Decrease In Shear Modulus Research Articles

Calculation of damage accumulation taking into account changes in material characteristics

One of the important issues in the study of composite materials are microdefects and their accumulation in the binder. Cracks that occur in the transverse directions of the layers are considered to be the most common macrodefect. During cracking, the elastic modulus and shear modulus decrease. This article discusses the issue of obtaining calculation formulas that take into account the accumulation of damage, taking into account cracks in the layers and interlayer cracks on the example of the wing joint with the center section.

INVESTIGATION OF THE PASSAGE OF VIBRATIONS THROUGH A FIXED SECTION OF AN ELONGATED PLATE CAUSED BY THE ACTION OF THE AXIAL FORCE AT THE END

A method has been developed for the experimental study of forced elastic vibrations of a cantilevered thin-walled structural element in the form of a rod-strip, excited due to the passage of vibrations through the section of a finite length fixed along one of the surfaces caused by axial loading by a harmonic force applied to the end of the fixed section. The experimental dependence of the amplitude values of the vibration accelerations of the point at the end of the console on the frequency of the excited bending vibrations of the end of the rod is obtained, indicating the passage of vibrations through the fixing section of the finite length, which occurs due to the transformation of longitudinal vibrations in the loading zone into longitudinal-transverse-shear vibrations of the rod-strip in the fixing zone, followed by their transformation into predominantly bending vibrations of the cantilever part of the rod. For the theoretical study of the described phenomenon, a transformational model of deformation of the rod-strip is constructed, taking into account the deformability of the fastening section of finite length on the basis of the refined model of S. Timoshenko. The cantilever part of the rod is represented by the classical Kirchhoff-Love model, taking into account geometric nonlinearity in determining axial deformations. The kinematic conditions of coupling of the fixed and cantilever parts of the rod are formulated. On the basis of the Hamilton-Ostrogradsky variational equation, the equations of motion of the non-fixed and fixed parts of the rod, as well as the boundary conditions for them and the force condition of conjugation of the marked parts of the rod are obtained. Numerical experiments have been carried out for a rod-strip made of aluminum alloy D16AT, showing a noticeable passage of vibrations through the fixing section of the final length into the cantilever part of the rod with a decrease in the dynamic shear modulus of the material to a certain value.

DYNAMIC PROPERTIES OF SAND FOR EARTHQUAKE RESPONSE ANALYSIS IN THE BAY OF CAMPECHE

The Bay of Campeche is located in a region of moderate to high seismic activity related to the active triple junction between the North American, Caribbean, and Cocos plate boundaries. Therefore, the fixed offshore platforms and subsea structures in the Bay of Campeche must be designed against earthquake loading. A database was developed of classification and index properties tests, in situ measurements of shear wave velocity (Vs) using downhole P-S suspension seismic velocity logging, in situ piezocone penetration tests, resonant column tests to characterize the shear modulus and material damping ratio at small shear strains (10−5 % to about 0.1 %), and strain-controlled cyclic direct simple shear tests to evaluate the decrease of shear modulus and the increase of material damping ratio at large shear strains (0.1 % to about 10 %) performed on sand from the Bay of Campeche, including sands with no carbonate content to 100 % carbonate content, retrieved from the seafloor to a penetration depth of 120 m below seafloor. The database was tailored specifically to develop empirical correlations for the Bay of Campeche sand to determine Vs when in situ measurements of Vs are not available and to develop numerical modeling to predict the variation of the normalized shear modulus (G/Gmax) and material damping ratio (D) as a function of shear strains (g) when dynamic test results are unavailable for all the sand layers. The equations developed to calculate Vs and the curves of G/Gmax-g and D-g of Bay of Campeche sands are recommended for preliminary or perhaps even final seismic site response evaluations.

