Variable Porosity Research Articles

Measurement of precision and quality characteristics of lattice structures in metal-based additive manufacturing using computer tomography analysis

Additive manufacturing, especially lattice structure fabrication, has garnered interest for its potential in high-precision aerospace and medical applications. Due to porosity and dimensional variation, obtaining mechanical characteristics and accuracy remains a research priority. This study addresses the current knowledge gap by providing a comprehensive methodology for the qualitative evaluation of cellular structures in additive manufacturing, focusing on the critical parameters of relative density, dimensional deviations, and porosity characteristics. The research utilizes advanced μCT analysis to investigate the impact of these factors on the overall quality and functionality of printed objects, particularly in metallic lattice structures fabricated using Laser Powder Bed Fusion (LPBF) technology. The cell structures were constructed using MS1 tool steel as the material base. An extensive investigation was carried out on a diverse array of lattice configurations, including Body-Centered Cubic (BCC), Diamond, Fluorite, Kelvin, Schwarz, and Fischer – Koch. It was observed that discrepancies between actual and designed relative densities in structures such as BCC, Diamond, and Kelvin indicate densification attributable to the manufacturing process, particularly in smaller cell structures. Furthermore, global porosity analysis demonstrated a clear relationship between increased density and reduced porosity. Optimal manufacturing conditions for minimizing defects and enhancing the precision and quality of additive manufactured metallic lattice structures were identified as a cell size of 3 mm and a 50 % relative density.

An Experimental Investigation of Interaction between CO2 Solution and Rock under Reservoir Conditions in the Jimsar Shale Oil Formation

Chemical sequestration is one important manner of CCUS. The injection of CO2 into an oil reservoir can not only sequestrate CO2 but also raise the oil recovery factor. The performance of chemical sequestration of CO2 depends on the interaction between CO2 solution and reservoir rock. In this paper, we have conducted three different scales of experiments, e.g., microscopic scale, core scale, and time scale, to fully investigate the interaction and resultant variation to mineral content, microscopic structure, porosity, and permeability under reservoir conditions (i.e., reservoir temperature of 90 °C) in Jimusar shale oil formation. The microscopic-scale experiment applied SEM and hyperspectral scanning to obtain microscopic pore throat structure and element distribution before and after soaking the rock in CO2 solution. The core-scale experiment employed XRD to evaluate mineral content variation caused by CO2 solution. Core flooding experiments were conducted to evaluate porosity and permeability variation caused by the dissolution of CO2 solution into the core samples. The third type of experiment was employed to investigate the effect of time sequence on the dissolution, in which the time ranged from 1 day to 14 days continuously. The experimental results indicate that, under Jimsar reservoir conditions, CO2 solution exhibits a relatively robust dissolution capability, causing significant alterations to the properties of the core samples. Specifically, the CO2 solution effectively dissolves carbonate upon contact. Calcite is the primary target for dissolution, followed by dolomite. In the presence of sufficient CO2, complete dissolution of all carbonates is achievable. On a microscopic scale, dissolution primarily occurs in the calcium-rich areas, leaving other regions unaffected. The typical pore size resulting from CO2 solution-induced dissolution ranges from several to dozens of micrometers. This dissolution process significantly enhances both porosity and permeability. For Jimsar shale core samples, porosity experienced an increase of over 20%, and permeability nearly doubled. Under Jimsar reservoir conditions at 90 °C, CO2 solution can consume all carbonates present in core samples within 8 days. The increase in porosity and permeability is rapid during the initial days and stabilizes around the 6th day. These research findings establish a theoretical foundation for CO2 chemical sequestration.

