Systematic Variation Of Parameters Research Articles

Molecular modeling and simulation of organic electrolyte solutions for lithium ion batteries.

Multi-criteria optimization is used for developing molecular models for ethylene carbonate (EC) and propylene carbonate (PC), organic solvents commonly used in Li-ion batteries. The molecular geometry and partial charges of the solvents are obtained from quantum mechanical calculations. Using a novel optimization strategy that combines systematic variations of the Lennard-Jones parameters with a reduced units approach, the models are fitted to experimental data on the liquid density, vapor pressure, relative permittivity, and self-diffusion coefficient. Since no experimental data for the self-diffusion coefficient of pure EC were available in the literature, they are measured in this work using a gradient-based nuclear magnetic resonance technique. For all pure component properties, excellent agreement between experiment and simulation is obtained. Moreover, the predictive capabilities of the new solvent models are assessed by comparison to experimental data for the liquid density and relative permittivity of mixtures of EC and PC. In addition, molecular models for the anions PF6-, BF4-, and ClO4- in solutions of their lithium electrolytes in PC are developed using experimental data on the solution densities. Finally, the self-diffusion coefficients of LiPF6 in PC and in aqueous solution are predicted and compared, showing that diffusion is much slower in the organic solution due to the formation of larger solvent shells around the ions. Furthermore, an analysis of the radial distribution functions in these solutions suggests that the ions have much less impact on the structure of the solvent PC than on water.

Hypervelocity impact against aluminium Whipple shields in the shatter regime with systematic parameter variation: An experimental and numerical study

Aluminium Whipple shields are commonly used to protect spacecraft against hypervelocity impacts (HVIs) from orbital debris and micrometeoroids. Since numerical models nowadays are vital in the design process of protective shields, experimental studies of HVI are important to ensure that the numerical methods are robust and capable of accurately describing a range of impact conditions and material responses. The shatter regime is the transition velocity range between ballistic impact and hypervelocity impact, typically defined from 3 to 7 km/s. In this region, the debris cloud generated by the impact transitions from a few large, solid fragments at the lower end of the velocity range, to a high number of smaller fragments and partial melting of the projectile at the higher velocities. In this study, an experimental campaign of 22 normal impacts of spherical AA1100 projectiles on AA6061-T6 Whipple shields is performed, where the impact velocity and bumper thickness are systematically varied to study the change in debris cloud characteristics and shield damage. Impact velocities from 2.6 to 5.0 km/s are investigated, combined with bumper thicknesses of 1.0, 1.5 and 2.0 mm. Analysis of the experimental results is conducted using high-speed camera footage of the debris clouds and post-impact analysis of bumpers and rear walls. A numerical model is then established using the Smoothed Particle Hydrodynamics (SPH) method in the IMPETUS Solver, and the numerical results are compared to the experimental data. The simulations are able to capture the main trends found in the experimental study, and show a similar level of damage as the experiments when varying the impact velocity and bumper thickness. The simulations have somewhat smaller fragments generated in the debris cloud than in the experiments, leading to slightly less damage inflicted on the rear wall.

Melt Pool characteristics on surface roughness and printability of 316L stainless steel in laser powder bed fusion

Purpose Surface quality and porosity significantly influence the structural and functional properties of the final product. This study aims to establish and explain the underlying relationships among processing parameters, top surface roughness and porosity level in additively manufactured 316L stainless steel. Design/methodology/approach A systematic variation of printing process parameters was conducted to print cubic samples based on laser power, speed and their combinations of energy density. Melt pool morphologies and dimensions, surface roughness quantified by arithmetic mean height (Sa) and porosity levels were characterized via optical confocal microscopy. Findings The study reveals that the laser power required to achieve optimal top surface quality increases with the volumetric energy density (VED) levels. A smooth top surface (Sa < 15 µm) or a rough surface with humps at high VEDs (VED > 133.3 J/mm3) can serve as indicators for fully dense bulk samples, while rough top surfaces resulting from melt pool discontinuity correlate with high porosity levels. Under insufficient VED, melt pool discontinuity dominates the top surface. At high VEDs, surface quality improves with increased power as mitigation of melt pool discontinuity, followed by the deterioration with hump formation. Originality/value This study reveals and summarizes the formation mechanism of dominant features on top surface features and offers a potential method to predict the porosity by observing the top surface features with consideration of processing conditions.

