Search Results (78)

Bolted connections are critical in deep-sea engineering, yet classical theories (such as VDI 2230) implicitly assume atmospheric pressure conditions, neglecting the volume contraction of components due to hydrostatic pressure. This fundamental flaw hinders accurate prediction of preload retention—especially when bolts and clamped components exhibit differential compressibility (a common scenario in practical applications). To bridge this scientific gap, this paper establishes the first analytical model for bolt preload under pressure-induced volumetric contraction based on deformation coordination relations. The derived closed-form expressions explicitly quantify residual preload as a function of deep-sea ambient pressure, component bulk modulus, and geometric parameters. Model predictions closely match finite element calculations, showing that stainless steel bolts clamping aluminum alloys under 110 MPa pressure can experience up to a 40% preload reduction. This theoretical framework extends classical bolt connection mechanics to high-pressure environments, providing a scientific basis for optimizing deep-sea connection designs through material matching and dimensional control to effectively mitigate pressure-induced preload loss. Full article

Alfalfa is a high-quality forage crop whose viscoelastic properties strongly influence the performance of baling, pickup, and stacking operations. In this study, small alfalfa block specimens were tested using a universal testing machine to investigate stress relaxation and creep behaviors under different moisture contents (12%, 15%, 18%), densities (100, 150, 200 kg/m³), and maximum compressive stresses (8, 12, 16 kPa). Experimental data were fitted using viscoelastic models for parameter analysis. Results indicated that the relaxation response consisted of a rapid attenuation followed by a slow stabilization phase. The five-element Maxwell model achieved a higher fitting accuracy (coefficient of determination, R² > 0.997) than the three-element model. The creep process exhibited three stages, including instantaneous elastic deformation, decelerated creep, and steady-state deformation, and it was accurately represented by the five-element Kelvin model (R² > 0.998). Increasing moisture content reduced stiffness, while moderate moisture improved viscosity and shape retention. Higher density enhanced blocks compactness, stiffness, and damping characteristics, resulting in smaller deformation. The viscoelastic response to compressive stress showed moderate enhancement followed by attenuation under overload, with the best recovery and deformation resistance observed at 12 kPa. These findings elucidate the viscoelastic behavior of alfalfa blocks and provide theoretical support and engineering guidance for evaluating bale stability and optimizing pickup–clamping parameters. Full article

A novel hydraulically actuated uniform clamping flange connection mechanism is proposed to address the long-standing challenges in high-pressure natural gas flowmeter calibration, including cumbersome bolt-by-bolt assembly/disassembly, high leakage risk, and severe non-uniform gasket contact pressure associated with conventional multi-bolt flanges. Unlike traditional discrete bolt loading, the proposed mechanism generates a continuous and actively adjustable circumferential clamping force via an integrated hydraulic annular piston, ensuring excellent sealing uniformity and rapid installation within minutes. A high-fidelity transient finite element model of the hydraulic clamping flange assembly is established, incorporating the nonlinear compression/rebound behavior of flexible graphite–stainless steel spiral-wound gaskets and one-way fluid–structure interaction under water hammer loading. Parametric studies reveal that reducing the effective clamping area to below 80% of the original design significantly intensifies stress concentration and compromises sealing integrity, while clamping force below 80% or above 120% of the nominal value leads to leakage or component overstress, respectively. Under steady 10 MPa pressurization, the flange exhibits a maximum stress of 150.57 MPa, a minimum gasket contact stress exceeding 30 MPa, and a rotation angle below 1°, demonstrating robust sealing performance. During a severe water hammer event induced by rapid valve closure, the peak flange stress remains acceptable at 140.41 MPa, while the minimum gasket contact stress stays above the critical sealing threshold (38.051 MPa). However, repeated water hammer cycles increase the risk of long-term gasket fatigue. This study introduces, for the first time, a hydraulic uniform-clamping flange solution that dramatically improves sealing reliability, installation efficiency, and operational safety in high-pressure flowmeter calibration and similar temporary high-integrity piping connections, providing crucial technical guidance for field applications. Full article

