Interfacial Cohesion Research Articles

A practical fracability evaluation for tight sandstone reservoir with natural interface

Hydraulic fracturing has been widely applied to enhance the conductivity in tight sandstone reservoirs, i.e. reservoirs with low porosity and permeability. The interaction between a hydraulic fracture (HF) and a natural fracture (NF), including crossing, arresting and opening (tensile or dilation), are crucial for controlling the fracability of a reservoir. Previous studies have elucidated that shear dilation is the main mechanism for enhancing the permeability of an unconventional reservoir. Moreover, the brittleness index (BI) is considered another critical parameter that controls the fracability of candidates. However, the fracability of candidates with respect to both shear dilation and BI have not been fully investigated. We performed a practical fracability evaluation by integrating the shear dilation mechanism and BI quantification. We obtained the mechanical parameters from mechanical tests conducted on synthetic tight sandstone samples, and we manufactured specimens with different friction coefficients and shear strengths. Next, we performed scaled hydraulic fracturing experiments on 15 identical 10 cm cubic samples using a true tri-axial stress cell, and the interaction mechanisms between HFs and NFs were investigated. We also evaluated the brittleness of each specimen based on a previous BI model and our own novel BI model. We found that a weak interface cohesion with an interaction (between HF and NF) angle of 60° exhibited a shear dilation (or reactivation) mechanism and a higher BI. We thus conclude that such conditions are more favourable for reservoir stimulation (i.e. hydraulic fracturing) in the field.

Effect of nano silica addition on enhancing the performance of cement composites reinforced with nano cellulose fibers

The utilization of cellulose nano fibers (NCell) as reinforcement to cement composites may account for enhancing particle packing and decreasing the crack growth at the nano level. Besides that, their high specific surface area can improve the bond between the cement hydration products. nano silica particles can also influence the performance of fiber reinforced cement composites through increasing the calcium-silicate-hydrate gel content, as well as enhancing the fiber to matrix interface cohesion. The aim of this investigation is to evaluate the effects of different contents of nano silica particles (0, 1, 1.5, and 2% by weight of cement) on the mechanical properties, and microstructure of cement composites reinforced with various contents of nano cellulose fibers (0, 0.35, 0.55, and 0.75% by weight of cement). The results out of studying such nano systems revealed that the addition of the NCell particles separately, helped in improving the tensile strength by about twice the value of the control mix when appropriate content of NCell was incorporated (0.35%). Moreover, the microstructural analyses demonstrated the effectiveness of nano silica particles to modify the transition zone between the nano cellulose fiber and the cementitious matrix and subsequently allowing greater reinforcement efficiency especially when external compression or tensile forces were transferred to the composite.

Damage destruction evolution law of high-speed railway CRTS II slab ballastless track interface under train braking and temperature load

The train braking and temperature load are simplified as shear loads and based on the cohesive stress constitutive model and test parameters, an interfacial nonlinear finite element model for the cohesion-displacement relationship of high-speed railway CRTS II slab ballastless track interface was established and verified by theoretical analysis. Damage destruction evolution law of the interface under shear loads, and the influence of shear steels on the interfacial longitudinal maximum cohesion and ultimate yield displacement are studied. Results indicates that the error between axial force difference of track slab and the interfacial constraint reaction is no more than 2%, which verified the correctness of the interfacial nonlinear finite element model; the longitudinal displacement of track slab increases with the increase of shear loads, and it decreases as the distance from the loading end increases; the interfacial longitudinal cohesion can fluctuate up and down at a certain value with the increase of longitudinal displacement, and then the interface gradually loses cohesion until it is completely destroyed and enters the sliding state. The three shear steels layout forms are all made the interfacial longitudinal maximum cohesion and ultimate yield displacement increase, the contributions of interfacial longitudinal maximum cohesion are 21.46%, 23.54% and 53.03%, respectively, and the contributions of ultimate yield displacement are 9.72%, 15.61% and 44.92%, respectively. Shear steel plays an important role in satisfying deformation demand of track structure.

