Microstructural Configurations Research Articles

Conductive Polymer-Based Hydrogels for Wearable Electrochemical Biosensors.

Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain desired properties through various tuning strategies extending from molecular design to microstructural configuration. However, significant challenges remain, such as the limited strain-sensing range, significant hysteresis of sensing signals, dehydration-induced functional failure, and surface/interfacial malfunction during manufacturing/processing. This review summarizes the recent developments in polymer-hydrogel-based wearable electrochemical biosensors over the past five years. Initially serving as carriers for biomolecules, polymer-hydrogel-based sensors have advanced to encompass a wider range of applications, including the development of non-enzymatic sensors facilitated by the integration of nanomaterials such as metals, metal oxides, and carbon-based materials. Beyond the numerous existing reports that primarily focus on biomolecule detection, we extend the scope to include the fabrication of nanocomposite conductive polymer hydrogels and explore their varied conductivity mechanisms in electrochemical sensing applications. This comprehensive evaluation is instrumental in determining the readiness of these polymer hydrogels for point-of-care translation and state-of-the-art applications in wearable electrochemical sensing technology.

Misorientation and dislocation evolution in rapid residual stress relaxation by electropulsing

This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process. An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration. AISI 1020 steel was chosen as it has a simple microstructure (plain ferritic) and composition with low alloying conditions. It is an appropriate material to study the effect of transmitting electric pulses on the microstructural defect evolution. A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electro pulsing effects critically. By application of electropulsing, a reduction in the surface residual stress layer was noticed. Also, reductions in misorientation and dislocation density together with the disentanglement of dislocations within the cold-worked layer were observed after electropulsing. Additionally, the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed. These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.

Enhanced corrosion fatigue strength of additively manufactured graded porous scaffold-coated Ti-6Al-7Nb alloy

Enhanced corrosion fatigue strength of additively manufactured graded porous scaffold-coated Ti-6Al-7Nb alloy

Extended multiscale FEM-based concurrent optimization of three-dimensional graded lattice structures with multiple microstructure configurations

In this work, a novel concurrent design method for three-dimensional graded lattice structures considering multiple microstructure configurations is proposed. Firstly, the Multiple Variable Cutting (M-VCUT) level set method is employed to represent the geometry of lattice microstructures and define the optimization parameters. Then, the extended multiscale finite element method (EMsFEM) is implemented for calculating the equivalent stiffness matrices of microstructures in offline form. Compared with the traditional homogenization-based multiscale approaches, the proposed method eliminates the scale separation assumptions and takes into account the coupling effects in different directions of materials. In addition, a data-driven method and a parallel computing approach are integrated together so that computational efficiency can be greatly improved. After the iteration process, the optimized full-scale graded structures are reconstructed using interpolation technology to generate well-connected microstructures in neighboring cells. Finally, several 3D numerical examples are utilized to validate the effectiveness of the proposed method, where multiple lattice microstructure configurations are considered, including truss-lattices and plate-lattices.

Enhancing strength–ductility synergy of AlNp/Al composite by regulating heterostructure of matrix grain and particle distribution

Three heterostructured AlNp/Al composites with different microstructure configurations were fabricated by liquid–solid reaction combined with subsequent thermal-mechanical treatment to obtain a superior strength and ductility combination. The effects of the microstructure configuration including the AlN particle distribution and matrix grain structure on the tensile strength and ductility were studied in detail. The results show that the simultaneous enhancement of tensile strength and ductility can be achieved. The Uniformed-AlNp/Al composite with relatively dispersed particles exhibits a superior ultimate tensile strength of ~387 MPa with an elongation to failure of ~9.1%. It shows an outstanding specific tensile strength and elongation combination compared with other reported particle reinforced aluminum matrix composites. Furthermore, the hetero-deformation induced (HDI) stress has been calculated and is shown to increase significantly in the Uniformed-AlNp/Al composite. It is revealed that the HDI stress plays a crucial role in the significant enhancement of strength and ductility for the AlNp/Al composite.

