Search Results (115)

Conventional adhesively bonded joints, such as single-lap, curved-lap, wavy-lap, double-lap, stepped-lap, and scarf joints, are widely used for aerospace, automotive, and medical applications. These adhesively bonded joints exhibit different load transfer mechanisms and stress distributions within adhesive layers, which depend primarily on their geometries and mechanical properties of bonded materials. As such, joint geometry and material properties play a critical role in determining the capability of the joints to withstand high loads, resist fatigue, and absorb energy under impact loading. This paper investigates the effects of geometry and material dissimilarity on the performance of both conventional bonded and interlocking joints under tensile loading based on the information available in the literature. In addition, bonding and load transfer mechanisms were analysed in detail. It was found that stress concentration often occurs at free edges of the adhesive layer due to geometric discontinuities, while most of the load is carried by these regions rather than its centre. Sharp corners further intensify resulting stresses, thereby increasing the risk of joint failure. Adhesives typically resist shear loads better than peel loads, and stiffness mismatches between adherents induce an asymmetric stress distribution. Nonetheless, similar materials promote symmetric load sharing. Among conventional joints, scarf joints provide the most uniform load distribution. In interlocking joints such as dovetail, T-slot, gooseneck, and elliptical types, the outward bending of the female component under tension can lead to mechanical failure. Full article

This study presents a unique and comprehensive application of ANSYS Mechanical R19.2’s SMART crack growth feature, leveraging its capabilities to conduct an unprecedented parametric investigation into fatigue crack propagation behavior under a wide range of positive and negative stress ratios, and to provide detailed insights into the influence of hole positioning on crack trajectory. By uniquely employing an unstructured mesh method that significantly reduces computational overhead and automates mesh updates, this research overcomes traditional fracture simulation limitations. The investigation breaks new ground by comprehensively examining an unprecedented range of both positive (R = 0.1 to 0.5) and negative (R = −0.1 to −0.5) stress ratios, revealing previously unexplored relationships in fracture mechanics. Through rigorous and extensive numerical simulations on two distinct specimen configurations, i.e., a notched plate with a strategically positioned hole under fatigue loading and a cracked rectangular plate with dual holes under static loading, this work establishes groundbreaking correlations between stress parameters and fatigue behavior. The research reveals a novel inverse relationship between the equivalent stress intensity factor and stress ratio, alongside a previously uncharacterized inverse correlation between stress ratio and von Mises stress. Notably, a direct, accelerating relationship between stress ratio and fatigue life is demonstrated, where higher R-values non-linearly increase fatigue resistance by mitigating stress concentration, challenging conventional linear approximations. This investigation makes a substantial contribution to fracture mechanics by elucidating the fundamental role of hole positioning in controlling crack propagation paths. The research uniquely demonstrates that depending on precise hole location, cracks will either deviate toward the hole or maintain their original trajectory, a phenomenon attributed to the asymmetric stress distribution at the crack tip induced by the hole’s presence. These novel findings, validated against existing literature, represent a significant advancement in predictive modeling for fatigue life assessment, offering critical new insights for engineering design and maintenance strategies in high-stakes industries. Full article

The presence of fissures poses significant threats to tunnel-lining structures, and the interaction between tunnels and linings under complex stress conditions remains poorly understood. This study investigated the failure modes of tunnel-lining structures with prefabricated fissures via 3D-printed samples, uniaxial compression experiments using DIC technology for full-field strain monitoring, and a particle-based meshless (SPH) numerical method to simulate tunnel–fissure interactions. The results show that under uniaxial compression, three crack types (main, upper/lower side cracks) initiate from the tunnel, while only wing cracks form at pre-existing fissures; wing crack initiation suppresses upper-side cracks, whereas more lining cracks (upper, middle, lower, corner, bottom) emerge without fissure-induced propagation. Fissure orientation (β) and inclination (α) significantly affect crack distributions: β = 90° induces maximum stress concentration and asymmetric deformation, while α ≥ 45° promotes wing crack initiation and reduces lining crack density. Along with our findings, we offer design recommendations to prioritize fissure orientation in tunnel engineering and expand SPH applications for predicting crack propagation in underground structures with complex fissures. Full article

