Linear Modulus Research Articles

Cell encapsulation in gelatin methacryloyl bioinks impairs microscale diffusion properties.

Light-assisted bioprinted gelatin methacryloyl (GelMA) constructs have been used for cell-laden microtissues and organoids. GelMA can be loaded by desired cells, which can regulate the biophysical properties of bioprinted constructs. We study how the degree of methacrylation (MA degree), GelMA mass concentration, and cell density change mass transport properties. We introduce a fluorescent-microscopy-based method of biotransport testing with improved sensitivity compared to the traditional particle tracking methods. The diffusion capacity of GelMA with a higher MA significantly decreased compared to a lower MA. Opposed to a steady range of linear elastic moduli, the diffusion coefficient in GelMA varied when cell densities ranged from 0 to 10 × 106 cells/ml. A comparative study of different cell sizes showed a higher diffusivity coefficient for the case of larger cells. The results of this study can help bioengineers and scientists to better control the biotransport characteristics in light-assisted bioprinted microtissues and organoids.

Thermomechanical Stress Analysis of Hydrated Vital Gluten with Large Amplitude Oscillatory Shear Rheology.

Vital gluten is increasingly researched as a non-food product for biodegradable materials. During processing, the protein network is confronted with increased thermal and mechanical stress, altering the network characteristics. With the prospect of using the protein for materials beyond food, it is important to understand the mechanical properties at various processing temperatures. To achieve this, the study investigates hydrated vital gluten under thermomechanical stress based on large amplitude oscillatory shear (LAOS) rheology. LAOS rheology was conducted at increasing shear strains (0.01-100%), various frequencies (5-20 rad/s) and temperatures of 25, 45, 55, 65, 70 and 85 °C. With elevating temperatures up to 55 °C, the linear viscoelastic moduli decrease, indicating material softening. Then, protein polymerization and the formation of new cross-links due to thermal denaturation cause more network connectivity, resulting in significantly higher elastic moduli. Beyond the linear viscoelastic regime, the strain-stiffening ratio rises disproportionately. This effect becomes even more evident at higher temperatures. Lacking a viscous contribution, the highly elastic but also stiff network shows less mechanical resilience. Additionally, at these elevated temperatures, structural changes during the protein's denaturation and network shrinkage due to water evaporation could be visualized with confocal laser scanning microscopy (CLSM).

Effect of mineral diets on the development of cartilage material properties

Vitamin D and minerals, including zinc (Zn) and manganese (Mn), are vital in the development of bones, but their roles in the development of articular cartilage material behavior are not well understood. In this study, articular cartilage material properties from a hypovitaminosis D porcine model were evaluated. Pigs were produced by sows fed vitamin D deficient diets during gestation and lactation, and the offspring were subsequently fed vitamin D deficient diets for 3 weeks during the nursery period. Pigs were then assigned to dietary treatment groups with inorganic minerals only or inorganic plus organic (chelated) minerals. Humeral heads were harvested from pigs at 24 weeks of age. Linear elastic modulus and dissipated energy were measured under compression to 15% engineering strain at 1 Hz. Anatomical location within the humeral head affected elastic modulus. Diet significantly affected linear modulus and dissipated energy. The largest modulus and highest energy dissipation was in the inorganic zinc and manganese group; the lowest modulus and the least energy dissipation was in the organic (chelated) zinc and manganese group. Pairwise results between the control group and all vitamin D deficient groups were not statistically significant. Overall, these results suggest that mineral availability during rapid growth subsequent to a vitamin-D deficiency during gestation and lactation had minimal effects on articular cartilage material properties in young growing pigs. Though not statistically significant, some of the numerical differences between mineral sources suggest the potential importance of mineral availability during cartilage formation and warrant further study.

Effect of Composition and Freeze-Thaw on the Network Structure, Porosity and Mechanical Properties of Polyvinyl-Alcohol/Chitosan Hydrogels.

