Cohesive Forces Research Articles

Interdependent evolution of deformation, fracture and recovering deposition during laser powder bed fusion

Common defects such as fracture and deformation seriously affect the quality of laser powder bed fusion (PBF) components. This work focuses on the understanding and the in situ monitoring of structural fracture and deformation during laser PBF. The transient interactive processes of normal deposition, fracture, severer warping deformation and recovering deposition during laser PBF are explored via a series representative cantilever structures. The interdependent evolutions of the critical factors are revealed via a novel model with validations of critical experimental results. The inherent strain and the cohesive force methods are integrated and the coupled stress-deformation-fracture processes can be computed by the model. It was found that the parts experienced different stages of the four interdependent processes of deposition, stresses, deformation, and fracture, depending on the structural features, input energy densities, and intermediate layer-wise processes. A typical phenomenon was discovered that components can exhibit a near-flat top surface but a curved bottom delaminated from the substrate, which implied the misleading monitoring information from the printing plane. The revealed mechanisms and visualized processes provide a useful guidance for the determination of the optimum time window for in situ monitoring which can judge the underneath fracture and deformations from the surface features.

Study on the mechanism of water-induced degradation of slip zone soils and FDEM coupled simulation of slopes based on multi-scale characteristic

The evolution of the mechanical properties of slip zone soils had a greater impact on the structure of soil slopes with large upper porosity and excellent infiltration conditions. Especially under the rainfall effect, it was easy to be affected by the infiltration effect of internal injury, which will lay a ‘hidden danger’ for the slope body to trigger sliding in the secondary transformation process. In this paper, based on Haijiao ping landslide in Guizhou, SEM image recognition techniques were used to reveal the water-induced degradation mechanism of the sliding zone soil from multiple scales and the damage parameters were obtained. Meanwhile, the FDEM numerical model was established to simulate the stability of the slope coupled with indoor TCT test results. The results proved that the angle of internal friction decreased linearly with the increase of water content on the macroscopic scale, but the cohesive force showed an increase and then a significant decrease. The effect of matrix suction in the microscopic scale was significant at lower water content, the internal cohesion formed a large number of agglomerate structures to resist external deformation, but the microstructure was loose and porous after sufficient water immersion. The pore space spreads directionally and the area increases by 2.66 times. The cross-scale discrete-finite element coupled simulation method based on image recognition can visually respond to the macroscopic mechanical properties and stability change response of the slope body caused by microscopic damage. The water-induced degradation effect of rainfall on slip zone soils was the inherent factors for the initiation deformation of landslide. The artificial excavation was the external factor that triggered the slope to slide. This type of landslide was more concealed in its natural state and prone to deformation when excavated after long-term rainfall.

Study of Fluidization Behavior Transition from Geldart B to A Induced by High Temperature Using Electrical Capacitance Tomography

The transition of the fluidization behavior of Geldart B particles to that of A particles induced by temperature change was investigated by a developed high-temperature electrical capacitance tomography (ECT) sensor. Silica particles with a Sauter mean diameter of 237 μm and density of 2650 kg/m3, typically Geldart B particles under ambient conditions, were fluidized in a column of 5.5 cm from 20 to 600 °C. With the increase in temperature, ECT measurements showed a decrease in minimum bubbling velocity (Umb), no bed expansion characteristic in the homogeneous fluidization regime, an absence of multiple-bubbles regime, and a larger bubble size. The pressure drop against superficial gas velocity curves at elevated temperatures confirmed homogeneous fluidization between the minimum fluidization velocity (Umf) and Umb. Our analysis demonstrates that cohesive interparticle forces, which increase linearly with temperature, are responsible for the fluidization behavior transition of the silica particles.