Enhanced heat flow assessment in Gulf of Hammamet and Pelagian Sea: Temperature corrections and conductivity adjustments

This study proposes new corrections of formation temperatures combined to correction of formation conductivities to reconstruct the heat flow map of the Gulf of Hammamet-Pelagian Sea, Eastern Tunisia. For that, a new linear Cross-Plot temperature correction approach, based on Bottom Hole Temperatures (BHT) and Drill Stem Temperatures (DST) of 63 drilled boreholes, was applied. In addition, and as temperature is transmitted from the substratum to the top of a stratigraphic column owing to the thermal conductivity, the latter was investigated according to a high appraisal of ±5 m and taking into account porosity variation with depth. The produced corrected thermal conductivity and geothermal gradient allowed to calculate the corrected heat flow in the Gulf of Hammamet – Pelagian Sea. Results show that the corrected geothermal gradient varies between 23 °C/Km and 58 °C/Km with a regional mean of about 39 °C/Km. The corrected heat flow rises from 49.5 to 119 mW/m2 with a regional mean of about 68 mW/m2. Variation of heat flow is dependent of the geodynamic evolution of the area where high heat flows follow folding structures and relatively low heat flows follow major trending faults. The major variations are E-W, N-S and NW-SE in direction following the major structural trends.

Hydromechanical simulation of a carbonate petroleum reservoir using pseudo-coupling

In the domain of petroleum reservoir management, numerical flow simulation stands as the primary tool for prediction and control. Traditionally, rock compressibility has been the key geomechanical parameter, often applied as a single, unchanging value across the entire reservoir model throughout the simulation. This study introduces a novel methodology that enhances reservoir simulation accuracy by incorporating rock mechanical behavior through a pseudo-coupling approach, without increasing computational costs. This approach empowers reservoir engineers to consider rock hydromechanical behavior in daily reservoir studies.The pseudo-coupling updates both porosity and permeability based on tables that correlate pore pressure to porosity and permeability multipliers, thereby replacing the conventional reliance on compressibility. It begins with reservoir-rock samples selection guided by lithological composition, followed by mechanical and hydromechanical laboratory tests, and numerical adjustments with ABAQUS stress analysis software. The resulting mechanical parameters serve for generating pseudo-coupling tables tailored to each facies.Validation experiments comparing pseudo-coupling simulations with conventional and fully coupled models reveal convergence in porosity and permeability variations with pore pressure between both coupled approaches. Extensive assessments further compare pseudo-coupling simulations against conventional reservoir simulations using a synthetic model based on a carbonate post-salt reservoir, denoted as Field B. The pseudo-coupling approach emerges as a more robust model capable of discerning preferential flow paths, all while maintaining computational efficiency. Moreover, these preferential flow paths were also predicted by the reservoir team responsible for the field development, but through a trial-and-error procedure to match production history, whilst the pseudo-coupling predicted it based on rock mechanical behavior.In this way, the proposed methodology enables an enhancement in the accuracy and efficiency of petroleum reservoir management by considering geomechanical effects, without incurring any additional computational costs when compared to conventional reservoir simulation.

Density structure of Kīlauea volcano: implications for magma storage and transport

SUMMARY A Bayesian linear regression to determine the bias in the Nafe–Drake relationship between compressional velocity and density provides an improved model for the density structure of Kīlauea volcano, Hawaiʻi. In previous work, we combined the results of seismic tomography with the Nafe–Drake relationship between compressional velocity and density to explain the large values of gravity disturbances overlying the summits and rift zones of the island's volcanoes. These results were used to determine mechanisms for gravitational instability of the island flanks. Here, we use laboratory measurements of the relationship of velocity and density for a wide range of Hawaiʻi island rocks as a prior in a Bayesian regression, with seismic tomography, to refine the 3-D density structure for Kīlauea volcano. This refined structure shows dense bodies (3220 kg m−3) between 5 and 8 km below sea level that underly regions of magma storage, found from geodetic and geophysical studies, beneath the summit and East Rift Zone of Kīlauea volcano. Above these bodies, density isosurfaces surround and cradle sources of pressure change determined from geodetic models, both at the summit and along the East Rift Zone. Continued subsidence of the summit following the 2018 eruption is aligned with a bowl-shaped density structure, formed primarily by density isosurfaces between 2800 and 2900 kg m−3 at 4–6 km depth. These surfaces underly the ∼3 km depth at which dyke injection initiates, are largely aseismic, and from their density values are inferred to contain high concentrations of olivine. Taken together, these density structures are consistent with an olivine-rich mush with variable porosity that increases in density with depth and provides a mechanism to form olivine cumulates both at the summit and along the rift zones. This structural framework for Kīlauea volcano is consistent with melt and mush transport occurring over a large range of depths to accommodate the growth and spreading of the volcano.