Characterisation of human penile tissue properties using experimental testing combined with multi-target inverse finite element modelling

This paper presents an inverse finite element (FE) approach aimed at estimating multi-layered human penile tissues. The inverse FE approach integrates experimental force–displacement and boundary deformation data of penile tissues with a developed FE model and uses new experimental data on human penile tissue. The experimental study encompasses whole organ plate-compression tests and individual layer tensile and compression tests, providing comprehensive insights into the tissue's mechanical behaviour. The biomechanical characterisation of penile tissue is of crucial significance for understanding its mechanical behaviour under various physiological and pathological conditions. The FE model is constructed using the realistic geometry of the penile segment and appropriate constitutive models for each tissue layer to leverage the accuracy and consistency of the model. Through systematic variation of tissue parameters in the inverse FE algorithm, simulations achieve the best match with both force–displacement and deformed boundary results obtained from the whole organ plate-compression tests. Test results from individual tissue layers are also utilised to assess the estimated parameters. The proposed inverse FE approach allows for the estimation of penile tissue parameters with high precision and reliability, shedding light on the mechanical properties of this complex biological organ. This work has applications not only in urology but also for researchers in various disciplines of biomechanics. As a result, our study contributes to advancing the understanding of human penile tissue mechanics whilst the methodology could also be applied to a range of other soft biological tissues. Statement of significanceThis research uses a multi-target inverse finite element (FE) approach for estimating the material parameters of human penile tissues. By integrating experimental data and a realistic FE model, this study achieves high-precision constitutive model parameter estimation, offering key insights into penile tissue mechanics under various loading conditions. The significance of this work lies in the use of this inverse FE approach for fresh-frozen human penile tissues, to identify the mechanical properties and constitutive models for both segregated tunica albuginea and corpus cavernosum as well as intact penile tissue segments. The study's scientific impact lies in its advancement of the understanding of human urological tissue mechanics, impacting researchers and clinicians alike.

Optical manipulation in Rubidium-87 atomic medium using Kerr field: Dynamic insights into two-interfering electromagnetic waves

In this manuscript, we investigate the intricate dynamical properties arising from the interaction of two-interfering electromagnetic waves within a Rubidium-87 four-level N-type atomic medium. The study employs a probe field to interact with the atomic medium while incorporating two control fields one of which would be the Kerr field to modulate the system dynamics. The key parameters under scrutiny include the probe field detuning (ΔP/γ), control field parameters such as Rabi frequencies and detunings (Ω1,2/γ, Δ1,2/γ), and the angular orientation (θ) between the two-interfering waves. The research delves into the Energy density W, Momentum density P, Spin Angular momentum density S, Absorption rate Arate, Gradient force Fgrad, and Torque T associated with the two-interfering waves within the atomic medium. Through systematic variations in the aforementioned parameters, significant insights are gained into the nuanced behaviour of the system. The results showcase a rich tapestry of variations in the dynamical properties, shedding light on the underlying physics governing the interaction of electromagnetic waves in this unique atomic medium. This investigation not only contributes to the fundamental understanding of the dynamics within complex atomic systems but also holds potential applications in fields such as quantum information processing and quantum optics. The findings of this manuscript pave the way for further exploration and utilization of these intricate phenomena in the realm of advanced technologies and quantum communication.

Porous Fe-Porphyrin as an Efficient Adsorbent for the Removal of Ciprofloxacin from Water.

