Decrease In Shear Modulus Research Articles

Analysis on dynamic characteristics of dam material and seismic response of embankment dam in Longyang Reservoir

PurposeThe geological conditions of Longyang Reservoir are complex and it is located in strong earthquake area. In order to determine its seismic characteristics, the seismic response and residual deformation of embankment dam should be studied to provide calculation basis for dam design and construction.Design/methodology/approachBased on the geological survey data of Longyang Reservoir, the dam filling materials are tested by dynamic deformation tests, and the equivalent linear constitutive model parameters of the filling materials are obtained. Based on Duncan-Chang E-B model, the stress state of embankment dam in Longyang Reservoir before earthquake is calculated, and the dynamic response and earthquake residual deformation of embankment dam in Longyang Reservoir under earthquake condition are calculated by using equivalent linear model and Shen Zhu-jiang’s residual deformation model.FindingsThe results show that with the increase of dynamic shear strain, the dynamic shear modulus decreases and the damping ratio increases. The scatter plot between dynamic shear modulus and dynamic shear strain, and the scatter plot between damping ratio and dynamic shear strain under different confining pressures show strips. The calculation results shows that the acceleration of embankment dam in Longyang Reservoir increases with the increase of dam height, and the acceleration distribution has obvious amplification effect. Combined with the maximum dynamic shear strain during the earthquake and the state before the earthquake, the maximum vertical residual deformation of embankment dam in Longyang Reservoir is 2.98 cm which occurs at the top of the dam, calculated by the Shen Zhu-jiang’s residual deformation model.Originality/value Finite element calculation model parameters of embankment dam are obtained by dynamic triaxial tests. Seismic dynamic responses and residual deformation of embankment dam are analyzed. With the increase of dam height, the acceleration distribution shows an obvious amplification effect. The vertical displacement of embankment dam is larger along the dam axis and decreases in the upstream and downstream direction. The maximum horizontal displacement of embankment dam occurs in the middle of upstream and downstream dam slopes.Highlights(1)Finite element calculation model parameters of embankment dam are obtained by dynamic triaxial tests.(2)Seismic dynamic responses and residual deformation of embankment dam are analyzed.(3)With the increase of dam height, the acceleration distribution shows an obvious amplification effect.(4)The vertical displacement of embankment dam is larger along the dam axis and decreases in the upstream and downstream direction.(5)The maximum horizontal displacement of embankment dam occurs in the middle of upstream and downstream dam slopes.

Stiffness Anisotropy and Micro-Mechanism of Calcareous Sand with Different Particle Breakage Ratios Subjected to Shearing Based on DEM Simulations

Stress-induced anisotropy in calcareous sand can cause an uneven displacement in island reef engineering. In this study, stiffness, as a quantitative indicator, is explored to reveal the stress-induced anisotropy in calcareous sand. Based on the discrete element method, the stiffness anisotropic characteristics of calcareous sand during shearing, as well as the impact of particle breakage, are investigated by numerical simulations. Both the macro and micro responses, i.e., the maximum shear modulus, contact normal, strong and weak contact normal force, and the direction of particle breakage, are explored for calcareous sand with different particle breakage ratios. The results show that calcareous sand exhibits notable anisotropy during shearing, with the maximum shear modulus in the vertical direction (deviatoric stress direction) being significantly greater than that in the horizontal direction. Moreover, the higher the particle breakage rate, the lower the stiffness and its anisotropy. The micro-mechanism results indicate that the primary particle breakage during the shearing process occurs in the vertical direction. That is, the particle breakage weakens the strong contact force in the vertical direction, leading to a redistribution of the strong contact forces from the vertical direction to other directions. This redistribution mainly manifests in a decrease in the anisotropy of contact normal and contact vector within the sample, as well as a decrease in the proportion of strong contact forces in the overall contacts. This, in turn, reduces the shear strength and stiffness of calcareous sand, particularly in the vertical direction, and results in a decrease in the maximum shear modulus and its anisotropy. The maximum reduction can be up to 50% of the original value. These insights can provide a certain theoretical support for the uneven displacement and long-term stability of calcareous sand for islands and reefs.