Connectivity patterns in lead-free piezocomposites: A critical analysis for 0-3 and 1-3 configurations

In the quest for eco-friendly alternatives within materials science, the development of sustainable and non-toxic piezoelectric composites is of utmost importance. This study undertakes a computational exploration to elucidate the influence of phase connectivity on the engineering performance of lead-free piezocomposites. Employing a combination of analytical and numerical methodologies, we critically evaluated various figures of merit across different microstructural configurations, juxtaposing these findings with traditional lead zirconate titanate (PZT)-based materials. Our analysis considers 0-3 and 1-3 connectivity patterns, incorporating active phases in the form of spherical particles and cylindrical fibers. We also examine the impact of carbon nanotubes (CNTs) in enhancing the polymeric matrix, which introduces the potential for network percolation and further mechanical and electrical property optimization. The study yields pivotal insights into the phase connectivity of lead-free piezocomposites, with direct implications for their application in sensing, actuating, and energy harvesting domains. We ascertain that the electromechanical performance of these composites is contingent upon the connectivity pattern and the proportion of active phase. Notably, the KNNS-BNZH & Polyethylene composite demonstrates exceptional potential in 1-3 configurations, while the BTO & PVDF composite distinguishes itself with superior dielectric and piezoelectric responses across varying volume fractions. The strategic infusion of CNTs into the PDMS matrix emerges as a significant enhancer of electromechanical attributes, albeit with performance improvements that are specific to the type of coefficient and CNT concentration. This investigation underscores the nuanced interplay between composite design and microstructural attributes, reinforcing the critical role these factors play in the advancement of effective and eco-conscious piezoelectric materials.

Alternative hydraulic concretes based on calcium sulfate-granulated blast furnace slag composites

Two series of hydraulic concretes were prepared with alternative and sustainable composite binders of mineral calcium sulfate hemihydrate or waste anhydrite fluorgypsum, both supplemented with granulated blast-furnace slag, and fly ash or silica fume. The mixtures with 300 and 400 kg m−3 of binder cured for up to 360 days showed strengths of up to 30 MPa and hydraulic character. The microstructural configuration, characterized by SEM, EDS and XRD, indicated that the precipitated framework of gypsum crystals was stable under water after being engulfed by C–S–H like products formed by the reactions of the slag, pozzolanas and Portland cement. Ettringite was identified and assumed in moderate amounts in some samples, indicating the sulphatic activation for the slag and fly ash. The environmental impact assessed by a simple LCA indicated that the studied concretes release GHG in average 64.6 or 81.3 kgCO2eq·m−3 depending on the binder content, which is up to 5.3 times lower relative to conventional Portland cement mixtures. Depending on the distances travelled, freight was an important factor of GHG, while grinding and sieving were very low.

A machine learning approach for predicting the Johnson-Champoux-Allard parameters of a fibrous porous material

Porous fibrous materials have been widely used as acoustic treatments for noise attenuation. Their acoustic properties are typically characterized by Johnson-Champoux-Allard (JCA) model, which includes five dominant parameters, i.e., open porosity, flow resistivity, tortuosity, viscous characteristic length, and thermal characteristic length. The JCA parameters depend on the microstructure configuration of the material, which can be attained by experimental measurements or numerically analyzing the flow field inside the microstructure, but significant efforts to predict the parameters are typically required. This study proposes a machine learning approach based on an artificial neural network (ANN) for predicting the JCA parameters of a fibrous material. Two geometric parameters that can characterize the fibrous material, i.e., the radius of the fiber and the equivalent throat size between neighbouring fibers, are set as inputs for the prediction model, while the five JCA parameters are set as outputs. The datasets for the network are prepared from finite element simulations. Results confirm that the trained model can predict the JCA parameters accurately and reliably based on the micro-structural geometric parameters. Finally, the model is further validated by the measured acoustic characteristics of a metal-based fibrous material in an impedance tube. The machine learning model opens up possibilities to facilitate the design of advanced porous materials.

