Tortuous Path Research Articles

Microstructural features influencing the mechanical performance of the Brazil nut (Bertholletia excelsa) mesocarp

Brazil nut (Bertholletia excelsa) fruits are capable of resisting high mechanical forces when released from trees as tall as 50 m, as well as during animal dispersal by sharp-teethed rodents. Thick mesocarp plays a crucial part in seed protection. We investigated the role of microstructure and how sclereids, fibers, and voids affect nutshell performance using compression, tensile and fracture toughness tests. Fractured specimens were analyzed through scanning electron microscopy (SEM) and microtomography (microCT). Mesocarp showed high deformability (strain at max. stress of ~30%) under compression loading, a critical tensile strength of ~24.9 MPa, a Weibull modulus of ~3, and an elastic modulus of ~2 GPa in the tensile test. The fracture toughness, estimated through the work of fracture of SENB tests, reached ~2 kJ/m2. The thick and strong walls of mesocarp cells, with a weaker boundary between them (compound middle lamella), promote a tortuous intercellular crack path. Several toughening mechanisms, such as crack deflection, breaking of fiber bundles, fiber pullout and bridging as well as crack branching, occur depending on how fiber bundles and voids are oriented.

The New Taxing Right under Pillar One: Preliminary Thoughts on Potential Implications for MNEs

The OECD has made relevant progress towards reaching a consensus-based long-term solution to address the tax challenges arising from the digitalization of the economy and Pillar One is the last milestone of this tortuous path. In this article, the authors, without pretending to be exhaustive given the multitude of topics, wish to raise awareness among the international business community, illustrating some selected aspects deriving from Pillar One implementation that deserve further and deeper consideration in order to avoid triggering discontinuity to the current principles applied by MNEs to allocate income.

Effects of γʹ size and carbide distribution on fatigue crack growth mechanisms at 650 °C in an advanced Ni-based superalloy

Two distinct and different unimodal γʹ size distributions have been produced in a disc alloy RR1000 to understand the combined effects of γʹ size (linked to slip character), grain boundary (GB) precipitates/carbides and dwell time on fatigue crack growth (FCG) mechanisms at elevated temperature. The FCG behaviour has been investigated on single edge notched bend samples of both γʹ variants at 650 °C under trapezoidal waveform loading with dwell times of 1 s and 90 s at maximum load. The fine γʹ variant has better FCG resistance for both dwell times, and the difference in FCG rate becomes even more marked with longer dwell time. The coarse γʹ variant exhibits faster and more time dependent FCG behaviour, with more evident intergranular fracture modes and rougher fracture surface than the fine γʹ variant. Intergranular failure modes become dominant with the 90 s dwell time in both variants. A more continuous distribution of carbides is seen on the GB in the coarse γʹ variant, which is likely to influence oxidation behaviour on GB and intergranular fracture behaviour. The effects of dwell time and consequent oxidation damage at the crack tip on fatigue behaviour are further investigated by transitioning between cyclic and time dependent regimes to assess the damage zones formed. The results show that an oxidation damage zone contributes to enhanced FCG after switching frequency from cyclic to time dependent regimes while a tortuous crack path is related to crack wake (shielding due to prior crack path tortuosity), resulting in improved FCG resistance.

Study on the Properties of Epoxy Composites Using Fly Ash as an Additive in the Presence of Nanoclay: Mechanical Properties, Flame Retardants, and Dielectric Properties

Small and light fly ash is a by-product of thermal power plants, in which oxides mainly present in fly ash are suitable to reinforce composite materials. Its content accounts for 10, 20, 30, 40, and 50% of those materials. However, due to the smooth surface, it cannot stick completely in plastics. Therefore, in this work, it was studied to combine nanoclay additive (I.30 E) with 1, 3, and 5% by weight to synergize to improve mechanical strength, fire retardation, and electrical properties. Mechanical properties and flame retardant properties have improved markedly. At the combined ratio of 40% by weight of fly ash and 3% nanoclay, nanocomposites have tensile strength values of 64.12 MPa, flexural strength of 89.27 MPa, compressive strength of 215.23 MPa, and impact resistance of Izod 14.45 kJ/m2, oxygen index limited to 26.8% of fire retardant material. In terms of dielectric strength, the electric strength of pure epoxy is 17.5 kV/mm, higher than that before adding nanoclay (12.7 kV/mm). The presence of nanoclays in the material creates a tortuous electric path, slowing the propagation of the power plant, which is the main factor that improves the breaking strength of the nanocomposite.

