Bending Stiffness Research Articles

Joints mechanical characteristics of prefabricated subway station considering bending stiffness difference

In prefabricated subway stations, the presence of joints leads to an uneven circumferential distribution of structural stiffness. However, there has been limited research focusing on the variability in bending stiffness of joints so far. Therefore, this paper proposes a theoretical framework to study deformation characteristics considering the differences in bending stiffness. This study aim to analyze the deformation characteristics of prefabricated structures, with a specific focus on the impact of variations in bending stiffness on the overall structural behavior. The research scope includes the calculation methods for the bending stiffness of joints, predicting maximum settlement of the top plate, and analyzing the influence of key parameters such as joint positions, geometric shapes, and dimensions, overburden density γ, lateral earth pressure coefficient λ, overburden thickness hf, and concrete density ρ on the joint bending stiffness. Results validate the reliability of the proposed method for calculating joint bending stiffness and demonstrate the key factors contributing to differences in bending stiffness.

A new approach to the calculation of variable tangent bending stiffness for helical strands

As the cross-section of the helical strand increases, the effect of its nonlinear bending characteristics becomes significant. To accurately simulate the response of helical strands under such conditions using the finite element method, determining the tangent bending stiffness of helical strands is indispensable. However, the approach of calculating the tangent bending stiffness of helical strands based on the stick-slip state of wires is not universally applicable across all strand models. In this study, we propose an approach for calculating the tangent bending stiffness of strands based on two mechanical models of helical strands. This proposed approach uses the ratio of the “actual increment” to the “theoretical maximum increment” of the nonlinear component of the wire axial force to calculate the contribution of one wire to the tangent bending stiffness of the strand. Significantly, this approach can be applied to different strand models, each of which may adopt different slip criteria. By comparing the results with the numerical solutions, we validate the effectiveness of the proposed approach for calculating the tangent bending stiffness of helical strands on different strand models. Furthermore, it is pointed out that the analytical results of wire sliding may vary significantly depending on the adopted slip criteria.

Comparative study on the bending moment capacity and stiffness of innovative and traditional furniture corner joints

ABSTRACT This study compares the bending moment capacity under compression and bending moment capacity under tension values of eight selected structural furniture joints. Specimens (type L) with a dimension of 150 × 150 × 366 mm were made from three-layer, 18 mm thick particleboard. The corner joints were tested in angular bending in compression and tension. Both classic and new joining elements (plastic cam, zinc cam, one-part plastic connector, screw cam, plastic connector with euroscrew, and birch dowel pre-glued) for the simple assembly of furniture were used in the study. Cam joints with wooden dowels can withstand high stress. There are only minimal differences between joints made of plastic or zinc cams with dowels. If birch dowels with an adhesive coating are added to the plastic joint from sample with plastic connector with euroscrew, this joint will reach 126% higher values in angular bending tests – compressive stress.

Machine learning enables the discovery of 2D Invar and anti-Invar monolayers

Materials demonstrating positive thermal expansion (PTE) or negative thermal expansion (NTE) are quite common, whereas those exhibiting zero thermal expansion (ZTE) are notably scarce. In this work, we identify the mechanical descriptors, namely in-plane tensile stiffness and out-of-plane bending stiffness, that can effectively classify PTE and NTE 2D crystals. By utilizing high throughput calculations and the state-of-the-art symbolic regression method, these descriptors aid in the discovery of ZTE or 2D Invar monolayers with the linear thermal expansion coefficient (LTEC) within ±2 × 10−6 K−1 in the middle range of temperatures. Additionally, the descriptors assist the discovery of large PTE and NTE 2D monolayers with the LTEC larger than ±15 × 10−6 K−1, which are so-called 2D anti-Invar monolayers. Advancing our understanding of materials with exceptionally low or high thermal expansion is of substantial scientific and technological interest, particularly in the development of next-generation electronics at the nanometer or even Ångstrom scale.