DYNAMIC PROPERTIES OF CLAY FOR EARTHQUAKE RESPONSE ANALYSIS IN THE BAY OF CAMPECHE

The Bay of Campeche is located in a region of moderate to high seismic activity related to the active triple junction between the North American, Caribbean, and Cocos plate boundaries. Therefore, the fixed offshore platforms and subsea structures in the Bay of Campeche must be designed against earthquake loading. A database was developed of classification and index properties tests, in situ measurements of shear wave velocity using downhole P-S suspension seismic velocity logging, in situ piezocone penetration tests, resonant column tests to characterize the shear modulus and material damping ratio at small shear strains (10−5 % to about 0.1 %), and strain-controlled cyclic direct simple shear tests to evaluate the decrease of shear modulus and the increase of material damping ratio at large shear strains (0.1 % to about 10 %) performed on clays from the Bay of Campeche, including clays with no carbonate content to 100 % carbonate content, retrieved from the seafloor to a penetration depth of 120 m below seafloor. The database was tailored specifically to develop empirical correlations for the Bay of Campeche clay to determine Vs when in situ measurements of Vs are not available and to develop numerical modeling to predict the variation of the normalized shear modulus (G/Gmax) and material damping ratio as a function of shear strains (g) when dynamic test results are unavailable for all the clay layers. The equations developed to calculate Vs and the curves of G/Gmax-g and D-g of Bay of Campeche clays are recommended for preliminary or perhaps even final seismic site response evaluations.

The Effects of Isometric Fatigue on Trunk Muscle Stiffness: Implications for Shear-Wave Elastography Measurements

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (-8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006-0.022; Cohen's d = 0.40-46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697-0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29-0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain.

Effect of Amplitude and Duration of Cyclic Loading on Frictional Sliding Instability in Granular Media: Implication to Earthquake Triggering of Landslides

AbstractStrong earthquakes with larger magnitude and longer durations trigger many landslides, however, how magnitude and duration affect landslides is still unclear. Many factors could contribute to this, including additional shear stress provided by strong ground motion, or “seismogenic liquefaction”; herein, we hypothesize that the dynamic weakening of sliding zone gouge is important. We explored the influence of earthquake magnitude and duration on landslide triggering by simulating the seismic response of sliding zone gouge using a dynamic ring‐shear device and glass spheres. The experiments showed that vibration with larger amplitudes and longer durations more easily trigger deformation and even instability in dry granular materials. We used a dynamic triaxial‐bender system to find that the shear modulus of these materials decreased with the increase in duration and amplitude of cyclic loading. We suggest that this universal decrease in shear modulus is an important landslide‐trigger mechanism. Our results revealed how magnitude and duration of earthquakes affect co‐seismic landslides and why earthquakes with larger magnitude and long durations can trigger more co‐seismic landslides.

Послойный динамический модуль сдвига в поперечном сечении древесностружечной плиты

The research results are aimed at the formation of ideas concerning the features of molecular motion of the components of the outer and inner layers of the particle board material in the temperature range from room temperature to 275–300 °C, as well as at revealing the fact of binder undercuring in the inner layers. The paper provides data on the temperature dependences of the dynamic shear modulus of the outer and inner layers of the particle board material, obtained by dynamic mechanical analysis using a torsion pendulum. We found significant differences in the nature of the dependencies for samples taken at different distances from the surface layers. The material of the outer layers is characterized by the typical pattern of a continuous irregularly consistent decrease in the dynamic shear modulus with increasing temperature, which is common to most polymeric and composite materials. A short-term intermittent increase in the dynamic shear modulus relative to neighboring areas was detected in the inner layers at 140±5 °C, which is not typical for materials in a stable state. There is also a tendency for the dynamic shear modulus of the particle board material to decrease at room temperature with distance from the outer layers, due to the heterogeneous fractional composition and differences in the nature of chemical cross-linking during hot pressing. It has been assumed that the detected anomalous increase in the dynamic shear modulus in the inner layers of the material at 140±5 °С is a symptom of the binder post-treatment process directly in conditions of its heating when measuring the dynamic shear modulus by dynamic mechanical analysis. Thus, it is concluded that the particle board sample shows maximum curing of the thermosetting binder in the layers, which are 4.5–5.0 mm distant from both surfaces. Partial undercuring of the binder occurs in the inner layers, which are more than 5.5 mm away from the surfaces. Thus, it is shown that the method of dynamic mechanical analysis can be used as a tool to control the presence in the inner layers of the particle board material of the components of thermosetting binder, undercured in the hot pressing process, which will help to obtain a material with more stable characteristics.

