Inhomogeneous Behavior Research Articles

Prediction of Delamination Defects in Drilling of Carbon Fiber Reinforced Polymers Using a Regression-Based Approach

Carbon fiber-reinforced polymer (CFRP) structures have been increasingly used in various aerospace sectors due to their outstanding mechanical properties in recent years. However, the poor machinability of CFRP plates, combined with the inhomogeneous behavior of fibers, poses a challenge for manufacturers and researchers to define the critical factors and conditions necessary to ensure the quality of holes in CFRP structures. This study aims to analyze the effect of drilling parameters on CFRP delamination and to predict hole quality using a regression-based approach. The design of the experiment (DOE) was conducted using Taguchi’s L9 3-level orthogonal array. The input drilling variables included the feed rate, spindle speed, and three different drill types. A regression-based model using partial least squares (PLS) was developed to predict delamination defects during the drilling of CFRP plates. The PLS model demonstrated high accuracy in predicting delamination defects, with a Mean Squared Error (MSE) of 0.0045, corresponding to an accuracy of approximately 99.6%, enabling the rapid estimation of delamination. The model’s predictions were closely aligned with the experimental results, although some deviations were observed due to tool inefficiencies, particularly with end mill cutters. These findings offer valuable insights for researchers and practitioners, enhancing the understanding of delamination in CFRPs and identifying areas for further investigation.

Through-thickness Work Hardening Variation in Thick High Strength Steel Plates: A Novel Inverse Characterization Method

Due to the production process, thick high strength steel plates potentially exhibit inhomogeneous plastic material behavior through the thickness. For example, the initial yield stress and work hardening behavior might vary through the plate thickness. In order to establish a reliable plasticity model that can be used in finite element simulations to optimize forming processes or to investigate the structural integrity of large structures, this material behavior needs to be characterized. A straightforward characterization method consists of slicing the thick high strength steel plate and conducting standard tensile tests. However, this approach comes with a large experimental effort. A novel specimen is proposed enabling to inversely identify the work hardening behavior at distinct locations through the thickness of a thick steel plate. To this end, a tensile specimen with circular pockets at different depths is used. The strain fields within the pockets are captured using digital image correlation (DIC). finite element model updating (FEMU) is used to inversely identify a predefined strain hardening law for each pocket. First, the procedure is optimized and numerically verified using virtual experiments generated by a finite element model with a known variation of the work hardening behavior. Finally, the procedure is experimentally validated by characterizing the strain hardening behavior of a 10 mm thick S690QL grade.

Inhomogeneous Fluid Transport Modeling in Dual-Scale Porous Media Considering Fluid-Solid Interactions.

Dynamics of fluid transport in ultratight reservoirs such as organic-rich shales differ from those in high-permeable reservoirs due to the complex nature of fluid transport and fluid-solid interaction in nanopores. We present a multiphase multicomponent transport model for primary production and gas injection in shale, considering the dual-scale porosity and intricate fluid-solid interactions. The pore space in the shale matrix is divided into macropores and nanopores based on pore size distribution. We employ density functional theory (DFT) to account for fluid-solid interactions and to compute the inhomogeneous fluid density distribution and phase behavior within a dual-scale matrix. The calculated fluid thermodynamic properties and transmissibility values are then integrated into the multiphase multicomponent transport model grounded in Maxwell-Stefan theory to simulate primary oil production from and gas injection into organic-rich shales. Our findings highlight DFT's adeptness in detailing the complex fluid inhomogeneities within nanopores─a critical concept that a cubic equation of state does not capture. Fluids within pores are categorized into confined and bulk states, restricted by a threshold pore width of 30 nm. Different compositions of fluid mixtures are observed in macropores and nanopores: heavier hydrocarbon components preferentially accumulate in nanopores due to their strong fluid-solid interactions. We utilize the developed model to simulate hydrocarbon production from an organic-rich shale matrix as well as CO2 injection into the matrix. During primary hydrocarbon production, strong fluid-solid interactions in nanopores impede the mobility of heavy components in the near-wall region, leading to their confinement. Consequently, heavy components mostly remain within the nanopores in the shale matrix during primary hydrocarbon production. During the CO2 injection process, the injected CO2 alters fluid composition within macropores and nanopores, promoting fluid redistribution. Injected CO2 engages in competitive fluid-solid interactions against intermediate hydrocarbons, successfully displacing a considerable number of these hydrocarbons from the nanopores.