Antibiotics are widely used in medicine, but they are not fully metabolized in the body and can end up in wastewater. Conventional wastewater treatment methods fail to completely remove antibiotic residues, which can then enter rivers and streams. Adsorption is a promising technique for removing antibiotics from wastewater, even at low concentrations. The successful one-pot synthesis of an adsorbent, iron-containing porphyrin-based porous organic polymer (Fe-POP), was achieved through the reaction of pyrrole groups and terephthalaldehyde in the presence of FeCl3. Characterized by a substantial BET surface area of 597 m2 g-1, Fe-POP was systematically investigated for its adsorption potential in the removal of the antibiotic Ciprofloxacin (CIP) from aqueous solutions. By systematic variation of key parameters, including pH, adsorbent loading, and CIP concentration, the adsorption conditions were optimized. Under the optimal conditions at pH = 3, CIP concentration of 5 ppm, and 25 mg of Fe-POP, the maximum adsorption capacity reached an impressive 263 mg g-1. The robust adsorption behavior was elucidated through the fitting of experimental data to the Langmuir adsorption isotherm (R2 = 0.962) and the pseudo-second-order kinetic model (R2 = 0.999) with lower error values. These models suggested that the adsorption process predominantly involved chemical interactions between CIP molecules and the Fe-POP surface. Fe-POP exhibited a robust structure with a high adsorption capacity, showcasing its efficacy in removing CIP contaminants from water. Therefore, Fe-POP can be considered a valuable adsorbent for water treatment applications, specifically for antibiotic removal.

Electrochemical Capacitance Traces with Interlayer Spacing in Two‐dimensional Conductive Metal–Organic Frameworks

AbstractElectrically conductive metal–organic frameworks (MOFs) are promising candidates for electrochemical capacitors (EC) for fast energy storage due to their high specific surface areas and potential for redox activity. To maximize energy density, traditional inorganic pseudocapacitors have utilized faradaic processes in addition to double‐layer capacitance. Although conductive MOFs are usually comprised of redox active ligands which allow faradaic reactions upon electrochemical polarization, systematic studies providing deeper understanding of the charge storage processes and structure‐function relationships have been scarce. Here, we investigate the charge storage mechanisms of a series of triazatruxene‐based 2D layered conductive MOFs with variable alkyl functional groups, Ni3(HIR3‐TAT)2 (TAT=triazatruxene; R=H, Et, n‐Bu, n‐Pent). Functionalization of the triazatruxene core allows for systematic variation of structural parameters while maintaining in‐plane conjugation between ligands and metals. Specifically, R groups modulate interlayer spacing, which in turn shifts the charge storage mechanism from double‐layer capacitance towards pseudocapacitance, leading to an increase in molar specific capacitance from Ni3(HIH3‐TAT)2 to Ni3(HIBu3‐TAT)2. Partial exfoliation of Ni3(HIBu3‐TAT)2 renders redox active ligand moieties more accessible, and thus increases the dominance of faradaic processes. Our strategy of controlling charge storage mechanism through tuning the accessibility of redox‐active sites may motivate further design and engineering of electrode materials for EC.

Electrochemical Capacitance Traces with Interlayer Spacing in Two-dimensional Conductive Metal-Organic Frameworks.

Electrically conductive metal-organic frameworks (MOFs) are promising candidates for electrochemical capacitors (EC) for fast energy storage due to their high specific surface areas and potential for redox activity. To maximize energy density, traditional inorganic pseudocapacitors have utilized faradaic processes in addition to double-layer capacitance. Although conductive MOFs are usually comprised of redox active ligands which allow faradaic reactions upon electrochemical polarization, systematic studies providing deeper understanding of the charge storage processes and structure-function relationships have been scarce. Here, we investigate the charge storage mechanisms of a series of triazatruxene-based 2D layered conductive MOFs with variable alkyl functional groups, Ni3(HIR3-TAT)2 (TAT=triazatruxene; R=H, Et, n-Bu, n-Pent). Functionalization of the triazatruxene core allows for systematic variation of structural parameters while maintaining in-plane conjugation between ligands and metals. Specifically, R groups modulate interlayer spacing, which in turn shifts the charge storage mechanism from double-layer capacitance towards pseudocapacitance, leading to an increase in molar specific capacitance from Ni3(HIH3-TAT)2 to Ni3(HIBu3-TAT)2. Partial exfoliation of Ni3(HIBu3-TAT)2 renders redox active ligand moieties more accessible, and thus increases the dominance of faradaic processes. Our strategy of controlling charge storage mechanism through tuning the accessibility of redox-active sites may motivate further design and engineering of electrode materials for EC.