Correlating the microstructural architecture and macrostructural behaviour of the brain

The computational simulation of pathological conditions and surgical procedures, for example the removal of cancerous tissue, can contribute crucially to the future of medicine. Especially for brain surgery, these methods can be important, as the ultra-soft tissue controls vital functions of the body. However, the microstructural interactions and their effects on macroscopic material properties remain incompletely understood. Therefore, we investigated the mechanical behaviour of brain tissue under three different deformation modes, axial tension, compression, and semi-confined compression, in different anatomical regions, and for varying axon orientation. In addition, we characterised the underlying microstructure in terms of myelin, cells, glial cells and neuron area fraction, and density. The correlation of these quantities with the material parameters of the anisotropic Ogden model reveals a decrease in shear modulus with increasing myelin area fraction. Strikingly, the tensile shear modulus correlates positively with cell and neuronal area fraction (Spearman’s correlation coefficient of rs=0.40 and rs=0.33), whereas the compressive shear modulus decreases with increasing glial cell area (rs=−0.33). Our study finds that tissue non-linearity significantly depends on the myelin area fraction (rs=0.47), cell density (rs=0.41) and glial cell area (rs=0.49). Our results provide an important step towards understanding the micromechanical load transfer that leads to the non-linear macromechanical behaviour of the brain. Statement of significanceWithin this article, we investigate the mechanical behaviour of brain tissue under three different deformation modes, in different anatomical regions, and for varying axon orientation. Further, we characterise the underlying microstructure in terms of various constituents. The correlation of these quantities with the material parameters of the anisotropic Ogden model reveals a decrease in shear modulus with increasing myelin area fraction. Strikingly, the tensile shear modulus correlates positively with cell and neuronal area fraction, whereas the compressive shear modulus decreases with increasing glial cell area. Our study finds that tissue non-linearity significantly depends on the myelin area fraction, cell density, and glial cell area. Our results provide an important step towards understanding the micromechanical load transfer that leads to the non-linear macromechanical behaviour of the brain.

Differentiation of thixotropy from damage for accurately characterizing fatigue resistance of asphalt binder

Accurate characterization of the fatigue resistance of asphalt binder is of great significance to the prediction of asphalt pavement performance. Traditionally, apparent changes in viscoelastic parameters, including dynamic shear modulus and phase angle, with the number of loading cycles are used to define the fatigue performance of the asphalt binder. However, thixotropy also leads to changes in these viscoelastic parameters, and its contribution is not yet well understood. This study develops a method to quantify the effects of damage and thixotropy on the changes of viscoelastic parameters under the cyclic stress-controlled loading mode. The new method includes the four key steps: (1) determining the thixotropy influence-dominated phase; (2) establishing a thixotropy model to characterize the influence of thixotropy on the effective dynamic shear modulus; (3) calculating damage density from the apparent and effective dynamic shear moduli; and (4) characterizing thixotropy behavior based on Black space diagram. The effectiveness of the newly developed method is verified by the time sweep test, which is conducted on two types of asphalt binder under varying stress levels.with a loading frequency of 10 Hz and a test temperature of 25 °C. The results show that: (1) the change of dynamic shear modulus is resulted from the damage and thixotropy, while that of phase angle is only caused by the thixotropy; (2) thixotropy leads to the decrease of dynamic shear modulus and increase of phase angle; and its influence on viscoelastic parameters increases with the loading time and stress level increased; (3) under the influence of thixotropy, the dynamic shear modulus is linearly related to the phase angle, which is independent of the stress level applied and the damage accumulated in the asphalt binder.