On the effect of deformation conditions on the metal flow behavior during upsetting process using finite element simulation DEFORM 3D software

AbstractThe study reports on the metal flow behaviour during upsetting or forging using the finite element method. Forging simulation studied the metal flow behaviour of a laboratory-sized specimen and a cylindrical engine connecting rod specimen of AISI 52100 high-chromium steel specified in the software database. The focus was to study the effect of deformation conditions (temperature and die velocity) on metal flow behaviour during forging. The simulation results showed heterogeneous metal flow behaviour during forging. Hence, this indicates that effective flow stress and flow strain, particle flow velocity, effective strain rate, damage and temperature distribution exhibited inhomogeneous deformation behaviour. As the temperature increased, the forging load decreased, thus a decrease in deformation resistance. The simulation of the engine connecting rod further confirmed inhomogeneous deformation during forging. Damage coefficient results show that the crack pin end had a higher damage probability during forging. This study clearly showed that finite element simulation can predict metal flow behaviour during the forging of AISI 52100 steel. The study output provides a basis for analysing and optimising most industrial metal forming processes using a numerical simulation approach. Hence, this method is effective in predicting flow behaviour.

Inhomogeneous deformation behavior and recrystallization mechanism of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar LPSO phase

Inhomogeneous plastic deformation and recrystallization behavior of Mg-Gd-Y-Zn-Zr alloy containing only intragranular lamellar long-period stacking ordered (LPSO) phase were investigated by isothermal compression experiments at the temperatures of 350–450 °C, and the strain rates of 0.001 ∼ 10 s−1. Results showed that Mg-Gd-Y-Zn-Zr alloys with varying degrees of bimodal structures were obtained after compression. The lamellar LPSO phase directions in residual coarse grains were aligned in the radial direction (RD). Dynamic recrystallization (DRX) grains induced at grain boundaries, kinked bands, and lamellar shearing regions during compression synergistically promoted coarse grain refinement. Moreover, the condition of high temperature and medium strain rate (450 °C-0.1 s−1) contributed to the uniform extension of "mantle layers" of fine DRX grains. In contrast, the condition of medium temperature and high strain rate (400 °C-10 s−1) could accelerate the deflection of CD-directed (compression direction) LPSO lamellae and the formation of local high-energy regions, facilitating the generation of recrystallization band. In addition, a high strain rate (400 °C-10 s−1) is more conducive to the formation of a heavily bimodal structure than a high temperature (450 °C-0.1 s−1). Only a larger spacing of LPSO lamellae (∼1.4 μm) could meet the spatial requirements of recrystallization. Further analysis revealed that the continuous dynamic recrystallization (CDRX) mechanism characterized by the expansion of "mantle layers" and nucleation along kinked boundaries and lamellar shearing regions was the primary grain refinement mechanism. The discontinuous dynamic recrystallization (DDRX) mechanism only exhibited a limited role due to the inhibition of the highly dense lamellar LPSO phase on grain boundaries bulging. After compression, the orientation of residual coarse grains gradually deviated toward the CD. While the recrystallization with limited proportion and random orientation cannot significantly weaken the basal texture.

Fully Consolidated Deposits from Oxide Dispersion Strengthened and Silicon Steel Powders via Friction Surfacing