Thermophysical–mechanical properties evaluations of porous geomaterials by CT images and digital–virtual modeling

AbstractIn this work, the color difference phase separation (CDPS) approach is proposed to segment the solid and pore phases. Pore‐scale variables are defined to describe the microstructural characteristics. Novel relations to quickly determine the deformation moduli and thermal conductivity are established. Digital–virtual modeling to investigate the mechanical and thermal properties is addressed. The correlation between pore‐scale variables and the mechanical and thermal properties is investigated. Results show that the calculated shear and Young's moduli decrease and the computed Poisson's ratio increases as porosity increases. The deformation moduli and thermal conductivity increase with increasing pore radius for different types of rocks. Excellent consistencies are found between the digital–virtual and realistic experimental results. The proposed method provides useful tools to fast and accurately determine the deformation moduli and thermal conductivity, which is helpful for the underground space and deep energy resource explorations.

Hamstrings passive and active shear modulus: Implications of conventional static stretching and warmup

PurposeThis study compares the acute effects of a static stretching and a warmup protocol on the active and passive shear modulus of the hamstring muscles. MethodsMuscle shear modulus was assessed at rest and during isometric contractions at 20 % of maximal voluntary isometric contraction (MVIC). ResultsAfter stretching, the passive shear modulus pattern was not altered, while at 20 % MVIC the biceps femoris short head (BFsh) and semimembranosus showed a shear modulus increase and decrease, respectively, which resulted on BFsh-SM pair differences (pre: 3.8 ± 16.8 vs. post: 39.3 ± 25.1 kPa; p < 0.001; d = 1.66) which was accompanied by a decrease of 18.3 % on MVIC. Following the warmup protocol, passive shear modulus remained unchanged, while active shear modulus was decreased for the semitendinosus (pre: 65.3 ± 13.5 vs. post: 60.3 ± 12.3 kPa; p = 0.035; d = 0.4). However, this difference was within the standard error of measurement (10.54 kPa), and did not impact the force production, since it increased only 1.4 % after the warmup. ConclusionsThe results of this study suggest that the passive and active shear modulus responses of the individual hamstring muscles to static stretching are muscle-specific and that passive and active hamstring shear modulus are not changed by a standard warmup intervention.

Detrimental Effects of Chlorhexidine on Articular Cartilage Viability, Matrix, and Mechanics

Background: Chlorhexidine gluconate (CHG) solution is commonly used as an antiseptic irrigation for bacterial decontamination during orthopaedic surgery. Although the chondrotoxicity of CHG on articular cartilage has been reported, the full extent of CHG-related chondrotoxicity and its effects on the extracellular matrix and mechanical properties are unknown. Purpose: To investigate the in vitro effects of a single 1-minute CHG exposure on the viability, biochemical content, and mechanics of native articular cartilage explants. Study Design: Controlled laboratory study. Methods: Articular cartilage explants (6 per group) were harvested from femoral condyles of the porcine stifle and sectioned at tidemark. Explants were bathed in CHG solution (0.05% CHG in sterile water) at varying concentrations (0% control, 0.01% CHG, and 0.05% CHG) for 1 minute, followed by complete phosphate-buffered saline wash and culture in chondrogenic medium. At 7 days after CHG exposure, cell viability, matrix content (collagen and glycosaminoglycan [GAG]), and compressive mechanical properties (creep indentation testing) were assessed. Results: One-minute CHG exposure was chondrotoxic to explants, with both 0.05% CHG (2.6% ± 4.1%) and 0.01% CHG (76.3% ± 8.6%) causing a decrease in chondrocyte viability compared with controls (97.5% ± 0.6%; P < .001 for both). CHG exposure at either concentration had no significant effect on collagen content, while 0.05% CHG exposure led to a significant decrease in mean GAG per wet weight compared with the control group (2.6% ± 1.7% vs 5.2% ± 1.9%; P = .029). There was a corresponding weakening of mechanical properties in explants treated with 0.05% CHG compared with controls, with decreases in mean aggregate modulus (177.8 ± 90.1 kPa vs 280.8 ± 19.8 kPa; P < .029) and shear modulus (102.6 ± 56.5 kPa vs 167.9 ± 16.2 kPa; P < .020). Conclusion: One-minute exposure to CHG for articular cartilage explants led to dose-dependent decreases in chondrocyte viability, GAG content, and compressive mechanical properties. This raises concern for the risk of mechanical failure of the cartilage tissue after CHG exposure. Clinical Relevance: Clinicians should be judicious regarding the use of CHG irrigation at these concentrations in the presence of native articular cartilage.