The dip angle and thickness of coal seams are key geological determinants in mine system engineering. Roadways excavated in steeply inclined or thick coal seams typically exhibit significant deformation, with the combined geological configuration of steeply inclined thick seams thus presenting heightened support demands. Therefore, taking the 1502 level roadway in the Dayuan Coal Industry—situated in a steeply inclined thick coal seam—as an engineering case, mechanical models of roadways with different cross-sectional shapes are established, and the deformation and failure mechanisms of surrounding rock under different coal seam dip angles are analyzed. Based on this analysis, an asymmetric support technology scheme is proposed, followed by surrounding rock deformation monitoring and a support effectiveness evaluation. Key findings include the following: (1) in steeply inclined thick coal seam roadways with different cross-sectional shapes, the stress distribution and plastic zone development of surrounding rock follow a descending sequence, inclined roof trapezoidal section > rectangular section > arched section. Among these, the arched section is identified as the optimal roadway cross-sectional shape for this engineering context. (2) The stress-concentration area in the arch roadway aligns with the inclined direction of the coal seam, forming asymmetric stress concentration patterns. Specifically, as the coal seam dip angle increases, stress increases at the arch shoulder of the upper sidewall and the wall foundation of the lower sidewall. Concurrently, such stress concentration induces shear failure in the surrounding rock, which serves as the primary mechanism causing asymmetric deformation and failure in steeply inclined thick coal seam roadways. (3) In the 1502 level roadway, the asymmetric support technology with dip-oriented reinforcement was implemented. Compared to the original support scheme, roof deformation and sidewall convergence decreased by 46.17% and 46.8%, respectively. The revealed failure mechanisms of steeply inclined thick coal seam roadways and the proposed asymmetric support technology provide technical and engineering references for roadway support in similar mining conditions. Full article

The interference fit is a common process for the assembly of mechanical parts on a shaft for diverse mechanical engineering applications. One of the manufacturing methods consists of introducing a shaft into a hub by applying a force being the hub diameter lower than the shaft diameter. This way, contact pressure is generated at the shaft–hub interface at the end of the process, enabling torque transmission. Thus, a non-uniformly distributed stress state appears at the shaft–hub interface with significant stress peaks at the hub edges. In addition, as a consequence of the manufacturing process, local plasticity is generated in the hub on the insertion side causing changes in stress distributions. In this paper, an analysis based on finite elements simulations is carried out to reveal the influence of, on one hand, manufacturing parameters such as friction on stress concentrations at the interface and, on the other hand, geometrical parameters such as hub chamfer angle, considering chamfer hubs and conventional hubs. To achieve this goal, different simulations of the mechanical manufacturing process of the axial assembly of press fits are carried out to reveal the stress fields at the interface. Thus, stress concentrations under different friction conditions from a case without friction to a dry friction case are revealed and analyzed. The results show, on one hand, the friction coefficient as a highly influential factor, causing asymmetrical stress distributions with high stress concentrations that reduce the mechanical performance of press fits and, on the other hand, the beneficial impact of chamfer hubs for lowering stress concentrations. Full article

As urban rail transit networks age, understanding the synergistic impacts of multi-defect interactions on tunnel structural safety has become critical for underground infrastructure maintenance. This study investigates defect interaction mechanisms in shield tunnels and cross passages of Beijing Metro Line 8, integrating field monitoring, numerical simulations, and Bayesian network analysis. Long-term field surveys identified spatiotemporal coupling characteristics of four key defects—lining leakage, structural voids, material deterioration, and deformation—while revealing typical defect propagation patterns such as localized leakage at track beds and drainage pipe-induced voids. A 3D fluid–solid coupling numerical model simulated multi-defect interactions, demonstrating that defect clusters in structurally vulnerable zones (e.g., pump rooms) significantly altered pore pressure distribution and intensified displacement, whereas void expansion exacerbated lining uplift and asymmetric ground settlement. Stress concentrations were notably amplified at tunnel–cross passage interfaces. The Bayesian network risk model further validated the dominant roles of defect volume and burial depth in controlling structural safety. Results highlight an inverse correlation between defect severity and structural integrity. Based on these findings, a coordinated maintenance framework combining priority monitoring of high-stress interfaces with targeted grouting treatments is proposed, offering a systematic approach to multi-defect risk management that bridges theoretical models with practical engineering solutions. Full article