Muddy interlayer forecasting and an equivalent upscaling method based on tortuous paths: A case study of Mackay River oil sand reservoirs in Canada

Abstract Based on the abundant core data of oil sands in the Mackay river in Canada, the termination frequency of muddy interlayers was counted to predict the extension range of interlayers using a queuing theory model, and then the quantitative relationship between the thickness and extension length of muddy interlayer was established. An equivalent upscaling method of geologic model based on tortuous paths under the effects of muddy interlayer has been proposed. Single muddy interlayers in each coarse grid are tracked and identified, and the average length, width and proportion of muddy interlayer in each coarse grid are determined by using the geological connectivity tracing algorithm. The average fluid flow length of tortuous path under the influence of muddy interlayer is calculated. Based on the Darcy formula, the formula calculating average permeability in the coarsened grid is deduced to work out the permeability of equivalent coarsened grid. The comparison of coarsening results of the oil sand reservoir of Mackay River with actual development indexes shows that the equivalent upscaling method of muddy interlayer by tortuous path calculation can reflect the blocking effect of muddy interlayer very well, and better reflect the effects of geological condition on production.

Customizable Heterogeneous Catalysts: Nonchanneled Advanced Monolithic Supports Manufactured by 3D-Printing for Improved Active Phase Coating Performance.

Three-dimensional (3D)-printed catalysts are being increasingly studied; however, most of these studies focus on the obtention of catalytically active monoliths, and thus traditional channeled monolithic catalysts are usually obtained and tested, losing sight of the advantages that 3D-printing could entail. This work goes one step further, and an advanced monolith with specifically designed geometry has been obtained, taking advantage of the versatility provided by 3D-printing. As a proof of concept, nonchanneled advanced monolithic (NCM) support, composed of several transversal discs containing deposits for active phase deposition and slits through which the gas circulates, was obtained and tested in the CO-PrOx reaction. The results evidenced that the NCM support showed superior catalytic performance compared to conventional channeled monoliths (CMs). The region of temperature in which the active phase can work under chemical control, and thus in a more efficient way, is increased by 31% in NCM compared to the powdered or the CM sample. Turbulence occurs inside the fluid path through the NCM, which enhances the mass transfer of reagents and products toward and from the active sites to the fluid bulk favoring the chemical reaction rate. The nonchanneled monolith also improved heat dispersion by the tortuous paths, reducing the local temperature at the active site. Thus, the way in which reactants and products are transported inside the monoliths plays a crucial role, and this is affected by the inner geometry of the monoliths.

Dispensing with Truthfulness: truth and liberty in Rorty’s thought

Abstract Rorty saw the course of philosophy in the twentieth century as an effort to part from two major philosophical trends, namely historicism and naturalism, only to inevitably return at the end of a tortuous path to these very same tendencies. If we can concede without major objections (although perhaps with many objections of detail) Rorty’s diagnosis of the trends in contemporary continental and analytical philosophy, which seem to reveal the exhaustion of modern philosophy, based as it has been on epistemology, we must, on the other hand, examine carefully the three main questions that this diagnosis leaves open: (1) How does Rorty reconcile continental idealist subjectivism with materialistic behaviorism? (2) Is it really inevitable that philosophy (and philosophers) blinded by Geist are unable to question prevalent beliefs? (3) Finally, is the acceptance of a liberalism that is not able to give reasons for itself the most effective and pragmatic liberalism? In answering these questions, it may not be possible to avoid a non-dogmatic, but pragmatic, metaphysics: a vocabulary of vocabularies that allows Rorty (and us) to speak of the problems of justice in Plato and Rawls, of the soul in Aristotle and Descartes, of the dystopias in Moro and Orwell. On pragmatic terms, perhaps a modest version of a metaphysic’s “vocabulary” turns out to be as legitimate and practical as any other vocabulary.