Wave propagation analysis of the overhead conductor rail system based on numerical simulation and full-scale experiment

The overhead conductor rail system (OCR) is an important current-transmitting structure for electric trains in tunnels. As the train speed increases, the wave propagation behaviour in the OCR plays an ever-increasingly important role in affecting the current collection quality. This paper is the first endeavour to numerically and experimentally explore wave behaviours in the OCR. With the help of a finite element model, the spatial propagation and frequency-domain characteristics of the wave propagation are investigated. Based on the time-space distribution of waves, the wave speed of the OCR is identified. Subsequently, a full-scale experimental test is conducted to identify a real-life OCR's wave speed for the first time. The relative error between the simulated and experimental speed is only 5.50 %, highlighting the effectiveness of the presented model. Then, the influence of wave propagation on the interaction performance of pantograph-OCR is analysed. A significant reduction of the interaction performance is observed when the train speed approaches the wave speed. Through sensitivity analysis, the bending stiffness, the linear density, and the span length are identified as sensitive parameters affecting the wave speed.

The interdependence of functional properties of a football boot outsole during the shape optimisation process

The aim of this study was to investigate the relationship and interdependence of functional properties of the football boot outsole during the shape optimisation process. Sensitivity-based shape optimisation technique was applied to a football boot outsole to modify its thickness to have various functional properties. Three functional properties of the outsole, which are the midfoot and forefoot bending stiffness and torsional stiffness, were investigated. The midfoot and forefoot bending stiffness were measured via a three-point bending test. Torsional stiffness was measured via a bespoken mechanical test. The functional properties were evaluated by finite element models, representing the developed mechanical tests. Through the optimisation tasks, it was explored how much each functional property could be changed individually and also while minimising the influence of the other two functional properties. With the modification of the regions of the outsole to optimise for various individual target functional property values, the changes in the other two functional properties were observed. Lastly, the optimised outsoles from the finite element models were 3D printed and tested to determine the accuracy of the process. Within a permitted thickness limit, modifying the region associated with the torsional stiffness measurement influenced the other two functional properties the most. Especially, the midfoot bending stiffness was influenced more than the forefoot bending stiffness. On the other hand, the areas involved in the midfoot and forefoot bending stiffness measurements were independent of each other. The conclusions drawn in this study are limited to the particular outsole design, single outsole component and mechanical test utilised.

A benign synergism of O2 plasma and protein biopolymer for improving some properties of polyester fabrics

Polyester (PET)is the most widely used fiber in the textile and clothing fields by virtue of its cheapness, strength, crease-resistance, stain-resistance, and ease of drying. However, PET fabric lacks the antistatic properties, hydrophilicity, and affinity for most classes of dyes. Here, freshly extracted keratin from poultry feathers and sericin from silkworm cocoons were used for the first time to make oxygen plasma-treated PET fabric surfaces hydrophilic, antistatic, and dyeable with cationic dye. Adopting the pad-dry-cure technique, oxygen plasma-activated PET fabrics were successfully coated with a layer of sericin or keratin as indicated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effects of plasma irradiation time as well as curing temperature and duration on the properties of the treated fabric were monitored. The results of this study revealed that the plasma/biopolymer-treated fabrics have become dyeable with the cationic dye C.I. Basic Violet 16. The effect of treatment of PET fabric on some of its physical and mechanical properties, such as wettability, antistatic properties, yellowness index, air permeability, water vapor permeability, ultraviolet protection factor, burst strength, and bending stiffness, was monitored. The durability of the finished sample against repeated washing in terms of the fabric resistivity was examined. The alterations in the chemical, crystal, and morphological structures of the treated fabric were assessed using Fourier transform infrared spectroscopy, XPS, X-ray diffraction, and SEM.

