Interfacial Shear Modulus Research Articles

Effect of matrix microstructure on micro- and macro- mechanical properties of 2.5D woven oxide fiber reinforced oxide matrix composites

A comprehensive learning of the mechanical behavior change mechanism of oxide/oxide composites is of great significance as a guide for their industrial applications. This study focused on examining how matrix microstructure impacted the micro- and macro- mechanical properties of the composites mainly by nanoindentation tests, macro-mechanical tests and x-ray computed tomography. The results showed that the sintering phenomenon of matrix sintered at 1200 ºC was more obvious, and there were visible transverse and longitudinal cracks. The in-situ modulus of matrix and interfacial shear modulus of the composite increased by 61.1% and 36.4%, respectively, with the increase of matrix sintering densification. Combined with these micro-mechanical parameters of the composites, the He-Hutchinson model predicted the same crack propagation modes as those obtained from fracture toughness tests. Moreover, more matrix cracks directly led to a 45.4% reduction in the flexural strength of the composites sintered at 1200 ºC compared to that sintered at 1100 ºC. In addition, a comparison analysis was conducted on the evolution of microstructure, micro- and macro- mechanical properties of 2.5D and 2D composites with the same preparation parameters.

Modeling the bond–slip behavior of the interface between a stiffened core and cemented soil based on machine learning approaches

The bond–slip behavior of stiffened deep cement mixing (SDCM) piles—which is crucial for their bearing capacity—evolves continuously with curing age. In the study reported here, 20 element tests were conducted on the interface between cemented soil and a stiffened core, analyzing the bond–slip behavior affected by curing temperature and age, and then ensemble learning methods (XGBoost, random forest) were used to establish models for the evolution of the bond–slip behavior considering thermal effects. The constructed models can predict the peak shear strength (τmax), the residual shear strength (τres), and the interfacial shear modulus (G). The test results show that the shear strength of the stiffened-core–cemented-soil interface grows with the increasing curing temperature and age, with faster growth at 0–14 days compared to 60–90 days. To lessen the reliance on ineffective brute-force searching, Bayesian optimization with a tree-structured Parzen estimator is used to select the hyperparameters of the established models. The results demonstrate the superior performance of the chosen approach, with R2 > 0.93 for the training set and R2 > 0.81 for the test set. The results of the XGBoost model are best for τmax, with a mean absolute percentage error of less than 5 %, thereby enabling accurate predictions of the mechanical parameters of the stiffened-core–cemented-soil. This research enhances the understanding of the mechanical properties of SDCM piles and provides valuable guidance for projects involving such piles.

Interfacial mechanics of β-casein and albumin mixed protein assemblies at liquid-liquid interfaces

Protein emulsifiers play an important role in formulation science, from food product development to emerging applications in biotechnologies. The impact of mixed protein assemblies on surface composition and interfacial shear mechanics remains broadly unexplored, in comparison to the impact that formulation has on dilatational mechanics and surface tension or pressure. In this report, we use interfacial shear rheology to quantify the evolution of interfacial shear moduli as a function of composition in bovine serum albumin (BSA)/β-casein mixed assemblies. We present the pronounced difference in mechanics of these two protein, at oil interfaces, and observe the dominance of β-casein in regulating interfacial shear mechanics. This observation correlates well with the strong asymmetry of adsorption of these two proteins, characterised by fluorescence microscopy. Using neutron reflectometry and fluorescence recovery after photobleaching, we examine the architecture of corresponding protein assemblies and their surface diffusion, providing evidence for distinct morphologies, but surprisingly comparable diffusion profiles. Finally, we explore the impact of crosslinking and sequential protein adsorption on the interfacial shear mechanics of corresponding assemblies. Overall, this work indicates that, despite comparable surface densities, BSA and β-casein assemblies at liquid–liquid interfaces display almost 2 orders of magnitude difference in interfacial shear storage modulus and markedly different viscoelastic profiles. In addition, co-adsorption and sequential adsorption processes are found to further modulate interfacial shear mechanics. Beyond formulation science, the understanding of complex mixed protein assemblies and mechanics may have implications for the stability of emulsions and may underpin changes in the mechanical strength of corresponding interfaces, for example in tissue culture or in physiological conditions.