Effect of Polymer Amendment on Hydraulic Conductivity of Bentonite in Calcium Chloride Solutions

Hydraulic conductivity of polyanionic cellulose (PAC)–amended bentonite (PB) in calcium chloride (CaCl2) solutions was investigated to access its chemical compatibility in vertical cutoff walls application. PB was synthesized by mixing conventional bentonite (CB) powder with PAC (2% dry weight). The specific gravity (Gs), liquid limit (wL), pH, swell index (SI), and cation exchange capacity (CEC) of CB and PB were measured, and hydraulic conductivities and microstructures of the PB and CB filter cakes were evaluated by performing modified fluid loss (MFL) tests and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) analyses, respectively. The results showed that PB had higher wL, SI, and CEC but lower Gs and pH than CB; in particular, PB possessed higher SI in CaCl2 solution as compared to CB. Increase in the applied overall pressure and decrease in the CaCl2 concentration resulted in a decreased hydraulic conductivity for both PB and CB. However, the hydraulic conductivity of PB was found to be one to two orders of magnitude lower than that of CB when exposed to the same CaCl2 solutions, indicating superior chemical compatibility of PB. SEM-EDS image analyses demonstrated that polymer formed a three-dimensional net structure between bentonite particles, which could clog the intergranular pore space, resulting in a narrow and tortuous flow path for liquid and low hydraulic conductivity.

Impacts of Multilayer Hybrid Coating on PSF Hollow Fiber Membrane for Enhanced Gas Separation.

One of the most critical issues encountered by polymeric membranes for the gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off effect for CO2/CH4 and O2/N2 separation. In this study, multilayer coated PSF hollow fibers were fabricated by incorporating a graphene oxide (GO) nanosheet into the selective coating layer made of polyether block amide (Pebax). In order to prevent the penetration of Pebax coating solution into the membrane substrate, a gutter layer of polydimethylsiloxane (PDMS) was formed between the substrate and Pebax layer. The impacts of GO loadings (0.0–1.0 wt%) on the Pebax layer properties and the membrane performances were then investigated. XPS data clearly showed the existence of GO in the membrane selective layer, and the higher the amount of GO incorporated the greater the sp2 hybridization state of carbon detected. In terms of coating layer morphology, increasing the GO amount only affected the membrane surface roughness without altering the entire coating layer thickness. Our findings indicated that the addition of 0.8 wt% GO into the Pebax coating layer could produce the best performing multilayer coated membrane, showing 56.1% and 20.9% enhancements in the CO2/CH4 and O2/N2 gas pair selectivities, respectively, in comparison to the membrane without GO incorporation. The improvement is due to the increased tortuous path in the selective layer, which created a higher resistance to the larger gas molecules (CH4 and N2) compared to the smaller gas molecules (CO2 and O2). The best performing membrane also demonstrated a lower degree of plasticization and a very stable performance over the entire 50-h operation, recording CO2/CH4 and O2/N2 gas pair selectivities of 52.57 (CO2 permeance: 28.08 GPU) and 8.05 (O2 permeance: 5.32 GPU), respectively.

Analysis of Capillary Flow in a Parallel Microchannel-Based Wick Structure with Circular and Noncircular Geometries.