Characterization of the Pb Coordination Environment and Its Connectivity in Lead Silicate Glasses: Results from 2D 207Pb NMR Spectroscopy.

The Pb-O coordination environment in binary (PbO)x(SiO2)100-x glasses with 30 ≤ x ≤ 70 is probed by using two-dimensional 207Pb nuclear magnetic resonance (NMR) isotropic-anisotropic correlation spectroscopy. The isotropic 207Pb NMR spectra show little composition-dependent evolution of the Pb-O nearest-neighbor coordination environment. The systematic variation of the chemical shift tensor parameters offers a unique insight into their local site symmetry and suggests the presence of pyramidal PbO3 and PbO4 sites with sterically active electron lone pairs and with Pb-O bond lengths ranging between 0.23 and 0.25 nm. The PbO3/PbO4 ratio shows a small but monotonic increase from ∼70:30 to 80:20 as the PbO content increases from 30 to 70 mol %. When taken together, the isotropic and anisotropic 207Pb NMR spectra suggest that the majority of the PbOn (3 ≤ n ≤ 4) pyramids in these glasses are connected to the SiO4 tetrahedra via Pb-O-Si linkages. A significant fraction of Pb-O-Pb linkages, where the oxygen is linked only to Pb atoms, appears only in glasses with PbO ≥ 60 mol %. These oxygen atoms appear to be corner-shared between the PbOn pyramids in the structure, and no evidence for edge-sharing between these pyramids is observed in this composition range. We hypothesize that a substantial fraction of the constituent PbOn pyramids start to participate in edge-sharing only at higher PbO contents (>70 mol %), which diminishes the glass-forming ability of the network. This work illustrates the potential of isotropic-anisotropic correlation NMR spectroscopy in structural studies involving nuclides with large chemical shift ranges and anisotropy.

Dynamic Modelling and Simulation of Industrial Plant Fire and Gas Detection Systems; Parametric Analysis of Nozzle Flow

Industrial plant safety is of paramount importance, and the effective operation of Fire and Gas Detection Systems (FGDS) plays a critical role in preventing and mitigating incidents. This study presents a comprehensive parametric computational fluid dynamics (CFD) analysis of nozzle flow, aimed at enhancing our understanding of the complex fluid dynamics within nozzle geometries. Nozzles find wide applications in industries ranging from aerospace propulsion systems to industrial processes. The analysis employs CFD simulations with varying geometric parameters, such as nozzle shape, throat diameter, and expansion ratio, to investigate their influence on flow characteristics, including velocity profiles, pressure distributions, and shock formations. The parametric study involves systematic variations of these geometric parameters, allowing for the identification of optimal configurations for specific applications. The results shed light on the intricate interplay between nozzle geometry and flow behavior, providing valuable insights for nozzle design and optimization.

A Rigid-Flexible Coupling Dynamic Model for Robotic Manta with Flexible Pectoral Fins

The manta ray, exemplifying an agile swimming mode identified as the median and paired fin (MPF) mode, inspired the development of underwater robots. Robotic manta typically comprises a central rigid body and flexible pectoral fins. Flexible fins provide excellent maneuverability. However, due to the complexity of material mechanics and hydrodynamics, its dynamics are rarely studied, which is crucial for the advanced control of robotic manta (such as trajectory tracking, obstacle avoidance, etc.). In this paper, we develop a multibody dynamic model for our novel manta robot by introducing a pseudo-rigid body (PRB) model to consider passive deformation in the spanwise direction of the pectoral fins while avoiding intricate modeling. In addressing the rigid-flexible coupling dynamics between flexible fins and the actuation mechanism, we employ a sequential coupling technique commonly used in fluid-structure interaction (FSI) problems. Numerical examples are provided to validate the MPF mode and demonstrate the effectiveness of the dynamic model. We show that our model performs well in the rigid-flexible coupling analysis of the manta robot. In addition to the straight-swimming scenario, we elucidate the viability of tailoring turning gaits through systematic variations in input parameters. Moreover, compared with finite element and CFD methods, the PRB method has high computational efficiency in rigid-flexible coupling problems. Its potential for real-time computation opens up possibilities for future model-based control.