Influence of temperature on the elastic properties of graphene and graphene-like nanosheets based on the asymptotic homogenization method

In this paper, the effective elastic properties of hexagonal monolayers such as graphene, boron nitride, silicon carbide, and aluminum nitride are evaluated using the asymptotic homogenization method taking into account temperature changes. The effective properties are determined analytically by considering temperature, force constants, bond lengths, and thickness, using atomic interactions within the context of the unit cell problem. The relationship between environmental temperature and the coefficient of thermal expansion is established by considering changes in the values ​​of bond stretching, bond angle bending, and torsion resistance constants at different temperatures from 0 to 1800 K. The results provided by the proposed homogeneous model are consistent with the valid findings of other researchers in the literature. It is found that these different hexagonal nanosheets exhibit isotropic temperature-dependent properties and their Young's and shear modulus decrease almost linearly as the temperature rises, considering a constant coefficient of thermal expansion. However, Poisson's ratio is found to be independent of temperature. Furthermore, the temperature-dependent elastic properties of these nanosheets become nonlinear when the variation of the coefficient of thermal expansion with temperature is taken into account. The Young and shear moduli of the nanosheets increase as the coefficient of thermal expansion decreases and vice versa. The highest elastic modulus values are obtained when the thermal expansion is close to its minimum threshold. However, it is recognized that the elastic modulus of graphene and boron nitride nanosheets is higher than that of silicon carbide and aluminum nitride at any temperature. As an alternative to lengthy computer modeling or rigorous testing, the homogeneous models provided can be used to simulate nanosheets.

On the mechanical behavior of carbon fiber/epoxy laminates exposed in thermal cycling environments

Carbon fiber reinforced polymer (CFRP) composites are commonly used for reflectors of artificial satellites operating in low earth orbit (LEO). The decay of the modulus of the CFRP composite varies under different thermal cycling environments, which can lead to a reduction in the accuracy of the reflector panels, affecting the transmission of signals. This paper investigates the impact of different thermal cycling conditions on the mechanical behavior of carbon fiber/epoxy laminated composites experimentally. Three kinds of thermal cycling conditions involving continuous temperature changes are employed to explore the influence of temperature range on the residual tensile and in-plane shear moduli of the laminates. Test results indicate that the upper temperature limit and the temperature span of the thermal cycling conditions jointly affect the mechanical properties of CFRP composite laminates, but the responses of the residual tensile and in-plane shear moduli are different under the variation of each temperature parameter alone. The residual tensile and in-plane shear moduli of the laminates under thermal cycling decrease with an expansion of the temperature span having the same upper limit. If the temperature span remains constant, an increase in the upper temperature limit leads to an increase in the residual tensile modulus, but a decrease in the residual in-plane shear modulus. The main damages causing the decay of residual tensile and in-plane shear moduli of unidirectional laminates were investigated by scanning electron microscopy (SEM) technology. Observations of the microscopic fracture of the material show that the post-curing reaction factor predominantly influences the residual tensile modulus of unidirectional laminates, while the fiber/matrix interface damage factor dominates the residual in-plane shear modulus of the unidirectional laminates. Furthermore, an increase in the fiber tensile modulus decreases both residual tensile and residual in-plane shear moduli. Notably, the residual in-plane shear modulus exhibits greater sensitivity to thermal cycling compared to the residual tensile modulus. The findings reported in this paper would provide valuable insights and guidance for the design and application of carbon fiber/epoxy composites subjected to thermal cycling conditions.

An Ab Initio Investigation of CdSnN2Under Uniaxial Compressions

Herein, the behaviors of CdSnN2are computationally investigated under uniaxial compressions based on density functional theory (DFT) calculations and a DFT‐1/2 scheme. When the compression is in [100] direction, phase transition is observed fromPna21toPnmaphase when the compression is larger than 30 GPa, while no phase change is observed for uniaxial compressions along [010] and [001] directions. For the former one, the bandgap first increases with a maximum at 20 GPa, followed with a reduction upon the critical pressure and nearly a constant above 30 GPa. The bulk modulus nearly increases monotonically except for the transit region from 20 to 29 GPa, and the shear modulus decreases to 29 GPa and then increases forPnmaphase. When compression is along [010] direction, the bandgap nearly remains around 0.620 eV. The bulk modulus increases with a maximum around 25 GPa and then decreases, while the shear modulus monotonically decreases. The bandgap first increases and then shrinks monotonically with increasing compression in [001] direction. The bulk modulus monotonically increases and the shear modulus decreases. The absorption is then calculated and discussed. The anisotropic behaviors of CdSnN2may hence indicate some potential applications.