Modelling and analysis of long floating hose string at different working states during the pumping ashore process

ABSTRACT During the pumping ashore process, a long floating hose string connects with the shoreline and the other end either free-floating or linking a Trailing Suction Hopper Dredger (TSHD), which suffered both motions of the TSHD and itself under the wind, wave and currents. It is necessary to evaluate the dynamics of the floating hose string to ensure its reliability because their deformation in waves matter the inside slurry flow transportation and may suffer unexpected damaged during the operation and even cause the project delay. Although the composite structure of the dredging hoses can refer to the floating hoses in offshore oil transportation, the bending stiffness, long-distance behaviour and coupling with the motions of the ship and the hose string bring new challenges for modelling and solving. In order to solve the problems, in this study, a numerical model of kilometres-long floating hose string with mechanical properties of the composite hose materials is established with single hose segment bending test data, macro model with lumped mass theory, dynamics of the hose string and coupling analysis with the ship motions. The dynamic performance of kilometres-long floating hoses during the free-floating state and connected TSHD for pumping state with different angles of wind, current, and wave are investigated. The analyses indicate that axial tensions and bending moments of the first 100 m and last 200 m of floating hose string should be noticed, and the amplitude of the tensions remain low and relatively stable when the 60° incoming wave to the ship, which is a better choice in practical operation. Finally, the effects of different sea conditions and lengths of hose string are carried out. The nonlinear geometry and forces of different lengths’ floating hoses during the pumping ashore process were obtained for practical operation reference. Results can help to evaluate long-distance floating hose motions under different sea conditions and provide practical operation suggestions for the working process.

Analytical modelling for residual stress prediction in multi-step side milling of GH4169 thin-wall parts based on deformation

GH4169 thin-walled parts are widely used in aerospace due to their high-temperature, corrosion resistance, and fatigue strength. However, they often deform from machining-induced residual stress, which is a significant unresolved manufacturing challenge. Additionally, initial residual stress from previous steps critically impacts subsequent processes. This study found that the residual stress of side milling of thin-walled parts under smaller cutting parameters is mainly caused by mechanical effects, and the influence of milling heat can be ignored. In this study, an analytical prediction model for residual stress of multi-step side milling thin-walled parts based on the deformation of thin-walled parts is proposed for the first time, which is suitable for smaller cutting parameters. Then, the proposed model is examined the mechanisms through which residual stresses develop during side milling and defined the applicability of model based on specific assumptions. To validate these assumptions, an experimental setup was devloped to simulate the movement of the heat source during milling. Subsequent two-step side milling experiments on GH4169 confirmed the accuracy of the analytical prediction model in predicting the residual stresses of multi-step side milling in thin-walled parts. It was observed that higher equivalent bending stiffness in thin-walled parts correlates with reduced machining deformation. The analytical model also provides a strategic approach to control machining deformation by managing the equivalent bending stiffness of the parts.

Design optimization of a snowboard performing an ollie

The ollie, a fundamental manoeuver in snowboarding, serves as a basis for various tricks requiring high altitude and extended airtime. The maximum ollie height depends on the snowboard’s geometry and structural characteristics. In this study, the influence of these properties is investigated with a flexible multibody dynamics simulation, where the snowboard is modeled by geometrically non-linear finite elements, snow contact is considered by a penetration depth and velocity proportional normal force and ollie motion is achieved by imposing measured loads to the bindings. To maximize the height, a genetic optimization procedure is presented, which yields substantial improvements. Optimizing the camber line and the bending stiffness distribution yields enhanced performance. Less damping as well as lighter boards lead to higher jumps, no noteworthy correlation between axial stiffness and damping distribution and jump height was found, and the strain energy stored in the board during takeoff is a useful indicator for estimating ollie heights. Nevertheless, further investigations should take a more advanced and realistic rider interaction into account.

An analytic solution for bending of multilayered structures with interlayer-slip

Layered structures are prevalent in both natural environments and engineered composite materials. The elastic bending behavior of these structures is primarily governed by properties of their abundant interfaces. While the behavior of two- and three-layered beams has been extensively studied, this research shifts the focus to the impact of elastic shearing at interfaces on the deflection of multilayered structures comprising a substantial number of layers. We present an analytical solution indicating that the bending properties of multilayered beams and plates are nonlinearly dependent on interfacial stiffness. Denoting Se as the effective bending stiffness of an n-layered beam of length L, and S0 as the bending stiffness of a perfectly bound counterpart, we arrive at SeS0=11+(n2−1)tanhαLαL where αL represents a dimensionless parameter related to geometry and material properties. The analytical solutions, validated through finite element simulations, highlight the substantial variations in stiffness across different layered structures. This solution could also be instrumental in assessing interfacial damage and delamination in lamellar composites.