We report the synthesis and characterization of poly (vinyl alcohol) (PVA)/Chitosan (CT) cryogels for applications involving the uptake and entrapment of particulate and bacterial colonies. In particular, we systematically investigated the network and pore structures of the gels as a function of CT content and for different freeze-thaw times, combining Small Angle X-Ray Scattering (SAXS), Scanning Electron Microscopy (SEM), and confocal microscopy. The nanoscale analysis obtained from SAXS shows that while the characteristic correlation length of the network is poorly affected by composition and freeze-thaw time, the characteristic size of heterogeneities associated with PVA crystallites decreases with CT content. SEM investigation evidences a transition to a more homogeneous network structure induced by the incorporation of CT that progressively builds a secondary network around the one formed by PVA. A detailed analysis of confocal microscopy image stacks allows to characterize the 3D porosity of the samples, revealing a significantly asymmetric shape of the pores. While the average volume of single pores increases with increasing CT content, the overall porosity remains almost unchanged as a result of the suppression of smaller pores in the PVA network with the progressive incorporation of the more homogeneous CT network. Increasing the freezing time in the FT cycles also results in a decrease of porosity, which can be associated with a growth in the crosslinking of the network due to PVA crystallization. The linear viscoelastic moduli measured by oscillatory rheology show a qualitatively comparable frequency-dependent response in all cases, with a moderate reduction with increasing CT content. This is attributed to changes in the structure of the strands of the PVA network.

Viscoelastic behavior of oral mucosa. A rheological study using small-amplitude oscillatory shear tests

The purpose of this work was to determine the viscoelastic behavior of porcine and human oral mucosa under physiological conditions of temperature, hydration and chewing. The linear elastic and viscous shear moduli of these soft tissues were determined by small-amplitude oscillatory shear (SAOS) tests at masticatory frequency using a stress-controlled rheometer equipped with an immersion cell on punched biopsies 8 mm in diameter. Non physiological conditions of temperature were also used to access other parameters such as the denaturation temperature of collagen.First, the different parameters such as normal force, frequency and maximal strain were adjusted to obtain reliable data on porcine mucosa. The optimal normal force was 0.1N and the linear viscoelastic limit was found for a strain amplitude of 0.5% for both 0.1 and 1 Hz. The storage moduli of porcine mucosa, ranging from 5 to 16 kPa, were in the same range as cutaneous tissues determined by SAOS at equivalent frequencies. The storage modulus, superior to the loss modulus G″, indicates a predominant elastic contribution to shear stress in chewing conditions.Second, this protocol evidenced an influence of the anatomic site of the mouth on the viscoelastic behavior of porcine mucosa, mandibular biopsies having higher storage moduli than maxillary biopsies. Temperature scans showed the mechanical manifestation of collagen denaturation in the 60–70 °C range as previous calorimetric analyses. Finally, this mechanical protocol was successfully adapted to characterize human mucosa in an elderly population. It was shown that the elastic modulus is impacted by local inflammation (gingivitis), decreasing significantly from 6 ± 1.4 kPa to 2.5 ± 0.3 kPa.

Investigation on the physicochemical properties of Nru clay deposit and its industrial application

The utility of Nru clay for industrial application, which was taken from the Nsukka local government area in Enugu State, Nigeria, is assessed in this study for its physical and chemical properties. The clay was investigated chemically which showed SiO 2 51.2%, Al 2 O 3 18.3% as the predominant constituents while other metallic oxides such as Fe 2 O 3 5.3%, MgO 2.2%, Na 2 O 1.8%, CaO 1.4%, K 2 O 1.3% and MnO 0.7% were present in considerable proportion. The physical and mechanical analysis acknowledged a range in the linear shrinkage (4.17 - 6.25%), total shrinkage (7.8 - 10.2%), apparent porosity (36.92 – 26.58%), apparent density (2.59 - 2.37 g/cm3), bulk density (1.63 - 1.74 g/cm3), water absorption (22.64 – 15.33%) and modulus of rupture (6.70 – 9.15 kg/cm2) with an increase in firing temperature from 900°C to 1200°C. Nru clay can withstand heat without melting or deforming at temperature up to 1200 °C and exhibited reasonable plasticity with a modulus of plasticity of 1.42. We can infer from our investigation that Nru clay is a potential raw material for industries in the production of ceramics, high melting clays, fired bricks, and paints. Alternatively, the clays’ properties can be tailored to achieve superior physical and mechanical properties by enhancing them with additives. Therefore, it can be employed to cushion the exorbitant cost of importing clay minerals from other nations.