Experimental investigation and machine learning modeling using LSTM and special relativity search of friction stir processed AA2024/Al2O3 nanocomposites

In this study, the friction stir technique is proposed to process aluminum nanocomposites reinforced with alumina nanoparticles. The effects of different processing parameters, including spindle speed (900–1800 rpm), feed (10–20 mm/min), and number of passes (1–3) on the mechanical and dynamic properties of the processed samples were investigated. The investigated properties were ultimate tensile strength, yield strength, natural frequency, and damping ratio. An advanced machine learning approach composed of a long short-term memory model optimized by a special relativity search algorithm was developed to predict the properties of the processed samples and different processing conditions. The adequacy of the developed model was tested and compared with three other machine learning models; the predicted properties were in good agreement with the measured properties. The developed model outperformed other tested models and was found to be a powerful prediction tool for predicting processing conditions to obtain high-quality nanocomposite samples. The model succeeded in predicting the ultimate tensile strength, yield strength, natural frequency, and damping ratio with good R2 of 0.912, 0.952, 0.951, and 0.987, respectively. The obtained results showed that the samples' damping ratio and loss factor increase with the number of passes, while the natural frequency, shear modulus, and complex modulus decrease with the number of passes. Thus, friction stir processing can be used to improve the damping properties of materials.

UV-induced gradient aging of bitumen films: A comprehensive study

The aging of bitumen materials under ultraviolet (UV) radiation is a highly intricate process involving volatilization of components and multiple photochemical reactions. To gain a comprehensive understanding of the mechanism and progression of UV aging in bitumen films within bitumen mixtures, this study investigates the formation and evolution of UV aging gradients in bitumen films from various perspectives, including morphology, composition, macro-, and micro-mechanical aspects. Initially, specific bitumen film specimens were subjected to aging, and a protocol for sample handing and testing was developed. Optical microscopy images, functional group indices, and component contents of the bitumen films were then measured and calculated to track the UV aging process from the surface to the interior. Additionally, profiling micro-mechanical tests and layer-by-layer dynamic mechanical tests were conducted to characterize the variations in mechanical properties induced by UV aging gradients within the bitumen films. The results indicate that UV radiation causes significant volatilization of light components on the film surface, resulting in wrinkling. Concurrently, photochromic reactions take place in both bitumen macromolecules (asphaltenes and resins) and small molecules (saturates and aromatic), while molecular photodegradation may also occur. Fluorescence imaging, infrared spectroscopy analysis, and component determination reveal that the degree of UV aging in the bitumen films increases with radiation time and gradually propagates towards the interior. C-S bonds are more sensitive to UV radiation than C = C bonds, leading to oxidation and the formation of sulfoxide groups. Due to the adsorption of light components by aggregates, the modulus values at the surface of aged bitumen films and the aggregate interface are higher, while the intermediate region exhibits lower values. Rheological indicators demonstrate that UV aging, to a certain extent, results in the decomposition of bitumen molecules, leading to a decrease in complex shear modulus and an increase in phase angle. This work significantly enhances our understanding of the mechanism of UV aging in bitumen films and holds important implications for the design and development of UV-blocking materials.

Effect of drying-wetting cycles on the durability of calcareous sand reinforced by MICP and recycled shredded coconut coir (RSC)

Microbial-induced carbonate precipitation (MICP) technique has been adopted in geotechnical engineering widely. In this study, the effect of drying-wetting cycles on MICP-recycled shredded coconut coir (RSC) reinforced calcareous sand was studied, and the deterioration mechanism under drying-wetting cycles was revealed. Test results indicated that drying-wetting cycles exert an important influence on the durability of MICP-RSC reinforced specimens. With the increase of drying-wetting cycles N, the specimens demonstrated significant increase in mass loss rate and critical void ratio, decrease in maximum shear modulus, peak strength and toughness. Furthermore, an increase in the initial relative density reduced the deterioration of MICP-RSC reinforced specimens exposed to drying-wetting cycles. Higher initial relative density of the specimen correlates with an increased maximum shear modulus, peak stress and toughness, a decreased in permeability and critical void ratio. Microanalysis revealed that the generated calcium carbonate adhering to sand particles and RSC gradually dropped off with the increase of N, weakened cementation, and led to the deterioration of MICP-RSC reinforced specimens, which is consistent with the deterioration characteristics under drying-wetting cycles.