Effect of Sc on the microstructure and room-temperature mechanical properties of Nb-Si based alloys

The microstructure and room-temperature mechanical properties of directionally solidified and heat-treated Nb‑16Si‑23Ti‑4Cr‑2Al‑2Hf‑0/0.3/0.5Sc (at.%) alloys were investigated. All alloys consisted of Nb-based solid solution (Nbss), α‑Nb5Si3 and γ‑Nb5Si3 with preferred 〈001〉 orientation for the first two phases, and Sc was enriched in γ‑Nb5Si3 phase. Sc-added alloys showed a more continuous Nbss matrix in which the finer Nb5Si3 phase distributed uniformly. The volume fraction of both α‑Nb5Si3 and γ‑Nb5Si3 phase was decreased by Sc addition. Sc alloying reduced the Young's modulus and nano-hardness of Nbss phase. 0.50 at.% Sc addition enhanced the fracture toughness and tensile strength from 9.88MPam1/2 and 430.3MPa to 25.95MPam1/2 and 1119.7MPa. The improvement in fracture toughness was due to the better deformability of Nbss phase. The high tensile strength was attributed to the dispersed and refined Nb5Si3 phase, which was not degraded by the increased Nbss volume fraction since dislocations were not open within most Nbss phase. Besides, the strong interface cohesion was preferable for the strength of Sc-added alloys.

Computationally predicted fundamental behaviors of embedded hydrogen at TiC/W interfaces

First-principles calculation has been performed to systematically investigate the solubility and interface cohesion of embedded hydrogen at titanium carbide/tungsten (TiC/W). It is found that hydrogen ion irradiation has quite different effects on hydrogen solubility of TiC/W interface and W bulk. That is, hydrogen solubility of TiC/W interface decreases with the rising of temperature, while hydrogen solubility of W bulk increases under the same conditions. We also show that the location of hydrogen has a decisive effect on cohesion properties of TiC/W interface, and that embedded hydrogen in the most interface sites could significantly reduce interface strength and stability of TiC/W. The derived results not only explore its fundamental properties as well as various potential applications, but also agree well with experimental observations in the literature.

Effects of physical and chemical aspects on membrane fouling and cleaning using interfacial free energy analysis in forward osmosis.

Natural organic matter (NOM) in micro-polluted water purification using membranes is a critical issue to handle. Understanding the fouling mechanism in the forward osmosis (FO) process, particularly identifying the predominant factor that controls membrane fouling, could have significant effects on exerting the advantages of FO technique. Cellulose triacetate no-woven (CTA-NW) membrane is applied to experiments with a high removal efficiency (> 99%) for the model foulant. Tannic acid (TA) is used as a surrogate foulant for NOM in the membrane fouling process, thus enabling the analysis of the effects of physical and chemical aspects of water flux, retention, and adsorption. The membrane fouling behavior is affected mainly by the combined effects of the osmotic dragging force and the interaction of the pH in the working solution, foulants, and calcium ions, as demonstrated by the water flux loss and the changes of membrane retention and adsorption. The fouled CTA-NW membrane (in PRO mode) could be flux-recovered by > 85% through physical cleaning methods. The interfacial free energy analysis theory was used to analyze the membrane fouling behavior with calculating the interfacial cohesion and adhesion free energies. The cohesion free energy refers to the deposition of foulants (TA or TA combined with calcium ions) on a fouled membrane. In addition, the adhesion free energy could be used to evaluate the interaction between foulants and a clean membrane.