Electrical conductivity upon sintering of pure Cu produced by material extrusion additive manufacturing: Effects of pore, grain size, and impurity

This study investigates the development of pores and microstructures at each processing step and sintering conditions in the material extrusion additive manufacturing process, examining their correlation with related physical properties. This is achieved by fabricating copper parts using material extrusion (MEX) and examining the primary factors that impact the electrical characteristics of the MEX parts. Initially, the application of solvent debinding to MEX-produced Cu parts effectively removes a portion of the binder, forming printing-pattern–induced pores and ineffectual pore channels. Subsequently, thermal debinding eliminates the remaining binder and promotes neck formation between the Cu particles. The process proceeds to a subsequent sintering step, where even after the final sintering, some pores remain. These pores are categorized as sintering-induced and printing-pattern–induced pores. The relatively large pore size due to the printing pattern is identified as the main reason for reduced density of MEX parts, especially those influenced by the contour pattern. As the sintering progresses, the grain size increases, with the overall grain size and shape becoming uniform during extended sintering periods. Impurities, specifically carbon and oxygen, are detected in the sintered part, and their concentrations rise with longer sintering times. After examining the variation in porosity, grain size, and impurity content with respect to sintering time, it becomes evident that porosity plays a pivotal role in influencing electrical conductivity. Consequently, the densest 48 h sintered sample, with a relative density of 95.5 %, achieves the highest electrical conductivity at 94.6 % IACS. This demonstrates that MEX can be effectively employed to craft complex-shaped Cu parts with outstanding electrical properties. In summary, densification is crucial for enhancing the electrical properties of Cu parts produced through MEX, achieved by minimizing printing-pattern–induced pores, the primary contributor to density reduction. This study is poised to advance the manufacturing of high-performance, intricate Cu components by providing insights into the development and locations of primary pores through detailed microstructural investigations.

Study on the fabrication and performance of hierarchical porous 3D printed PCL-based artificial bone scaffold with anti-bacterial effect

Nonunion and large bone defects caused by trauma, tumor resection, and other bone diseases pose great challenges for clinical treatment. In this work, we fabricated a hierarchical porous scaffold mimicking the natural bone in structure and component. The inner MC/PCL/VCM (MCP-V) scaffold with pore sizes of 10–30 μm was prepared by vacuum freeze-drying, which has drug loading and mimics the bone component and structure. Then outer PT scaffold with pore sizes of 400–500 μm was prepared and a hole reserved for embedding the prepared MCP-V scaffold by 3D printing. The results showed that the compressive strength increased from 1.6 ± 0.01 MPa to 11.0 ± 0.38 MPa, and the compressive modulus increased from 1.1 ± 0.40 MPa to 12.4 ± 0.42 MPa, separately. As the variation of porosity for scaffolds, the cumulative drug release percentage decreased from (55.3 ± 1.43) % to (44.3 ± 2.47) % at 6 days. Furthermore, CCK-8 and the Live/Dead assay were utilized to assess the viability of MC3T3-E1 cells on scaffolds, which revealed no significant cytotoxicity. The hierarchical scaffold meets the mechanical requirement of cancellous bone, with slow drug release properties and excellent cytocompatibility, providing an effective repair strategy for clinical bone defects.

Sintering simulations for ceramic multilayer laminates with paper-derived ceramics: From sintering dilatometry to anisotropic sintering simulation

Alumina-based multilayer laminates with layers of varied porosities and ceramic fiber reinforcements, which can be achieved by including paper-derived ceramic layers, are interesting candidates for chemically stable and thermal shock resistant materials. In order to investigate the complex sintering behavior of these laminates, the sintering of each alumina layer contained within a laminate, each one with its individual sintering anisotropy and sintering shrinkage, has to be considered separately. For this purpose, sintering curves are determined by dilatometry measurements, serving a consecutive examination by an analytical model. Modeling parameters specific to each layer, are applied in finite-element-type sintering simulations for symmetrical multilayer laminates. Differences in the sintering shrinkages may cause internal stresses at layer interfaces and, in turn, may influence the thermal and mechanical properties of multilayer laminates after sintering. Accordingly, the prediction of developing internal stresses within alumina-based multilayer laminates by the presented sintering simulations is a key aspect of this study.