Abstract The objective of this work is to study the ability of friction surfacing to deposit metal alloys that are difficult to process with traditional methods. Creep and neutron irradiation resistant oxide dispersion strengthened (ODS) materials cannot be produced via conventional casting route due to insolubility of the oxidic and metallic alloy constituents, causing unintended inhomogeneous oxide dispersion and material behavior. Increasing silicon content of Iron-Silicon (Fe-Si) improves electromagnetic properties but embrittles the material significantly and the fusion based manufacturing methods unable to process this steel. The solid-state nature of the friction surfacing process offers a potential alternative processing route to enable wider usage of difficult to process alloy systems. Both ODS and Fe-Si materials are available in powder forms. While the existing literature in friction surfacing focuses on depositing composites by incorporating small quantities powders through holes in consumable rod, this is a first study that shows a large charge of powder can be converted to a homogeneous fully consolidated deposit in friction surfacing. A novel methodology is used that incorporates the high portion of powder feedstock into hollow consumable friction surfacing rods (up to 35% volume fraction). It was found that fully consolidated deposits can be produced with powder feedstocks using proposed methodology. A recrystallized, homogeneous, equiaxed microstructure was observed in Fe-Si 6.8 wt% and a new generation FeAlOY ODS alloy deposits processed with hollow stainless-steel friction surfacing rods. Both powder and rod material plasticize and deposit without bulk intermixing.

Numerical Investigation of the Effect of Inhomogeneous Flow Behaviors inside a Particle Cluster in the OCM Reaction

Numerical Investigation of the Effect of Inhomogeneous Flow Behaviors inside a Particle Cluster in the OCM Reaction

Inhomogeneous Strain Behaviors of the High Strength Pipeline Girth Weld under Longitudinal Loading.

Unforeseen failures in girth welds present a significant challenge for the pipeline industry. This study utilizes 3D Digital Image Correlation (DIC) assisted cross-weld tensile testing to analyze the strain response of high-strength thick-walled pipelines, providing essential insights into the strain migration and fracture mechanisms specific to girth welds. The results reveal that the welding process significantly affects the mechanical distribution within the girth weld. The tested Shielded Metal Arc Welded (SMAW-ed) pipe exhibited undermatched girth welds due to high heat input, while Gas Metal Arc Welding (GMAW) introduced a narrower weld and Heat-Affected Zone (HAZ) with higher hardness than the base metal, indicative of overmatched girth welds. Strain migration, resulting from a combination of metallurgical heterogeneous materials and geometrical reinforcement strengthening, progressed from the softer HAZ to the base metal in the SMAW-ed sample with reinforcement, ultimately leading to fracture in the base metal. In contrast, the GMAW-ed sample shows no strain migration. Reinforcement significantly improves the tensile strength of girth welds and effectively prevents failure in the weld region. Sufficient reinforcement is crucial for minimizing the risk of failure in critical areas such as the weld metal and HAZ, particularly in SMAW-ed pipes.

Quantification of microscale factors for fatigue failure in NiTi shape memory alloys

Fatigue behavior is intrinsically linked to microstructural alterations induced by cyclic loading. However, the quantification of microstructural defects associated with fatigue damage of NiTi shape memory alloys (SMAs) is lacking, which hinders the development of a physically based fatigue criterion. To this end, a multi-scale experimental analysis was conducted on cyclically deformed NiTi SMAs, which evidenced a strong correlation between microstructural inhomogeneity and localized deformation behavior. The microstructural change associated with fatigue was quantified in terms of stored strain–energy, with the highest values observed in the regions where fatigue cracks initiate. Consequently, stored energy is deemed as an effective fatigue indicator, offering valuable insights for future work in the design and optimization of SMAs’ structures against fatigue.

Homogeneously Planar-Exposure LiB Fiber Skeleton Toward Long-Lifespan Practical Li Metal Pouch Cells.

LiB alloy is promising lithium (Li) metal anode material because the continuous internal LiB fiber skeleton can effectively suppress Li dendrites and structural pulverization. However, the unvalued surface states limit the practical application of LiB alloy anodes. Herein, the study examined the influence of the different exposure manners of the internal LiB fiber skeleton owing to the various surface states of the LiB alloy anode on electrochemical performance and targetedly proposed a scalable friction coating strategy to construct a lithiated fumed silica (LFS) functional layer with abundant electrochemically active sites on the surface of the LiB alloy anode. The LFS significantly suppresses the inhomogeneous interfacial electrochemical behavior of the LiB alloy anode and enables the exposure of the internal LiB fiber skeleton in a homogeneously planar manner (LFS-LiB). Thus, a 0.5Ah LFS-LiB||LiCoO2 (LCO) pouch cell exhibits a discharge capacity retention rate of 80% after 388 cycles. Moreover, a 6.15Ah LFS-LiB||S pouch cell with 409.3Whkg-1 exhibits a discharge capacity retention rate of 80% after 30 cycles. In conclusion, the study findings provide a new research perspective for Li alloy anodes.