Fragmentation and mechanical performance of tailored nickel-aluminum laminate compacts

The fragmentation of materials is a complex sequence of physical processes in which the kinetic energy is converted into deformation and fracture energy. The incorporation of reactive mixtures adds a third form of energy, chemical energy. The fragmentation and mechanical performance of nickel-aluminum compacts was examined under dynamic conditions using mesostructured powder compacts in which the interfaces between the powders (having initial sizes between 355 and 500 µm) were tailored during the swaging fabrication process. Fragmentation was created in ring samples of this material through explosively driven expansion (generating velocities around 100 m/s) and analyzed through high-speed photography, laser interferometry and soft capture of fragments. Quasi-static and dynamic mechanical testing was conducted to examine the mechanical performance and to provide parameters for the constitutive description. Experimental results are compared with fragmentation theories to characterize the behavior of reactive powders based on the material’s mesostructure by introducing the fracture toughness of the compacts, following the principal elements of the earlier work on tailored aluminum compacts. The fracture toughnesses, which ranged from 0.17 to 0.67 MPa m1/2, are related to the interfacial cohesion between particles and the fragmentation is a direct consequence of these parameters. The mean fragment size is calculated using a modified form of Mott’s theory and successfully compared with experimental results; it ranges from 10 µm to 40 µm. Finite element simulations on Al compacts confirm that the fragmentation increases (smaller fragment sizes) with a decrease in fracture toughness. The methodology developed here can be applied for tailoring the fragmentation of reactive munitions.

Density Functional Theory plus Hubbard U Study of the Segregation of Pt to the CeO2- x Grain Boundary.

Grain boundaries (GBs) can be used as traps for solute atoms and defects, and the interaction between segregants and GBs is crucial for understanding the properties of nanocrystalline materials. In this study, we have systematically investigated the Pt segregation and Pt-oxygen vacancies interaction at the ∑3 (111) GB in ceria (CeO2). The Pt atom has a stronger tendency to segregate to the ∑3 (111) GB than to the (111) and (110) free surfaces, but the tendency is weaker than to (112) and (100). Lattice distortion plays a dominant role in Pt segregation. At the Pt-segregated-GB (Pt@GB), oxygen vacancies prefer to form spontaneously near Pt in the GB region. However, at the pristine GB, oxygen vacancies can only form under O-poor conditions. Thus, Pt segregation to the GB promotes the formation of oxygen vacancies, and their strong interactions enhance the interfacial cohesion. We propose that GBs fabricated close to the surfaces of nanocrystalline ceria can trap Pt from inside the grains or other types of surface, resulting in the suppression of the accumulation of Pt on the surface under redox reactions, especially under O-poor conditions.

A New Closed‐Form Solution of the Side Abutment Pressure Distribution of Roadway

Instability of coal wall is one of the hot‐button and difficult issues in the study of coal mine ground control. The shallow side coal of roadway in the coal measures is usually weak and consequently easy to bring about failure. Hence, the side abutment pressure redistributes and dramatically influences the roadway stability. Since the previous closed‐form solutions of the side abutment pressure do not take into account all the necessary parameters which include the properties of the coal and the interface between coal and roof/floor, the roadway height, and the support strength, a mechanical model is established based on the equilibrium of the plastic zone, and a new closed‐form solution is derived in this paper. Moreover, a numerical investigation is conducted to validate the accuracy of the closed‐form solution. The numerical results of the side abutment pressure distribution are in good agreement with the closed‐form solution. Afterwards, a parametric analysis of the width of the plastic zone is carried out, and the results show that the width of the plastic zone is nearly negatively linearly correlated with the friction angle and the cohesion of the coal, the interfacial cohesion, and the support strength. By contrast, it is positively linearly correlated with the roadway height and negatively exponentially correlated with the interfacial friction angle. The results obtained in the present study could be useful for the evaluation process of roadway stability.

Aging Behavior of Quillaja Saponin – Pea Protein Interfaces

This study investigated the interfacial shear rheology of mixed Quillaja saponin - pea protein systems to better understand their interactions and adsorption behaviors over time (5–720min). The interfacial storage (Gi′) and loss (Gi″) moduli of the individual and mixed surfactants were recorded as amplitude sweeps (0.05Hz, strain 1–100%) using a rheometer equipped with a biconical disk. Quillaja saponins formed highly viscoelastic interfaces within 5min. Pea proteins formed less viscoelastic interfacial layers within 5–240min, and led viscoelasticities increase greatly after 720min of aging. This is indicative of much slower rearrangement processes compared to a rapid establishment of Quillaja saponin interfacial layers. Quillaja saponin - pea protein mixtures had lower Gi′- than Gi″-values than either of the individual. This mixed interface weakened upon aging which was suggested to be indicative of the development of particulates unable to interlink thereby decreasing the interfacial cohesion.