Cardiovascular clamping procedures can cause tissue traumatization, leading to serious adverse events interrupting blood flow and causing life-threatening hemorrhage. The aim of the study is to evaluate the properties of 3D-printed, high-elasticity elastomeric materials—BioMed Flex 50A and 80A (Formlabs Inc., Sommerville, MA, USA)—in terms of their suitability for the fabrication of atraumatic inserts used for surgical clamping instruments. To show the importance of the elaboration of the new atraumatic materials, finite element simulations of blood vessel compression by a surgical tool were validated experimentally with porcine vessels, and histopathology assessed the tissue response. These results confirm that excessive clamping forces can cause vessel wall stratification and rupture. Specimens BioMed Flex 50A and 80A underwent surface, mechanical, and biological testing, including topography, wettability, acoustic microscopy for structural voids, cytotoxicity with human dermal fibroblasts, pro-inflammatory marker analysis, and bacterial biofilm assessment. The results of the testing of the 3D-printed BioMed Flex 50A and 80A materials show good potential for applications in safe atraumatic surgical instruments. Further research may include the possibilities to develop 3D-printed metamaterials with pressure adapting properties. Full article

A touch-off explosion on concrete slabs is considered one of the simplest yet most destructive forms of adversarial loading on building elements. It causes far greater damage than explosions occurring at a distance. The impact is usually concentrated in a small area, leading to surface cratering, scabbing of concrete, and even tearing or rupture of the reinforcement. Studies available on the behavior of reinforced concrete (RC) slabs under touch-off (contact) and standoff explosions commonly indicate that the maximum damage occurs when the blast is applied to the center of the slab. This observation raises an important question about how the position of an explosive charge, especially relative to the free edge of the slab, affects the overall damage pattern in slabs supported on only two sides with clamped supports. This study uses a modeling strategy combining Eulerian and Lagrangian domains using the finite element tools of Abaqus Explicit v2020 to examine the behavior of a square slab supported on two sides with clamped ends subjected to blast loads at different positions, ranging from the center to the free edge and beyond, under touch-off explosion conditions. The behavior of concrete was captured using the Concrete Damage Plasticity model, while the reinforcement was represented with the Johnson–Cook model. Effects of strain rate were included by applying calibrated dynamic increase factors. The developed numerical model is validated first with experimental data available in the published literature for the case where the explosive charge is positioned at the slab’s center, showing a very close agreement with the reported results. Along with the central blast position, five additional cases were considered for further investigation as they have not been investigated in the existing literature and were found to be worthy of study. The selected locations of the explosive charge included an intermediate zone (between the slab center and free edge), an in-slab region (partly embedded at the free edge), a partial edge (partially outside the slab), an external edge (fully outside the free edge), and an offset position (250 mm beyond the free edge along the central axis). Results indicated a noticeable transition in damage patterns as the detonation point shifted from the slab’s center toward and beyond the free edge. The failure mode changed from a balanced perforation under confined conditions to an asymmetric response near the free edge, dominated by weaker surface coupling but more pronounced tensile cracking and bottom-face perforation. The reinforcement experienced significantly varying tensile and compressive stresses depending on blast position, with the highest tensile demand occurring near free-edge detonations due to intensified local bending and uneven shock reflection. Full article

Background: In spinal fusion surgery, intersomatic compression force is currently applied subjectively by the operating surgeon, despite its critical role on implant stability and risk of subsidence. No standardized measurement or guideline exists to control or quantify the amount of force applied. Methods: In a two-phase exploratory study, we evaluated whether proprioceptive muscle memory allows reliable reproduction of applied manual compression forces. In Phase 1, 30 participants applied force to a compression clamp equipped with a strain gauge, simulating spinal interbody compression on a 3D-printed vertebral model. They were then asked to reproduce this force using a hand dynamometer at defined time intervals. In Phase 2, intraoperative compression forces applied during spinal fusion procedures were retrospectively assessed by having the operating surgeon reproduce the force on a dynamometer. Results: Participants were able to reproduce their initial manual compression force within a 15% deviation, even 15 min after the initial application. In 116 clinical cases, an average compression force of 146.3 ± 18.5 N was recorded. No significant differences were observed across different spinal segments. Conclusions: These findings provide initial data toward defining a reproducible reference range for indirect intraoperative compression assessment. Standardization of applied force may help improve biomechanical outcomes and reduce complications such as implant migration, pseudarthrosis, or cage subsidence. Full article