Effect of interphase layer on matrix cracking in fiber reinforced ceramic matrix composites

The onset of matrix steady-state cracking stands as a pivotal mechanical characteristic in fiber reinforced ceramic matrix composites (FRCMCs), garnering substantial attention and investigations. Experimentally, it has been demonstrated that increasing interphase layer thickness may cause non-monotonic changes in matrix cracking stress. However, the existing models can hardly elucidate this phenomenon thoroughly due to the neglect of interphase thickness. This paper presents a comprehensive analytical model for the matrix cracking incorporating interphase, the Poisson effect, Coulomb friction, fiber asperities, residual thermal stress (RTS), and their coupling effects, along with a modified criterion for interfacial debonding that accounts for the presence of the axial RTS. Based on the proposed model, three distinct cracking domains, i.e., perfectly bonded, debonding with and without interfacial separation, have been identified with the critical conditions deduced analytically. Thereby the mechanism of the non-monotonic influence of interphase thickness is thoroughly revealed as the transition of cracking modes. Meanwhile, the role of interphase on the matrix cracking is systematically studied, and the results indicate that interphase has a notable effect through relieving axial RTS, adjusting interfacial friction, altering interfacial shear modulus, and influencing debonding toughness. The outcomes of this study offer valuable guidance for the interphase design of FRCMCs.

Construction of “hard‐soft‐hard” structures with ammonium cerium nitrate/sodium alginate/carbon nanotubes on carbon fiber surfaces for superior mechanical

AbstractThe interface between carbon fiber (CF) and the resin matrix is of paramount importance in determining the overall performance of composite materials. This study employed ammonium ceric nitrate (ACN), sodium alginate (SA), and aminated carbon nanotubes (CNTs) to fabricate “hard‐soft‐hard” nanostructure on the surface of CFs with the aim of enhancing the interfacial properties of the composites. The results indicated that interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength, and modulus of the composites demonstrated a respective increase of 31.0%, 51.8%, 44.3%, and 85.3% following the modification process. The observed positive outcome can be ascribed to the creation of “hard‐soft‐hard” nanostructures achieved by the combination of ACN, SA, and CNTs through both hydrogen and covalent bonding. The nanostructures serve to augment the surface chemical activity of the fibers and amplify the specific surface area, thereby facilitating enhanced mechanical interlocking between the fibers and the resin. Furthermore, the composites of CF prepared through this method demonstrate outstanding mechanical characteristics, rendering them appropriate for the construction of longer‐lasting and more resilient wind turbine blades.Highlights ACN, SA, and CNT create a “hard‐soft‐hard” multi‐phase structure. ACN/SA/CNT synergistically enhances composite interfacial bonding. Inorganic–organic–inorganic materials on CF form novel interfacial phases. Resultant structure improves composite interface properties.

Viscoelasticity of a carbon nanotube-laden air-water interface.

The viscoelasticity of a carbon nanotube (CNT)-laden air-water interface was characterized using two different experimental methods. The first experimental method used a Langmuir-Pockels (LP) trough coupled with a pair of oscillating barriers. The second method is termed the Bicone-Trough (BT) method, where a LP trough was custom-built and fit onto a rheometer equipped with a bicone fixture to standardize the preparation and conditioning of a particle-laden interface especially at high particle coverages. The performance of both methods was evaluated by performing Fast Fourier Transform (FFT) analysis to calculate the signal-to-noise ratios (SNR). Overall, the rheometer-based BT method offered better strain control and considerably higher SNRs compared to the Oscillatory Barriers (OB) method that oscillated barriers with relatively limited positional and speed control. For a CNT surface coverage of 165mg/m2 and a frequency of 100mHz, the interfacial shear modulus obtained from the OB method increased from 39 to 57mN/m as the normal strain amplitude increased from 1 to 3%. No linear viscoelastic regime was experimentally observed for a normal strain as small as 0.5%. In the BT method, a linear regime was observed below a shear strain of 0.1%. The interfacial shear modulus decreased significantly from 96 to 2mN/m as the shear strain amplitude increased from 0.025 to 10%.