A stiffness prediction method for variable cross‐section CFRP laminated beam

AbstractTo efficiently design the stiffness of the laminated composite blade‐like structure, an analytical method to assess deformation of variable cross‐section laminated beam under cantilever bending load was developed, in which a local ply density matrix method was introduced to characterize the ply‐up in arbitrary cross‐section after ply drop‐off process and infinitesimal element segment method was used to convert complex variable cross‐section specimen into local equal cross‐section beam structure. The model was validated by the cantilever beam experiment with relative predicted error of stiffness of 5.7%. Inner and outer ply drop‐off models were analyzed using the proposed analytical method. The results show that: (1) stiffness of the outer ply drop‐off model is the highest, at 13.07 N/mm, while that of the inner ply drop‐off model 2 is the lowest, about 17.8% lower than the outer ply drop‐off model; (2) maximum relative deformation difference between the inner ply drop‐off model 2 and outer ply drop‐off model is 21.7% at the free side of the cantilever beam. It indicates that anti‐deformation ability of the variable cross‐section laminated structure can be efficiently designed by the proposed analytical method, especially for the section close to the free side.Highlights Developed a bending stiffness prediction method for composite beam. Variable cross‐section feature of the composite laminate was considered. Local ply density matrix method was introduced to characterize ply drop‐off. Proposed method was validated by cantilever beam bending experiment. Inner and outer ply drop‐off models were compared by the proposed method.

Incorporation of short-chain alcohols into fluid bilayers and its effect on membrane dynamic properties as seen by neutron scattering

In this work, we investigate the effect of concentrated alcoholic solutions (up to 40%w) on extruded 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes using scattering techniques. Extrusion in alcoholic aqueous solutions (methanol, ethanol, or butanol) reduces liposome size, evidenced from the decrease in hydrodynamic radius (RH) obtained from dynamic light scattering. Short-chain alcohols such as ethanol and butanol soften the lipid membranes, as observed by the decrease of the unrelaxed bending modulus (κ̃ ) obtained by neutron spin-echo spectroscopy. Thus, softer membranes are easily ruptured during extrusion, leading to a reduction in vesicle radius corroborated by a reduction in both RH and radius of gyration as seen by dynamic and static light scattering. Moreover, model-free analysis of small-angle neutron scattering (SANS) curves suggests that solvent molecules become incorporated into the lipid membrane. Analysing deviations in the scattering invariant from values predicted by mass balance, we find that the volume fraction of liposomes increases, modifying the scattering length density of the assemblies. By quantifying these changes, we estimate that 12% to 18% of the liposome membrane is composed of solvent molecules (alcohol + water), depending on the type of alcohol and its concentration present in solution, with the exception of glycerol where next to no incorporation was observed. Finally, structural parameters obtained through light scattering and changes in contrast profiles calculated from analysis of the invariant were corroborated through modelling of the SANS curves. Modelling suggests that a reduction of bilayer thickness takes place for liposomes dispersed in ethanolic and butanolic solutions, but not in the presence of methanol or glycerol.

Bending Collapse and Energy Absorption of Dual-Phase Lattice Structures.

A dual-phase lattice structure composed of mixed units with hard and soft phase characteristics is proposed in this work. The proposed lattice structure has high specific energy absorption and high compressive strength. The load response and energy absorption characteristics under bending loads were studied through three-point bending tests and numerical analysis methods. The research results indicate that although the deformation modes of the given lattice structure are the same, the dual-phase design strategy significantly improves the bending performance of the lattice structure: the bending modulus is increased by 744.7%, and the specific energy absorption is increased by 243.5%.