Capillary flow in porous media is of great significance to many different applications including microfluidics, chromatography, and passive thermal management. For example, heat pipe has been widely used in the thermal management of electronic system due to its high flexibility and low thermal resistance. However, the critical heat flux of heat pipe is often limited by the maximum capillary-driven liquid transport rate through the wicking material. A significant number of novel porous material with complex structures have been proposed in past studies to provide enhanced capillary-driven flow without substantial reduction in pore size and porosity. However, the increasing level of structural complexity often leads to a more tortuous flow path, which deprives the merits of enhanced capillarity. In this study, we examined the capillary performance of a porous material with simple geometric structures both analytically and numerically. Specifically, the capillary rate of rise of water in parallel hollow microchannels with different cross-sectional shapes is derived by solving the momentum transport equation. The relationships between the capillary flow rate and wicking height are further validated by two-phase flow simulation based on the conservative level-set method. The results demonstrate that parallel microchannel configuration, despite its geometric simplicity, provides superior capillary performance than most existing porous media in terms of both capillary flow rate and ultimate wicking height. In addition, design of noncircular cross section reduces the viscous drag and increases the packing density of the microchannels in the bulk solid without affecting the capillary pumping pressure. These features contribute to a further enhancement in the capillary performance by up to 32%. These results provide important guidance to the rational design of porous material with enhanced fluid transport property in a variety of microfluidic systems.

In-situ growth of boron nitride for the effect of layer-by-layer assembly modified magnesium hydroxide on flame retardancy, smoke suppression, toxicity and char formation in EVA

This work investigates the application of polyphosphazene (PZN) modified magnesium hydroxide (MH) crosslinked by boric acid (BA) (MH-PZPI-BA) for simultaneous flame retardant, smoke suppression and mechanical properties enhancement of ethylene-vinyl acetate (EVA) nanocomposites. The MH-PZPI-BA was prepared by a PZN nano-coating made from hexachlorocyclotriphosphazene and branched polyethyleneimine (bPEI) was deposited onto the MH followed by BA cross-linking bPEI. Then MH-PZPI-BA was incorporated into EVA, and the properties were examined. Compared with pure EVA, the peak heat release rate and total heat released decreased by 82.7% and 44.2%, respectively. The MH-PZPI-BA has an excellent performance in reducing the smoke, CO, and CO2 production rates. The "tortuous path" effect of the boron nitride of in-situ growth hindered the transfer of volatile products, and led to the formation of a compact and robust char layer in condensed phase during combustion, in the combustion process of EVA/MH-PZPI-BA. The tensile strength and elongation at break are improved by 26.1% and 33.5%, respectively.

Boron nitride self-assembly cladding structure promoting thermal property and dimensional stability of polymer composites

A common problem in thermal conductive materials is poor interface compatibility between fillers and the matrix, which has caused high interfacial thermal resistance and lower thermal conductivity than expected. In this work, highly reactive graphene oxide (GO) was introduced as a bridge to simplify the complex surface treatment between inactive boron nitride (BN) and inert polyolefin matrix. Through electrostatic self-assembly and rapid alkylation modification in aqueous solution, the BN coated by modified GO (BN@MGO) is acquired. After treatment, the surface concentration of C element has increased for an order of magnitude, which builds a strong interface interaction between fillers and polypropylene (PP). Later in-situ reduction improved phonon matching of hybrid fillers and furtherly reduced phonon interface scattering. The effects of structure and dispersion on performance were characterized. The thermal conductivity of PP/BN@RGO composites is 22.8 and 1.9 times higher than that of the raw PP and PP/BN, respectively. Modified Hashin-Shtrikman model demonstrates that PP/BN@RGO composites possess lower thermal resistance. Tortuous path effect and high thermal stability make the composites exhibit highly flame-retardant property. The thermal expansion coefficient of the material is also effectively reduced to 26.58 ppm/°C. The comprehensive features of PP/BN@RGO make it a promising material with broad potential in highly efficient heat dissipation electronic equipment, household appliances and thermal management field.