Time-course of physical properties of the psoas major muscle after exercise as assessed by MR elastography

This study aimed to analyze the time-course of the physical properties of the psoas major muscle (PM) before and after exercise using magnetic resonance elastography (MRE). Muscle stiffness is one of the important properties associated with muscle function. However, there was no research on the stiffness of the PM after exercise. In this study, we investigated time-course changes of the shear modulus of the PM after exercise. Furthermore, T2 values and apparent diffusion coefficient (ADC), as the additional information associated with muscular physical properties, were also measured simultaneously.Healthy young male volunteers were recruited in this study (n = 9) and they were required to perform a hand-to-knee isometric and unilateral exercise (left side). At each time-point before and after exercise, a set of 3 types of MR scans to measure multiple physical properties of the PM [shear modulus (MRE), T2 values, and ADC] were repeatedly taken. On day 1, a single set MR scan was taken before exercise (pre-exercise MR scan), and 6 sets MR scans were taken (5.5 to 38.0 min after exercise). After about 10-min rest (46.0 to 56.0 min after exercise), 4 sets MR scans were taken (57.5 to 77.0 min after exercise). About 10-min rest was taken again (85.0–95.0 min after exercise), 4 sets MR scans were taken (96.5 to 116.0 min after exercise). On days 2 and 7, a single set MR scan (MRE, T2 value, and ADC) was taken on each experimental day. The data were analyzed as relative changes (%) of the given parameters to the pre-exercise values.The results indicated significant decreases in PM shear modulus up to about 30 min after exercise. Then, it gradually increased and showed significant increases at about 100 min after exercise compared to that before exercise. T2 values and ADC showed significant increases up to about 65 min after exercise compared to those before exercise, and then returned to the pre-exercise values. On days 2 and 7, all values showed no significant changes compared to the pre-exercise values.This study is the first to report the time-course of the physical properties of the PM after exercise.

Effect of Cr and Al on Elastic Constants of FeCrAl Alloys Investigated by Molecular Dynamics Method

The FeCrAl alloy system is recognized as one of the candidate materials for accident-tolerant fuel (ATF) cladding in the nuclear power industry due to its high oxidation resistance under irradiation and high-temperature environments. The concentrations of Cr and Al have a significant effect on elastic properties of the FeCrAl alloy. In this work, elastic constants C11, C12, C44, bulk modulus and shear modulus of FeCrAl alloy were calculated with molecular dynamics methods. We explored compositions with 1–15 wt.% Cr and 1–5 wt.% Al at temperatures from 0 K to 750 K. The results show that the concentrations of Al and Cr have different effects on the elastic constants. When the concentration of Al was fixed, a decrease in bulk modulus and shear modulus with increasing Cr content was observed, consistent with previous experimental results. The dependence of elastic constants on temperature was also the same as in the experiments. Investigations into elastic properties of defect-containing alloys have shown that vacancies, voids, interstitials and Cr-rich precipitations have different effects on elastic properties of FeCrAl alloys. Investigations of elastic properties of defect-containing alloys have shown that vacancies, void, interstitials and Cr-rich precipitations have different effects on elastic properties of FeCrAl alloys. Therefore, the present results indicate that both the Cr and Al concentrations and radiation defects should be considered to develop and apply the FeCrAl alloy in ATF design.

Characterizing the Diffusion and Rheological Properties of Aged Asphalt Binder Rejuvenated with Bio-Oil Based on Molecular Dynamic Simulations and Laboratory Experimentations.