(Invited) Deformable Electronics Based on Strain-Engineered Van Der Waals Materials

Materials exhibit drastically different physical and chemical properties as their dimensionality varies. Atomically-thin van der Waals (vdW) materials possess unique mechanical, electrical, optical, and thermal characteristics, originated from quantum confined low-dimensionality and a lack of dangling bond. In particular, strong in-plane covalent bonding and weak interlayer vdW interaction of two-dimensional (2D) vdW materials enable exceptional combination of mechanical properties, such as high Young’s modulus, high in-plane strength, and ultralow bending stiffness at a level of cell membrane. Moreover, mechanical strain can induce modulation of electronic and phononic band structures of 2D vdW materials more effectively due to mechanical resilience and high surface-to-volume ratio. For these reasons, deformation engineering has garnered substantial interest in mechanics, materials and electronics communities as a new tuning knob for emerging phenomena and functionalities of 2D vdW materials. In this talk, I will discuss deformation engineering of 2D vdW materials – (1) active and dynamic deformation strategies, including in-plane interfacial slippage and out-of-plane structural deformation, (2) deformation strain induced phenomena, and (3) emerging device concepts based on deformation engineering of 2D vdW materials.

MATERIAL PROPERTIES OF THE EMBRYONIC SMALL INTESTINE DURING BUCKLING MORPHOGENESIS.

During embryonic development, tissues undergo dramatic deformations as functional morphologies are stereotypically sculpted from simple rudiments. Formation of healthy, functional organs therefore requires tight control over the material properties of embryonic tissues during development, yet the biological basis of embryonic tissue mechanics is poorly understood. The present study investigates the mechanics of the embryonic small intestine, a tissue that is compactly organized in the body cavity by a mechanical instability during development, wherein differential elongation rates between the intestinal tube and its attached mesentery create compressive forces that buckle the tube into loops with wavelength and curvature that are tightly conserved for a given species. Focusing on the intestinal tube, we combined micromechanical testing with histologic analyses and enzymatic degradation experiments to conclude that elastic fibers closely associated with intestinal smooth muscle layers are responsible for the bending stiffness of the tube, and for establishing its pronounced mechanical anisotropy. These findings provide insights into the developmental role of elastic fibers in controlling tissue stiffness, and raise new questions on the physiologic function of elastic fibers in the intestine during adulthood.

Experimental and theoretical analysis of flexural performance for EPCFA-CSP novel composite structure

The article proposes a novel composite structure, namely the Elastic Polyurethane Coal Fly Ash Corrugated Steel Plate (EPCFA-CSP). One specimen consisting solely of corrugated steel plate and seven composite structure specimens were designed to investigate the bending behavior of the EPCFA-CSP composite structure through four-point bending tests. The results indicate that incorporating mushroom-shaped steel pin shear keys into the combination of EPCFA and CSP yields the most favorable effect. With an increase in structural layer thickness from 30 mm to 50 mm, when the mushroom-shaped steel pin shear key contributes to the stress distribution within the composite structure, both bending stiffness and ultimate load of the composite structure specimen increases by 150.35 % and 63.93 %, respectively. Specimen EPCFA-(50)-CSP-II achieves a flexural stiffness of 89.40 kN/mm, a cracking load of 187.7 kN, and an ultimate load of 205.4 kN. Finally, based on experimental results, a deflection correction formula considering the reduction factor due to combination effects was derived to correct deflections at characteristic points accurately. This formula is applicable at approximately 0.6 times the ultimate load, and calculations using this formula yield ratios between calculated deflections and experimental deflections ranging from 0.88 to 0.97. This demonstrates its effectiveness in correcting deflections and provides valuable insights for designing related composite structures.

Exploiting interfacial instability during peeling a flexible plate from elastic films

Adhesive interactions between soft materials are prevalent in both biological systems and various engineering applications, including soft robots, flexible electronics, and antifouling coatings. Many studies have demonstrated that cavitation and fingering instabilities emerge at the adhesive interface between rigid objects and soft films, owing to the geometric attributes of the contact region. However, in the context of peeling configurations, defining the geometric features is challenging, resulting in relatively scant exploration of interfacial instabilities. Hence, the modulation of instability patterns during the peeling process of a flexible plate from a thin elastic film, alongside the consequential effects on mechanical responses, remains poorly understood. To elucidate the mechanisms underlying interfacial instability during peeling process and its impacts on peel-off force, we use finite element methods to simulate the evolution of interface separation. Consistent with previous experimental observations, we find that the interfacial instability will occur when the bending stiffness of the flexible plate is bigger than a critical value. We show that the interfacial instability is mainly induced by the competition between the adhesion energy and the strain energy of the film, and the incompressibility of the thin film is critical for the appearance of the interfacial instability. Combining theory and finite element simulation, we propose the scaling laws for the critical peel-off force for stable and unstable peelings, respectively, and show that the critical peel-off force will decrease when the interfacial instability occurs. Finally, we demonstrate that weakening the tangential adhesion strength and loosening the constraints between the film and the rigid substrate effectively suppress fingering instability. Collectively, our findings elucidate the pivotal factors influencing interfacial instability, offering invaluable insights for the design of structures or systems involving soft materials.