Mechanical behavior assessment of retaining wall structure due to frost heave of frozen ground

Frost heave action is a major issue in permafrost regions, leading to various geotechnical engineering problems. In this study, we assess the mechanical behavior of a concrete retaining wall subjected to frost heave under different ground conditions. The assessment utilizes ABAQUS integrated with several user subroutines. The numerical simulation model employs a thermo-mechanical coupled analysis with a porosity rate function, which enables to simulate time-dependent variations in porosity and frost heave of the backfill soil. After verification of the predictive reliability of the simulation model, the frost heave action in the soil and mechanical response of the retaining wall were evaluated regarding the initial groundwater level and presence of a drainage material on the backside of the retaining wall. According to the simulation results, as the initial groundwater level decreased in the backfill soil, the area susceptible to frost heave decreased. However, the von Mises stresses applied to the retaining wall increased. Under the same ground conditions, when the drainage material was installed on the backside of the retaining wall, the frost heave pressure acting on the wall significantly decreased, and less deformation and distortion of the retaining wall occurred.

Study of structure and properties of a new porous composite material obtained by direct laser deposition

The possibility of formation of porous materials for biomedical applications from VT6/Ta/Zr alloy by direct laser deposition has been shown. Varying the laser power allowed to obtain alloys with variable porosity. The modes providing formation of porous material with normal elasticity modulus corresponding to human bone were selected. It was found that the porosity value of 32% is achieved at the laser power of 50 W, which meets the requirements, for example, for dental prosthetics. In the process of direct laser deposition of materials in VT6/Ta/Zr alloys with variable porosity tantalum particles do not melt and act as crystallization centers. Such conditions ensure the formation of a highly dispersed metal structure consisting mainly of VT6 powders with evenly distributed Ta and Zr particles.

Mechanical properties of minerals in lunar and HED meteorites from nanoindentation testing: Implications for space mining

AbstractThis study analyzes the mechanical and elemental properties of lunar meteorites DHOFAR 1084, JAH 838, NWA 11444, and HED meteorite NWA 6013. Utilizing microscale rock mechanics experiments, that is, nanoindentation testing, this research reveals significant heterogeneity in both mechanical and elemental attributes across the mineral samples. Olivines, pyroxene, feldspar, and spinel demonstrate similar compositional and mechanical characteristics. Conversely, other silicate and oxide minerals display variations in their mechanical properties. Terrestrial olivines subjected to nanoindentation tests exhibit increased hardness and a higher Young's modulus than their lunar counterparts. A linear correlation is observed between the H/Er ratio and both plastic and elastic energies. Additionally, the alignment of mineral phases along a constant H/Er ratio suggests variations in local porosity. This study also highlights the need for further research focusing on porosity, phase insertions within the matrix, and structural orientations to refine our understanding of these mechanical characteristics. The findings have direct implications for in situ resource utilization strategies and future state‐of‐the‐art impact models. This comprehensive characterization serves as a foundational resource for future research efforts in space science and mining.

Influence of vortical structures on fibrin clot formation in cerebral aneurysms: A two-dimensional computational study

Thrombosis is an important contributor to cerebral aneurysm growth and progression. A number of sophisticated multiscale and multiphase in silico models have been developed with a view towards interventional planning. Many of these models are able to account for clotting outcomes, but do not provide detailed insight into the role of flow during clot development. In this study, we present idealised, two-dimensional in silico cerebral fibrin clot model based on computational fluid dynamics (CFD), biochemical modelling and variable porosity, permeability, and diffusivity. The model captures fibrin clot growth in cerebral aneurysms over a period at least 1000 s in five different geometries. The fibrin clot growth results were compared to an experiment presented in literature. The biochemistry was found to be more sensitive to mesh size compared to the haemodynamics, while larger timesteps overpredicted clot size in pulsatile flow. When variable diffusivity was used, the predicted clot size was 25.4% lesser than that with constant diffusivity. The predicted clot size in pulsatile flow was 14.6% greater than in plug flow. Different vortex modes were observed in plug and pulsatile flow; the latter presented smaller intermediate modes where the main vortex was smaller and less likely to disrupt the growing fibrin clot. Furthermore, smaller vortex modes were seen to support fibrin clot propagation across geometries. The model clearly demonstrates how the growing fibrin clot alters vortical structures within the aneurysm sac and how this changing flow, in turn, shapes the growing fibrin clot.