Construction and mechanism study of clean N2 foam fracturing fluid stabilized by viscoelastic surfactant in concentrated brines for unconventional oil and gas

As a much-anticipated clean thickener, viscoelastic surfactants (VESs) have drawn much attention in the development of foam fracturing fluids for unconventional oil and gas stimulation. Herein, the mechanism of foam stabilization by VESs and wormlike micelles (WLMs) under a high-salinity environment was investigated by evaluating three kinds of salt-tolerant VESs with different molecular structures through a series of experiments, including drainage tests, foam microscopic characteristic observations and interface rheology tests. The drainage test proved that the liquid film drainage was effectively inhibited under the proper salinity range for WLM construction. Based on microscopic observation, although WLMs are formed, gas diffusion inevitably occurs in each foam fluid as bubble size diversity exists, while the foam stabilized by VES-BC, the Gemini structure with steric hindrance on its spacer, exhibits comparably high uniformity of bubble size. Relying on the Gibbs criterion, this further proves that the foam stabilized by VES-BC resists gas diffusion better than the other two foams, as the critical shrinking speed of the VES-BC solution droplet to resist gas diffusion is lowest, which explains why the foam stabilized by VES-BC exhibits the best anti-coarsening capacity under static conditions. The oscillation droplet test proves that the VES-BC molecules and WLMs they construct impart the interface with the best resistance to external disturbance and deformation under the proper salinity range for WLM construction. Meanwhile, the interface shear modulus measurement indicates that the WLMs construed by VES-BC molecules and the interaction between WLMs and the VESs on the interface play crucial roles in anti-coalescence between bubbles. Under high-temperature and high-pressure conditions, the VES-C and VES-BC foam fracturing fluids prepared by brines, with 80% foam quality, both exhibit excellent thickening and proppant carrying capacity, and the VES-BC foam fracturing fluid can withstand 140 °C to sustain a low settling rate of proppant, which potentially decreases the cost of cleaning fracturing fluid by displacing 80% of the fluid into N2 and causes little damage to unconventional reservoirs. All experiments prove that foam coarsening is the key factor causing foam decay regardless of whether WLMs exist, yet WLMs can efficiently inhibit the drainage of liquid film and resist bubble coalescence by interacting with the molecules on the interface.

Apparent Failures in Interpretation of Interfacial Characterization When Formulating Emulsions Stabilized by Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are sustainable particles that are effective at stabilizing emulsions by adsorbing at droplet interfaces and providing a steric barrier to coalescence. However, CNCs have surface charges that reduce the coverage of the emulsion droplets due to the electrostatic repulsion between CNCs. In such cases, adding salt is a typical (and straightforward) way to adjust the formulation so that the charges are screened, allowing increased coverage of the droplets. At the outset of this work, we hypothesized that characterization of the interfacial tension and interfacial shear rheology of the oil-water interface would be correlated to interfacial coverage and therefore predictive of the optimal salt concentration for emulsion stability. Included in the methods section as a useful reference to others is the presentation of a detailed derivation for the equations needed to compute interfacial shear moduli in a custom, double-gap geometry. In contrast to our hypothesis, we found that interfacial tension did not correlate well with emulsion stability and that the native surface-active compounds in corn oil overwhelmed any influence of the CNCs on the interfacial tension. Additionally, we found that interfacial shear rheology (which can be painstakingly difficult to measure) was not a useful tool for formulating these emulsions. This is because at commonly used concentrations of CNCs, the bulk rheology is increased to a much greater degree than that of the interface, making the details of the interfacial rheology unimportant. Finally, we found that at concentrations of CNCs that are typical in industrial processes, characterizing the bulk viscoelastic properties of the aqueous suspending phase without added oil (a relatively simple measurement) is sufficient to predict the influence of NaCl concentration on charge screening between the CNCs and, by extension, increased surface coverage of droplets for greater emulsion stability.