Quantitative analysis of multiple deformation mechanisms in NiCrCoFe high-entropy alloy

Multiple deformation mechanisms were often observed during the deformation processes of high-entropy alloys (HEAs), but the quantitative analysis of the contribution of different deformation mechanisms to the total deformation is few involved. In this work, the multiple deformation mechanisms in NiCoCrFe HEA are studied by molecular dynamics (MD) method. The average flow stress transforms from Hall-Petch (HP) relationship to inverse Hall-Petch (IHP) relationship with grain refinement at critical grain size (dc ≈ 27.31 nm). And the microstructural evolutions of microstructures during the deformation process are revealed by means of the crystal-analysis-tool (CAT). The contributions of various microstructural configurations to the total deformation are systematically studied by means of post-processing metrics. In the strengthening regime, the deformation mechanisms are dominated by stacking fault, grain boundary (GB) activity, and HCP martensitic transformation, accompanied with twinning and dislocation. In the softening regime, the deformation mechanisms are dominated by GB activity and stacking fault. The deformation mechanisms revealed according to the percentages of total strain accommodated by various microstructural configurations is more accurate than their atomic fractions. These results would provide an accurate and deep insight into the multiple deformation mechanisms of HEAs.

Effect of Ni element on microstructure and properties of cold-rolled 316 L austenitic stainless steel

In this current investigation, the impact of Nickel (Ni) on the microstructural attributes and properties of a cold-rolled 316 L sheet was examined. The microstructure and phase configuration of austenitic stainless steels, specifically 316 L and 316LNi, were meticulously characterized through the utilization of metallography, X-ray Diffraction (XRD), and Electron Backscatter Diffraction (EBSD) techniques. Subsequent assessments were conducted to evaluate magnetic characteristics, microhardness, and tensile properties. The phase structure of both austenitic stainless steels conforms to a Face-Centered Cubic (FCC) crystal lattice, whereby the grain content oriented along the (110) plane progressively escalates with augmenting degrees of cold rolling. The magnetic conductivity of these austenitic stainless steels satisfactorily adheres to established standards. The incorporation of Nickel (Ni) into the alloy composition enhances the cold deformation capacity of 316 L stainless steel. However, substantial plastic deformation yields heightened dislocation density, thereby promoting enlarged grain dimensions upon solution treatment. Throughout subsequent cold rolling deformation sequences, the augmented grain size observed in 316LNi stainless steel leads to a reduction in dislocation density within the equivalently ordered cold-rolled plate. Simultaneously, this augmented grain size engenders a decline in grain boundary content coupled with an augmentation in twin content. Consequently, the interplay of grain coarsening, diminished dislocation density, and twin-induced softening collectively bestows upon 316LNi stainless steel a lower tensile strength compared to 316 L stainless steel, albeit accompanied by heightened plasticity.

Strain localization in the Alloy 718 Ni-based superalloy: From room temperature to 650 °C

Irreversible deformation in relation to the microstructure was investigated for a polycrystalline Ni-based superalloy (Alloy 718) from room temperature to 650 °C using high-resolution digital image correlation (HR-DIC) techniques. Interrupted tensile tests were performed under a protective atmosphere to ensure the stability of the speckle pattern to track kinematics fields from surface analyses. In-plane strain localization was captured using HR-DIC on scanning electron microscopy (SEM) images. A statistical analysis of different strain localization events in relation to the microstructural features was conducted, i.e., intragranular slip localization, slip localization parallel to and near Σ3-twin boundaries (Σ3-TB), and grain boundary sliding (GBS). Alloy 718 exhibited slip localization at room temperature and 350 °C. Intense strain localization develops parallel and in the vicinity of Σ3-TB from the onset of the microplasticity. Few intense slip stimulated-grain boundary sliding events were found due to slip localization on both grains adjacent to the grain boundary. At 650 °C, Alloy 718 experienced grain boundary sliding at the onset of the yield without particular slip localization in adjacent grains. At lower temperatures, strain localization parallel to and near Σ3-TB was intense, and intragranular slip localization intensified with increasing macroscopic deformation. Particular microstructural configurations were found at 650 °C leading to premature damage: (i) sub-surface cavitation at grain boundaries, and (ii) grain boundary cracking due to intense shearing near a Σ3-TB.