In recent years, flexible piezoresistive sensors based on polydimethylsiloxane (PDMS) matrix materials have developed rapidly, showing broad application prospects in fields such as human motion monitoring, electronic skin, and intelligent robotics. However, achieving a balance between structural durability and fabrication simplicity remains challenging. Traditional methods for preparing PDMS flexible substrates with high porosity and high stability often require complex, costly processes. Breaking through the constraints of conventional material systems, this study innovatively combines the high elasticity of polydimethylsiloxane (PDMS) with the stochastically distributed porous topology of a sponge-derived biotemplate through biomimetic templating replication technology, fabricating a heterogeneous composite system with an architecturally asymmetric spatial network. After 5000 loading cycles, uncoated samples experienced a thickness reduction of 7.0 mm, while PDMS-coated samples showed minimal thickness changes (2.0–3.0 mm), positively correlated with curing agent content (5:1 to 20:1). The 5:1 ratio sample demonstrated exceptional mechanical stability. As evidenced, the PDMS film-encapsulated architecturally asymmetric spatial network demonstrates superior stress dissipation efficacy, effectively mitigating stress concentration phenomena inherent to symmetric configurations that induce matrix fracture, thereby achieving optimal mechanical stability. Compared to the pre-test resistance distribution of 10–248 Ω, after 5000 cyclic loading cycles, the uncoated samples exhibited a narrowed resistance range of 10–50 Ω, while PDMS-coated samples maintained a broader resistance range (10–240 Ω) as the curing agent ratio increased (from 20:1 to 5:1), demonstrating that increasing the curing agent ratio helps maintain conductive network stability. The 5:1 ratio sample displayed the lowest resistance variation rate attenuation—only 3% after 5000 cycles (vs. 80% for uncoated samples)—and consistently minimal attenuation at all stages, validating superior electrical stability. Under 0–6 kPa pressure, the 5:1 ratio device maintained a linear sensitivity of 0.157 kPa⁻¹, outperforming some existing works. Human motion monitoring experiments further confirmed its reliable signal output. Furthermore, the architecturally asymmetric spatial network of the device enables superior conformability to complex curvilinear geometries, leveraging its structural anisotropy to achieve seamless interfacial adaptation. By synergistically optimizing material composition and structural design, this study provides a novel technical method for developing highly durable flexible electronic devices. Full article

The sunny–shady slope effect (SSSE) disrupts the thermal balance of permafrost subgrades, resulting in asymmetric thaw plates that lead to structural deformations such as longitudinal cracking and slope instability along the Qinghai–Tibet Highway (QTH). This study proposes three morphological indicators—road shoulder thawing depth difference (RSTDD), offset distance (OD), and active layer thickness difference (ALTD)—to quantitatively characterize the asymmetry of thaw plates. Through integrating remote sensing data and large-scale geological survey results with an earth–atmosphere coupled numerical model and a random forest (RF) prediction framework, we assessed the spatial distribution of thaw asymmetry along the permafrost section of the QTH. The results indicate the following: (1) The ALTD values are overall very small and almost unaffected by the SSSE. The RSTDD increases with mean annual ground temperature (MAGT) before stabilizing, while the OD shows no significant response to the MAGT. The RSTDD and OD ranges are 0–3.38 m and 0–8.65 m, respectively, and they are greatly affected by the SSSE. (2) The RSTDD and OD show obvious spatial differences in different geographical regions of the QTH. An RSTDD greater than 2 m is concentrated in the Xidatan Faulted Basin and Chumar River High Plain. An OD greater than 3 m is mainly distributed from the Chumar River High Plain to the Tongtian River Basin. (4) The RSTDD and OD are most affected by subgrade orientation with importance values of 49.84% and 51.80%, respectively. The importance of the effect of mean average ground temperature (MAGT) on the active layer thickness is 80.58%. Full article

In deeply buried, small-clearance tunnels, the failure of the surrounding rock is profoundly influenced by the superposition of stresses and the cumulative disturbance effects from multiple blasting events. Consequently, the failure characteristics and mechanisms of the surrounding rock are highly complex. Through a comprehensive analysis encompassing failure investigations, geological assessments, and surrounding rock pressure monitoring, this study systematically examines the spatio-temporal failure characteristics and geological discrepancies across 3 parallel tunnels (namely, a pilot tunnel, a left tunnel, and a right tunnel). The analysis reveals the asymmetric failure behavior of the surrounding rock and offers a detailed discussion of the underlying mechanisms. The temporal and spatial evolution of the surrounding rock pressure in these tunnels is carefully analyzed, with an emphasis on uncovering the asymmetric failure mechanisms during the excavation of deep, small-clearance tunnels. The results demonstrate that the failure of the surrounding rock exhibits significant asymmetry during excavation, with the damage being more pronounced on the valley side compared to the mountain side. Furthermore, the degree of damage in the advance tunnel is substantially greater than that in the backward tunnel, particularly in sections following the excavation of the backward tunnel. Additionally, the distribution of the surrounding rock pressure in the advance tunnel also exhibits pronounced asymmetry. The asymmetric failure of the surrounding rock is primarily attributed to the stress concentration in the deep valley and the disturbances introduced by the excavation process, which induces tangential stress concentrations in the surrounding rock mass. The findings of this study hold considerable significance for the design and optimization of tunnel support systems, as well as for disaster prevention strategies in deeply buried, small-clearance tunnels. Full article