Antibodies Adsorbed to the Air-Water Interface Form Soft Glasses.

When monoclonal antibodies are exposed to an air-water interface, they form aggregates, which negatively impacts their performance. Until now, the detection and characterization of interfacial aggregation have been difficult. Here, we exploit the mechanical response imparted by interfacial adsorption by measuring the interfacial shear rheology of a model antibody, anti-streptavidin immunoglobulin-1 (AS-IgG1), at the air-water interface. Strong viscoelastic layers of AS-IgG1 form when the protein is adsorbed from the bulk solution. Creep experiments correlate the compliance of the interfacial protein layer with the subphase solution pH and bulk concentration. These, along with oscillatory strain amplitude and frequency sweeps, show that the viscoelastic behavior of the adsorbed layers is that of a soft glass with interfacial shear moduli on the order of 10-3 Pa m. Shifting the creep compliance curves under different applied stresses forms master curves consistent with stress-time superposition of soft interfacial glasses. The interfacial rheology results are discussed in the context of the interface-mediated aggregation of AS-IgG1.

Co-Surfactant-Free Bioactive Protein Nanosheets for the Stabilization of Bioemulsions Enabling Adherent Cell Expansion.

Bioemulsions are attractive platforms for the scalable expansion of adherent cells and stem cells. In these systems, cell adhesion is enabled by the assembly of protein nanosheets that display high interfacial shear moduli and elasticity. However, to date, most successful systems reported to support cell adhesion at liquid substrates have been based on coassemblies of protein and reactive cosurfactants, which limit the translation of bioemulsions. In this report, we describe the design of protein nanosheets based on two globular proteins, bovine serum albumin (BSA) and β-lactoglobulin (BLG), biofunctionalized with RGDSP peptides to enable cell adhesion. The interfacial mechanics of BSA and BLG assemblies at fluorinated liquid-water interfaces is studied by interfacial shear rheology, with and without cosurfactant acyl chloride. Conformational changes associated with globular protein assembly are studied by circular dichroism and protein densities at fluorinated interfaces are evaluated via surface plasmon resonance. Biofunctionalization mediated by sulfo-succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) is studied by fluorescence microscopy. On the basis of the relatively high elasticities observed in the case of BLG nanosheets, even in the absence of cosurfactant, the adhesion and proliferation of mesenchymal stem cells and human embryonic kidney (HEK) cells on bioemulsions stabilized by RGD-functionalized protein nanosheets is studied. To account for the high cell spreading and proliferation observed at these interfaces, despite initial moderate interfacial elasticities, the deposition of fibronectin fibers at the surface of corresponding microdroplets is characterized by immunostaining and confocal microscopy. These results demonstrate the feasibility of achieving high cell proliferation on bioemulsions with protein nanosheets assembled without cosurfactants and establish strategies for rational design of scaffolding proteins enabling the stabilization of interfaces with strong shear mechanics and elasticity, as well as bioactive and cell adhesive properties. Such protein nanosheets and bioemulsions are proposed to enable the development of new generations of bioreactors for the scale up of cell manufacturing.

On buckling of layered composite heavy columns—Effect of interlayer bonding imperfection