Investigation on microscopic forces between methane hydrate particles in gas phase dominated system

Hydrate aggregation and deposition on the pipe wall are the main causes of hydrate plugging in pipelines. Microscopic forces between hydrate particles are an important reference for determining the behavior of aggregation or separation from the pipe wall of hydrate particles. Based on a high-pressure visual micro-force measurement system, this study measured the hydrate particle-hydrate particle cohesive force and hydrate particle–wall liquid droplet adhesion force under pure water, as well as hydrate particle–wall liquid droplet adhesion force under anti-agglomerants (AAs). It was found that the magnitude of hydrate particle-hydrate particle cohesive force was ×10 mN/m, and the magnitude of hydrate particle–wall liquid droplet adhesion force was ×103 mN/m. The effects of 4 AAs in the methane gas-dominated system were evaluated from a micro-perspective, revealing that after adding DDBAB, D1021, AEO-9, and CDEA, the maximum reduction of adhesion force was 67%, 64%, 51%, and 53% compared with that under pure water, respectively. The mechanism of AAs reducing adhesion force was further explored, revealing that the adhesion force arose from a liquid bridge and was affected by the gas–water interfacial tension of solutions at low subcoolings. While at high subcoolings, the force was determined by the combined force of the liquid bridge and the hydrate shell. The addition of AAs reduced the gas–water interfacial tension of solutions, and the steric hindrance effect of AA molecules also weakened the tensile strength of the hydrate shell, leading to a decreased adhesion force. These experimental data can help deepen our understanding of the microscopic forces between methane hydrate particles, and provide experimental data and scheme design basis for wellbore flow assurance of deepwater gas wells.

Poroelastic problem of a non-penetrating crack with cohesive contact for fluid-driven fracture

A new class of unilaterally constrained problems for fully coupled poroelastic models stemming from hydraulic fracturing is introduced and studied with respect to its well-posedness. The poroelastic medium contains a fluid-driven crack, which is subjected to non-penetration conditions and cohesion forces between the crack faces. Existence of solution for the governing elliptic–parabolic variational inequality under the unilateral constraint with a small cohesion is established using the incremental approximation based on Rothe’s semi-discretization in time.

Sensitivity Analysis of Mechanical Parameters of Collapse Roof of Carbonate Rock Deep Buried Oilfield

Carbonate rock oilfields account for two-thirds of proven marine carbonate oilfield reserves, which are the primary way to increase future oil and gas energy reserves. Cave collapses occur during the process of oil reservoir development, seriously affecting oil production. In order to reveal the collapse failure mechanism of carbonate karst caves and predict whether the fracture cave type oil reservoir will collapse before drilling, a binary depth reduction method for determining the critical collapse depth of karst caves is proposed based on the Tahe fracture cave type oil reservoir. The sensitivity of karst cave collapses to multiple factors is analyzed, and a prediction formula for the critical collapse depth of karst caves with changes in the deformation modulus, the internal friction angle, and the cohesion is established through multiple regression analysis. By calculating and analyzing the numerical values of a large number of operating conditions under different mechanical parameters, the failure process, failure mode, and the change law of collapse depth during the Tahe oilfield destruction process were obtained. We used the established formula for predicting the collapse depth of karst caves to predict and analyze the actual distribution of karst caves in the Tahe oilfield. The calculation and analysis results showed that in the karst cave failure mode characterized by vertical shear failure, the cohesive force is the most sensitive factor affecting cave collapse, followed by the internal friction angle. The deformation modulus is hardly sensitive to the influence of the karst collapse. Through the geomechanical model test, the result verified the accuracy and reliability of the calculation results. The research results will provide necessary theoretical support for the large-scale safe extraction of deep petroleum resources, increase oil production in China, and have important theoretical significance and engineering application value.

Finite Element Method of the Influence Evaluation of the Percentage of Fine Particles of Marine Clay at the Different Depth Variations to the Total Volumetric Strain of the Soft Clay Ground

Finite element method of the influence evaluation of the percentage of fine particles of marine clay at the different depth variations to the total volumetric strain of the soft clay ground is determined by the Viet Nam standard TCVN 4196:2012; TCVN 4102:2012; TCVN 4197:2012; TCVN 4199:2012. Results show clearly the percentage of the fine clay particle and the total volumetric strain (ε) with depths. The minimum value of 12% and 0.00002617 at 19.3m depth; whereas the maximum value of 38% and 0.00002609 at 25.3m depth. Moreover, a consideration of the relationship between Internal friction angle, Cohesive force, Water content, Saturation, Porosity, Viscosity, and Plasticity index with depths. Results show remarkably the increasing of the depths as the variations of the percentage of fine particles of marine clay and cohesive force, viscosity, water content, and porosity; compared with the decrease of the plasticity and internal friction angle. It is easy to conclude that the total volumetric strain of the soft clay ground is a stable and safe state to use and design the building, construction, and reference of engineers, geologists, scientists, and so on in the future.

