Low Bending Rigidity Research Articles

Dynamic analysis of orthotropic bridge deck under moving vehicular loads by using Hencky bar-net model

This study extends the Hencky Bar-Net model (HBM) to dynamic analysis of vehicle-orthotropic bridge deck interaction system. The HBM was used to investigate the dynamic behaviour of an orthotropic bridge deck under moving vehicular loads and random road irregularities. The results indicate that the lower bending rigidity in width direction change the deformations of orthotropic deck from a global mode into a localized one, and dynamic magnification factors do not necessarily increase with higher vehicle speeds. However, dynamic magnification factors demonstrate an obvious increase in relation to higher vehicle speeds when the bending rigidity ratio is high. In addition, the HBM can easily handle damage of the bridge deck because of its discrete characteristic. Hence, the common longitudinal cracks that keep open are modelled by reducing the spring stiffness in the HBM. The results demonstrate longitudinal cracks show a complex influence on dynamic magnification factors of the bridge deck depending on the crack depth and location.

Structural properties of the Late Pleistocene Liujiang femoral diaphyses from southern China

The characterization of the femoral diaphysis in Pleistocene hominins with chronoecogeographical diversity plays a crucial role in evaluating evolutionary shifts in locomotor behavior and body shape. However, Pleistocene hominin fossil remains in East Asia are scarce and are widely dispersed temporally and spatially, impeding our comprehension of the nature and polarity of morphological trends. Here, we present qualitative and quantitative analyses of the cross-sectional properties and structural organization of diaphyses in two Late Pleistocene hominin femora (Liujiang PA91 and PA92) from southern China, comparing them to other Eurasian and African Pleistocene hominins. By integrating surface features and internal structure, our findings reveal that the Liujiang femora exhibit modern human-like characteristics, including a developed pilaster, a gluteal buttress, and minimum mediolateral breadth located at the midshaft. The presence of a femoral pilaster may relate to posterior cortical reinforcement and an increased anteroposterior bending rigidity along the mid-proximal to mid-distal portion of the diaphysis. Compared to archaic Homo, Liujiang and other Late Pleistocene modern human femora show a thinner mediolateral cortex and lower bending rigidity than the anteroposterior axis, and a lack of medial buttress, potentially indicating functionally related alterations in a range of pelvic and proximal femoral features throughout the Pleistocene. The femoral robusticity of the Liujiang individual resembles that of other Pleistocene hunter–gatherers from East Asia, implying comparable overall mobility or activity levels. The investigation of Liujiang femoral diaphyseal morphology contributes to a more comprehensive understanding of early modern human postcranial structural morphology in East Asia.

A statistic study on raspberry vesicles: Formation and properties

This paper gives a statistic study on the formation of ABC raspberry vesicles under bulk swelling with DPD simulations. All vesicles formed through a disc wrap-up process, i.e. a disc micelle wraps up to form a vesicle. The lifetimes of the disc micelles before they become vesicles can be characterized as short and long (tfastandtslow). Vesicles formed with tfast have a high loading efficiency and a wide size distribution. Most of them have low membrane permeability. They resist structural deformation under shear due to their high bending rigidity. Vesicles formed with tslow have a narrow size distribution. They are small, and have low loading efficiency. A large portion of them have permeable membranes with low bending rigidity and structural defects. Shear could restructure these vesicles, and hence modify their permeability. Adjusting the repulsion between solvophobic polymers and solvents impacts on lifetimes of disc micelles. A reduction in such repulsion favours tslow. The knowledge obtained can be used to design raspberry vesicles of desired size, loading and cargo release properties.

Evaluation of railhead material damage of insulated rail joints due to cyclic wheel loadings

Although insulated rail joints (IRJs) are important railway track components and, because of their low bending rigidity, a dynamic wheel impact results as wheels pass over them. Proper attention is needed to address this problem. Focussing on this point, a 3D finite element analysis (FEA) is carried out on IRJs to evaluate on damage analysis of sub-surface railhead material for endpost materials: fiberglass (fb), nylon 66 (ny), and polytetrafluoroethylene (ptfe). A cyclic vertical wheel load up to a total of 2000 cycles in non-Hertzian pressure form is applied at the wheel/rail contact patch on an IRJ. The residual longitudinal stress damage parameter is considered to rank the endpost material based on sub-surface railhead damage. It exhibits a new pattern described as ‘vertical flat type’ for a depth up to 8 mm initially and, as the cyclic loading increases, the vertical flat pattern damage changes to an ‘inclined flat type’ pattern.