Mechanical Characterization of the Male Lower Urinary Tract: Comparison among Soft Tissues from the Same Human Case Study

Background: Nowadays, a challenging task concerns the biomechanical study of the human lower urinary tract (LUT) due to the variety of its tissues and the low availability of samples. Methods: This work attempted to further extend the knowledge through a comprehensive mechanical characterization of the male LUT by considering numerous tissues harvested from the same cadaver, including some never studied before. Samples of the bladder, urethra, prostate, Buck’s fascia and tunica albuginea related to corpora cavernosa were considered and distinguished according to testing direction, specimen conformation and anatomical region. Uniaxial tensile and indentation tests were performed and ad hoc protocols were developed. Results: The tissues showed a non-linear and viscoelastic response but different mechanical properties due to their specific functionality and microstructural configuration. Tunica albuginea longitudinally displayed the highest stiffness (12.77 MPa), while the prostate transversally had the lowest one (0.66 MPa). The minimum stress relaxation degree (65.74%) was reached by the tunica albuginea and the maximum (88.55%) by the bladder. The prostate elastic modulus was shown to vary according to the presence of pathological changes at the microstructure. Conclusions: This is the first experimental work that considers the mechanical evaluation of the LUT tissues in relation to the same subject, setting the basis for future developments by expanding the sample population and for the development of effective in silico models to improve the solutions for most LUT pathologies.

Multiple degrees‐of‐freedom programmable soft‐matter‐photonics: Configuration, manipulation, and advanced applications

AbstractFor centuries, humans have never stopped exploring the nature of light and manipulating it, since light carries multiple information through its intrinsic wave‐particle dualism, including wavelength, amplitude, phase, polarization, spin/orbital angular momentum, etc., which determines the physical language and basic manners we perceive the objective world. Conventional optical devices, such as lenses, prisms, and lasers, are composed of solid elements that are bulky, making it difficult to manipulate light dynamically with multiple degrees‐of‐freedom. Comparatively, some responsive soft matters, especially represented by liquid crystals (LCs), possess distinctive orientational order and spontaneous self‐assembled superstructures, enabling the digital programming of microstructures and multiple degrees‐of‐freedom manipulation of their optical characteristics. The optical manipulation based on these soft superstructures, that is, the “soft‐matter‐photonics”, is playing an impressive role in integrated functional devices, especially in the present age of information explosion. Herein, we review the latest advances, respectively, in the microstructure configurations, multiple degrees‐of‐freedom manipulations, and the relevant prospective applications. Additionally, scientific issues and technical challenges that hinder the programing operation and optical manipulations are discussed. Toward a four‐dimensional optical manipulation of soft condensed matter, this review may have wide implications on a variety of applications, including the integrated fabrication of compact elements, multi‐channel information processing and high‐capacity optical communications.

Evolution of Microstructure and Fe/Fe3C Interface Structure in Cold‐Drawn Pearlitic Steel Wires

The microstructure, texture, and dislocation configuration of cold‐drawn pearlitic steel wires were investigated by scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). In addition, Fe/Fe3C interface structure at the atomic level was clearly observed and analyzed by high‐resolution TEM (HRTEM), and the microscopic deformation mechanism of cementite lamellae at different drawing strains is revealed. The results show that pearlite lamellae turn to the drawing direction to form ferrite <110> fiber texture, and the cementite and ferrite lamellae are simultaneously thinned with the increase of drawing strain. During the cold drawing process, shear‐bands(S‐bands) are formed in the cementite lamellae; the dislocation of ferrite transits from single slip to multi‐slip stage, and the dislocation density increases. After drawing, the lattice structures of cementite and ferrite phases show the evolution from single‐crystal to polycrystal, and the cementite lamellae are divided into a multilayer structure: central relative large‐size cementite crystal and outside relative small‐size cementite crystal layer; the dissolution of cementite lamellae in some regions results in the lattice expansion of ferrite phase and the occurrence of neck‐down regions in the cementite lamellae.

