Interfacial Cohesion Research Articles

Pullout Tests Study on Performance of Interface between Geogrid and Soil

The interface interaction between geogrid and soil is one of key issues on stability of geosynthetic-reinforced soil structures. Comparative analysis of properties of geogrid-clay interface under the different kinds of geogrid, different normal stresses, speeds of pullout and water contents of clay are conducted by medium-sized pullout tests. The tests results showed that ultimate pullout force of geogrid, interfacial cohesion and frictional coefficient are significantly affected by various water contents of clay. Ultimate pullout forces of geogrid tending to remarkably difference when subject to different normal stresses at lower water contents, and frictional coefficient of interface decrease with the increase of water content, interfacial cohesion has a tendency to increase followed by decreasing with increase of water contents. Moreover, the curves of load and displacement possess three piecewise consisting of linear increase, non-linear increase and ultimate pullout, and as water content increase interval nonlinear changing stage is not conspicuous.

Slip-line field solution for ultimate bearing capacity of a pipeline on clay soils

A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account of circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe may degenerate into those for the conventional rectangular-shaped strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils.

Multiscale Structure, Interfacial Cohesion, Adsorbed Layers, and Thermodynamics in Dense Polymer-Nanoparticle Mixtures

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion.

Yield strength of attached copper film

Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method. A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion. So the slope of the initial elastic segment of the X-ray stress (or X-ray strain directly) of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength. The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.

Ideal mechanical strength and interface cohesion property of Ir-base superalloys from first principles calculation

First principles calculation reveals that ideal mechanical strengths of L1 2 Ir 3Nb are higher than those of L1 2 Ir 3Hf, and that Hf and Nb atoms have different effects on the brittle behavior of Ir, i.e., the Ir 3Hf bulk seems less brittle than f c c Ir, while Ir 3Nb becomes more brittle. Densities of states suggest that the chemical bonding formed in Ir 3Nb should be stronger and more directional than that in Ir 3Hf. Calculation also shows that compared with pure Ir bulk, the bond strengths of (1 0 0)-I and (1 1 0) Ir/Ir 3X (X = Hf, Nb) interfaces have increased, while the bond strengths of (1 0 0)-II and (1 1 1) Ir/Ir 3X interfaces have decreased, due to the formation of the interface. In addition, it is found out that the (1 0 0)-I interfaces are energetically favorable with negative interface energies, which is good agreement with similar experimental observations in the literature.

Deformation and fracture mechanisms in fine- and ultrafine-grained ferrite/martensite dual-phase steels and the effect of aging

Three ferrite/martensite dual-phase steels varying in the ferrite grain size (12.4, 2.4 and 1.2 μm) but with the same martensite content (∼30 vol.%) were produced by large-strain warm deformation at different deformation temperatures, followed by intercritical annealing. Their mechanical properties were compared, and the response of the ultrafine-grained steel (1.2 μm) to aging at 170 °C was investigated. The deformation and fracture mechanisms were studied based on microstructure observations using scanning electron microscopy and electron backscatter diffraction. Grain refinement leads to an increase in both yield strength and tensile strength, whereas uniform elongation and total elongation are less affected. This can be partly explained by the increase in the initial strain-hardening rate. Moreover, the stress/strain partitioning characteristics between ferrite and martensite change due to grain refinement, leading to enhanced martensite plasticity and better interface cohesion. Grain refinement further promotes ductile fracture mechanisms, which is a result of the improved fracture toughness of martensite. The aging treatment leads to a strong increase in yield strength and improves the uniform and total elongation. These effects are attributed to dislocation locking due to the formation of Cottrell atmospheres and relaxation of internal stresses, as well as to the reduction in the interstitial carbon content in ferrite and tempering effects in martensite.