Morphology characterization of dendrites on lithium metal electrodes by NMR spectroscopy.

Despite the considerable potential offered by lithium metal's high capacity for rechargeable batteries, challenges such as dendrite formation and safety concerns persist. As strategies continue to advance in dendrite management, the demand for efficient monitoring tools becomes increasingly pronounced. In this study, we delve into the characterization of dendrites, elucidating the influence of microstructure morphology on the NMR spectrum using a combination of simulations and experiments. Systematic variations in various geometrical parameters highlight dendrite density as a pivotal distinguishing feature. Furthermore, the investigation explores the effectiveness of a pulse sequence in selectively exciting microstructures over the bulk, providing valuable insights into mitigating dendrite-related challenges in lithium-metal batteries.

(Invited) Electrochemical Characterization of Catalyst/Ionomer Interfaces

Electrochemical energy conversion devices such as polymer-electrolyte fuel cells, water-splitting or carbon dioxide reduction electrolyzers, utilize ionically-conductive polymers (ionomers) in their electrode structure where an ionomer forms interfaces with the catalysts. The ionomers exist as nanometer-thick film to cover the catalyst particles and act as a binder while enabling the transport of active species necessary for the reactions. While the nature of species and operational environment differs across these devices, their overall efficiency and performance is influenced by the electrode architecture, where the interfaces and interactions between the ionomers and catalysts play an important role. In hydrogen technologies, for example, ionomer thin films bind the catalyst sites and carbon supports to facilitate transport of ionic (e.g. protons), liquid (water) and gaseous (e.g., oxygen) species under a nano-confined environment. Such confinement effects not only change the ionomer structure and properties, usually with a tendency to increase transport resistances, but also amplify the impact of the electrocatalyst-ionomer interactions in the electrodes, thereby reducing the catalyst activity. Thus, understanding the behavior of nano-confined ionomers and their interactions with the catalyst surfaces is key for mitigating the transport resistances in catalyst ionomers and improving the electrode performance and cell efficiency.This talk will provide insights into electrochemical characterization of catalyst ionomers by focusing on varying chemistries of perfluorosulfonated cation-exchange ionomers with additional examples of anion-exchange ionomers for emerging technologies. The hydration and transport properties of proton-exchange catalyst-ionomers will be examined with the effects of chemistry, processing and thickness (degree of confinement), along with their impact on the morphological changes governing the film function. Through a systematic variation of material chemistries and environmental parameters, primary factors impacting the structure-property relationship of catalyst ionomers are described along with a discussion of secondary factors altering the cation-anion interactions. Then, the interplay between the effects of chemistry and ion exchange (capacity) on modifying the transport function and the strength of ionomer-catalyst interactions will be presented. The results will be collated to elucidate the underlying origins of the transport resistances occurring in electrodes, and to develop materials and processing strategies for their mitigation for improved performance and efficiency in electrochemical energy devices.

Reappraisal of clinical trauma trials: the critical impact of anthropometric parameters on fracture gap micro-mechanics—observations from a simulation-based study