FE-Simulation and Experimental Characterisation of Environmental Effects on the Diffusion and Mechanical Performance of Hyperelastic Adhesive Joints

In operational applications, hyperelastic adhesive joints are exposed to environmental conditions (moisture and temperature) that affect their mechanical performance. The understanding of how the environment can influence the joint durability through both static and cyclic loading is a key aspect to ensure safety and avoid over-dimensioning. The current work presents an investigation of the effect of environment conditions on the diffusion and mechanical performance of two different hyperelastic adhesive joints (a polyurethane and a silicon-modified polymer). To assess the process of moisture mass diffusion, pure adhesive samples were weighted for 387 days when subjected to outdoor weathering conditions. An FEA-diffusion procedure method was demonstrated by (i) predicting the saturation concentration at steady conditions of 40 °C/15% r.h. (40/15) and 40 °C/60% r.h. (40/60), and (ii) predicting the experienced mass change due to outdoor weathering. The reversibility of the effect of conditioning at 40 °C/60% r.h. on the mechanical properties of the adhesives was assessed via quasi-static and fatigue tensile shear testing. The results support the conclusion that conditioning with the surrogate climate of 40 °C/60% r.h. does not cause irreversible damage, as any potential decrease in shear modulus, tensile shear strength and fatigue life due to 40/60 conditioning can be reversed by re-drying at 40/15.

Creep and ageing of granular materials under isotropic pressure

Single- and multi-stage isotropic creep tests including bender element and acoustic emission measurements are carried out to investigate the relationship between ageing and creep in dense silica sand. In the considered pressure range, the experimental results show an inversely proportional relationship between ageing and creep: the small-strain shear modulus increases with decreasing isotropic pressure,, while the axial creep strain and the acoustic emissions show the opposite pressure dependence. In the multi-stage creep test, the small-strain shear modulus increases monotonically, while the rates of axial strain, number of acoustic emissions and small-strain shear modulus decrease with time according to a power law. In the single-stage creep tests, the ageing and creep indicators initially evolve as in the multi-stage creep test, but then the small-strain shear modulus reaches a peak value and decreases with time thereafter. At the same time, the rates of axial strain, number of acoustic emissions and small-strain shear modulus deviate from the power law. A conceptual model assuming a time-dependent behaviour of the normal and shear forces at the particle contacts in order to explain the experimental observations qualitatively is proposed. Accordingly, an increase in small-strain shear modulus results from homogenisation of the force chains, while a decrease in small-strain shear modulus results from a temporary formation followed by a time-delayed collapse of strong force chains.

The impact of potassium peroxymonosulphate and chlorinated cyanurates on biofilms of Stenotrophomonas maltophilia: effects on biofilm control, regrowth, and mechanical properties

The activity of two chlorinated isocyanurates (NaDCC and TCCA) and peroxymonosulphate (OXONE) was evaluated against biofilms of Stenotrophomonas maltophilia, an emerging pathogen isolated from drinking water (DW), and for the prevention of biofilm regrowth. After disinfection of pre-formed 48 h-old biofilms, the culturability was reduced up to 7 log, with OXONE, TCCA, and NaDCC showing more efficiency than free chlorine against biofilms formed on stainless steel. The regrowth of biofilms previously exposed to OXONE was reduced by 5 and 4 log CFU cm−2 in comparison to the unexposed biofilms and biofilms exposed to free chlorine, respectively. Rheometry analysis showed that biofilms presented properties of viscoelastic solid materials, regardless of the treatment. OXONE reduced the cohesiveness of the biofilm, given the significant decrease in the complex shear modulus (G*). AFM analysis revealed that biofilms had a fractured appearance and smaller bacterial aggregates dispersed throughout the surface after OXONE exposure than the control sample. In general, OXONE has been demonstrated to be a promising disinfectant to control DW biofilms, with a higher activity than chlorine. The results also show the impact of the biofilm mechanical properties on the efficacy of the disinfectants in biofilm control.