Porous, low thickness carbon-fiber reinforced epoxy composites with excellent flexibility and superior electromagnetic radiation protection

Fiber reinforced polymers, especially carbon fiber reinforced polymers, are expected in the future to contribute more than 50% of the structural mass of an aircraft. With increasing application and experience increased attention is paid to carbon-fiber reinforced composites with improved advanced properties, such as mechanical, structural and electrical, allowing them to displace the more conventional materials, such as metal alloys. In this paper, we used the Design of experiment methodology to investigate the design and properties of newly developed unique porous carbon-fiber reinforced composites intended for electromagnetic shielding purposes. The main goal was therefore to fabricate a composite with low thickness, high permeability to air and water vapor with a satisfactory ability to shield electromagnetic fields, whereas the investigation of the influential variables of the reinforcement and the investigation of the influence of the matrix on the overall shielding efficiency of the composite belongs to the sub-objectives. Furthermore, other important properties of the composites including heat and mass transfer, mechanical and electrical properties were evaluated. A quality index evaluation approach using weighted and normalized data was implemented to choose a composite with properties, which best fits to its intended use. The highest quality index was achieved by the composite containing reinforcement with warp and weft sett 18 dm−1 using carbon tape 2 mm wide. This composite provides electromagnetic shielding 36 dB at 1.5 GHz, having high air permeability 1000 mm/s, relatively low bending rigidity of around 2.5 Nmm and thickness of only 0.37 mm.

Conductive Cellulose-Derived Carbon Nanofibrous Membranes with Superior Softness for High-Resolution Pressure Sensing and Electrophysiology Monitoring

Here, a strategy to overcome the stiff and brittle nature of cellulose-derived carbon nanofibrils (CCNFs) is proposed through a facile, low-cost, and scalable approach. Flexible and conformal CCNFs with a low bending rigidity below 55.4 mN and tunable conductivities of 0.14-45.5 S m-1 are developed by introducing silanol as a multieffect additive in the electrospun hybrid nanofibrous network and subsequent carbonization at a relatively high temperature (900 °C) and chemical vapor deposition of polypyrrole (PPy) on the hybrid carbon nanofibril surface. Silica acts as a lubricant in each rigid carbon fiber to improve flexibility of the CCNF structure as well as a template during cellulose carbonization to prevent the melting of carbon nanofibrils. Meanwhile, the uniform coating of PPy leads to an improvement in electrical conductivity while conserving the porous structure and compressibility of the CCNF nets. These conductive hybrid CCNF films are evaluated as mechanoreceptors and physiological sensors, which are demonstrated to be applied in intelligent electronics including electronic skin, human-machine interfaces, and epidermic electrodes. The design or working principles of the hybrid CCNFs for achieving optimum applicable effects when applied in different scenarios are revealed.

Interaction of new VV-hemorphin-5 analogues with cell membrane models

New analogues of the endogenous heptapeptide VV-hemorphin-5 (valorphin) synthesised by amino acid replacement allow for tailoring the peptide activity in vivo. Investigation of hemorphin-induced alterations of lipid bilayers’ physicochemical parameters unravels membrane-mediated mechanisms of interaction with cells and subcellular structures. We studied the effect of modified valorphins with nociceptive activity on the structure, mechanical and electrical properties of lipid membrane models. Lower bending rigidity and higher specific capacitance of phosphatidylcholine bilayers were found in the presence of VV-hemorphin-5 analogues. Peptide partition constants for the transfer from the aqueous solution into the membrane were determined by isothermal titration calorimetry. It was found that the inclusion of non-proteinogenic acids with different number of methylene groups lead to alterations of hemorphin-membrane binding. The highest membrane affinity was obtained for a hemorphin derivative with dose-dependent variable effects on visceral nociception in mice. The valorphin analogue with the most pronounced anti-nociceptive effect in vivo induced the highest dipole and zeta potential change without significantly affecting the lipid packing at glycerol level in phosphatidylcholine bilayers.