Polymer-mediated spatial organization of nanoparticles in dense melts: Transferability and an effective one-component approach

We study two problems in the framework of the integral equation theory of polymer-mediated spatial organization of nanoparticles in dense melts motivated by multiscale simulation and many body physics issues. How nonspherical nanoparticle shape modifies polymer-induced interactions under dilute nanoparticle conditions is investigated over a range of primary particle sizes and interfacial cohesion strengths. Nonuniversal consequences of nonspherical shape are found for the pair-correlation function on local scales and some qualitative differences on larger scales due primarily to intraparticle connectivity constraints. For a large enough nanoparticle site diameter, the potentials of mean force (PMF) for all shapes studied (sphere, rod, disk, compact tetrahedral cluster) exhibit linear scaling with the size ratio of nanoparticle to polymer monomer site diameter and quite good "transferability." The ability of a simple effective one-component approach, based on the dilute nanoparticle PMF as an effective pair-decomposable potential, to describe interparticle structure at nonzero volume fractions is also studied. Although not generally quantitatively accurate due to neglect of many body correlation effects, especially at high nanoparticle loadings and near contact separations, the simple approach captures rather well many aspects of the real space structure. The errors incurred depend systematically on whether interfacial cohesion strength results in contact aggregation, steric stabilization, or bridging. For the filler collective static structure factor, many body effects are weakest for local cage scale correlations and grow significantly at smaller wavevectors under depletion or bridging conditions.

Synthesis, Morphology, and Properties of Self-Assembled Nanostructured Aramid and Polystyrene Blends

Aramid (Ar), produced from the reaction of aromatic diamines and diacid chloride, was reactively compatibilized with amino-functionalized polystyrene (APS) to explore blend morphology and interfacial cohesion. Two blend systems, Ar/PS and Ar/APS, were investigated over a range of pristine polystyrene (PS) or modified APS ratios. Morphology and thermal and mechanical properties were probed to evaluate the effect of amine units of APS on the compatibility with Ar. π-π stacking interactions in tandem with the random distribution of graft attachment locations and polydispersity of graft length in Ar-g-APS copolymer, aided merger of unreacted chains to drive molecular self-assembly process thus fortifying the nanostructured blends. Considerable augmentation of the blend morphology and thermal stability was achieved by incorporation of reactivity into Ar/APS system. A 20 wt % APS-containing blend was found to demonstrate optimum mechanical reinforcement, complemented by the optimal, thermal, and morphological profiles of the same blend. Future prospects are envisaged.

Reinforcing silk scaffolds with silk particles.

Silk fibroin is a useful protein polymer for biomaterials and tissue engineering. In this work, porogen leached scaffolds prepared from aqueous and HFIP silk solutions were reinforced through the addition of silk particles. This led to about 40 times increase in the specific compressive modulus and the yield strength of HFIP-based scaffolds. This increase in mechanical properties resulted from the high interfacial cohesion between the silk matrix and the reinforcing silk particles, due to partial solubility of the silk particles in HFIP. The porosity of scaffolds was reduced from approximately 90% (control) to approximately 75% for the HFIP systems containing 200% particle reinforcement, while maintaining pore interconnectivity. The presence of the particles slowed the enzymatic degradation of silk scaffolds.

On the role of μ phase during high temperature creep of a second generation directionally solidified superalloy

The role of μ phase in a second generation directionally solidified Ni-base superalloy during high temperature creep has been characterized in the present work. A large amount of blocky μ phase enveloped by thick γ′-film is found at the grain boundaries and in the vicinity of primary MC carbides after heat treatment. However, the creep-rupture properties of the alloy are not affected by the presence of the blocky μ phase at 760–1070 °C under a stress of 120–850 MPa. By the investigation of creep microstructure at 975 °C/255 MPa, it is found that the thick γ′-film plays a pivotal role in toughening the grain boundaries and the interfaces between the μ phase (or carbides) particles and the matrix, and preventing the formation of cracks. Meanwhile, during high temperature creep, M 23C 6 carbides are continuously coarsening with the dissolution of the μ phase particles and MC carbides, especially at the grain boundaries. The poor interface cohesion strength between such large M 23C 6 carbides and the γ matrix at the vertical segments of the directionally solidified grain boundaries leads to the final creep failure of the present alloy.

Microstructure and Compressive Properties of <I>In-Situ</I> Martensite CuZr Phase Reinforced ZrCuNiAl Metallic Glass Matrix Composite

In-situ micro-level martensite CuZr phase reinforced Zr50:5Cu27:45Ni13:05Al9 metallic glass matrix composite was synthesized by copper mold casting. Microstructure and compressive properties of the composite are investigated. The martensite CuZr phase possesses numerous coherent twin boundaries, and holds strong interfacial cohesion with the matrix. They both effectively induce the seeding and branching of shear bands during compression. The compressive properties of the composite are therefore improved. The fracture strength and plastic strain of composite with a diameter of 3 mm is up to 2190 MPa, 5.7% respectively. [doi:10.2320/matertrans.M2010031]