Semi-analytical solution for interfacial debonding of high-speed railway ballastless track under thermal loading using a quasi-dynamic method

Interfacial debonding of multi-layered ballastless track systems has proved to be one of the most common diseases in the high-speed railway during long-term operations. This paper focuses on the theoretical modeling of track temperature field and consequent bond-slip behavior between track layers under thermal loading. By establishing heat conduction differential equations, whose boundary conditions are combined with complicated geographical and meteorological factors, the temperature field of a multi-layered track structure is obtained via the integral transform technique. The reliability of the heat conduction model is well-validated by an on-site experiment in a high-speed railway line. Then, we originally extend an explicit integration algorithm for dynamics analysis to solve nonlinear statics problems with small deformation by proposing a quasi-dynamic method (QDM). Equilibrium equations of a track slab subjected to quasi-dynamic equivalent thermal loads and mixed-mode interfacial cohesive forces are constructed based on the Mindlin plate in-plane and flexural vibration equations. The application of the QDM to solve interface responses is verified by comparing results obtained from finite element (FE) software. Finally, numerical discussions are conducted to reveal the nonlinear distribution characteristics of temperature field, evolution process of the interface damage and failure modes under time-varying thermal loads, which provide a better understanding of the interfacial debonding phenomenon encountered in ballastless track systems.

Molecular origins of nonideality in surface properties of Surfactant-Ionic liquid mixed monolayers

Experimental surface pressure − area (π–A) isotherms revealed partial miscibility between the cationic surfactant dioctadecyldimethylammonium bromide, DODAB, and the ionic liquid trihexyl(tetradecyl)phosphonium dicyanamide, [P66614][N(CN)2]. To address the origins of this nonideal behavior, the interaction of 3:1 mixture of DODAB and [P66614][N(CN)2] was studied at the water-vacuum interface at different pressure − area regimes using molecular dynamics simulations. At low pressure regime there is indication of the existence of surfactant-rich and IL-rich regions at the water surface. Further compression results in increment of the vertical distance between cation headgroups and a mismatch between tilt angles of the octadecyl chains of [DODA]+ and [P66614]+. The cohesion forces between neighboring hydrocarbon chains of the surfactant displaces the ionic liquid out from the contact with water surface, inducing phase separation. On the other hand, the anion exchange between the bulk water subphase and the interface with vacuum closely follows the ideal behavior, indicating no preferential interaction of bromide or dicyanamide anions with cation headgroups. Also, the surface tensions of the pure and mixed-composition monolayers were successfully evaluated from the density profiles by a group contribution method.

The Bearing Characteristics of Sand Anchors under Vibrating Load

In particular environments, such as the Gobi Desert, the problems encountered in a project are complex, resulting in reduced stability of the anchoring system and multiple forms of failure. This paper takes the factors influencing the stability of sand anchors under vibration loads as the research background. Theoretical analysis and indoor model tests were used to study the load-bearing performance of sand anchors under vibration loads; in addition, a comparative analysis of this performance along with failure forms of sand anchor systems, various sand soil moisture contents, and vibration parameters was performed. The results of the study showed that as the water content becomes higher, the cohesive force of the sand decreases and produces a higher displacement in the water content, with most of the anchor solids becoming prone to fatigue failure. When the water content and vibration frequency remain stable and the vibration amplitude increases, the anchor rod is disturbed after the ultimate pullout bearing capacity forms a decreasing trend, with a decline rate of approximately 40%. By keeping the water content and vibration amplitude stable and changing the vibration frequency, the ultimate pullout capacity of the anchor does not change significantly, and the frequency reaches a certain level when it attains a compacting effect on the surrounding soil and thus has less influence on the anchor. The anchor pullout resistance bearing is most sensitive to the change in sand moisture content, more sensitive to the vibration amplitude, and less sensitive to the vibration frequency, but its correlation is not significant.