Self-healing three-dimensional bulk materials based on core-shell nanofibers

In this study, electrospun core-shell nanofibers containing healing agents are embedded into a three-dimensional bulk matrix in a simple versatile process. Two types of the healing agents (resin monomer and cure) are encapsulated inside the nanofiber cores. The core-shell fibers are encased in the macroscopic three-dimensional bulky material. To achieve this goal, the electrospun core-shell fibers containing two components of PDMS (either resin monomer or cure) are directly embedded into an uncured PDMS bath and dispersed there, essentially forming a monolithic composite. For the evaluation of the self-healing features, the interfacial cohesion energy is measured at the cut surface of such a material. Namely, the bulk of the prepared self-healing material is entirely cut into two parts using a razor blade and then re-adhered due to the self-curing process associated with the released healing agents. The results reveal that the self-healing fiber network works and releases a sufficient amount of resin monomer and cure at the cut surface to facilitate self-healing. In addition, chopped into short filaments core-shell fibers were embedded into highly porous sponge-like media. After a mechanical damage in compression or shearing fatigue, this sponge-like material also revealed restoration of stiffness due to the released self-healing agents. The sponges revealed a 100% recovery and even enhancement after being damage in the cyclic compression and shearing tests, even though only 0.086% of the healing agents were embedded per sponge mass and finely dispersed in it.

Derivative effect of laser cladding on interface stability of YSZ@Ni coating on GH4169 alloy: An experimental and theoretical study

Abstract Yttria-stabilized zirconia YSZ@Ni core-shell nanoparticles were used to prepare a thermal barrier coating (TBC) on a GH4169 alloy by laser cladding. Microstructural analysis showed that the TBC was composed of two parts: a ceramic and a bonding layer. In places where the ZrO 2 /Al 2 O 3 eutectic structure was present in the ceramic layer, the Ni atoms diffused into the bonding layer, as confirmed by energy-dispersive X-ray spectroscopy (EDS). The derivative effect of laser cladding results in the original YSZ@Ni core-shell nanoparticles being translated into the Al 2 O 3 crystal, activating the YSZ. The mechanism of ceramic/metal interface cohesion was studied in depth via first-principles and molecular dynamics simulation. The results show that the trend in the diffusion coefficients of Ni, Fe, Al, and Ti is D Ni > D Fe > D Ti > D Al in the melting or solidification process of the material. The enthalpy of formation for Al 2 O 3 is less than that of TiO 2 , resulting in a thermally grown oxide (TGO) Al 2 O 3 phase transformation. With regard to the electronic structure, the trend in Mulliken population is Q O−Ni > Q Zr−O > Q O−Al . Although the bonding is slightly weakened between ZrO 2 /Al 2 O 3 ( Q Zr−O = 0.158 Q O−Ni = 0.220) compared to that in ZrO 2 /Ni, TGO Al 2 O 3 can improve the oxidation resistance of the metal matrix. Thus, by comparing the connective and diffusive processes, our findings lay the groundwork for detailed and comprehensive studies of the laser cladding process for the production of composite materials.

Experimental analysis of drilling induced damage in biocomposites

This paper focuses on the analysis of drilling induced damage on biocomposites (woven fibers of cotton, flax and jute combined with polylactic acid, PLA, as the matrix). The main contribution of this work is the analysis of the influence of cutting parameters and drill geometry on fully biodegradable composites based on two different types of PLA and different fibers types. The damaged area was studied both at the hole entry and exit. Contrary to the behavior commonly observed when drilling conventional composites, delamination was negligible. The hole entry and exit damage were analyzed and quantified in terms of the fraying extension being the dominant. The damage extension was found to be dependent on the matrix, fiber type and drill geometry. The combination between cotton fiber and the small drill point angle showed the lowest level of damage. On the other hand, composite reinforced with flax fibers (those that exhibited the highest tensile strength) presented the greatest damage extension, increasing with the number of layers of the composite. The matrix based on polymer 10361D PLA, recommended for natural fibers because of the better interface cohesion, resulted in reduced fraying. Concerning the influence of cutting parameters, damage decreased when increasing the cutting speed and feed rate.