Multifractal analysis has been used in the exploration of soil grain size distributions (GSDs) in environmental and agricultural research. However, multifractal studies regarding the GSDs of sediments in braided delta-front are currently scarce. Open-source software designed for the realization of this technique has not yet been programmed. In this paper, the multifractal parameters of 61 GSDs from braided delta-front in the Paleogene Enping Formation in Huilu Low Uplift, Pearl River Mouth basin, are calculated and compared with traditional parameters. Multifractal generalized dimension spectrum curves are sigmoidal and decrease monotonically. Multifractal singularity spectrum curves are asymmetric, convex, and right-hook unimodal. The entropy dimension and singularity spectrum width ranges of silt-mudstones and gravelly sandstones are wider than those of fine and medium-coarse sandstones. The symmetry degree scopes from different lithologies are concentrated in distinguishing intervals. With the increase of grain sizes, the symmetry degree decreases overall. Both the symmetry degree and mean of GSDs are effective to distinguish the different lithologies from various depositional environments. A flexible and easy-to-use MATLAB (2021b)^® GUI (graphic user interface) package, MfGSD (Multifractal of GSD, V1.0), is provided to perform multifractal analysis on sediment GSDs. After raw GSDs imported into MfGSD, multifractal parameters are batch calculated and graphed in the interface. Then, all multifractal parameters can be exported to an Excel file, including entropy dimension, singularity spectrum, correlation dimension, symmetry degree of multifractal spectrum, etc. MfGSD is effective, and the multifractal parameters outputted from MfGSD are helpful to distinguish depositional environments of GSDs. MfGSD is open-source software that can be used to explore GSDs from various kinds of depositional environments, including water or wind deposits. Full article

Conventional numerical models frequently neglect the effects of strain softening and the spatial variability of surrounding rock when addressing the design and construction of deep tunnels in complex geological settings, which leads to a large deviation from the actual situation and potential security risks. In this case, symmetrical and asymmetric failure of surrounding rock usually occurs. In this paper, a numerical model considering strain softening and spatial variability is established for deep tunnel excavation based on the constitutive theory and probability distribution functions, and their effects on the mechanical behavior of tunnel excavation are systematically examined using FLAC3D software. The findings indicate that symmetrical failure will occur in strain-softening rock mass, and spatial variability will lead to asymmetric failure of surrounding rock. The strain-softening behavior of the internal friction angle has a pronounced impact on the plastic zone radius and post-excavation displacement. The distribution of stress and displacement in the surrounding rock is notably influenced by the spatial variability of the elastic modulus, while the variability in the internal friction angle can cause localized stress concentrations within the tunnel, potentially triggering partial collapse and instability. The coupling effect of strain softening and the spatial variability of surrounding rock properties will aggravate the mechanical response during tunnel excavation, resulting in greater displacement and more severe stress redistribution. Based on these findings, disaster prevention and control strategies are proposed for tunnels in complex geological regions, offering valuable guidance for engineering applications. Full article

This research examines the free vibration characteristics of composite ring-like structures enhanced with carbon nanotubes (CNTs), taking into account the effects of CNT agglomeration. The structural framework comprises two concentric composite rings linked by elastic springs, creating a coupled beam ring (CBR) system. The first-order shear deformation theory (FSDT) is applied to account for transverse shear deformation, while Hamilton’s principle is employed to formulate the governing equations of motion. The effective mechanical properties of the composite material are assessed with regard to CNT agglomeration, which has a significant impact on the elastic modulus and the overall dynamic behavior of the structure. The numerical analysis explores the influence of porosity distribution, boundary conditions (BCs), and the stiffness of the springs on the natural vibration frequencies (NVFs). The results demonstrate that an increase in CNT agglomeration leads to a reduction in the stiffness of the composite, consequently decreasing the NVFs. Furthermore, asymmetric porosity distributions result in nonlinear fluctuations in NVFs due to irregularities in mass and stiffness, whereas uniform porosity distributions display a nearly linear relationship. This study also emphasizes the importance of boundary conditions and elastic coupling in influencing the vibrational response of CBR systems. These findings offer significant insights for the design and optimization of advanced composite ring structures applicable in aerospace, nanotechnology, and high-performance engineering systems. Full article