A coupled bio-chemo-hydro-wave model and multi-stages for MICP in the seabed

As an environmentally friendly technology, the microbially induced calcite precipitation (MICP) has been gradually applied for the seabed reinforcement. However, there are few models for the simulation of the MICP process in marine environment. A coupled bio-chemo-hydro-wave model for MICP in the seabed was proposed in this paper. This model can capture the bacterial behaviour (growth, decay, attachment, diffusion), the evolutions of chemical substances (urea, calcium, ammonium, calcium carbonate), and the variations of porosity and permeability. It is indicated that (1) distributions of the bacteria and chemical substances show obvious heterogeneity, and are related to the injection rate and injection time; (2) The calcium carbonate content, porosity, and permeability are significantly affected by the initial bacterial concentration, injection rate, injection time and cementing solution concentration. The reduction ratios of porosity and permeability show significant linear increasing trend with the increase of calcium carbonate content; (3) Although MICP process increases the vertical excess pore pressure gradient in the shallow seabed, the seabed can remain stable under the large waves due to the increasing of soil weight and inner cohesive force.

Using Different Surface Energy Models to Assess the Interactions between Antiviral Coating Films and phi6 Model Virus.

High molecular weight chitosan (HMWCh), quaternised cellulose nanofibrils (qCNF), and their mixture showed antiviral potential in liquid phase, while this effect decreased when applied to facial masks, as studied in our recent work. To gain more insight into material antiviral activity, spin-coated thin films were prepared from each suspension (HMWCh, qCNF) and their mixture with a 1:1 ratio. To understand their mechanism of action, the interactions between these model films with various polar and nonpolar liquids and bacteriophage phi6 (in liquid phase) as a viral surrogate were studied. Surface free energy (SFE) estimates were used as a tool to evaluate the potential adhesion of different polar liquid phases to these films by contact angle measurements (CA) using the sessile drop method. The Fowkes, Owens-Wendt-Rabel-Kealble (OWRK), Wu, and van Oss-Chaudhury-Good (vOGC) mathematical models were used to estimate surface free energy and its polar and dispersive contributions, as well as the Lewis acid and Lewis base contributions. In addition, the surface tension SFT of liquids was also determined. The adhesion and cohesion forces in wetting processes were also observed. The estimated SFE of spin-coated films varied between mathematical models (26-31 mJ/m2) depending on the polarity of the solvents tested, but the correlation between models clearly indicated a significant dominance of the dispersion components that hinder wettability. The poor wettability was also supported by the fact that the cohesive forces in the liquid phase were stronger than the adhesion to the contact surface. In addition, the dispersive (hydrophobic) component dominated in the phi6 dispersion, and since this was also the case in the spin-coated films, it can be assumed that weak physical van der Waals forces (dispersion forces) and hydrophobic interactions occurred between phi6 and the polysaccharide films, resulting in the virus not being in sufficient contact with the tested material during antiviral testing of the material to be inactivated by the active coatings of the polysaccharides used. Regarding the contact killing mechanism, this is a disadvantage that can be overcome by changing the previous material surface (activation). In this way, HMWCh, qCNF, and their mixture can attach to the material surface with better adhesion, thickness, and different shape and orientation, resulting in a more dominant polar fraction of SFE and thus enabling the interactions within the polar part of phi6 dispersion.

A multiphase model developed for mesoscopic heat and mass transfer in thawing frozen soil based on lattice Boltzmann method

Subgrade engineering in cold region collapsed and settled under the influence of global warming, this was mainly due to the thawing frozen soil. The heat and mass transfers in thawing frozen soils are generally described with continuity equations on the macroscopic scale. However, the processes of ice melting and water migration in soil were rarely described on the mesoscopic scale. In this study, a multiphase pseudo-potential model with enthalpy-based module was developed based on lattice Boltzmann method to predict the distributions of temperature and water content in the thawing process of frozen soil. The force source terms in pseudo-potential model were given as adhesive force, cohesive force, temperature drive force and bulk force to describe the interaction between multiple components in thawing process, and the enthalpy-based module was employed to realize the process of phase transition in soil. The complex initial conditions of thawing process were measured and then set in simulation for the first time. The results showed that as compared with the measured soil temperatures and water contents at different top soil temperature (5 °C and 10 °C) and times (0, 12, and 36 h), the relative errors of model were 0.01 % ∼ 0.72 % and 0.10 % ∼ 19.31 % for the soil temperatures and water contents, respectively. Further, the developed pseudo-potential model can also be used to detail the mesoscopic heat and mass transfers in thawing soils.