Torsion delamination test, a new method to quantify the adhesion of coating: Application to car coatings

Abstract A torsion delamination test was developed to characterize the interfacial cohesion of multilayer organic coatings. It consists in applying an increasing torque on a hexagonal plot directly glued on the coating until delamination occurs. The test is quantitative and allows the calculus of the shear stress that generates delamination. This torsion test was successfully used to test the adhesion of multilayer car coatings. The delaminating interfaces were directly observed via optical and electron microscopy. We have shown that the critical delaminating shear stress and the delaminating interface are dependent of both the primer and of the curing temperatures respectively. Furthermore, an interpretation of the delamination process is proposed.

Influence of nitrodopamine-functionalized barium titanate content on the piezoelectric response of poly(vinylidene fluoride) based polymer-ceramic composites

Piezocomposites were elaborated by incorporating barium titanate (BT) ceramic particles into a poly(vinylidene fluoride) (PVDF) matrix. A key issue of the process is to obtain the electroactive β crystal phase in PVDF by stretching the polymer-ceramic composite. For this purpose, as well as in view of enabling the poling step of the composite film, the interfacial cohesion between ceramic and polymer has to be efficient and this has been achieved by nitrodopamine functionalization of the ceramic surface (nBT). The structural evolution associated to the deformation-induced α-β crystal phase transformation in the presence of nBT has been analyzed in situ under stretching. The piezoelectric properties of these composites have been characterized in parallel poling. In the range of nBT filler loading under investigation, it is shown that the d33 piezoelectric coefficient of the composite is modulated by the ceramic content. Polymer matrix dominated response yields a negative d33 value at low nBT content. Interestingly enough, the piezoelectric response is null at 26 wt% nBT loading and the piezoelectric coefficient becomes positive beyond that filler fraction.

Apparent anisotropy of adhesive bonds with weak adhesion and non-destructive evaluation of interfacial properties

The present research attempts to non-destructively characterize mechanical properties, which are representative of the interfacial adhesion and bond line cohesion of adhesively bonded assemblies, using an ultrasonic method. Eight bonded samples made of two aluminium substrates and of an epoxy-based adhesive layer were manufactured: four in which the adhesive is fully cured (100%) and four in which crosslinking is partial (80%). For each level of curing, four different surface treatments were applied to the aluminium substrates before assembling, in order to vary the quality of adhesion. Ultrasonic plane wave transmission coefficients (UPWTC) were either measured in a water tank, or simulated using the well-known stiffness matrix method that micmics the experiments, to produce input data for the inverse problem. This latest consists in the evaluation of the elastic properties of either the adhesive bond or the interphases between both substrates and the adhesive layer. If the interphases are of nominal quality, the values of the inferred properties of the adhesive bond match those previously measured on individual epoxy samples, whether the epoxy is fully or partially cured. However, when interphases are not of nominal quality level, the optimized bond moduli reveal an apparent anisotropy, although the epoxy layer is known to be isotropic. This apparent anisotropy is explained by an analytical rule of mixture, thus giving confidence in the proposed ultrasonic technique, which is then suggested as a potential way to detect weaknesses of interphases. Finally, the optimization of the interphases elastic properties is carried out. The measured normal and shear stiffnesses are shown to decrease as the interphases get degraded. All ultrasonically-measured parameters (apparent anisotropy of the bond and interfacial stiffnesses) vary monotonically with the bonds strength, which was measured via mechanical tests. The proposed UPWTC method was shown to have a strong potential to distinguish between adhesive and cohesive weaknesses of bonded joints, and to estimate corresponding mechanical properties.

Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface: A first-principles study

The application of silicon as ultrahigh capacity electrodes in lithium-ion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segregate at the (lithiated) Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene. These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.

Level set topology optimization of structural problems with interface cohesion

SummaryThis paper presents a finite element topology optimization framework for the design of two‐phase structural systems considering contact and cohesion phenomena along the interface. The geometry of the material interface is described by an explicit level set method, and the structural response is predicted by the extended finite element method. In this work, the interface condition is described by a bilinear cohesive zone model on the basis of the traction‐separation constitutive relation. The non‐penetration condition in the presence of compressive interface forces is enforced by a stabilized Lagrange multiplier method. The mechanical model assumes a linear elastic isotropic material, infinitesimal strain theory, and a quasi‐static response. The optimization problem is solved by a nonlinear programming method, and the design sensitivities are computed by the adjoint method. The performance of the presented method is evaluated by 2D and 3D numerical examples. The results obtained from topology optimization reveal distinct design characteristics for the various interface phenomena considered. In addition, 3D examples demonstrate optimal geometries that cannot be fully captured by reduced dimensionality. The optimization framework presented is limited to two‐phase structural systems where the material interface is coincident in the undeformed configuration, and to structural responses that remain valid considering small strain kinematics. Copyright © 2017 John Wiley & Sons, Ltd.

Evolution mechanism of interface cohesion for the coating inducing by laser cladding YSZ@Ni core-shell nanoparticles: Experimental and theoretical research

Abstract Stainless steel coated by multi-layers of YSZ@Ni core-shell nanoparticles was sintered by laser cladding. Microstructure shows that the coating by laser cladding YSZ@Ni core-shell nanoparticles has a nanometer microstructure with stratification feature. Therein to cladding layer, amount of chromium atoms appear, and the Ni atoms are diffused largely in matrix layer, which results in the original YSZ@Ni core-shell nanoparticles translated into Cr crystal arming YSZ ceramics crystal. Such influence of variable bonding mechanism on ceramics/metal interface was studied deeply by first principle and molecular dynamics simulation. The results show that in diffusion process of solid state, the element diffusion of Zr↔Ni and Fe↔Ni are both hard to happen. But in Cr↔Ni diffusion process, it is hard only when they are at the nearest neighbor. Diffusion process in cooling process before liquid→solid phase transformation, the diffusion coefficient of Fe, Cr and Ni is DFe > DCr > DNi. But in nucleation process, its trend becomes DNi > DFe ≈ DCr, although all of them are too small. Deeply investigating on their electronic structure, the different distribution of Fe and Cr in cladding layer is originated from their trend of Mulliken population QO-Cr > QO-Fe. As a result, such weaken bonding of ZrO2/Cr has destroyed the initial purpose on the Ni as the excellent transition layers between ceramics enforcing phase and metal matrix phase. Thus comparing the connective and diffusive processes, our findings open an avenue for detailed and comprehensive studies of laser cladding process in producing composites.

Bond strength between concrete substrate and metakaolin geopolymer repair mortar: Effect of curing regime and PVA fiber reinforcement

The suitability of repairing Portland cement concrete with geopolymer mortars is explored as a viable way to replace Portland cement in concrete repairs and reduce their carbon footprint. Bond tests are performed through non-standard slant shear tests with variable bond plane inclination to assess concrete-geopolymer shear bond strength under different combinations of normal and shear stresses at the concrete-geopolymer interface. Interfacial cohesion and friction coefficients, two inherent mechanical properties of the substrate-repair interface, are extrapolated from experimental data and compared among different types of geopolymer repairs. The adoption of different curing temperatures for the geopolymer repair mortar (20°C and 45°C) and its reinforcement with various contents of Polyvinyl Alcohol fibers (volume fractions Vf = 0%, 0.5%, and 1%) are investigated to optimize the substrate-repair bond. Mechanical tests are supported by statistical analysis and microscope observation.