A linear finite element for timber–concrete layered beams with interlayer slip

In this paper, a beam theory for linear two-layer beams is presented in the framework of the Finite Element (FE) method. In particular, the beam theory aims to represent the static and dynamic response of timber–concrete layered structures, in which a concrete slab is supported by timber girders. Since the timber layer has a rather low shear stiffness, a shear-flexible formulation of the displacement field is adopted. In general, it cannot be assumed that the layers of such members are perfectly bonded. Therefore, the relative interlayer displacement in the longitudinal direction is considered, which is determined by a linear slip modulus in a smeared approach. Based on these assumptions, the stiffness matrix, mass matrix and load vector of a finite beam element are derived. Modal analyses on a single-span beam with clamped, free and hinged supports are performed and compared to the outcomes of 3D FE simulations to verify the applicability of the proposed beam theory over a wide frequency range. Static analyses on two structural systems illustrate the accuracy of the beam deflection and the interlayer slip, as well as the realistic assessment of normal and shear stresses in the two layers.

CHARACTERIZATION OF NATIVE AND DECELLULARIZED PORCINE TENDON UNDER TENSION AND COMPRESSION: A CLOSER LOOK AT GLYCOSAMINOGLYCAN CONTRIBUTION TO TENDON MECHANICS

Decellularised porcine superflexor tendon (pSFT) has been demonstrated to be a suitable scaffold for anterior cruciate ligament reconstruction[1]. While the role of collagen in tendons is well known, the mechanical role of glycosaminoglycans (GAGs) is less clear and may be altered by the decellularisation process.To determine the effects of decellularisation on pSFT GAG content and mechanical function and to investigate the consequences of GAG loss in tensile and compressive loading.pSFTs were decellularised following previous techniques [2]. For GAG removal, native pSFTs were treated with chondroitinase ABC (ChABC; 0.1U/mL, 72h). Cell and GAG removal was validated using histology and quantitative assays. Native, decellularised and ChABC treated groups (n=6) were biomechanically characterised. In tension, specimens underwent stress relaxation and strength testing using previous protocols [1]. Stress relaxation data was fitted to a modified Maxwell-Weichert model to determine time-dependent (E1 & E2) and time-independent moduli (E0). The toe and linear region moduli (Etoe, Elinear), in addition to tensile strength (UTS) and failure strain were determined from strength testing. In compression, specimens underwent confined loading conditions (ramp at 10 s-1 to 10% strain and hold). The aggregate modulus (HA) and zero-strain permeability (k0) were determined using previous techniques [3]. Data was analysed by one-way ANOVA with Tukey post-hoc test to determine significant differences between test groups (p<0.05).Quantitative assays showed no GAG reduction post-decellularisation, but a significant reduction after ChABC treatment. HA was only significantly reduced in the ChABC group. k0 was significantly higher for the ChABC group compared to decellularised. E0 was significantly reduced in the decellularised group compared to native and ChABC groups, while E1 and E2 were not different between groups. Etoe, Elinear, UTS and failure strain were not different between groups.Decellularisation does not affect GAG content or impair mechanical function in pSFT. GAG loss adversely affects pSFT compressive properties, revealing major mechanical contribution under compression, but no significant role under tension.