Mastitis is one of the most frequent diseases in dairy farms and occurs in both clinical and subclinical forms, resulting in substantial economic losses. Asymmetrical dimethylarginine (ADMA) and symmetrical dimethylarginine (SDMA) are biomarkers that inhibit nitric oxide synthesis. Elevated ADMA levels are associated with an increased risk of mortality both in human medicine and in dogs and a potential need for intensive care, while SDMA correlates with poor prognoses in humans and the progression of renal disease in horses, though its impact varies depending on renal function. This study examines the plasma levels of ADMA and SDMA in healthy cows (H) and cows with subclinical mastitis (SCM) and clinical mastitis (CM). Cows were classified as having mastitis when CMT > 1 and SCC ≥ 250,000 cells/mL. The SCM group showed no clinical signs or milk alterations, whereas the CM group exhibited udder and/or milk changes. The study included 196 blood samples to determine ADMA and SDMA concentrations, with 96 from healthy cows and 100 from pathological cows (58 SCM and 42 CM). The descriptive statistics were reported as the median because the data were not normally distributed (Shapiro–Wilk test). Data were analyzed using the Kruskal–Wallis test with Bonferroni post hoc correction, and the cut-off and accuracy index were calculated using the gold-standard measurement, the SCC. Statistically significant differences in ADMA levels were observed between healthy cows (0.11 µmol/L) and cows with mastitis (SCM 0.26 µmol/L; CM 0.26 µmol/L), but no differences were found in their SDMA levels. The cut-off for ADMA was >0.164 µmol/L, with a sensitivity of 80.41% and specificity of 77.78%. This study suggests that the blood concentration of ADMA is statistically higher in cows with subclinical and clinical mastitis and could be further explored as a potential biomarker for diagnosing these diseases. Full article

This article proposes an arbitrary polygonal hybrid stress element considering gravity. It derives an arbitrary polygonal hybrid stress element considering gravity alone for slope stability related engineering analysis. In the stability analysis of slopes, slope disasters caused by gravity erosion have recently become an urgent problem to be solved through engineering. The traditional finite element analysis of slope stability faces problems such as a large number of divided elements and slow calculation efficiency. By introducing high-order stress fields through stress hybridization elements, accurate results can be simulated using a small number of elements. When dividing the mesh, most of the cell shapes are asymmetric, and the shape of the cell can be any polygon, which can simulate the geometric shape of complex slopes well and more accurately calculate the stress distribution in different parts, thus accurately simulating the stability situation in engineering. By comparing with the corresponding commercial software MARC 2020, the effectiveness and efficiency of the element were verified. It has been proven that any polygonal hybrid stress element has the advantage of flexible mesh division, which can obtain high-order stress fields and stress concentration phenomena with fewer elements. Applying this element to practical problems of slopes in engineering has also achieved good calculation results. Full article

Phenotypic variability in isogenic bacterial populations is a remarkable feature that helps them cope with external stresses, yet it is incompletely understood. This variability can stem from gene expression noise and/or the unequal partitioning of low-copy-number freely diffusing proteins during cell division. Some high-copy-number components are transiently associated with almost immobile large assemblies (hyperstructures) and may be unequally distributed, contributing to bacterial phenotypic variability. We focus on the nucleoid hyperstructure containing numerous DNA-associated proteins, including the replication initiator DnaA. Previously, we found an increasing asynchrony in the nucleoid segregation dynamics in growing E. coli cell lineages and suggested that variable replication initiation timing may be the main cause of this phenomenon. Here, we support this hypothesis revealing that DnaA/DNA variability represents a key factor leading to the enhanced asynchrony in E. coli. We followed the intra- and intercellular distribution of fluorescently tagged DnaA and histone-like HU chromosomally encoded under their native promoters. The diffusion rate of DnaA is low, corresponding to a diffusion-binding mode of mobility, but still one order faster than that of HU. The intracellular distribution of DnaA concentration is homogeneous in contrast to the significant asymmetry in the distribution of HU to the cell halves, leading to the unequal DNA content of nucleoids and DnaA/DNA ratios in future daughter compartments. Accordingly, the intercellular variabilities in HU concentration (CV = 26%) and DnaA/DNA ratio (CV = 18%) are high. The variable DnaA/DNA may cause a variable replication initiation time (initiation noise). Asynchronous initiation at different replication origins may, in turn, be the mechanism leading to the observed asymmetric intracellular DNA distribution. Our findings indicate that the feature determining the variability of the initiation time in E. coli is the DnaA/DNA ratio, rather than each of them separately. We provide a likely mechanism for the ‘loss of segregation synchrony’ phenomenon. Full article