Soft g-C3N4 phases in amorphous CNx coatings

Carbon-Nitride (CNx) coatings deposited using plasma-based physical and chemical vapor deposition led to the formation of g-C3N4 phase in crystalline and mainly amorphous forms respectively, Nanoindentation was performed on these coatings deposited on 304 SS (stainless steel) substrates. The positioning of the indentation i.e. inside the grain formed and at the boundary showed prolific features about the understanding of the extension of plastic volume and variations in interfacial fracture energies and the role played by ductile substrates in preventing damage to a component. The softer CVD-grown g-C3N4 phase, due to its larger grain size provides lubrication, wear resistance, and protection against chemical attack to the steel substrate underneath at the same time causing nanoindentation-induced strain hardening in it. The grain boundary regions as compared to grain center regions. were susceptible to failure due to their amorphous nature found in both PVD-grown g-C3N4 coatings. This inhomogeneous behavior is detrimental to the overall performance of the system as confirmed by the strain rate variations. A heat treatment post-deposition leading to crystallization and grain growth can improve the coating quality.

Terahertz-frequency oscillator driven by spin–orbit torque in NiF2/Pt bilayers

Exploration and manipulation of terahertz signal generators are crucial steps in the creation of numerous applications. Antiferromagnets can boost output signal frequency to the terahertz range. We propose a nanometer-scale generating device that produces terahertz signals by DC-exciting in a bilayer structure. The structure comprises a heavy metal layer (Pt) and a non-collinear antiferromagnetic layer (NiF2), where the magnetic moments in NiF2 with single-ion anisotropy are excited by the spin current from the Pt layer through spin–orbit torque. The inhomogeneous dynamic behaviors of the magnetic moments of NiF2 are calculated by the Landau–Lifshitz–Gilbert equation. It is found that terahertz-frequency AC can be reliably output from the bilayer structure, with the frequency that can reach to 1.82 terahertz. The oscillator shows the best performance when the polarized direction of the spin current is along the hard-axis of NiF2. The frequency and the amplitude of the AC can be adjusted by the current density, thickness and damping constant of the NiF2 layer. The threshold currents for exciting and maintaining the stable oscillation increase with the thickness and damping constant of the NiF2.

Simulation of Structure Inhomogeneity and Stress Behavior Generation in Titanium Alloys During Pulsed Electromechanical Treatment

Simulation of Structure Inhomogeneity and Stress Behavior Generation in Titanium Alloys During Pulsed Electromechanical Treatment

Regulating Li Nucleation and Growth Heterogeneities via Near-Surface Lithium-Ion Irrigation for Stable Anode-Less Lithium Metal Batteries.

The inhomogeneous nucleation and growth of Li dendrite combined with the spontaneous side reactions with the electrolytes dramatically challenge the stability and safety of Li metal anode (LMA). Despite tremendous endeavors, current success relies on the use of significant excess of Li to compensate the loss of active Li during cycling. Herein, a near-surface Li+ irrigation strategy is developed to regulate the inhomogeneous Li deposition behavior and suppress the consequent side reactions under limited Li excess condition. The conformal polypyrrole (PPy) coating layer on Cu surface via oxidative chemical vapor deposition technique can induce the migration of Li+ to the interregional space between PPy and Cu, creating a near-surface Li+-rich region to smooth diffusion of ion flux and uniform the deposition. Moreover, as evidenced by multiscale characterizations including synchrotron high-energy X-ray diffraction scanning, a robust N-rich solid-electrolyte interface (SEI) is formed on the PPy skeleton to effectively suppress the undesired SEI formation/dissolution process. Strikingly, stable Li metal cycling performance under a high areal capacity of 10mAhcm-2 at 2.0mAcm-2 with merely 0.5×Li excess is achieved. The findings not only resolve the long-standing poor LMA stability/safety issues, but also deepen the mechanism understanding of Li deposition process.