The Effect of Fracture Roughness on the Onset of Nonlinear Flow

AbstractIn fractures where surface fluctuations are large compared to their aperture (narrow fractures), the flow is forced to move in tortuous paths that produce additional viscous friction and are subject to inertia effects. We consider the relation between the magnitude of surface roughness and the onset of inertial effects in the pressure driving the flow through a single open fracture. We performed experiments systematically varying the average aperture of the open fracture and covering a wide range of Reynolds numbers. For each aperture, we analyze the data in terms of the Forchheimer equation and show that the critical Reynolds number, defined as the Reynolds number at which inertial effects contribute 10% of the total pressure losses, is highly correlated with the roughness of the surface. In particular, we show that significant inertial effects appear earlier as the relative importance of surface roughness increases. Finally, we present results showing that the magnitude of the deviations in the pressure field compared to a linear profile, taken at different points in the fracture along the flow direction, is directly related to the relative surface roughness of the fracture.

Groundwater Flow and Moisture Dynamics in the Swash Zone: Effects of Heterogeneous Hydraulic Conductivity and Capillarity

AbstractA density‐dependent, variably saturated groundwater flow and solute transport model was used to investigate the influence of swash motions on subsurface flow and moisture dynamics in beach aquifers with heterogeneous distributions of hydraulic conductivity (K) and capillarity. The numerical simulations were performed within a Monte Carlo framework using field measurements conducted in the swash zone of a sandy beach. Our results show that heterogeneous capillarity causes spatially variable capillary rise above the groundwater table. In response to swash motions, heterogeneity creates capillary barriers that result in pockets of elevated moisture content beneath the swash zone. These moisture hotspots persist within the unsaturated zone even at ebb tide when the swash motions recede seaward. Heterogeneous capillarity also results in highly tortuous preferential flow paths and alters the flow rates from the sand surface to the water table. Heterogeneous K greatly enhances the seawater infiltration into the swash zone and modulates its spatial distribution along the beach surface. Due to heterogeneous K and capillarity, complex mixing patterns emerge. Both strain‐dominated and vorticity‐dominated flow regions develop and dissipate as tides and waves move across the beach surface. Complex mixing patterns of seawater percolating from the swash zone surface to the water table, with localized areas of high and low mixing intensities, are further demonstrated by analysis of dilution index. Our findings reveal the influence of geologic heterogeneity on swash zone moisture and flow dynamics, which may have important implications for sediment transport and chemical processing in beach aquifers.

Balancing on a tightrope: Opinion 1/17 and the ECJ’s narrow and tortuous path for compatibility of the EU’s investment court system (ICS)

Like a tightrope walker, the Court is engaging in a delicate balancing act in its Opinion 1/17, seeking a path of compatibility of the ICS with the treaties that will allow it not to compromise its requirement of compliance with the Constitutional Charter of the European Union.With a benevolent interpretation of the provisions of the CETA and the acts accompanying its development, it stipulates the obligations that the EU institutions will have to fulfil to ensure the implementation of Chapter 8 Section F of the CETA, and its long-term compatibility with EU law. In doing so, it validates the European model of the investor-State dispute settlement mechanism, enabling it to be applied in other bilateral agreements and, eventually, on a multilateral basis.

Liquid Flow through Defective Layered Membranes: A Phenomenological Description

We present a realistic phenomenological description of liquid transport through defective, layered membranes. We derive general expressions based on conventional models of laminar flow and extend the formalism to accommodate slip flow. We consider different types of defects including in-layer vacancies that provide an activation-free tortuous path through the membrane. Of the many factors that affect flow, the most important is the radius of in-layer vacancy defects, which enters in the fourth power in expressions for the flux density. We apply our formalism to water transport through defective multilayer graphene oxide membranes and find that the flow remains in the laminar regime. Our results show that observed high water permeability in this system can be explained quantitatively by a sufficient density of in-layer pores that shorten the effective diffusion path.