The evidence base of surgical fracture care is extremely sparse with only few sound RCTs available. It is hypothesized that anthropometric factors relevantly influence mechanical conditions in the fracture gap, thereby interfering with the mechanoinduction of fracture healing. Development of a finite element model of a tibia fracture, which is the basis of an in silico population (n = 300) by systematic variation of anthropometric parameters. Simulations of the stance phase and correlation between anthropometric parameters and the mechanical stimulus in the fracture gap. Analysis of the influence of anthropometric parameters on statistical dispersion between in silico trial cohorts with respect to the probability to generate two, with respect to anthropometric parameters statistically different trial cohorts, given the same power assumptions. The mechanical impact in the fracture gap correlates with anthropometric parameters; confirming the hypothesis that anthropometric factors are a relevant entity. On a cohort level simulation of a fracture trial showed that given an adequate power the principle of randomization successfully levels out the impact of anthropometric factors. From a clinical perspective these group sizes are difficult to achieve, especially when considering that the trials takes advantage of a „laboratory approach “, i.e. the fracture type has not been varied, such that in real world trials the cohort size have to be even larger to level out the different configurations of fractures gaps. Anthropometric parameters have a significant impact on the fracture gap mechanics. The cohort sizes necessary to level out this effect are difficult or unrealistic to achieve in RCTs, which is the reason for sparse evidence in orthotrauma. New approaches to clinical trials taking advantage of modelling and simulation techniques need to be developed and explored.

Copula-based modeling and simulation of 3D systems of curved fibers by isolating intrinsic fiber properties and external effects

In this paper we lay the foundation for data-driven 3D analysis of virtual fiber systems with respect to their microstructure and functionality. In particular, we develop a stochastic 3D model for systems of curved fibers similar to nonwovens, which is fitted to tomographic image data. By systematic variations of model parameters, efficient computer-based scenario analyses can be performed to get a deeper insight how effective properties of this type of functional materials depend on their 3D microstructure. In a first step, we consider single fibers as polygonal tracks which can be modeled by a third-order Markov chain. For constructing the transition function of the Markov chain, we formalize the intuitive notions of intrinsic fiber properties and external effects and build a copula-based transition function such that both aspects can be varied independently. Using this single-fiber model, in a second step we derive a model for the entire fiber system observed in a bounded sampling window and fit it to two different 3D datasets of nonwovens measured by CT imaging. Considering various geometric descriptors of the 3D microstructure related to effective properties of the pore space, we evaluate the goodness of model fit by comparing geometric descriptors of the 3D morphology of model realizations with those of tomographic image data.

Calibration procedure of Discrete Element Method (DEM) parameters for wet and sticky bulk materials

The downtimes associated with blockage events in the materials handling sector have prompted the mining industry to optimise its operations to maximise the profitability of fines and lump products. These blockage events are caused by materials with a high clay or moisture content typically referred to as Wet and Sticky Material (WSM). Numerous methods are commonly used to prevent such blockage events, however, in the majority of cases, they are often too late to prevent the downtime of the system. The Discrete Element Method (DEM) is commonly used to predict and visualise the bulk material flow. DEM is capable of replicating the flow of non-cohesive granular materials with reasonable accuracy, however, when cohesive materials are considered the mechanism becomes much more complex. With the advancement of computational power over the last few decades, it is now more practical to simulate WSMs into DEM.This paper evaluates the capability of three cohesion models to simulate WSMs; the Simplified Johnson-Kendall-Roberts (SJKR) model, the Easo Liquid Bridging model and the Edinburgh Elasto-Plastic Adhesion (EEPA) model. A calibration procedure is proposed where the parameters for each cohesion model are discussed in detail. A series of calibration simulations with systematic parameter variation is undertaken to define a set of calibration matrices. These matrices allow the formation of a parameter database, used for the simulation of on-site applications to optimise plant geometry and other operational parameters. Finally, the numerical model was validated using a lab-scale vertical impact testing facility. Individually, in a transfer chute application, it was determined that none of the 3 cohesion models were suited to WSMs; the SJKR and Easo liquid bridging models were unable to replicate the behaviour, and while the EEPA model was able to replicate the behaviour, extensive solve times deemed it impractical for industrial applications. These limitations were overcome through the coupling of the SJKR and Easo Liquid Bridging models.