Unveiling the Mechanism of Spontaneous Nanoscroll Formation from Janus Transition Metal Dichalcogenide Nanoribbons.

Due to the atomic asymmetry, Janus transition metal dichalcogenide monolayers possess spontaneous curling and can even form one-dimensional nanoscrolls. Unveiling this spontaneous formation mechanism of nanoscrolls is of great importance for precise structural control. In this paper, we successfully simulate the process of Janus MoSSe nanoscroll formation from flat nanoribbons, based on molecular dynamics (MD) simulations with hybrid potentials. The spontaneous scrolling is purely driven by the relaxation of intrinsic strain in Janus MoSSe. The final structure of nanoscroll is strongly affected by the length of nanoribbon with a nonmonotonous relation. To further understand the mechanism, we establish a thermodynamic model to determine the inner radius of MoSSe nanoscrolls, which is shown to be related to spontaneous curvature, bending stiffness, interlayer van der Waals interaction, interlayer distance, and length of initial nanoribbon. The results correspond well with MD simulations of nanoscrolls from flat nanoribbons and the molecular static simulations of directly built nanoscrolls. Moreover, the inner radii of MoSeTe and MoSTe nanoscrolls are predicted based on the model. Our results provide insights into the Janus TMD nanoscroll formation and a pathway for controllable fabrication of nanoscrolls.

Correlation between Dental Composite Filler Percentage and Strength, Modulus, Shrinkage Stress, Translucency, Depth of Cure and Radiopacity.

Filler content in dental composites is credited for affecting its physical and mechanical properties. This study evaluated the correlation between the filler percentage and strength, modulus, shrinkage stress, depth of cure, translucency and radiopacity of commercially available high- and low-viscosity dental composites. Filler weight percentage (wt%) was determined through the burned ash technique (800 °C for 15 min). Three-point bend flexural strength and modulus were measured according to ISO 4049 with 2 mm × 2 mm × 25 mm bars. Shrinkage stress was evaluated using a universal testing machine in which composite was polymerized through two transparent acrylic rods 2 mm apart. Shrinkage was measured from the maximum force following 500 s. The translucency parameter (TP) was measured as the difference in color (ΔE00) of 1 mm thick specimens against white and black tiles. The depth of cure was measured according to ISO 4049 in a cylindrical metal mold (4 mm diameter) with a 10 s cure. Radiopacity was measured by taking a digital X-ray (70 kVp for 0.32 s at 400 mm distance) of 1 mm thick specimens and comparing the radiopacity to an aluminum step wedge using image analysis software. The correlation between the filler wt% and properties was measured by Pearson's correlation coefficient using SPSS. There was a positive linear correlation between the filler wt% and modulus (r = 0.78, p < 0.01), flexural strength (r = 0.46, p < 0.01) and radiopacity (r = 0.36, p < 0.01) and negative correlation with translucency (r = -0.29, p < 0.01). Filler wt% best predicts the modulus and strength and, to a lesser extent, the radiopacity and translucency. All but two of the high- and low-viscosity composites from the same manufacturer had statistically equivalent strengths as each other; however, the high-viscosity materials almost always had a statistically higher modulus. For two of the flowable composites measured from the same manufacturer (3M and Dentsply), there was a lower shrinkage stress in the bulk-fill version of the material but not for the other two manufacturers (Ivoclar and Tokuyama). All flowable bulk-fill composites achieved a deeper depth of cure than the flowable composite from the same manufacturer other than Omnichroma Flow Bulk.