Soybean-derived bio-oil is one of the vegetable-based oils that is gaining the most interest for potential use in the rejuvenation of aged asphalt binders. This laboratory study was conducted to characterize and quantify the diffusion and rheological properties of bio-oil-rejuvenated aged asphalt binder (BRAA) using soybean oil. In the study, the chemical structure of the soybean oil was comparatively characterized using an element analyzer (EA), gel permeation chromatography (GPC), and a Fourier infrared (FTIR) spectrometer, respectively. Based on the chemical structure of the bio-oil, BRAA molecular models were built for computing the diffusion parameters using molecular dynamic simulations. Likewise, a dynamic shear rheometer (DSR) test device was used for measuring and quantifying the rheological properties of the aged asphalt binder rejuvenated with 0%, 1%, 2%, 3%, 4%, and 5% soybean oil, respectively. The laboratory test results indicate that bio-oil could potentially improve the diffusion coefficients and phase angle of the aged asphalt binder. Similarly, the corresponding decrease in the complex shear modulus has a positive effect on the low-temperature properties of BRAA. For a bio-oil dosage 4.0%, the diffusion coefficients of the BRAA components are 1.52 × 10−8, 1.33 × 10−8, 3.47 × 10−8, 4.82 × 10−8 and 3.92 × 10−8, respectively. Similarly, the corresponding reduction in the complex shear modulus from 1.27 × 107 Pa to 4.0 × 105 Pa suggests an improvement in the low-temperature properties of BRAA. Overall, the study contributes to the literature on the potential use of soybean-derived bio-oil as a rejuvenator of aged asphalt binders.

Experimental study of the influence of gradation on the dynamic properties of centerline tailings sand

Gradation is an important factor that affects the dynamic characteristics of tailings by the centerline method. For underflow tailings and overflow tailings under different grading effects of the cyclone, resonant column tests of saturated and unsaturated samples of different graded tailings sands are performed under the design dry density and isotropic consolidation conditions to analyse the influence of the gradation characteristics on the dynamic shear modulus and damping ratio of tailings sand. The test results show that under different grading conditions, the maximum dynamic shear modulus gradually increases, and the maximum damping ratio gradually decreases with increasing fine particle content of underflow tailings sand; meanwhile, the maximum dynamic shear modulus of overflow tailings sand gradually decreases, and the maximum damping ratio gradually increases with increasing fine particle content of overflow tailings sand. In underflow tailings sand, coarse particles (diameter >0.075 mm) act as the skeleton, and fine particles (diameter <0.075 mm) can fill the gaps among the coarse particles. When the content of fine particles in underflow tailings sand increases, the dynamic shear modulus increases, and the damping ratio decreases with the gradual increase in the fine particle content of the overflow tailings sand, the effective contact area among the coarse particle skeletons decreases, and the connection effect decreases; hence, the dynamic shear modulus decreases, and the damping ratio increases. The results of this research can provide basic data for the dynamic response analysis of tailings sand of different grades and a reference for the design and management of centerline method tailings ponds in areas with high seismic intensity.

Effects of a Single Proprioceptive Neuromuscular Facilitation Stretching Exercise With and Without Post-stretching Activation on the Muscle Function and Mechanical Properties of the Plantar Flexor Muscles.

A single proprioceptive neuromuscular facilitation (PNF) stretching exercise can increase the range of motion (ROM) of a joint but can lead to a decrease in performance immediately after the stretching exercise. Post-stretching activation (PSA) exercises are known as a possible way to counteract such a drop in performance following a single stretching exercise. However, to date, no study has investigated the combination of PNF stretching with PSA. Thus, the aim of this study was to compare the effects of a PNF stretching exercise with and without PSA on the muscle function (e.g., ROM) and mechanical properties of the plantar flexor muscles. Eighteen physically active males volunteered in the study, which had a crossover design and a random order. The passive shear modulus of the gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) was measured in a neutral position with shear wave elastography, both pre- and post-intervention. Maximum voluntary isometric contraction (MVIC) peak torque, maximum voluntary dynamic contraction peak torque, dorsiflexion ROM, and passive resistive torque (PRT) were also measured with a dynamometer. The interventions were 4×30s of PNF stretching (5s of contraction) and two sets of three exercises with 20 or 40 fast ground contacts (PNF stretching+PSA) and PNF stretching only. ROM was found to have increased in both groups (+4%). In addition, the PNF stretching+PSA group showed a decrease in PRT at a given angle (−7%) and a decrease in GM and mean shear modulus (GM+GL; −6%). Moreover, the MVIC peak torque decreased (−4%) only in the PNF stretching group (without PSA). Therefore, we conclude that, if PNF stretching is used as a warm-up exercise, target-muscle-specific PSA should follow to keep the performance output at the same level while maintaining the benefit of a greater ROM.

