (MA-CS) in AC-EPD to create antimicrobial coatings on titanium substrates. We optimize AC-EPD parameters for uniform MA-CS coatings and compare AC-EPD with conventional dipping. AC-EPD MA-CS coatings exhibit enhanced surface topography and amphiphilic, isotropic behavior, while other MA-CS-treated samples display anisotropic, monopolar behavior. We assess AC-EPD MA-CS-coated metallic substrates' biofunctionality, focusing on protein adsorption and antimicrobial properties. These coatings effectively adsorb proteins through diverse interactions with bovine serum albumin. To combat peri-implant diseases, we evaluate antimicrobial activity against oral bacterial communities, showing that AC-EPD successfully concentrates water-soluble MA-CS on titanium without compromising its biological performance. In summary, this study highlights AC-EPD as a versatile, efficient method for depositing polysaccharides in biomedical applications. It offers the potential for enhancing dental implant surface antimicrobial properties, addressing peri-implant diseases, and promoting overall dental health.

Data-driven methods for computational mechanics: A fair comparison between neural networks based and model-free approaches

We present a comparison between two approaches to modelling hyperelastic material behaviour using data. The first approach is a novel approach based on Data-driven Computational Mechanics (DDCM) that completely bypasses the definition of a material model by using only data from simulations or real-life experiments to perform computations. The second is a neural network (NN) based approach, where a neural network is used as a constitutive model. It is trained on data to learn the underlying material behaviour and is implemented in the same way as conventional models. The DDCM approach has been extended to include strategies for recovering isotropic behaviour and local smoothing of data. These have proven to be critical in certain cases and increase accuracy in most cases. The NN approach contains certain elements to enforce principles such as material symmetry, thermodynamic consistency, and convexity. In order to provide a fair comparison between the approaches, they use the same data and solve the same numerical problems with a selection of problems highlighting the advantages and disadvantages of each approach. Both the DDCM and the NNs have shown acceptable performance. The DDCM performed better when applied to cases similar to those from which the data is gathered from, albeit at the expense of generality, whereas NN models were more advantageous when applied to wider range of applications.