Inhomogeneous oxidation behaviors of FeCoNiTiCu high-entropy alloy nanoparticles confined within graphite shells

The oxidation of magnetic high-entropy alloy nanoparticles (HEA-NPs) is an inevitable process in service environments, which can induce unexpected properties and result in the failure of devices. Graphite shells coating is an effective approach to prevent the oxidation of nanoparticles, and the defects on graphite shells can also have a significant impact on the physical and chemical properties of nanoparticles. Thus, it is significant to uncover the oxidation process and understand the change of magnetic properties of HEA-NPs encapsulated in graphite shells (HEA@C-NPs). Herein, we demonstrate the microstructure evolution of HEA@C-NPs under different annealing temperatures. With the increase of annealing temperatures, the graphite shell is broken gradually and then oxygen atoms enter into the HEA core across the defects in graphite shell. An inhomogeneous partial-empty structure is observed at 300 ℃, which can result from the heterogeneous diffusion of different elements across graphite shell with ununiform defects. Accompanied with the formation of the oxide, the saturation magnetization decreases linearly and the exchange bias effect increases gradually. Our results give some understanding for the oxidation process and thus provide a guidance for designing HEA-NPs on complex service environments.

(Invited) Theoretical Analysis of Reaction Inhomogeneity and Lithium Plating Onset at Fast Charge Rates for Lithium Ion Batteries

Inhomogeneous reactions in porous anodes may lead to lithium plating at high C-rates. Inhomogeneous lithium intercalation behavior in cathodes and anodes has been studied on particle and macroscale (i.e., cell) length scales. The effects of various physical and electrochemical phenomena (e.g., ionic transport, mass transport, interface reaction kinetics, and electrode thermodynamic behavior) have been studied in the context of reaction inhomogeneity. However, an accurate theoretical understanding of how these accelerate lithium metal plating has not been established in fast charging applications. Here, analytical and numerical modeling is used to develop a more complete understanding of how these coupled, nonlinear electrochemical and physical effects interplay to cause lithium plating. Specifically, it is shown that simple analytical solutions (which are functions of one or several nondimensional numbers) can with surprising accuracy approximate the onset of lithium plating predicted by calibrated numerical models of graphite half-cells. These analytical and numerical results are compared against in situ experimental observations of lithium plating onset during fast charging. This work attempts to use simplified analytical analysis to clarify and unify findings in more complex numerical models, which can ultimately provide strategies for mitigating Li metal plating during fast charging. Application of this theory for design and optimization of electrodes with engineered architectures is discussed.

Synthetic Mueller Imaging Polarimetry

The transformation of the state of polarization of a light beam via its linear interaction with a material medium can be modeled through the Stokes–Mueller formalism. The Mueller matrix associated with a given interaction depends on many aspects of the measurement configuration. In particular, different Mueller matrices can be measured for a fixed material sample depending on the spectral profile of the light probe. For a given light probe and a given sample with inhomogeneous spatial behavior, the polarimetric descriptors of the point-to-point Mueller matrices can be mapped, leading to respective polarimetric images. The procedure can be repeated sequentially using light probes with different central frequencies. In addition, the point-to-point Mueller matrices, consecutively measured, can be combined synthetically through convex sums leading to respective new Mueller matrices, in general with increased polarimetric randomness, thus exhibiting specific values for the associated polarimetric descriptors, including the indices of polarimetric purity, and generating new polarimetric images which are different from those obtained from the original Mueller matrices. In this work, the fundamentals for such synthetic generation of additional polarimetric images are described, providing a new tool that enhances the exploitation of Mueller polarimetry.