Structure, scattering patterns and phase behavior of polymer nanocomposites with nonspherical fillers

Polymer nanocomposites made with carbon nanotubes, clay platelets, laponite disks and other novel nonspherical fillers have been the focus of many recent experiments. However, the effects of nanoparticle shape on statistical structure, polymer-mediated effective interactions, scattering patterns, and phase diagrams are not well understood. We extend and apply the polymer reference interaction site model liquid state theory to study the equilibrium properties of pseudo one-, two- and three-dimensional particles (rod, disk, cube) of modest steric anisotropy and fixed space-filling volume in a dense adsorbing homopolymer melt up to relatively high volume fractions. The second virial coefficient, nanoparticle potential-of-mean force, osmotic compressibilities, and isotropic spinodal demixing boundaries have been determined. The entropic depletion attraction between nanoparticles is dominant for weakly adsorbing polymer, while strongly adsorbing chains induce a bridging attraction. Intermediate interfacial cohesion results in the formation of a steric stabilizing adsorbed polymer layer around each nanoparticle, which can partially damp inter-filler collective order on various length scales and increase order on an averaged length scale. The details of depletion, stabilization, or bridging behavior are shape-dependent and often, but not always, trends are monotonic with increasing filler dimensionality. Distinctive nanoparticle shape-dependent low angle features are predicted for the collective polymer structure factor associated with competing macrophase fluctuations and microphase-like ordering. The influence of nonzero mixture compressibility on the scattering profiles is established.

Concentration Fluctuations, Local Order, and the Collective Structure of Polymer Nanocomposites

A combined theory−experiment analysis of adsorbing polymer mediated structural reorganization of silica nanoparticles in equilibrated and miscible poly(ethylene oxide) (PEO) and polytetrahydrofuran (PTHF) nanocomposites is presented. Quantitative comparison of microscopic liquid state theory calculations with small-angle X-ray scattering experiments demonstrate the theoretical approach properly accounts for the effects of adsorbed polymer layers on nanoparticle concentration fluctuations over all length scales for a wide range of volume fractions and interfacial cohesion strengths. The mixture total packing fraction is increased as particles are added to the polymer melt in order to account for equation-of-state effects which are important at very high filler loadings. A distinctive microphase separation like peak in the collective polymer structure factor is predicted. Nanoparticle potential of mean force calculations suggest a criterion for the onset of depletion or bridging induced kinetic gelation which is consistent with the observation of complete miscibility for the PEO system but nonequilibrium behavior in the PTHF nanocomposite.

Atomistic calculations on interfaces: Bridging the length and time scales

Phase field simulations suitable to describe interfacial phenomena at the mesoscale require as input parameters accurate interfacial energies as well as the interface mobilities. However, this information is not directly accessible by experiment. Furthermore, phenomena such as impurity segregation cannot be decoupled and their independent role in interfacial cohesion and mobility cannot be deduced. On the other hand ab-initio calculations and/or classical interatomic potentials are suitable tools which can provide an on-atomic-scale description of the interfaces. However, there are a number of challenges that one encounters: multidimensional phase space of the interfacial misorientation degrees of freedom, suitable driving forces, and large length and time scales just to mention a few. In the present report we provide an extended review on the atomistic calculations and the simulation strategies proposed to tackle the corresponding problems.

The influence of phosphorus on the microstructure and stress-rupture properties in a low thermal expansion superalloy

The influence of phosphorus on the microstructure and stress-rupture properties of IN783 alloy, the newly developed low thermal expansion superalloy, was investigated. Addition of phosphorus markedly promotes the precipitation of β-NiAl phase which improves the intergranular oxidation resistance of high P-doped alloys. However, phosphorus segregation deteriorates the interfacial cohesion of intergranular β/γ matrix and induces many intergranular cracks. Consequently, the stress-rupture life is reduced in high P-doped alloys.

Application of spinodal decomposition to produce metallic glass matrix composite with simultaneous improvement of strength and plasticity

An original two-step procedure, based on the miscibility gap between two elements, produced an in-situ bulk metallic glass matrix composite. The Zr-Ta binary alloy, which exhibits a large immiscible region in solid state, formed a two-phase mixture of Zr- and Ta-rich solid solution by phase separation. When the Zr-Ta binary alloy was remelted with Cu, Zr, and Ti, the Ta-rich solid solution, which has a high melting temperature, did not melt, while the remaining melt containing Zr-rich solid solution mixed with the other elements and solidified into an amorphous phase at lower temperatures. The improvement of strength in the composite indicates that the interfaces between the Ta-rich particles and the BMG matrix formed by phase separation are strong enough to hold a high interfacial cohesion strength.