Issue Information

Cover Photograph: (Top) An additively manufactured ceramic matrix composite part produced by 3D printing a pre‐ceramic polymer with embedded ceramic reinforcements and converting the polymer to a ceramic by pyrolysis. (Bottom) Particle reinforcements within the printed ceramic (A) increase the mode I fracture toughness, whereby the particles (C) create a more tortuous crack path as compared to (B) the glassy fracture surface of the unreinforced ceramic. Mark O'Masta credit. image

Role of microstructure in plastic deformation and crack propagation behaviour of an α/β titanium alloy

The deformation and crack propagation behaviour have been comparatively investigated in a titanium alloy with bimodal microstructure (BM) and bilamellar microstructure (BLM). The results show that higher fracture toughness (58 MPa m1/2) was obtained for the BLM than that BM one (45 MPa m1/2). The deformed microstructure, crack initiation and propagation and surface damage morphology were observed by SEM and EBSD. Fatal cracks easily nucleated at the larger primary α phase, especially at the equiaxed αe/β interface and primary α lath (αl), and often grow along a straight line, which accelerated the crack propagation and leaded to non tortuous crack path in BM. For the BLM, slip hardly transferred the αl/βtrans interface due to the secondary α(αs) precipitation in the β lamellas. Cracks initiated at the boundaries of α colony and propagated with a zig-zag way, which leaded to a high branch and fluctuation of the crack of BLM and generated a relatively superior fracture toughness performance. These results indicate that a small amount of αl colony surrounded with βtrans matrix is beneficial to the improvement of fracture toughness, which can provide a good theoretical support to tailor the microstructure and mechanical performance of titanium alloys.

Wettability alteration implications on pore-scale multiphase flow in porous media using the lattice Boltzmann method

Multiphase flow in porous media is found in a variety of engineering problems, including in technologies focused on satisfying the energy needs of an expanding global population while minimizing the effects of human activity on climate change. The objective of this study is to provide a better understanding of the importance and interdependence of the wettability-altered fraction, the degree of wettability alteration, and the spatially-varying contact angle assignment in influencing the pore-scale and macroscale flow properties. In order to conduct this investigation and analyze the effects on the relative permeability curves and fluid configurations, the Shan-Chen multi-relaxation-time multicomponent lattice Boltzmann model with explicit forcing is utilized, and domains of increasing fractions of wettability-altered pores are generated. We find that the fraction altered, the degree of alteration, and the accurate contact angle assignment are all correlated, and play a role to varying extents in influencing the flow behavior and the resulting relative permeability curves. The fraction altered displays the strongest effect, and the effects of the degree of alteration and contact angle assignment become more significant when a larger fraction of the sample has undergone wettability alteration. A sample that has undergone fractional wettability alteration results in a larger resistance to the overall flow and more tortuous flow paths, at intermediate saturations, in comparison to a strongly water/oil wetting domain. In a high porosity domain that is becoming increasingly oil-wet, the degree of wettability alteration has a more pronounced effect on the flow behavior of the oil phase, whereas the flow of the water phase remains dictated by the large pore spaces and the regions of the domain that have not undergone wettability alteration until a significant fraction of the domain has been altered. Moreover, a spatially-varying contact angle assignment becomes more important for a system with a large distribution of contact angles. The results demonstrate the correlations between wettability alteration and pore geometry and highlight the need for an algorithm that captures the true time-dependent wettability state of a porous medium sample.

Gas barrier properties evaluation for boron nitride nanosheets-polymer (polyethylene-terephthalate) composites

Hexagonal boron nitride nanosheets (BNNS) are dispersed in polyethylene-terephthalate (PET) via temperature-induced solution processing. The BNNS/PET composites are evaluated for carbon dioxide (CO2) and oxygen (O2) permeation reduction. The free-standing composite membranes have shown a maximum 96% permeation reduction at very minute filler loading (0.005 wt% BNNS) in comparison to the base polymer when subjected to an 8 h test run. Interestingly, BNNS loading beyond 0.005 wt% rendered complete permeation reduction. The inclusion of high aspect ratio BNNS, homogeneous dispersion inside PET and the wiggling effect around nanosheets per flake have increased the tortuous path for the gas flow. The experimental results have been verified through Bharadwaj’s, Neilson’s, Lape’s and Cussler’s models. The dispersion state is assessed via scanning electron microscope (SEM) while x-ray diffraction (XRD) has confirmed the formation of composites. Tensile testing results showed the enhanced mechanical robustness of BNNS/PET composites as a function of filler loading.