To address the issues of high stalk breakage rate and the mismatch between extraction force and operational speed in current horizontal shaft counter-rolling cotton stalk pullers, this study presents a novel clamping mechanism. The mechanism enables precise adjustment of the rollers’ rotational speed, inter-roller gap, and surface topography. The objective is to systematically investigate the effects of these key parameters on the peak extraction force and its timing during the stalk pulling process. Initially, pre-compressed cotton stalks were employed as test specimens. Their tensile properties post-compression were investigated by simulating the extraction forces using a universal testing machine. Subsequently, the structural design of the critical components for the test rig was created based on these experimental findings. Theoretical analysis identified the surface texture of the clamping rollers, their rotational speed, and the clamping gap as the primary experimental factors. The effects of these factors on the peak extraction force and its timing were analyzed using Response Surface Methodology (RSM). The results indicated that the optimal combination—striped surface texture for both rollers, a speed of 220 rpm, and a zero gap—yielded a time to peak force of 0.05 s and a peak force of 710.77 N, which is significantly below the measured tensile strength limit of 994.60 N for compressed stalks. This indicates that the designed clamping device for the horizontal shaft counter-rolling cotton stalk extraction machine achieves faster extraction speed while ensuring stalk integrity, and the research results can provide theoretical foundation and design guidance for the development of horizontal shaft counter-rolling cotton stalk extraction machinery. Full article

In traditional scallion cultivation, the bare-root transplanting method—which involves direct seeding, seedling raising in the field, and lifting—is commonly adopted to minimize seedling production costs. However, during the mechanized transplanting of bare-root scallion seedlings, practical problems such as severe seedling damage and poor planting uprightness exist. In this paper, the Hertz–Mindlin with Bonding contact model was used to establish the scallion seedling model. Combined with the Plackett–Burman experiment, steepest ascent experiment, and Box–Behnken experiment, the bonding parameters of scallion seedlings were calibrated. Furthermore, the accuracy of the scallion seedling model parameters was verified through the stress–strain characteristics observed during the actual loading and compression process of the scallion seedlings. The results indicate that the scallion seedling normal/tangential contact stiffness, scallion seedling normal/tangential ultimate stress, and scallion Poisson’s ratio significantly influence the mechanical properties of scallion seedlings. Through optimization experiments, the optimal combination of the above parameters was determined to be 4.84 × 10⁹ N/m, 5.64 × 10⁷ Pa, and 0.38. In this paper, the flexible planting components of scallion seedlings were taken as the research object. Flexible protrusions were added to the planting disc to reduce the damage rate of scallion seedlings, and an EDEM-ADAMS coupling interaction model between the planting components and scallion seedlings was established. Based on this model, optimization and verification were carried out on the key components of the planting components. Orthogonal experiments were conducted with the contact area between scallion seedlings and the disc, rotational speed of the flexible disc, furrow depth, and clamping force on scallion seedlings as experimental factors, and with the uprightness and damage status of scallion seedlings as evaluation criteria. The experimental results showed that when the contact area between scallion seedlings and the disc was 255 mm², the angular velocity was 0.278 rad/s, and the furrow depth was 102.15 mm, the performance of the scallion planting mechanism was optimal. At this point, the uprightness of the scallion seedlings was 94.80% and the damage rate was 3%. Field experiments were carried out based on the above parameters. The results indicated that the average uprightness of transplanted scallion seedlings was 93.86% and the damage rate was 2.76%, with an error of less than 2% compared with the simulation prediction values. Therefore, the parameter model constructed in this paper is reliable and effective, and the designed and improved transplanting mechanism can realize the upright and low-damage planting of scallion seedlings, providing a reference for the low-damage and high-uprightness transplanting operation of scallions. Full article