Basal complex: a smart wing component for automatic shape morphing

Insect wings are adaptive structures that automatically respond to flight forces, surpassing even cutting-edge engineering shape-morphing systems. A widely accepted but not yet explicitly tested hypothesis is that a 3D component in the wing’s proximal region, known as basal complex, determines the quality of wing shape changes in flight. Through our study, we validate this hypothesis, demonstrating that the basal complex plays a crucial role in both the quality and quantity of wing deformations. Systematic variations of geometric parameters of the basal complex in a set of numerical models suggest that the wings have undergone adaptations to reach maximum camber under loading. Inspired by the design of the basal complex, we develop a shape-morphing mechanism that can facilitate the shape change of morphing blades for wind turbines. This research enhances our understanding of insect wing biomechanics and provides insights for the development of simplified engineering shape-morphing systems.

Simulative Determination of Effective Mechanical Properties for Digitally Generated Foam Geometries

Metal foams constitute a promising and emerging material class in the context of lightweight construction. There exists a variety of different foam topologies, on which resulting mechanical properties depend. To maximize the potential of foams in material use under mechanical load, the present work addresses the question how different geometrical parameters influence the material behaviour. Therefore, an algorithm for digital generation and design of open pore foam structures is presented, that allows to regulate the geometry precisely. A method for retrieving effective mechanical properties from numerical simulations of compression tests in the elastic regime is introduced. Additionally, the representativeness of foam volumes considered for simulations is investigated. This yields a fully digital workflow, which enables the investigation of geometry influence on mechanical properties. This approach is used to conduct simulation studies on generated foam structures with a systematic variation of geometrical parameters. Herein, a range of effective Young's moduli varying by up to a factor of 1.3 for different foam structures at the same porosity is found. This shows a significant impact of the foam geometry on the elastic properties of metal foams. The presented methodology yields insights, which can guide design and optimization of materials for specific applications.

Control of mechanical and shape memory characteristics in martensitic NiTi by setting L-PBF parameters and build orientation

The current work encompasses a study of as-fabricated martensitic NiTi samples printed via Laser Powder Bed Fusion (L-PBF) in the horizontal and vertical build orientations, with systematic variations in the L-PBF process parameters. The sample densities, compositions, thermal characteristics, and mechanical responses were analysed and correlated with L-PBF parameters. Mechanical responses measured and analysed included microhardness, impact energies, and elastic modulus. The process parameters were found to have a significant effect on the resulting properties. The variation in physical properties and mechanical responses between each sample of the vertical build were less compared to those measured for the horizontal built samples. The L-PBF samples were compressed to 6% engineering strain (within elastic limit), and their shape memory strains were thermally recovered. Digital Image Correlation (DIC) based full-field strain analysis was performed during compression to measure local strain fields which revealed in detail the macroscopic effects during detwinning. The shape memory capability of the L-PBF samples was quantised based on strain recoveries attained after thermal recovery. Microstructural variations in submicron scale were also analysed in as-fabricated, post-compression and post-recovery stages, showing the sample response during different deformation mechanisms.

The Interaction Between Interface Morphology of Particles with Anisotropic Effect of Interface Kinetics in an Alloy Melt

AbstractThe conventional theory of crystal growth presents an irreversible outward increase of the crystal size through solute deposition on the nuclei; however, the asymptotic solution of the dynamics model of the particle reveals that the crystal growth undergoes a locally reversible inward growth process in the early stage of crystal growth. Immediately after nucleation, some parts of the interface first grow inward through solute rejection along certain crystal orientations from the interface of nucleation, while the other parts of the interface grow outward through solute deposition along other crystal orientations. Until the inward growth attains a certain distance, the interface grows outward along each crystal orientation. This growth behavior is attributed to the interaction between interface morphology of particles with the anisotropic effect of interface kinetics. Through a systematic variation of the anisotropy parameters, the particle exhibits a continuous transition from one growth morphology to other growth morphologies. During the morphological transition process, as initial concentration increases, the growth of the particle is inhibited in the preferred growth directions, whereas it is facilitated in other growth directions. As a result, the interface morphologies of the particle with different petal‐shaped morphologies in the early stage of crystal growth are formed.