Buckling loads of partial composite columns under distributed axial loads is investigated in this paper for the first time. The interlayer interaction corresponding to the level of interfacial bonding imperfection in the layered heavy composite columns is formulated in the model by a shear slip/stiffness modulus. Governing differential equations and boundary equations are derived and represented in a general dimensionless form. A semi-analytical solution is applied to the governing buckling equations of the presented model using power-series technique to extract critical loads of partial composite columns. Five different classical end types are considered namely clamped–clamped (C-C), clamped-pinned (C-P), clamped-sliding (C-S), clamped-free (C-F) and pinned–pinned (P-P). Also, for two extreme cases of non-composite/zero-interaction and full-composite/perfectly-bonded layered columns, exact closed-form characteristic buckling equations are introduced. A convergence study is conducted to ensure stability of the applied power-series solution. It is demonstrated that the obtained buckling loads for partial composite columns with different end conditions approach those obtained from the exact closed-from solution for the full-composite extreme case when the interfacial shear modulus approaches infinity. Effect of imperfect bonding between the column layers and slip on critical buckling loads is investigated. It is shown that a more realistic model based on the partial composite interaction hypothesis predicts critical loads that are less than those based on idealized composite columns with perfect interfacial bonding.

Relation between interfacial shear and friction force in 2D materials.

Understanding the interfacial properties between an atomic layer and its substrate is of key interest at both the fundamental and technological levels. From Fermi level pinning to strain engineering and superlubricity, the interaction between a single atomic layer and its substrate governs electronic, mechanical and chemical properties. Here, we measure the hardly accessible interfacial transverse shear modulus of an atomic layer on a substrate. By performing measurements on bulk graphite, and on epitaxial graphene films on SiC with different stacking orders and twisting, as well as in the presence of intercalated hydrogen, we find that the interfacial transverse shear modulus is critically controlled by the stacking order and the atomic layer-substrate interaction. Importantly, we demonstrate that this modulus is a pivotal measurable property to control and predict sliding friction in supported two-dimensional materials. The experiments demonstrate a reciprocal relationship between friction force per unit contact area and interfacial shear modulus. The same relationship emerges from simulations with simple friction models, where the atomic layer-substrate interaction controls the shear stiffness and therefore the resulting friction dissipation.

Surface modification of UHMWPE fibers with chlorination and polydopamine for enhancing the mechanical properties of composites

AbstractUltra‐high molecular weight polyethylene (UHMWPE) fibers had many excellent mechanical properties, but their applications in composites were limited due to the weak interfacial adhesion between UHMWPE fibers with non‐polar methylene and resin matrix. This paper explored an efficient method for the damage‐free modification of fibers by chloride grafting followed by polydopamine (PDA) deposition to obtain UHMWPE‐Cl‐PDA fiber while maintaining the excellent mechanical properties of the fiber. The chemical components of surface treated fibers were observed by XPS and FTIR‐ATR, and the results proved that the fiber surface has been successfully chlorinated and then coated with PDA layer. The surface morphologies of fibers measured by SEM showed the rough surface of UHMWPE‐Cl‐PDA fibers was beneficed to anchor the resin matrix. The different mechanical properties of composites were studied, such as interfacial shear strength (IFSS), impact strength, flexural strength and modulus, especially the IFSS between UHMWPE‐Cl‐PDA and epoxy matrix and the impact strength of UHMWPE‐Cl‐PDA composite were increased by 29.1% and 53.8%, respectively, compared with UHMWPE fibers deposited by PDA.

Experimental Study and Degradation Analysis on Interfacial Shear Modulus of Steel and Steel Fiber-Reinforced Concrete Composite Structure

To address the problems of mutual interference between shaped steel and reinforcement bars and the difficulty of concrete pouring in the construction of steel-reinforced concrete (SRC) composite structure, the steel and steel fiber-reinforced concrete (SSFRC) composite structure without rebars was proposed. Bond behavior between the shaped steel and steel fiber reinforced concrete is the basis to ensure two kinds of materials work together. 20 square specimens were designed and tested by push-out test to study the bond performance and shear modulus of the interface between the shaped steel and steel fiber reinforced concrete. The effects of steel fiber ratio (ρsf), embedded length (Le), and concrete cover thickness (Css) on the interfacial shear modulus (G) were analyzed quantitatively. The degradation law of G was studied by defining the degradation variable of interfacial shear modulus (Da). The results show that the increase of ρsf contributes to the ascent in G, and the loading end displacement (D) at the end of degradation related to G also increase. With the rise of Le, the value of G decreases gradually and the D becomes larger when G starts to deteriorate. In addition, there is a positive correlation between G and Css. Besides, the higher Css leads to a slower degradation process of G.