Phase transition of DNA knotting in spherical space

Knots have been discovered in various biological systems, such as DNA. The knotting probability of DNA in free space depends non-monotonically on its bending rigidity and has a prominent peak. The current work aims to understand the underlying mechanism of the non-monotonic dependence of DNA knotting probability on bending rigidity. Monte Carlo simulations are performed on a closed DNA molecule confined in spherical space described by a worm-like chain model and a flexible kink model, respectively. The closed DNA’s contour length and the spherical space radius both increase knotting probability, but also alter the unimodal dependence of knotting probability on bending rigidity. This is generalized using universal phase diagrams based on the two models. Under the flexible kink model, the total knotting probability of closed DNA is obviously increased at a relatively high excited energy. This supports the expectation that the entropy effect of knot size favours knot formation at a relatively low bending rigidity. In a given spherical space, the increasing contour length of closed DNA described by the worm-like chain model results in a visible shift in the knotting probability distribution. At the same time, the gyration radius of non-trivial closed DNA becomes comparable to that of trivial closed DNA, so that their ratio is not anti-correlated with average knot length. For closed DNA of various contour lengths, the relationship between average knot length and bending rigidity has a universal behaviour: the average knot length decreases to a local minimum at a bending rigidity of ∼5 and then gradually increases to a constant value. The existence of the local minimum is determined by the cut-off distance in repulsive Lennard–Jones potential. The bending rigidity corresponding to the beginning of the constant average knot length is consistent with that at the peak in the knotting distribution. At this point, the knot-size effect balances with the fragment free-energy effect and, at an even greater bending rigidity, knot length breathes around the average knot length value.

Optimisation of bending and shear rigidities of woven fabrics using hybrid DOE-NSGA-II approach

Bending and shear rigidities of woven fabrics depend on various materials and structural parameters. Achieving low bending rigidity and high shear rigidity in woven fabrics is a challenging and complicated task. In this work, engineering design of woven fabrics was optimised with respect to bending and shear rigidities using design of experiments (DOE) and non-dominated sorting genetic algorithm II (NSGA-II). The relationships between input parameters (proportion of fibre, yarn count and fabric sett) and rigidities of fabrics were obtained using Box-Behnken DOE method. The NSGA-II was used to determine the Pareto optimal front for low bending rigidity and high shear rigidity. The user can choose any option from the Pareto optimal front based on the end-use requirement. For the validation of the proposed approach, two engineered fabrics were produced using the optimised values of input parameters. The results demonstrated that target values and achieved values of rigidities are reasonably close to each other with average error of 6.24% and 3.33%, respectively. The proposed method can pave the way for intelligent manufacturing of woven fabrics in industrial scale.

Simulation of interacting elastic sheets in shear flow: Insights into buckling, sliding, and reassembly of graphene nanosheets in sheared liquids

In liquid-based material processing, hydrodynamic forces are known to produce severe bending deformations of two-dimensional (2D) materials such as graphene. The non-linear rotational and deformation dynamics of these atomically thin sheets is extremely sensitive to hydrodynamic particle-particle interactions. To investigate this problem, we developed a computational model of the flow dynamics of elastic sheets suspended in a linear shear flow, solving the full fluid-solid coupling problem in the two-dimensional, slender-body, Stokes flow regime. Both single and pairs of sheets in close proximity are analyzed. Despite the model being two-dimensional, the critical non-dimensional shear rate yielding single-particle buckling is comparable in order of magnitude to that reported for fully three-dimensional, disk-like sheets. For pairs of interacting sheets, hydrodynamic interactions lead either to parallel sliding or bending, depending on the value of an elasto-viscous number based on particle length. For sufficiently low bending rigidity or large shear rates, large deformations of initially stacked sheets lead to sheet reattachment after separation, unlike for the rigid case. A peeling-like dynamics where lubrication provides a viscous bonding force is observed for sheet pairs when one of the two sheets is more rigid than the other. Practical implications for graphene processing and exfoliation are discussed.