Compressional behavior of the aragonite-structure carbonates to 6 GPa

The behaviors of aragonite (CaCO_3), strontianite (SrCO_3), cerussite (PbCO_3), and witherite (BaCO_3) at increasing pressure have been studied up to 6 GPa using density functional theory with plane waves. A parallelism of the orthorhombic carbonates with the closed-packed AsNi structure is considered in our analysis, being the CO_3^{2-} groups not centered in the interstice of the octahedron. The decomposition of the unit-cell volume into atomic contributions using the Quantum Theory of Atoms in Molecules has allowed the analysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distances, and atomic compressibilities are calculated. The largest compression is on the c crystallographic axis, and the c linear modulus has a linear function with the mineral bulk modulus (K_0). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) only gives linear functions when K_0 is related either with the CC distances modulus or the modulus of the distances of the C to the faces of the octahedron perpendicular to c. These last distances are the projections of the Metal–Oxygen (MO) distances to the center of the octahedron. K_{0AE} carbonates also show linear functions with the atomic moduli of their cations. However, the whole series show a linear relation with the atomic modulus of C atoms. Therefore, the whole series highlight the importance of the C atoms and their interactions in the mechanism of compression of the orthorhombic carbonate series.

Large amplitude oscillatory shear stress (LAOStress) analysis for an acid-curd Spanish cheese: Afuega'l Pitu atroncau blancu and roxu (PDO)

Large amplitude oscillatory shear stress (LAOStress) was used to study the nonlinear rheological properties of Afuega'l Pitu (PDO) cheese atroncau blancu and roxu, a Spanish acid-curd cheese made from cow's milk, from nine manufacturers. Composition, physicochemical and lipolytic parameters were determined. The moisture content varied between (23.60 ± 0.75)% and (45.84 ± 0.01)% and the percentage of salt-in-moisture was <(8.17 ± 0.86)%. Stress amplitude sweeps were conducted at 20 °C, 50 °C and 75 °C at frequencies of 0.628 rad/s, 6.28 rad/s and 31.4 rad/s, for each temperature. Experiments were analyzed using the MITlaos software modified to extract LAOStress quantitative material functions. The large number of experiments and the high dimensionality of the LAOS signals were carefully analyzed and reduced to understand the material response and extract the relevant properties. All cheeses showed a distinct signature that motivates us to introduce the concept of “pseudo-linear LAOS” where nonlinear rheology is evident in only some measures while others minimally change from the linear regime. We geometrically interpret these different LAOS measures as rotation and distortion of Lissajous curves; all cheeses showed pseudo-linear LAOS regimes where rotation is strong and distortion is minimal, i.e. first-harmonics change dramatically in a regime where higher-harmonics are small enough that Lissajous curves are nearly elliptical. The pseudo-linear behavior enabled low-dimensional data reduction and three metrics were discovered to be the most relevant: linear elastic modulus (G′), critical stress (σcrit) and strain (γcrit) amplitudes. All Afuega'l Pitu cheese samples softened as stress amplitude increased while maintaining a solid-like behavior (tanδ^1∼ 0.3), regardless of frequency and temperature. Moreover, the difference between blancu and roxu was statistically insignificant compared to difference between manufacturers. Linear G′ and nonlinear σcrit decreased with increasing temperature, while the nonlinear γcrit maintained a constant value at 50 °C and 75 °C. Although G′, σcrit and γcrit metrics establish comparison between cheeses, more metrics are still required to fully connect rheology to cheese texture and sensory profiles.

Stiffening and Toughening of Asphalt Mastic Induced by Bitumen–Mineral Selective Molecular Adsorption and Nanostructural Reconstruction