Enhancing mechanical and interfacial properties of PEEK/epoxy/SWCNT composites employing aromatic hydroxyl and amine-functionalized SWCNTs

Employing epoxy polymer and pristine and aromatic amine and hydroxyl functionalized SWCNTs in poly(ether ether ketone) (PEEK), novel polymer nanocomposite models were created. Molecular dynamics (MD) simulations were used to explore the interfacial, mechanical, and structural features of single-walled carbon nanotube (SWCNT) reinforced PEEK/epoxy matrix (BM) systems. We used MD simulation techniques to show how covalently functionalizing SWCNTs and blending PEEK with a polymer containing hydroxy‑functional groups can improve the interfacial and mechanical properties of PEEK nanocomposites. This study showed that –CH2C6H4NH2, –CH2C6H4OH group grafted SWCNT improve the interfacial and mechanical properties of PEEK-based nanocomposites due to the formation of hydrogen bonds between the filler materials and the polymer matrix, as well as better filler dispersion into the polymer matrix. The improvement of properties of polymer nanocomposites depends on the extent of the interaction of nanoparticles with the polymer matrix. Aromatic amine and hydroxyl (-CH2C6H4NH2, and -CH2C6H4OH) functionalization of SWCNTs is required for their high-performance engineering applications. Because epoxy polymer has a great ability to form hydrogen bonds with fictionalized SWCNT, adding 10% epoxy polymer to the BM increased the interfacial strength, elastic modulus, and shear modulus of SWCNT composites. This study provides a novel technique to improve the properties of polymer nanocomposites by covalently functionalizing SWCNTs.

Tensile modulus of halloysite-nanotube-based system assuming the defective interfacial bonding between polymer medium and halloysite nanotube

In this paper, essential interfacial shear modulus (Gc) in halloysite nanotubes (HNT) nanocomposites is expressed to define the effective inverse aspect ratio and effective volume portion of HNT in the samples. Additionally, Halpin-Tsai model is advanced by the mentioned terms for the modulus of HNT-filled system assuming the defective bonding between polymer medium and HNT. The approximations of the advanced model are linked to the numerous experimented data and the stimuli of all factors on the modulus of system are clarified. Halpin-Tsai model overestimates the moduli of system, whereas the advanced model produces the accurate results matching to the experimental facts. “Gc” inversely governs the modulus of system. The variation of “Gc” from 1 to 5 GPa changes the nanocomposite’s modulus by 57%. The interfacial shear modulus (Gi) positively controls the modulus of system and Gi = 20 GPa improves the modulus of samples by 63%.

Engineering large, anatomically shaped osteochondral constructs with robust interfacial shear properties

Despite the prevalence of large (>5 cm2) articular cartilage defects involving underlying bone, current tissue-engineered therapies only address small defects. Tissue-engineered, anatomically shaped, native-like implants may address the need for off-the-shelf, tissue-repairing therapies for large cartilage lesions. This study fabricated an osteochondral construct of translationally relevant geometry with robust functional properties. Scaffold-free, self-assembled neocartilage served as the chondral phase, and porous hydroxyapatite served as the osseous phase of the osteochondral constructs. Constructs in the shape and size of an ovine femoral condyle (31 × 14 mm) were assembled at day 4 (early) or day 10 (late) of neocartilage maturation. Early osteochondral assembly increased the interfacial interdigitation depth by 244%, interdigitation frequency by 438%, interfacial shear modulus by 243-fold, and ultimate interfacial shear strength by 4.9-fold, compared to late assembly. Toward the development of a bioprosthesis for the repair of cartilage lesions encompassing up to an entire condylar surface, this study generated a large, anatomically shaped osteochondral construct with robust interfacial mechanical properties and native-like neocartilage interdigitation.