Lateral Variations Across the Southern San Andreas Fault Zone Revealed From Analysis of Traffic Signals at a Dense Seismic Array

AbstractWe image the shallow seismic structure across the Southern San Andreas Fault (SSAF) using signals from freight trains and trucks recorded by a dense nodal array, with a linear component perpendicular to SSAF and two 2D subarrays centered on the Banning Fault and Mission Creek Fault (MCF). Particle motion analysis in the frequency band 2–5 Hz shows that the examined traffic sources can be approximated as moving single‐ or multi‐point sources that primarily induce Rayleigh waves. Using several techniques, we resolve strong lateral variations of Rayleigh wave velocities and Q‐values across the SSAF, including 35% velocity reduction across MCF toward the northeast and strong attenuation around the two fault strands. We further resolve 10% mass density reduction and 45% shear modulus decrease across the MCF. These findings suggest that the MCF is currently the main strand of the SSAF in the area with important implications for seismic hazard assessments.

Poster 152: Detrimental Effects of Chlorhexidine on Articular Cartilage Viability, Matrix, and Mechanics

Objectives: Chlorhexidine gluconate (CHG) is commonly used in antiseptic irrigation solutions for bacterial decontamination during orthopaedic surgery. Although the chondrotoxicity of CHG to articular cartilage has been reported, CHG irrigation is utilized by some surgeons to limit surgical site infection and to salvage grafts after accidental contamination during joint surgery. The full extent of CHG irrigation-related chondrotoxicity, as well as its effects on articular cartilage extracellular matrix and mechanical properties, are unknown. The purpose of this study was to determine the in vitro effects of a single one-minute CHG exposure on the viability, biochemical content, and mechanics of native articular cartilage explants. Methods: Articular cartilage explants (n=6 per group) were harvested from the femoral condyles of the porcine stifle and sectioned at the tidemark. Explants were bathed in Irrisept® chlorhexidine solution (0.05% CHG in sterile water) at varying concentrations (0% control, 0.01% CHG, and 0.05% CHG) to stimulate surgical irrigation for 1 minute, followed by complete phosphate-buffered saline wash and culture. After seven days of culture in chondrogenic medium, the explants were analyzed for viability (live/dead assay); collagen content (hydroxyproline assay); glycosaminoglycan (GAG) content (dimethyl methylene blue assay); and compressive mechanical testing (creep indentation testing). Statistical analyses were performed using a one-way ANOVA with post hoc Tukey test. Results: Seven days after CHG exposure, a dose-dependent decrease in mean chondrocyte viability was observed in the CHG groups (p&lt;0.001), with &lt;3% viability observed in the 0.05% CHG group (Figure 1). There was no significant difference in mean collagen content per wet weight among groups. Conversely, 0.05% CHG exposure led to a decrease in mean GAG per wet weight compared to negative control (p=0.029) and 0.01% CHG (p=0.046) (Figure 2). These changes in GAG content corresponded to observed changes in the compressive mechanical properties of the explants. A dose-dependent decrease in mean aggregate modulus and shear modulus was observed after CHG exposure (p&lt;0.029), indicating weakening of the cartilage matrix and increased deformation in response to compressive loads (Figure 3). Conclusions: One-minute CHG exposure to articular cartilage explants led to dose-dependent decreases in chondrocyte viability, GAG content, and compressive mechanical properties. These detrimental effects were observed for both 0.05% and 0.01% CHG concentrations. There is a paucity of literature examining the effects of CHG on articular cartilage matrix and mechanics, and the findings of this study suggest a lack of matrix maintenance following cell death, raising concern for risk of mechanical failure of the cartilage tissue. Clinicians should be judicious regarding the use of CHG irrigation at these concentrations in the presence of native articular cartilage.

Trends in structural, electronic and elastic properties of Ti2AC (A = Al, Zn, Cu, Ni) based on late transition metals substitution

Recently, the substitutional incorporation of late transition metals in the “A” sublattice of MAX phases further extends the physical properties and diversity of this class of materials. In this study, the structural, electronic and elastic properties of Ti2AC (A = Al, Zn, Cu, Ni) were investigated using the density functional theory. The calculated results reveal that a large number of d orbital bands of Zn, Cu, and Ni atoms accumulate around −6.5 eV, −2.5 eV, and −2.0 eV, respectively, leading to stronger ionic and metallic characteristics for Ti2ZnC, Ti2CuC, and Ti2NiC. Three Ti2AC (A = Zn, Cu, Ni) phases are ductile and consequently damage tolerant, whereas Ti2AlC is brittle in nature. When Al is replaced by Zn, Cu, and Ni, there is a remarkable decrease of hardness and shear modulus, indicating high machinability. Ti2ZnC, Ti2CuC, and Ti2NiC are expected to be promising thermal barrier coating materials.