The role of porosity in the dynamic disturbance resistance of water-saturated coal

Porosity significantly affects the dynamic response of water-saturated coal and the safety of coal mine engineering in water-rich areas. For mastering the dynamic response of water-saturated coal to the porosity, this study used the coal with four levels of the porosity for dynamic tests. In this process, the dynamic compressive tests were operated on these coal specimen in both of water saturation and dry states, and the reduction factor of dynamic mechanical parameters of the coal in water-saturated state to these in dry state were focused to eliminate the effect of self dynamic properties of the coal. The results indicate that the dynamic mechanical properties non-linear positively correlate with the porosity, and its sensitivity to porosity gradually weakens as with the increase of the porosity. This effect is intuitively expressed in the dominant fracture propagation features recorded by a high-speed camera, and microscopically attributed by the size and number of microfractures around the dominant fracture. The dynamic stress intensity factor model of the dominant fracture was further established with consideration of total cohesive force for the equivalent particle on the fracture surface. It well reveals the effect mechanism of porosity on the meso-deterioration and macroscopic mechanical properties of the coal around the roadway. On this basis, the applicable conditions and suggested methods were put forward to improve the dynamic stability of water-saturated coal with various porosity.

CFD-DEM investigation on the agglomeration behavior of micron-sized combusted iron fines

The occurrence of agglomeration due to particle sintering is one of the most significant technical issues hindering the direct reduction process of iron oxide fines (DRI) in a high-temperature fluidized bed. To get a better understanding of the agglomeration mechanism, the (de-)fluidization behavior of micron-sized iron oxide particles in a 3-D fluidized bed is investigated using Computational Fluid Dynamics coupled with a coarse-grained Discrete Element Method (CFD-cgDEM). The inter-particle cohesive force is considered as a temperature-dependent solid bridge force. The coarse-grained method is first verified by comparing results for different scaling factors. Subsequently, the effects of temperature on the bed pressure drop, void fraction distribution, particle velocity distribution, and agglomerate size are investigated. In conclusion, the developed model shows the capacity for reliable prediction of particle agglomeration behavior, which can shed light on the design of the DRI process in high-temperature fluidized beds.

Abstract 1346: Phagocytosis of solid tumors favors macrophage clusters and cooperativity in tumor elimination

Abstract Macrophages are abundant in many solid tumors and are potential effector cells for monoclonal antibody-based immunotherapies because they can in principle phagocytose IgG-opsonized cancer cells. However, it remains unknown whether phagocytic macrophages can overcome the cohesive forces between cancer cells in solid tumors. We show that maximum phagocytosis of B16 melanoma tumors and ‘tumoroids’ requires IgG-opsonization and very deep suppression of the macrophage checkpoint ligand CD47. Under these conditions, phagocytic macrophages cluster or ‘phase separate’, and the elimination exhibits clear cooperativity with respect to macrophage number and phagocytic activity. In vitro disruption of phagocytic clusters specifically implicates Mg2+ and macrophage integrins. Cytokine treatments and other inhibitors further implicate roles for integrins and phagocytic surface receptors. Although tumor-associated macrophages correlate with negative prognoses in many cancers, our findings are among the first to reveal advantages of high macrophage numbers, macrophage clusters, and resulting cooperative effects when combined with opsonizing antibodies and CD47 disruption. Lastly, the challenging B16 tumors are durably eliminated by the approach and induce de novo IgG's that also drive anti-cancer phagocytosis. Citation Format: Dennis E. Discher. Phagocytosis of solid tumors favors macrophage clusters and cooperativity in tumor elimination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1346.