Effects of fibre content on mechanical properties and fracture behaviour of short carbon fibre reinforced geopolymer matrix composites

Geopolymer matrix composites reinforced with different volume fractions of short carbon fibres (Cf/geopolymer composites) were prepared and the mechanical properties, fracture behaviour and microstructure of as-prepared composites were studied and correlated with fibre content. The results show that short carbon fibres have a great strengthening and toughening effect at low volume percentages of fibres (3·5 and 4·5 vol.%). With the increase of fibre content, the strengthening and toughening effect of short carbon fibres reduce, possibly due to fibre damage, formation of high shear stresses at intersect between fibres and strong interface cohesion of fibre/matrix under higher forming pressure. The property improvements are primarily based on the network structure of short carbon fibre preform and the predominant strengthening and toughening mechanisms are attributed to the apparent fibre bridging and pulling-out effect.

Determining Intrinsic Healing Properties of Asphalt Binders

A self-healing material has the inherent ability to partially reverse damage. There is consensus that the healing of damage has a substantial effect on the performance of asphalt pavements. It is important to understand the mechanisms responsible for healing in asphalt binders, to develop a model to predict healing on the basis of these mechanisms, and to develop test methods to determine the properties required for use with such a model. A healing model for asphalt materials comprises a convolution of wetting and intrinsic healing processes that occur across a crack interface. According to the proposed convolution process, intrinsic healing or strength gain across a crack surface occurs in two steps: an instantaneous strength gain resulting from the interfacial cohesion between the crack faces, and a time-dependent strength gain resulting from intermolecular diffusion and randomization across the crack interface. A modified form of the Avrami equation, which includes a parameter for instantaneous strength gain, is used to describe the intrinsic healing in asphalt binders. A test method is described that is based on the use of a dynamic shear rheometer for estimating the parameters of the intrinsic healing function. Five asphalt binders with considerably different compositions were studied. Limited validation of this test method and the intrinsic healing model are presented by comparing the parameter related to instantaneous healing with the thermodynamic work of cohesion for the selected binders.

Numerical simulation of relation between interface topography and residual stress in thermal barrier coatings

With respect to thermal barrier coating, the analysis of interface cohesion and residual stress is important to the life of TBC from mechanical view point. Up to now, there is not a model of describing interface cohesion. In the paper, we give a simple model of computing residual stress and study the residual stress of TBC with ANSYS. The distribution of the residual stress in different interface topography and the relationship between the residual stress and the interface topography dimension are presented.

Many body effects on the phase separation and structure of dense polymer-particle melts

Liquid state theory is employed to study phase transitions and structure of dense mixtures of hard nanoparticles and flexible chains (polymer nanocomposites). Calculations are performed for the first time over the entire compositional range from the polymer melt to the hard sphere fluid. The focus is on polymers that adsorb on nanoparticles. Many body correlation effects are fully accounted for in the determination of the spinodal phase separation instabilities. The nanoparticle volume fraction at demixing is determined as a function of interfacial cohesion strength (or inverse temperature) for several interaction ranges and nanoparticle sizes. Both upper and lower critical temperature demixing transitions are predicted, separated by a miscibility window. The phase diagrams are highly asymmetric, with the entropic depletion-like lower critical temperature occurring at a nanoparticle volume fraction of approximately 10%, and a bridging-induced upper critical temperature at approximately 95% filler loading. The phase boundaries are sensitive to both the spatial range of interfacial cohesion and nanoparticle size. Nonmonotonic variations of the bridging (polymer-particle complex formation) demixing boundary on attraction range are predicted. Moreover, phase separation due to many body bridging effects occurs for systems that are fully stable at a second order virial level. Real and Fourier space pair correlations are examined over the entire volume fraction regime with an emphasis on identifying strong correlation effects. Special attention is paid to the structure near phase separation and the minimum in the potential of mean force as the demixing boundaries are approached. The possibility that nonequilibrium kinetic gelation or nanoparticle cluster formation preempts equilibrium phase separation is discussed.