The significant potential loss of proton exchange membrane fuel cells (PEMFCs) at high current densities is primarily attributed to the high mass transfer resistance of the gas diffusion layer (GDL). The underlying mechanism of how structural parameters of the GDL under actual assembly conditions affect oxygen transport resistance remains unclear, particularly the quantitative relationship between the compression ratio (α) and tortuosity (γ). This study systematically evaluated the output performance and mass transfer overpotential of three commercially available GDLs with similar thickness and porosity under different compression ratios (5.4% to 27%) and four inlet humidity conditions (RH0% to RH100%). By accurately extracting and comparing mass transfer overpotentials, it was observed that the mass transfer overpotential initially decreased and then increased with the rising compression ratio, with an optimum observed at 21.6%. An empirical correlation between the compression ratio (α) and tortuosity (γ) was established as γ = 3.42α + 2.1. Based on this, a modified oxygen diffusion equation was proposed to accurately describe oxygen transport behavior within the GDL under compressed conditions. A modified oxygen diffusion equation was proposed to more accurately characterize the oxygen transport process within compressed GDLs. These findings establish a foundation for optimizing GDL design and stack assembly processes. Future work will build upon this study by incorporating multiphysics conditions such as stack clamping pressure, number of cells, intercell contact resistance, and assembly conditions (temperature and relative humidity), with the aim of elucidating the force–thermal–electrical–mass coupling mechanisms within the stack, thereby enhancing the overall performance and reliability of high-power-density proton exchange membrane fuel cell (PEMFC) stacks. Full article

In frame structures, connections play a vital role in governing both serviceability and ultimate strength. For pultruded fiber-reinforced polymer (PFRP) frames, connection design is even more critical due to the anisotropic and viscoelastic nature of the composite materials used in the primary elements (e.g., beams and columns) and their joints. This study presents a finite element model (FEM) to evaluate the influence of several connection parameters—namely, connection stiffening, bolt diameter, washer diameter, and clamping force—on the elastic behavior of beam-column joints composed of PFRP elements. The results demonstrate that stiffening the upper and lower connection angles significantly enhances joint performance. Increasing the bolt diameter improves moment capacity, reduces rotational deformation, decreases stress concentrations around bolt-hole edges, and increases both minor principal and compressive stresses beneath the bolt shank. Similarly, a larger washer diameter contributes to higher connection stiffness and reduces stress concentrations at bolt holes. Although the clamping force has a relatively modest effect on global connection behavior, it positively influences the through-thickness stress distribution in the angle beneath the bolt shank. Finally, regression equations were developed to quantify the relationship between rotation, moment, bolt diameter, washer diameter, and clamping force, providing a valuable tool for the design and optimization of PFRP connections in structural applications. Full article

A simple analytic procedure for the linear static analysis of short thin-walled beams with monosymmetric open cross-sections subjected to eccentric axial loading is presented. Under eccentric compressive loading, the beam is subjected to compression/extension, to torsion with influence of shear with respect to the principal pole and to bending with influence of shear in two principal planes. The approximate closed-form solutions for displacements consist of the general Vlasov’s solutions and additional displacements due to shear according to the theory of torsion with the influence of shear, as well as the theory of bending with the influence of shear. The internal forces and displacements for beams clamped at one end and simply supported on the other end, where eccentric loading is acting, are calculated using the method of initial parameters. The shear coefficients for the monosymmetric cross-sections introduced in these equations are provided. Solutions for normal stress and total displacements according to Vlasov’s general thin-walled beam theory, and those obtained with the proposed method taking shear influence into account, are compared with shell finite element solutions analyzing isotropic and orthotropic I-section beams. According to the results for normal stress relative differences, and Euclidean norm for displacements, it has been demonstrated that shear effects must be accounted for in the analysis of such structural problems. Full article

This study investigates the long-term performance of flexible anti-collision rings after 12 years of service on the Xiangshan Port Highway Bridge. Stepwise loading–unloading tests at multiple loading rates (0.8–80 mm/s) were performed on the anti-collision rings, with full-field strain measurement via digital image correlation (DIC) technology. The results show that: The mechanical response of the anti-collision ring shows significant asymmetric tension–compression, with the tensile peak force being 6.8 times that of compression. A modified Johnson–Cook model was developed to accurately characterize the tension–compression force–displacement behavior across varying strain rates (0.001–0.1 s⁻¹). The DIC full-field strain analysis reveals that the clamping fixture significantly influences the tensile deformation mode of the anti-collision ring by constraining its inner wall movement, thereby altering strain distribution patterns. Despite exhibiting a corrosion gradient from severe underwater degradation to minimal surface weathering, all tested rings demonstrated consistent mechanical performance, verifying the robust protective capability of the rubber coating in marine service conditions. Full article