Insight into the microstructure configuration and strengthening mechanisms of a cast in-situ Al3Zr reinforced Al–Li matrix composite

In this work, a cast Al3Zr/Al–2Li composite was fabricated using the in-situ method, which shows improvements of ∼32 % in strength and ∼12 % in stiffness compared with the Al–2Li matrix alloy. The refined grains, microscale D023-Al3Zr particles, nanoscale Al3(Zr, Li) phases, finer Al3Li precipitates, and narrowed Al3Li precipitate-free zones (PFZ) were observed in the composite. The interface between the reinforcement and matrix is well-combined. It was indicated that Orowan strengthening of Al3(Zr, Li) and coefficient of thermal expansion (CTE) mismatch strengthening of D023-Al3Zr were two main strengthening contributors. The fracture of the composite was transformed from intergranular to transgranular mode due to the narrowed PFZ and the stress concentration effect of Al3Zr.

Significantly enhanced fatigue resistance and mechanisms of hypoeutectic Al-Si composite calibrated using trace in-situ nanocrystals

Fatigue resistance under extreme stress conditions is an important indicator to evaluate industrial application potential of Al-Si-Mg alloys, but their fatigue resistance is inherently weakened by large grain size, long-needle Si phases and coarse precipitates. This work reports significantly optimized microstructure configuration and fatigue resistance of hypoeutectic Al-Si composite optimized by the nanocrystallization products of a NiNbTi metallic glass. It was proved the in-situ NiTi (B2) nanocrystals can serve as the heterogeneous nucleation sites of α-Al and β-Mg2Si and the growth retarder of eutectic Si. Particularly, the optimized composite exhibited nearly 5 times and 6 times longer fatigue life than the unoptimized alloy at 120 MPa (60 Hz) and 240 MPa (20 Hz), respectively. The fatigue strength (N = 107) was increased by 21.7 % and 25.9 % at 60 Hz and 20 Hz, respectively. The α-Al refinement enhanced the resistance to fatigue crack initiation. The refinement and spheroidization of eutectic Si phases reduced stress concentration. Also, the austenite-martensite phase transformation of NiTi afforded more energy for precipitation. Refined β-Mg2Si and β'' phases were facilitated to interact with dislocations, improving the resistance to dislocation slip during cyclic strain through the dislocation shearing effect. This work provides a theoretical basis for the future development of Al-Si alloys and composites with excellent fatigue resistance for expanding their industrial application scope.

New understanding on the critical factors determining stability of passive film on Fe-Cr alloy based on aberration-corrected TEM study

Purpose In recent years, using aberration-corrected transmission electron microscopy, the authors have achieved precisely detecting the structural evolution of passive film as well as its interface zone at atomic scale. The purpose of this paper aims to make a brief review to show the authors’ new understanding and perspective on the issue of critical factors determining stability of passive film of Fe-Cr alloy. Design/methodology/approach The introduction of single crystal enabled the authors to obtain a distinct metal/passive film interface and better characterize the structure of the interface region. The authors use aberration-corrected TEM to conduct cross-sectional observation and directly capture the details across the entire film at a high spatial and energy resolution. Findings Apart from the passive film itself, the interface zone, including metal/film (Me/F) interface and the adjacent metal side, is also the site which is attacked. Accordingly, the nature of the interface zone, such as microstructure, composition and atomic configuration, is one of the critical factors determining the stability of passive film. Originality/value Deciphering the critical factors determining the stability of passive film is of great significance and has been a fundamental issue in corrosion science. Great attention has been paid to the nature of the passive film itself. In contrast, the possible role of the interface between the passive film and the metal is rarely taken into account. Based on the advanced analytical tool with high spatial resolution, the authors have specified the significant role of interface structures on the macro-scale stability of passive film.