Drained cyclic behaviour and state-dependent stress–dilatancy relationship of sand in direct simple shear tests

Direct simple shear tests were conducted to investigate the cyclic behaviour, dynamic properties, and stress–dilatancy relationship of fine-grained silica sand for a wide range of constant vertical stresses, including low stresses. Multi-stage cyclic tests were conducted by increasing the shear strain amplitude from low to high values in subsequent loading stages. Test results show that the volumetric strain is related to the vertical stress and shear strain amplitude. The cyclic shear modulus decreases and the damping ratio increases with shear strain amplitude, and they are influenced by the low-amplitude cyclic loading history. The volume change is related to the cyclic stress–dilatancy relationship, which depends on the vertical stress, shear strain amplitude, number of cycles, and shearing direction. In some tests, the stress–dilatancy relationship can be represented by two parallel lines for unloading and reloading, except for the initial parts. The increase in density with cyclic loading reduces the contractive behaviour and increases the dilative response in the large-amplitude loading cases, which reduces the rate of volumetric compaction with the number of cycles.

Geotechnical characterization of collapsible salty sands subjected to monotonic and cyclic loadings – A case study for areas with high seismicity

Collapsible soils are typically found in arid regions and often have an aeolian or alluvial origin. In their natural states, they may have a low moisture content and cemented structure that can contribute to high strength and stiffness; however, wetting or saturation can reduce the strength and stiffness due to loss of the cementation. This paper presents a geotechnical characterization of collapsible salty sands in the highly seismic southern coast of Peru, which makes the characterization of their dynamic properties and expected response to earthquake-induced demands (e.g., liquefaction) of primary importance. The geotechnical characterization was performed on intact and remolded samples utilizing various field and laboratory tests, including oedometer, direct shear, static triaxial, cyclic simple shear, torsional resonant column, plate loading, and MASW tests. The results revealed insights on the geotechnical properties and mechanical response of collapsible soils and the effects of salt cementation. The results indicated: 1) a decreasing brittle and collapsible behaviors with decreasing cementation while maintaining consistent post-collapse residual strength; 2) oedometer and in situ plate loading tests showed a sudden increase in deformations once cementation is broken; 3) higher dilation potential of collapsible soils as compared to natural sands; 4) decrease in the maximum shear modulus due to the loss of cementation; 5) increase in the stress dependence of the maximum shear modulus with loss of cementation; and 6) a higher resistance to liquefaction for the collapsible soils, even after washing, as compared to natural sands, which may be ascribed to the more pronounced dilation potential.

Theoretical study on longitudinal deformation of adjacent tunnel subjected to pre-dewatering based on Pasternak-Timoshenko beam model

In this research, under the disturbance of pre-dewatering, the analytical solution of vertical displacement of the adjacent tunnel is derived using the two-stage analysis method. In the first stage, the effective stress principle was used to calculate the additional stress of the adjacent tunnel caused by dewatering. In the second stage, the Pasternak-Timoshenko beam model was used to simulate the interaction between the tunnel and soil, taking the tunnel shear deformation into account. By referring to the calculation results of existing literature, the correctness of the proposed method is verified, and the influencing factors of the longitudinal displacement of the tunnel are further analyzed. The results show that with the increase of the distance from the dewatering well and soil elastic modulus, the vertical displacement of the tunnel is reduced. The deformation of the existing tunnel increases with the permeability coefficient. The decrease of the tunnel shear modulus can lead to the rapid increase of the tunnel’s vertical displacement, so the shear stiffness should be considered in the analysis of its deformation. The increase in the dropping amplitude of the water level in the well will decrease the water level in the surrounding strata. According to the different relative positions of the tunnel and the water table, there are two forms of additional load on the tunnel. Before the water level drops to the tunnel axis, the tunnel’s Additional load and displacement gradually increase.