Asphalt mastic is the most important binder in asphalt mixtures and its rheology is inevitably influenced by the mineral aggregates. Due to the little consideration that has been paid to aggregates’ effects, the rheological properties of mastic films have not been accurately characterized for the present method. Therefore, this study aimed to investigate the rheological characteristics of mastic affected by mineral aggregates and reveal its fundamental mechanism of interfacial interaction. The results suggest that the aggregates increased the stiffness and toughness of mastic within the linear and nonlinear viscoelastic regions. The mastic on limestone had a higher linear viscoelastic modulus than that on basalt below 35 °C, and its ratio reached up to 1.18. However, the modulus of the mastic on basalt surpassed that on limestone by over 50 °C, and the maximum ratio reached 2.17. The mastic in contact with the limestone had a higher failure strain and failure modulus than that in contact with the basalt, the ratios of which reached 1.60 and 1.32, respectively. The macrorheological characteristics are closely related to the nanostructures and intermolecular interactions of bitumen–mineral systems. The coexistence of a stable bitumen nanostructure and an adsorbed layer on the calcite substrate provided a strong bonding energy and high resistance to external shear deformation, leading to the high stiffness and toughness of the limestone. Abundant metal ions from augite and albite diffused into the bitumen layer and destroyed its nanostructure, decreasing the stability of the mastic–basalt interface system. The non-bond energy of bitumen-calcite was 14.15% higher than that of bitumen-albite, and the ratio of shear stress of the bitumen-calcite to the bitumen-albite reached up to 6.8. Therefore, the calcite in limestone reinforced the bitumen, and the augite and albite in basalt destroyed the bitumen colloidal structure. This provides a fundamental understanding of the rheological characterization of mastic on mineral aggregates.

Scaling relations in rheology of proteins present in meat analogs

In this paper, we investigate whether the rheology of plant proteins is following similar scaling rules, as recently found for maltodextrins. The aim is to construct master curves of the rheology measurements, such that in combination with the scaling rules, the rheology can also be extrapolated to relevant practical conditions, that are not accessible with rheometers. We have analysed 4 different plant proteins, which are currently used in the manufacturing of meat analogs, on which we have performed frequency and amplitude sweeps for a wide range of temperatures and moisture contents. The frequency sweeps show that for all investigated temperatures and moisture contents the protein doughs show elastic behaviour for small strains and low frequencies, which maps on to a single master curve. Yet, the linear elastic modulus is governed by the ratio of the (moisture-dependent) glass transition temperature and the actual processing temperature ( T g / T ). Furthermore, we have constructed master curves for the strain sweeps, characterized by a critical strain that is independent of moisture content and temperature. Beyond the critical strain, the protein dough is showing strain thinning behaviour. Also with the use of literature data, we have found for pea a similar scaling exponent for shear thinning, strain thinning, and the moduli in the transition zone. This seems to confirm that plant protein doughs adhere to the Cox-Merz and Rutgers-Delaware rule, allowing translation to practical steady flow conditions as occurring during manufacturing. • For small strains all protein doughs show elastic behaviour for all investigated temperatures and moisture contents. • The linear elastic modulus is a function of T g /T. • Beyond a critical strain, which is temperature and moisture independent, doughs exhibit strain thinning. • An identical scaling exponent is found for transition zone, strain and shear thinning.

Characterisation of native and decellularised porcine tendon under tension and compression: A closer look at glycosaminoglycan contribution to tendon mechanics

Decellularised porcine superflexor tendon (pSFT) has been characterised as a suitable scaffold for anterior cruciate ligament replacement, with dimensions similar to hamstring tendon autograft. However, decellularisation of tissues may reduce or damage extracellular matrix components, leading to undesirable biomechanical changes at a whole tissue scale. Although the role of collagen in tendons is well established, the mechanical contribution of glycosaminoglycans (GAGs) is less evident and could be altered by the decellularisation process. In this study, the contribution of GAGs to the tensile and compressive mechanical properties of pSFT was determined and whether decellularisation affected these properties by reducing GAG content or functionality.PSFTs were either enzymatically treated using chondroitinase ABC to remove GAGs or decellularised using previously established methods. Native, GAG-depleted and decellularised pSFT groups were then subjected to quantitative assays and biomechanical characterisation. In tension, specimens underwent stress relaxation and strength testing. In compression, specimens underwent confined compression testing.The GAG-depleted group was found to have circa 86% reduction of GAG content compared to native and decellularised groups. There was no significant difference in GAG content between native (3.75 ± 0.58 μg/mg) and decellularised (3.40 ± 0.37 μg/mg) groups. Stress relaxation testing discovered the time-independent and time-dependent relaxation moduli of the decellularised group were reduced ≥50% compared to native and GAG-depleted groups. However, viscoelastic behaviour of native and GAG-depleted groups resulted similar. Strength testing discovered no differences between native and GAG-depleted group's properties, albeit a reduction ∼20% for decellularised specimens' linear modulus and tensile strength compared to native tissue. In compression testing, the aggregate modulus was found to be circa 74% lower in the GAG-depleted group than the native and decellularised groups, while the zero-strain permeability was significantly higher in the GAG-depleted group (0.86 ± 0.65 mm4/N) than the decellularised group (0.03 ± 0.04 mm4/N).The results indicate that GAGs may significantly contribute to the mechanical properties of pSFT in compression, but not in tension. Furthermore, the content and function of GAGs in pSFTs are unaffected by decellularisation and the mechanical properties of the tissue remain comparable to native tissue.

Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

Interfacial rheology is crucial in dictating morphology and ultimate properties of particle-stabilized polymer blends, but is challenging to be determined. In this study, a fully polymeric dumbbell-shaped Janus nanoparticle (JNP) of polymethyl methacrylate (PMMA) and polystyrene (PS) spheres with equal sizes (∼80 nm) was prepared and used as an efficient compatibilizer for PMMA/PS blends. The JNPs were preferentially localized at the PMMA/PS interface, thereby reducing the interfacial tension and refining the morphology in both droplet-matrix and co-continuous type blends, whereby a JNP concentration ∼2.5 wt % is sufficient to reach a saturation in droplet size reduction due to compatibilization. Based on the linear viscoelastic moduli and corresponding relaxation spectra (H(τ)*τ) of JNP-compatibilized droplet-matrix blends, besides the droplet shape relaxation time (τF), a longer relaxation time (τβ), typically related to interfacial viscoelasticity, was readily identified. The dependence of τβ on the JNP concentration (WJNPs) was significantly dominated by the droplet size reduction induced by the JNP compatibilization, with τβ decreasing with increasing WJNPs. The viscoelastic properties extracted from τβ typically originate from a combination of gradients in interfacial tension due to the particle redistribution at the droplet interface (Marangoni stresses) and the deviatoric stresses of intrinsic rheological origin. The latter originate from the intrinsic viscoelasticity of the particle-laden interface, which is enhanced by particle jamming and particle–polymer interactions, such as entanglements between chains from the polymeric spheres and those penetrating from the bulk into the spheres. To address the challenge of isolating these contributions, a JNP-sandwiched PMMA/PS multilayer structure was designed to exclude the effect of Marangoni stresses and droplet curvature, thus having no τF but a new relaxation (τ′β), which characterizes the contribution of intrinsic interfacial viscoelasticity. The τ′β was observed to increase with JNP coverage (Σ) following the Vogel–Fulcher–Tammann model that is typically used to describe the divergent behavior of the “cage” effect in classical colloidal glasses. Moreover, a multimode Maxwell model fitting allows to split the interfacial relaxation into the confined diffusion of JNPs within their cage and the entanglements between the JNPs and the bulk.

Topology of singular set of semiconcave function via Arnaud's theorem

We proved the (local) path-connectedness of certain subset of the singular set of semiconcave functions with linear modulus in general. The proof is based on a theorem by Marie-Claude Arnaud ([4]). We also gave a new proof of the theorem in time-dependent case.

Soil-structure pile foundation interaction model due to lateral loading

Experimental research on piles, by models and physical tests on a laboratory scale, using materials and sizes that are different from the prototypes. The model is designed, treated, and interpreted the results of observing the response based on similarity using Model theory, but the soil sample cannot be modeled with model theory, giving rise to doubts similarity of the research. This study was conducted to examine the effect of pile-soil interaction on several views of the elastic modulus of the soil due to lateral loads. Laboratory model pile foundations are laterally loaded, on soil samples in a test box. The deflection of the pile foundation is analyzed based on the use of linear, layered, and non-linear modulus of elasticity. A non-linear simulation of the Winkler model with a spring along the depth of the pile was carried out to calibrate the horizontal deflection of the laboratory experimental model. The results showed that the Winkler model's modulus of elasticity was approximately 40% of the pile length, and the non-linear difference between the Winkler and laboratory models was 10.77%, comparisons can be conclusive about the need for similar research on lateral loading of laboratory model piles. The analysis also noted that the surface deflection was determined by winkler’s model elastic modulus analysis with an excess of about 12% to 14% in the first 10% of the pile length.