Thermal buckling in multi-directional porous plates: The effects of material grading and aspect ratio

In the present study, a trigonometric shear deformation plate theory was employed to perform a thermal buckling analysis of multi-directional functionally graded (FG) plates. During the manufacturing of the multi-directional graded plate, the formation of pores is abounded. Hence, the effect of porosity on the buckling performance was investigated by considering the variation of porosity in the plate for power law gradation variation of material properties. The adverse effect of porosity on the material properties was taken into account by employing the rule of mixture relation. Finite element results show that the thermal expansion coefficient is unaffected by the presence of porosity. For simply supported boundary conditions, the non-linear governing equations are solved for different thermal loads such as uniform, linear, and non-linear. A parametric study was performed in which the effect of grading parameters, aspect ratio, and side-to-thickness ratio under variable temperature change was studies. Critical material grading indices for multi-directional plates have been identified that help researchers and industry personnel in fabrication planning.

Petrophysical Property Prediction from Seismic Inversion Attributes Using Rock Physics and Machine Learning: Volve Field, North Sea

An accurate petrophysical model of the subsurface is essential for resource development and CO2 sequestration. We present a new workflow that provides a high-resolution estimate of petrophysical reservoir properties using seismic data with rock physics modeling and machine-learning techniques (i.e., deep learning neural networks). First, we compare the sequential prediction of the following petrophysical attributes: mineralogy, porosity, and fluid saturation, with the simultaneous prediction of all of the properties using the Volve field in the Norwegian North Sea as an example. The workflow shows that the sequential prediction produces a more efficient and accurate classification of petrophysical properties (the RMS error between the predicted and the original seismic trace is 50% smaller for the sequential compared to the simultaneous procedure). Next, the seismic amplitude response of the reservoirs was studied using rock physics modeling and amplitude versus offset (AVO) analysis to distinguish the different lithologies and fluid types. To ascertain the optimal hydrocarbon production areas, we performed Bayesian seismic inversion and applied machine learning to estimate the petrophysical properties. We examined how porosity, Vclay, and fluid variations affect the elastic properties. In Poisson’s ratio versus the P-wave impedance domain, a 10% porosity increase decreases the acoustic impedance (AI) by 30%, while a 20% Vclay decrease increases the AI by 12%. The Utsira Formation in the Volve field (5 km north of the Sleipner Øst field) was evaluated as a potential CO2 geological storage unit using Gassmann fluid substitution and seismic modeling. We look to assess the elastic property variation caused by CO2 saturation changes for monitoring purposes and simulate the effect. In the first 10% CO2 substitution, the P-wave velocity decrease is 12%, a subtle effect is observed for higher CO2 saturation values, and S-wave velocity (Vs) increases with CO2 saturation. Our analysis aspires to assist future reservoir studies and CO2 sequestration in similar fields.

Exploring the application of dual‐energyCTto discriminate sediment facies in a varved sequence

AbstractDual‐energy X‐ray computed tomography consists of imaging objects using two incident X‐ray beams of different energy to distinguish the different compounds within a sample based on their density (electron density,ρe) and elemental composition (effective atomic number,Zeff). The stoichiometric calibration for dual‐energy X‐ray computed tomography was already successfully implemented to identify single and homogeneous minerals easily and non‐destructively. It is here applied for the first time to a more complex and heterogeneous sample, a varved sediment core with three distinct facies. The output of dual‐energy X‐ray computed tomography was compared against elemental geochemistry obtained at the same resolution using a micro‐XRF core scanner. The three individual facies can be successfully differentiated using dual‐energy X‐ray computed tomography because their range ofρeandZeffvalues allow their discrimination. Correlations with elemental geochemistry are also discussed but are less conclusive, probably because of variations in grain size and porosity, and because these high resolution analyses were not performed at the exact same location. The paper not only eventually discusses the limitations when using dual‐energy X‐ray computed tomography on sediments but also demonstrates its potential to quantitatively study sediment cores in a non‐destructive way.