Tensile modulus of clay‐reinforced system supposing the interphase effectiveness for load transferring

AbstractIn this work, we focus on the minimum interfacial shear modulus (Sc) and interfacial shear modulus (Si) controlling the efficiency of interphase zone in polymer clay nanocomposites, since the stress transferring through interphase section handles the stress bearing of samples. The roles of “Sc” and “Si” in the effective thickness and concentration of interphase zone are clarified. Moreover, a model based on Kolarik system is developed for modulus of clay‐reinforced nanocomposites, which reflects the efficiency of interphase zone. The experimental data of tensile modulus for many samples display good matching with the predictions of the advanced model. Also, all model parameters properly manipulate the nanocomposite's modulus. Thick clay (t > 4 nm) cannot generate the interphase zone in the samples. A poor “Sc,” high “Si,” and thin clay improve the modulus of nanocomposites, but very high “Sc,” extremely poor “Si,” or thick clay cause a poor nanocomposite. A high value of Sc = 0.21 GPa deteriorates the reinforcing efficiency of clay in nanocomposites. Furthermore, low Si < 35 GPa produces a poorer nanocomposite than the polymer matrix. Additionally, complete exfoliation of thin clay (t = 1 nm) causes 900% improvement in the nanocomposite's modulus.

Shear performance of recycled asphalt mixture based on contact interface parameter analysis

The mechanical characteristics, quantity, and distribution of contact interfaces in the composite skeleton of recycled asphalt mixture affect the consistency of deformation of new and old aggregate composite skeleton, further affecting the macroscopic mechanical properties of material. To quantitatively analyze the effect of reclaimed asphalt pavement (RAP) content on the mechanical characteristics of contact interface and shear performance of recycled asphalt mixture, the tangential elastic stiffness of interface of new-new, new-old, and old-old contact types is defined as ksnew-new, ksnew-old, and ksold-old, respectively; interfacial shear tests were carried out for new-new, new-old, and old-old contact types. Digital image technology and statistical analysis were used to obtain the proportion distribution of αnew-new, αnew-old, αold-oldof three aggregate contact types under different RAP contents. Combined with the calculation results of interface tangential elastic stiffness and shear modulus with different RAP contents, an interface tangential elastic stiffness estimation model and a shear modulus calculation model were established, and the rationality of the model was verified. The results show that different interface contact types significantly affected the shear test results. The tangential elastic stiffness of old-old contact type is the highest, 0.3416 × 106 N/m. The tangential elastic stiffness of new-old and new-new contact types are 0.2254 × 106 N/m and 0.0992 × 106 N/m, respectively. The results of contact interface shear test of recycled asphalt mixture with different RAP contents show that the overall trend of shear curve is similar, and the peak value and mean value of shear force do not change consistently with the increase of RAP content. Using the least square mathematical analysis method for overdetermined equation, the goodness-of-fit ofks regression model with different RAP contents is 0.85. There is a good correlation between the shear modulus calculation results and uniaxial penetration test results, and the correlation coefficient is 0.80.

Modification of advanced Takayanagi model for the modulus of nanoclay/polymer systems comprising the effectual networks of both nanoclay and interphase section

AbstractThe interphase section around clays establishes the network in clay/polymer systems. In this article, we focus on the effectual features of interphase net using clay properties and interphase/interfacial factors to progress the Takayanagi model for modulus of clay‐reinforced systems. The effectual loading of interphase district in the samples and the percolation onset define the portion of interphase area in the net. The forecasts of the model are associated to the experiential quantities of several examples and the roles of whole factors in the modulus are vindicated. The lowest crucial interfacial shear modulus (Sc) of 0.01 GPa produces the highest relative modulus (nanocomposite's modulus per matrix modulus) of 3.5, but a higher ''Sc'' than 0.04 GPa deteriorates the fortifying yield of clays in the specimens. Additionally, the full exfoliation of clay platelets and the highest interfacial shear modulus of 90 GPa recover the relative modulus to 3.5, while the clays cannot reinforce the polymer matrix when the number of clays in the stacks is higher than 3 or at interfacial shear modulus less than 25 GPa.