An efficient data-driven optimization framework for designing graded cellular structures

Cellular structures are increasingly applied in engineering practice since they have excellent mechanical and multifunctional properties, such as light weight, energy absorption and noise reduction. In this paper, an efficient data-driven M-VCUT (multiple variable cutting) optimization framework is developed for designing the graded cellular structures. Three main parts are included in this method, i.e., the establishment of problem-independent offline database, the coarse-scale optimization, and the geometry reconstruction of full-scale cellular structure. The advantage of this method is that: (1) it has high computational efficiency due to the establishment of a problem-independent database in an offline manner; (2) it directly adopts numerical derivation, which makes the calculation of sensitivity more convenient; (3) it has fewer design variables. Based on the proposed method, the designer can predefine a variety of different basic microstructure configurations, and then combine them into different microstructures according to different requirements, realizing the integrated design of microstructure and macrostructure. Numerical examples are carried out for verifying the validation and efficiency of the proposed method.

Influence of heterogeneity due to toughness variations on weakest-link modeling for brittle failure

The effect of heterogeneous microstructures on the macroscopic probability of failure is studied by use of weakest-link modeling. Heterogeneity is here associated with a local variation of toughness, where a size scale characteristic of this variation defines a length parameter. The ratio between this length parameter and the size of the active fracture process zone, defined as the heterogeneity ratio, is key to evaluating the impact of a heterogeneous microstructure. Two extremes are identified; small-scale heterogeneity (SSH) and large-scale heterogeneity (LSH). For these cases, it is possible to formulate analytical expressions based on the weakest-link concept, and references are made to existing models in the literature. Typically, heterogeneity along the crack front, where gradients of the mechanical fields are small, falls under the category of SSH. On the other hand, the effect of heterogeneity in a plane perpendicular to the crack front depends strongly on the heterogeneity ratio. Cases that can neither be identified with SSH nor LSH must be addressed with care. How this can be done is discussed, and examples are given for four different microstructure configurations of interest. The investigation is carried out by numerical analysis of a modified boundary layer model. The cumulative probability of failure by cleavage fracture is evaluated in a post-processing step, where two different statistical models are examined; the Beremin model and the Kroon–Faleskog model. Both models render the same conclusion about the alteration of the overall failure probability distributions caused by heterogeneity.

3D nano-structured sepiolite dynamic membranes for enhanced ultrafiltration treatment and membrane fouling mitigation

The construction of replaceable dynamic membranes (DMs) on membrane surfaces is a promising strategy to effectively mitigate membrane fouling. Nevertheless, the efficiency of DMs in mitigating membrane fouling remains low due to the lack of microstructural configurations. Herein, we report a natural sepiolite (SEP) DM with a three-dimensional (3D) network structure for mitigating PES ultrafiltration (UF) membrane fouling. The abundant oxygen-containing groups on the surface of SEP nanofibers endowed SEP DM with good organic adsorption capacity, hindering the migration of contaminants such as humic acid (HA) and bovine serum albumin (BSA). Owing to the porous 3D network structure, SEP DM prevented the formation of a dense filter cake layer, which effectively mitigated the sharp rise in membrane resistance when filtering ideal HA and BSA solutions. For the actual secondary wastewater, SEP DM improved the removal of UV254 and DOC by 29.8% and 22.5%, respectively, over the pristine PES membrane. The decrease in membrane-specific flux was mitigated by about 20%. Notably, the dynamic nature of SEP DM allowed the contaminated DM layer to be replaced by hydraulic cleaning, resulting in 99% flux recovery (only 89% for the pristine PES membrane). These findings are beneficial in providing new ideas for the mitigation and control of UF membranes.