Stiffened panels are extensively used in aerospace applications, particularly in wing and fuselage sections, due to their favorable strength-to-weight ratio under in-plane loading conditions. This research employs the commercial finite element software Ansys-19 to analysis the critical buckling and ultimate collapse load of an aluminum stiffened panel having a dimension of 1244 mm (Length) × 957 mm (width) × 3.5 mm (thickness), with three stiffener blades located 280 mm away from each other. Both the critical buckling load and post-buckling ultimate failure load of the panel are validated against the experimental data found in the available literature, where the edges towards the length are clamped and simply supported, and the other two edges are free. For nonlinear buckling analysis, a plasticity power law is adopted with a small geometric imperfection of 0.4% at the middle of the panel. After the numerical validation, the investigation is further carried out considering four different lateral pressures, specifically 0.013 MPa, 0.065 MPa, 0.085 MPa, and 0.13 MPa, along with the compressive loading boundary conditions. It was found that even though the pressure application of 0.013 MPa did not significantly impact the critical buckling load of the panel, the ultimate collapse load was reduced by 18.5%. In general, the ultimate collapse load of the panel was severely affected by the presence of lateral pressure while edge compressing. Three opening shapes—namely, square, circular, and rectangular/hemispherical—were also investigated to understand the behavior of the panel with openings. It was found that the openings significantly affected the critical buckling load and ultimate collapse load of the stiffened panel, with the lateral pressure also contributing to this effect. Finally, in critical areas with higher lateral pressure load, a titanium panel can be a good alternative to the aluminum panel since it can provide almost twice to thrice better buckling stability and ultimate collapse load to the panels with a weight nearly 1.6 times higher than aluminum. These findings highlight the significance of precision manufacturing, particularly in improving and optimizing the structural efficiency of stiffened panels in aerospace industries. Full article

Flexible piezoresistive pressure sensors have great potential in wearable electronics due to their simple structure, low cost, and ease of fabrication. Porous polymer materials, with their highly deformable internal pores, effectively expand the sensing range. However, a single-sized pore structure struggles to achieve both high sensitivity and a broad sensing range simultaneously. In this study, a PDMS-based flexible pressure sensor with a bilayer porous structure (BLPS) was successfully fabricated using clamping compression and a sacrificial template method with spherical sucrose cores. The resulting sensor exhibits highly uniform pore sizes, thereby improving performance consistency. Furthermore, since different pore sizes and thicknesses correspond to varying Young’s moduli, this study achieves tunable sensitivity across a wide pressure range by adjusting the bilayer thickness ratio (maximum sensitivity of $0.063 {\mathrm{kPa}}^{-1}$ in the 0–23.6 kPa range, with a pressure response range of 0–654 kPa). The sensor also demonstrates a fast response time (128 ms) and excellent fatigue stability (>10,000 cycles). Additionally, this sensor holds great application potential for facial expression monitoring, joint motion detection, pressure distribution matrices, and Morse code communication. Full article

Secondary pre-tightening of clamping cable joints can effectively improve the load-bearing performance of U-shaped steel supports. However, the underlying mechanism of secondary pre-tightening has remained a critical knowledge gap in ground control engineering, and its design still relies on empirical approaches without theoretical guidance. To address these challenges, this study proposes a novel mechanistic framework integrating mathematical modelling, experimental validation, and parametric analysis. Specifically, a first-principle-based mathematical expression for the slip resistance of clamping cable joints under secondary pre-tightening was derived, explicitly incorporating the effects of bolt torque and interfacial friction; and a dual-phase experimental protocol combining axial compression tests and numerical simulations was developed to systematically quantify the impacts of initial pre-tightening torque, secondary pre-tightening torque (T₂), and the timing of secondary pre-tightening (u/u_max). Three groundbreaking thresholds were identified, as follows: critical initial pre-tightening torque (T₁ > 250 N·m) beyond which secondary pre-tightening becomes ineffective (<5% improvement); minimum effective secondary pre-tightening torque (T₂/T₁ > 1) for significant load-bearing enhancement; and the optimal activation window (u/u_max < 50%) balancing capacity gain (<10%) and deformation control. These findings establish the first quantitative design criteria for secondary pre-tightening applications, transitioning from empirical practice to mechanics-driven optimization. Full article