Study of the Influence of SBS and APDDR on the Low-Temperature Properties of Road Bitumen

A comparative assessment of the effect of two modifiers on the low-temperature properties of BND 90/130 bitumen was investigated using Asphalt Binder Cracking Device (ABCD test) and Dynamic Shear Rheometer (DSR 4-mm test). These modifiers are styrene-butadiene-styrene block copolymer (SBS) and active powder of discretely devulcanized rubber (APDDR) - powder elastomeric modifier obtained by high-temperature shear grinding of waste tire crumb rubber. ABCD results of RTFO-aged samples showed clear and gradual decrease of the ABCD cracking temperature (improvement) for all BC as the modifier concentration increases. It is noteworthy that the Bitumen Composites (modified bitumens) were cracking at higher strain and fracture stress values compared to neat bitumen. Results of DSR-4 mm test showed a decrease in the complex shear modulus (G*), storage modulus (G¢) and loss modulus (G²) BC compared to the neat bitumen. It is shown that bituminous composites have no maximum on the Cole-Cole diagram (dynamic vitrification) at T = -28°C which is observed in the neat bitumen.

Doping effects on mechanical and thermodynamic properties of zirconium carbide systems: a first-principles study

Zirconium carbide (ZrCx) is an important high temperature structural material, whose wide engineering applications are limited by carbon vacancies. Doping various impurity elements (O, B, etc) into ZrCx may lead to a significant change in its mechanical properties and thermodynamic properties behaviors. In this paper, based on the density functional theory, the effects of carbon vacancy contents and dopant on mechanical properties and deformation behaviors of zirconium carbide were discussed. With the increase of the carbon vacancy contents, the Young’s modulus, bulk modulus, and shear modulus decrease gradually. When the tensile strain is greater than 0.4, ZrC0.75 has stronger plasticity than ZrC0.875, ZrC0.9375 and ZrC. Furthermore, the mechanical properties of ZrC, ZrC0.75O0.25, ZrC0.75B0.25 and ZrC0.75 were studied. Compared with ZrC0.75, the mechanical properties of ZrC0.75O0.25 and ZrC0.75B0.25 are improved, and the mechanical properties of the systems are improved the most by doping O atoms. Based on the quasi-harmonic approximation, the influence of doping atoms on thermodynamic properties of ZrC0.75O0.25, ZrC0.75B0.25 and ZrC0.75 was also investigated. Doping O and B atoms in ZrC0.75 can improve the thermal conductivity at high temperature, and ZrC0.75B0.25 has the highest thermal conductivity. The results also show that the thermal properties of ZrC0.75 can be improved by doping O and B atoms. With the increase of temperature, ZrC0.75O0.25 has the largest thermal expansion.

Unusually thick shear-softening surface of micrometer-size metallic glasses

SummaryThe surface of glass is crucial for understanding many fundamental processes in glassy solids. A common notion is that a glass surface is a thin layer with liquid-like atomic dynamics and a thickness of a few tens of nanometers. Here, we measured the shear modulus at the surface of both millimeter-size and micrometer-size metallic glasses (MGs) through high-sensitivity torsion techniques. We found a pronounced shear-modulus softening at the surface of MGs. Compared with the bulk, the maximum decrease in the surface shear modulus (G) for the micro-scale MGs reaches ~27%, which is close to the decrease in the G upon glass transition, yet it still behaves solid-like. Strikingly, the surface thickness estimated from the shear-modulus softening is at least 400 nm, which is approximately one order of magnitude larger than that revealed from the glass dynamics. The unusually thick surface is also confirmed by measurements using X-ray nano-computed tomography, and this may account for the brittle-to-ductile transition of the MGs with size reductions. The unique and unusual properties at the surface of the micrometer-size MGs are physically related to the negative pressure effect during the thermoplastic formation process, which can dramatically reduce the density of the proximate surface region in the supercooled liquid state.