Consolidation of multilayered soil with fractional derivative viscoelasticity due to surface loading and internal pumping

Classical Terzaghi’s solution provides a useful tool to predict the one-dimensional consolidation of homogeneous elastic soil layer with fully drained/undrained boundary condition under instantaneous loading. Due to the sedimentation process and complex internal structure, natural soils usually exhibit multilayered inhomogeneity and viscoelastic behavior. In practical cases, the drainage capacity of the boundaries can change with time. Thus, these practical factors should be well in considered for accurate prediction of the consolidation. This paper extends the classical Terzaghi’s solution to multilayered viscoelastic soil with continuous drainage boundaries and subjected to time dependent loading. The fractional derivative Kelvin-Voigt model is used to describe the viscoelasticity of soil. Two loading cases namely surface loading and internal pumping are considered. The consolidation problem is solved by Laplace transform technique and a transfer matrix formulation. Analytical solutions for excess pore water pressure, effective stress and settlement are given. The present solution is general and can reduce to existing solutions available in the literatures. Numerical studies are conducted to investigate the effects of viscoelastic parameters, boundary drainage capacity and loading rate on the consolidation behavior. It is shown that the multilayered soil system with large viscosity coefficient and small fractional order can consolidate fast. For the consolidation due to internal pumping, the drainage parameters have no influence on the consolidation process.

Behavioural responses to horizontal vibrations of quasi-2D ideal granular beds: an experimental approach

In this experimental study, granular bed response to horizontal vibrations of various frequencies and amplitudes are examined with high-speed imaging. Ideal granular beds consisting of spherical glass beads are horizontally vibrated in a quasi-two-dimensional arrangement, firstly with homogeneous granular media and then with a ternary mixture to explore how bed response deviates with changes to material composition. Phenomena of note are the tendency for the homogeneous material to subdivide into discrete areas of crystalline lattice structures, bounded by non-crystalline lines of bead contacts, labelled in this paper as ‘shear lines’. Shear line failure arises as neighbouring crystalline areas slide relative to one another along their shared non-crystalline border, combining to form one larger crystalline area. Under vibration conditions where particle agitation and relative movement is high, sloshing occurs in the upper bed and triangular granular-gas regions form in the top corners. The ternary mixture also exhibits sloshing at low frequency and large amplitude, but the inhomogeneity of its composition prevents formation of ordered crystalline regions and shear lines, instead promoting low percolation and a jamming effect underneath the sloshing region. Surprisingly strong convective responses are induced in the inhomogeneous bed with more energetic vibrations. From the analysis of shear lines in the homogeneous beds, and of convection in the inhomogeneous beds, comparisons between homogeneous and inhomogeneous bed behaviour are drawn. Results are used to discuss how behavioural response of non-cohesive granular material to horizontal vibrations is ultimately tied to, and changes with, the geometric complexity of the internal packing structure. The concept of ‘geometric compatibility’ between constituent particle species in an inhomogeneous granular medium is proposed as an explanation for the low percolation and strong convective response to vibration.Graphical abstract

A study on micro‐mechanical deformation behaviour of heat‐treated 20MnMoNi55 steel

AbstractSeveral heat treatment procedures are designed considering critical temperatures of phase transformation evaluated through dilatometric testing of 20MnMoNi55 steel to transform low carbon bainitic as‐received material into ferrite‐martensite dual‐phase steels consisting of varied martensite fractions. A thorough metallographic study correlated with the micro‐hardness of constituent phases ensures morphological characteristics along with its fractional variations in as‐received and dual‐phase steels. The impact of fractional variation in constituent phases on the uniaxial monotonic deformation characteristics of dual‐phase steels has been observed with a correlation study between experimental tensile and finite element simulated results. Therefore, a physical‐based model with a 2‐dimensional representative volume element has been established, addressing actual morphological characteristics obtained from metallographic studies. Moreover, the constitutive flow behaviours of ferrite and martensite are also derived from the dislocation‐based hardening model to address the actual deformation phenomenon. Finally, an inhomogeneous deformation behaviour among constituent phases and localization of plastic strain in ferrite matrix has been observed with von‐Mises stress, and equivalent plastic strain distribution through finite element simulated results. This phenomenon is again confirmed with kernel average misorientation mapping and geometrically necessary dislocation density evaluation through electron backscattered diffraction of tensile samples subjected to different degrees of plastic strain.