Mechanical Properties and Buckling of Kagome Graphene under Tension: A Molecular Dynamics Study

Kagome graphene is a carbon allotrope similar to graphene, with a single-atom thickness and a co-planar atomic structure. Despite interesting electronic properties, its mechanical behavior is still elusive. We have investigated the tensile properties of Kagome graphene under various strain rates and finite temperatures using molecular dynamics simulations. The Young’s modulus, ultimate tensile strength, fracture strain, and fracture toughness of the unsupported bulk material were measured as 96 GPa, 43 GPa, 0.05, and 1.9 J m−3, respectively, at room temperature and a strain rate of 109 s−1. Two deformation-stages were observed under tensile loading: normal and wrinkled. Initially, the Kagome graphene system stays in a co-planar structure without wrinkling until the tensile strain reaches 0.04, where it starts to wrinkle, unlike graphene. The wrinkle wavelength and magnitude suggest a very low bending rigidity, and wrinkle formation does not follow a rate predicted by continuum mechanics. Furthermore, the fracture mechanism of wrinkled Kagome graphene is briefly discussed.

Substantiation of systems for reducing noise and vibrations of grinding wheels in the processing of bodies of transport vehicles

The grinding process is a dynamic technological operation for processing vehicle body parts, which actually determines the accuracy of the macro and microgeometry of the product surface. It is known that exposure to elevated noise levels negatively affects the health of operators’ health, reduces labor productivity, and increases the rejection of products. Therefore, the problem of reducing acoustic discomfort is the most relevant for machine operators of the grinding group. Of particular note are the options for processing with thin grinding wheels that have a relatively low bending rigidity, which is typical for profile grinders and gear grinders, according to the copying method, as well as grinding tools for manual processing machines. The article presents the results of theoretical and experimental studies of the vibroacoustic characteristics of grinding wheels, on the basis of which methods have been developed to reduce noise and vibration of thin grinding wheels. It is shown that the application of protective measures can reduce the sound pressure level to 12 dB.

Nonlinear elasticity of wrinkled atomically thin membranes

Owing to their atomic thickness and low bending rigidity, suspended two-dimensional (2D) materials are prone to wrinkle formation. Here, we use molecular dynamics (MD) simulations to probe the effect of these wrinkles on the nonlinear elasticity of atomically thin graphene membranes. We observe a stress–strain response that consists of two linear regions that are separated by a transition. It is found that this transition is sharp in membranes where wrinkles are formed by uneven stresses at the boundaries. However, when wrinkles are formed by crystal defects, this nonlinear transition is seen to be more gradual. To capture these effects, we use a phenomenological model based on experimentally measurable quantities. We demonstrate the model’s fidelity by fitting it to the MD simulated nonlinear response of many graphene membranes providing evidence that the sharpness of the transition between the linear regions in the stress–strain response is a measure of the type of wrinkles and can be quantified by our model.

Mechanical response of composite fiber networks subjected to local contractile deformation

The extracellular matrix (ECM), forming the cell microenvironment, is a random fiber network whose heterogeneous microstructure serves a vital role in cellular functions such as migration, proliferation, and differentiation. Although prior computational studies used a network of randomly crosslinked fibers for investigating the ECM mechanical response due to the cell contraction, we hereby investigate the cell-induced deformation by considering the interplay between the collagen fibers and soft proteoglycan matrix domain. For this purpose, we represent the complex ECM microstructure by a double network model in which a random network of relatively stiff fibers (representing collagens) is embedded in a homogeneous network (representing the matrix domain). We demonstrate that the interaction between the network of stiff fibers and the network of matrix fibers plays a significant role in the propagation of cell-induced displacements. In particular, as the stiffness of the matrix domain increases, the long-range displacement propagation becomes suppressed. Furthermore, the degree of inhomogeneity in the displacement propagation is controlled by the relative stiffness of fiber and matrix networks. The influence of matrix stiffness becomes prominent for composite networks with random networks having a low average network connectivity and/or composed of fibers with low bending rigidity.