Molecular Dynamics-Based Cohesive Law for Epoxy–Graphene Interfaces

Molecular dynamics simulations are used to obtain mode I and mode II fracture energies and cohesive laws for bulk epoxy and interfaces formed between epoxy and single-layer graphene (SLG), multilayer graphene (MLG), and multilayer graphene oxide (MLGO). The elastic moduli and ultimate tensile and shear strengths of epoxy–graphene interfaces are calculated from uniaxial tension and simple shear loadings. The results show that Young’s modulus and the ultimate tensile strength increase relative to bulk epoxy, whereas the shear modulus and ultimate shear strength are reduced. Failure of epoxy–graphene interfaces in tension occurs due to the formation of voids in the epoxy. Failure in shear is due to tangential slipping at the interface. Under mixed-mode conditions, the shear modulus and shear strength decrease with increasing tensile load. The critical energy release rate $$G_{\text{c}}$$ for the studied epoxy–SLG/MLG/MLGO systems is obtained using a continuum fracture mechanics approach and is found to be significantly lower than for bulk epoxy. All of the results are combined to define mode I and II cohesive laws for bulk epoxy and epoxy–SLG/MLG/MLGO interfaces that can be used in theoretical models and numerical methods, such as finite elements, that employ cohesive zones.

Experimental study on unconfined compressive and cyclic triaxial test behavior of agar biopolymer–treated silty sand

The need for space for infrastructure development has plummeted studies in ground improvement to an eminent research topic. But in the present day where the need for sustainability is of utmost importance, efficient and environment-friendly improvement methods have been coming up among which the use of biopolymers as a soil additive have gained popularity. In the current research, various strength aspects of agar biopolymer–treated silty sand soil have been explored. The unconfined compressive strength property of treated silty sand at varying agar dosages (0.5%, 1%, and 2%) at different curing periods (3 days, 7 days, and 28 days) was analyzed using laboratory investigations. Furthermore, the effect of frequency of loading on dynamic properties and pore pressure response of the agar-treated silty sand was also investigated by performing a set of strain-controlled cyclic triaxial test at different frequencies (0.2 Hz, 1 Hz, 1.5 Hz, and 2 Hz). The tests were performed at constant axial strain amplitude of 1% and at confining pressure of 100 kPa. The results demonstrated that with the increase in agar content and curing time, the unconfined compressive strength of soil also increased. Besides, a decrease in pore pressure build-up, decrease in secant shear modulus, and an increase in damping was observed on increasing the frequency of cyclic loading.

Methodology to Characterize the Seismic Compression of Unsaturated Sands under Different Drainage Conditions

Abstract This study focuses on a new experimental setup and methodology to characterize the volumetric contraction of unsaturated sands during cyclic shearing under different drainage conditions. A new cyclic simple shear device was developed with suction-saturation control using a hanging column suitable for testing unsaturated granular soils with a maximum suction of 11 kPa. The pore water and pore air pressures are monitored during cyclic shearing using an embedded tensiometer and a gauge pressure transducer protected by a hydrophobic filter, respectively. In addition to describing the specimen preparation techniques and testing methodology, typical results for the seismic compression of nearly saturated, dry, and unsaturated sand specimens during cyclic shearing under different drainage conditions are compared. The differences in the response of these sand specimens were interpreted using the changes in mean effective stress and secant shear modulus during cyclic shearing. In drained conditions, the unsaturated sand specimen showed lower seismic compressions than the dry sand specimen and the nearly saturated sand specimen. In undrained conditions, a greater contraction was observed for the unsaturated conditions due to decreases in mean effective stress and secant shear modulus. The decrease in effective stress occurred due to a decrease in matric suction associated with different rates of increase in pore water and air pressure and an increase in degree of saturation with volumetric contraction.