Base lubricants for green stamping: The effects of their structure and viscosity on tribological performance

The requirements for green and sustainable manufacturing mean that stamping lubricants must be continuously re-evaluated and re-designed. In this investigation, the tribological performance of four base oils with different chemical structures (paraffinic and naphthenic) and viscosities (2 and 20 cSt), as well as water, was evaluated for the stamping of steel sheets and compared with a non-lubricated contact. Most lubricants reduce the coefficient of friction and maintain a similar wear coefficient for steel sheets as in dry contacts. Low-viscosity (LV) naphthenic oil performs very like both high-viscosity (HV) oils. A surprising exception is the LV paraffinic oil, with several-times-higher friction and wear compared to dry contact. This is due to the excellent wetting-spreading and very low cohesion forces that enable oil to escape from extremely thin-film contacts because the viscosity is so low, leading to lubricant starvation. In contrast, HV oils provide a sufficiently thick lubricating film, while strong cohesive forces help in the film’s strength, lessening wear, and reducing friction. In thin-film lubrication with LV oils, such as when stamping, it is thus extremely important that the lubricant’s wetting behaviour and viscosity are sufficient to provide enough film in the contact and prevent starvation, thus ensuring lower friction, less wear, and a longer lifetime of the contact.

Elastic–plastic constitutive model of the milled mixture of sugarcane based on phase transition state

AbstractExtracting juice from sugarcane is a complex and nonlinear process. It is very important to comprehend mechanical properties and constitutive model of the milled mixture of sugarcane for understanding sugarcane crushing process. In this paper, mechanical properties of the milled mixture were investigated by uniaxial compression tests, repeated loading tests and direct shear tests. The elastic–plastic constitutive model was established by using isotropic elastic materials and Modified Cam‐Clay model based on phase transition state. Both Poisson's ratio and Young's modulus of the milled mixture were proportional to the loading stress; the compression index and swelling index are 2.23 and 0.10, respectively; and the cohesive force and friction angle are 25.25 kPa and 21.63°, respectively. At last, the proposed constitutive model was verified by uniaxial compression tests. This paper can provide a theoretical basis for the study of mechanism and simulation of sugarcane crushing processes, and is of guidance for the improvement of sugar production process and equipment.Practical applicationsIn this article, the prepared cane and bagasse are collectively called the milled mixture of sugarcane, which includes solid fiber, juice, and air. The interaction of three components of milled mixture can lead to difficulties in extracting juice, an increase in processing energy consumption and other undesirable conditions. In this paper, the mechanical properties and constitutive model of milled mixture of sugarcane are studied. This research can provide a new method for the simulation of sugarcane milling process, and has enlightening significance for the optimization of crushing equipment and technological parameters to improve juice extraction efficiency.

Effects of interface agent and cooling methods on the interfacial bonding performance of engineered cementitious composites (ECC) and existing concrete exposed to high temperature

The interfacial bonding performance between engineered cementitious composites (ECC) and concrete exposed to high temperature was investigated in this paper, and the effects of the exposure temperature, cooling methods and interface agent on the interfacial bonding performance were considered. The crystal morphology of the interface was observed by SEM. The pore structure near the interface was analysed by X-CT. The relationship between the ECC residual bonding area (ERBA) on the failure surface and the splitting tensile strength of the repair systems was investigated. The results showed that the interfacial bonding strength decreases with increasing temperature. High temperature will not only reduce the compressive strength of sample, but also increase the porosity of ECC at the interface area. Although water cooling reduces the compressive strength of the substrate, the rehydration products sometimes fill the cracks and increases the chemical cohesive force between the cover and the substrate and thus enhances the interfacial bonding properties. The effect of interface agent is influenced by the damage degree of substrates, interface agent may improve the interfacial bonding strength of substrates with high damage degree and reduces that with less damage degree. The change trend of the splitting tensile strength and ERBA is consistent with increasing temperature, and they are approximately positively correlated.

High mobility of asteroid particles revealed by measured cohesive force of meteorite fragments.

The cohesive force of asteroid particles is a crucial parameter in microgravity. The cohesive force was evaluated under the assumptions of lunar regolith and proportionality to particle size; however, it is sensitive to particle shape. In this study, cohesive-force measurements of meteorite fragments and aggregates consisting of silica microspheres revealed that the cohesive force is independent of the sizes of the fragments and aggregates as well as of the fragment preparation methods. The cohesive forces of the asteroid particles were found to be orders of magnitude smaller than previously predicted, explaining the high mobility of asteroid surface particles identified by space exploration.