Effects of Thermal Radiation and Variable Porosity on Unsteady Magnetoconvective Heat-Mass Transport Past a Vertical Perforated Sheet

Effects of Thermal Radiation and Variable Porosity on Unsteady Magnetoconvective Heat-Mass Transport Past a Vertical Perforated Sheet

A novel method to design gradient porous structures with conformal density

This work introduces a rapid modeling method for gradient porous structures with conformal density, aiming to address the challenges of transitional variation of porosity, and control of complex gradient variations in multiple directions. In comparison to other methods, this approach overcomes the limitations associated with coordinate systems and shape functions when designing complex gradient variations in multiple directions while achieving density variation with shape under different gradients. The method involves mapping the volumetric distance field to a density field using control functions. By adhering to the constraints of the density field, it employs a weighted random sampling method to attain gradient sites with shape-adaptive distribution. Voronoi polyhedron are then constructed based on these sites, and smooth Voronoi struts are generated using strut distance fields and improved Boolean operations. The boundary adaptation of the porous structure is subsequently achieved based on the volumetric distance field. By establishing the relationship between density and volumetric distance field values, the study illustrates the similarity between density variation in the structure and gradient variations in the control function, indicating the controllability of density variation with shape. Furthermore, the method enables the integration design of structural shape and mechanical properties through adjustments to the number of sites, radius size of struts, and gradient control functions. Finally, the method was validated through numerical simulation and experiments, demonstrating its controllability and effectiveness in generating random porous structures with conformal density gradients, providing important theoretical and practical support for research and application in related fields.

Enhanced Catalytic Activity through the Variation of Hierarchical Porosity in a Zr-Based Metal–Organic Framework

Enhanced Catalytic Activity through the Variation of Hierarchical Porosity in a Zr-Based Metal–Organic Framework

Numerical simulations of flow inside a stone protection layer with a modified k-ω turbulence model

A numerical model is developed to investigate the flow in porous media, for the purposes of simulating scour protection around coastal and offshore structures. In the present model, the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations are solved, coupled with the volume-averaged k-ω turbulence closure. The volume-averaged k-ω equations are derived by taking the spatial average of the standard k-ω equations. The unknown coefficients caused by the averaging procedure are determined by large eddy simulation (LES). The developed model is validated against existing experimental results of flow in stone covers under both oscillatory and steady current conditions. A gradual transition of porosity towards unity at the interface between the porous media and the free flow is assumed in the simulation to fit the irregular interface in practical engineering. In the presence of parabolic porosity variation at the interface, the calculated velocity profile, bed shear stress, and turbulent fluctuations inside the porous medium are compared to measurements. The numerical results match well against the experimental data. Comparison with the volume-averaged k-ε turbulence model shows that the volume-averaged k-ω turbulence model provides more accurate flow behavior within the porous media.

Parametric study on hematite pellet direct reduction by hydrogen

This study investigates the intrinsic kinetics of hematite reduction to iron using hydrogen through the utilization of a computational fluid dynamics (CFD) coupled with a modified unreacted shrinking core model. The new mathematical model is developed to analyze the reduction process of a real pellet, taking into account the variation in porosity at different reaction rates. The impact of temperature, particle size, gas inlet velocity, and porosity on hydrogen-based direct reduction were investigated. The study reveals that size affects reduction degree at temperatures below 973 K, while it is independent of size at 1273 K. The optimal inlet velocity is 0.28 m∙s−1, and the time for complete reduction is over 3500 s and 800 s at 973 K and 1273 K, respectively. The numerical results align with experimental results. The study provides a solid foundation for dynamic modeling of reduction process but further work is needed for a realistic model.