Mechanical properties and two damage models of frozen-thawed rocks under triaxial compression

Freeze-thaw induced damage in rock engineering is common in cold regions. However, a damage model for capturing the whole failure process of frozen-thawed rocks is still lacking. In this paper, triaxial compression tests of red sandstone experienced with different freeze-thaw cycles (FTCs) were conducted. Subsequently, the variation of mechanical properties with the numbers of FTCs under different confining pressures were obtained, including peak deviator stress, peak strain, linear elastic modulus, residual strength, friction angle and cohesion. The completely compacted point on stress-strain curve of rock was determined by calculating the strain difference between the stress-strain curve and a reference line. On theses bases, two damage constitutive models considering the initial compaction phase and residual deformation phase were established by means of the continuum damage mechanics and statistical microelement strength theory together with the random exponential function of strain difference. The calculated data obtained from the two proposed models and measured data were then compared. The results shows that the proposed model I is suitable for all rocks samples experienced with FTCs, while the proposed model II is suitable for rocks with small residual strength or large stress difference between peak strength and residual strength. Meanwhile, the two proposed models were compared with the existing ones by evaluating the factor Ω . The influence of confining pressure and FTCs on damage evolution of rock was discussed, and the physical meanings of the parameters in the two models were analyzed in details. The findings are beneficial for providing a reference in developing a constitutive damage model for rocks in cold regions.

Linear and Nonlinear Elastic Properties of Polystyrene-Based Nanocomposites with Allotropic Carbon Fillers and Binary Mixtures.

We report measurements of linear and nonlinear elastic properties of polystyrene-based nanocomposites with six types of nanofillers, including single and binary mixtures of allotropic carbon nanoparticles. Composite samples were fabricated by the same technology and contained the same filler concentration (5% wt.), which allowed for a direct comparison of their properties. It was shown that the most significant variations of linear and nonlinear elastic properties occur in different nanocomposites. In particular, the most pronounced enhancements of linear elastic moduli (in about 50%) obtained in tensile and flexural tests and in dynamic mechanical analysis were recorded in the sample filled with spherical fullerene nanoparticles. While the most profound rise of absolute values of nonlinear elastic moduli (tens of times) was obtained in the sample filled with the mixture of carbon nanotubes and graphene. The observed tendencies demonstrated the synergistic effect of fillers of different dimensionality on the elastic properties of nanocomposites.

Auxetics and Other Systems with Unusual Characteristics

Auxetics and Other Systems with Unusual Characteristics

A more accurate fatigue characterization of GO-modified asphalt binder considering non-linear viscoelastic behaviour and UV exposure effects

The non-linear viscoelastic (NLVE) behaviour at high load levels is often neglected when characterizing the fatigue performance of asphalt materials, leading to a conservative or even underestimated assessment of the fatigue durability. The incremental stress sweep tests were conducted to define the threshold load amplitudes of the graphene oxide-modified asphalt binders (GO-MA) in the NLVE domain. The linear and non-linear dynamic shear modulus (|G*|LVE and |G*|NLVE) at fatigue test conditions were separately incorporated into the simplified viscoelastic continuum damage (S-VECD) model to rigorously quantify the fatigue life of asphalt binders. The damage evolution and the corresponding fatigue life of GO-MA binders in LVE-based and NLVE-based S-VECD models were analyzed comparatively. The outcomes manifested that GO nanoparticles could enhance the fatigue life of the asphalt binder. The comparison outcomes demonstrate an increase in fatigue life prediction for the base binder and GO-MA when both NLVE behavior and aging effects are taken into account.