Creasing of flexible membranes at vanishing tension.

The properties of freestanding tensionless interfaces and membranes at low bending rigidity κ are dominated by strong fluctuations and self-avoidance and are thus outside the range of standard perturbative analysis. We analyze this regime by a simple discretized, self-avoiding membrane model on a frame subject to periodic boundary conditions by use of Monte Carlo simulation and dynamically triangulated surface techniques. We find that at low bending rigidities, the membrane properties fall into three regimes: Below the collapse transition κ_{BP} it is subject to branched polymer instability where the framed surface is not defined, in a range below a threshold rigidity κ_{c} the conformational correlation function are characterized by power-law behavior with a continuously varying exponent α,2<α≤4 and above κ_{c},α=4 characteristic for linearized bending excitations. Response functions specific heat and area compressibility display pronounced peaks close to κ_{c}. The results may be important for the description of soft interface systems, such as microemulsions and membranes with in-plane cooperative phenomena.

Stress magnification effect of initial deformation on the notch stress field and fatigue strength of thin plate welded joints

Compared with thick plate welded joint, the welding joint of thin plate will produce initial deformation due to its low bending rigidity. The existence of initial deformation will cause the welded structure to produce secondary bending effect, which will produce greater stress magnification effect at the weld toe and seriously affect the fatigue strength of thin plate welded joints. Therefore, based on the correction formula of thick plate, considering the influence of initial deformation and geometric nonlinearity of thin plate, this paper deduces the stress magnification factor formula at the weld toe of T-shaped and cruciform specimens. The accuracy of the revised formula is further verified by comparing the notch stress calculated by the modified formula with the FE results. Finally, the modified formula is applied to the notch stress and fatigue evaluation of typical thin plate welded joints respectively. The results show that the proposed notch stress calculation formula can fully consider the stress amplification effect of thin plate structure, and can be used to quickly evaluate the notch stress field and fatigue strength of thin plate welded joints.

Membrane stiffness and myelin basic protein binding strength as molecular origin of multiple sclerosis

Myelin basic protein (MBP) and its interaction with lipids of the myelin sheath plays an important part in the pathology of multiple sclerosis (MS). Previous studies observed that changes in the myelin lipid composition lead to instabilities and enhanced local curvature of MBP-lipid multilayer structures. We investigated the molecular origin of the instability and found that the diseased lipid membrane has a 25% lower bending rigidity, thus destabilizing smooth >1,µm curvature radius structures such as in giant unilamellar vesicles. MBP-mediated assembling of lipid bilayers proceeds in two steps, with a slow second step occurring over many days where native lipid membranes assemble into well-defined multilayer structures, whereas diseased lipid membranes form folded assemblies with high local curvature. For both native and diseased lipid mixtures we find that MBP forms dense liquid phases on top of the lipid membranes mediating attractive membrane interactions. Furthermore, we observe MBP to insert into its bilayer leaflet side in case of the diseased lipid mixture, whereas there is no insertion for the native mixture. Insertion increases the local membrane curvature, and could be caused by a decrease of the sphingomyelin content of the diseased lipid mixture. These findings can help to open a pathway to remyelination strategies.

Pressure distribution over the leaflets and effect of bending stiffness on fluid–structure interaction of the aortic valve

We describe a three-dimensional (3-D) fluid–structure interaction (FSI) simulation study of the aortic valve, where the flow is driven by a specified transient pressure drop along the aorta tube. The thickness of the leaflets is varied from 0.05 mm to 0.8 mm so that the normalized bending rigidity by the systolic pressure gradient covers a wide range from to 0.6. The non-uniform pressure distribution over the leaflets and the transient valve force are calculated, including the ‘water hammer’ effect during rapid closure. With low bending rigidity, the valve functions normally and produces physiological characteristics of healthy valves. However, exceedingly low rigidity leads to flapping motion of the leaflets and, in some cases (e.g. the normalized bending rigidity around 0.001), may reduce the performance index. As the leaflets become much stiffer, the valve is more difficult to open and slower to close, which leads to higher resistance and a reduced flow rate. Therefore, our results suggest that there is an optimal range of bending rigidity for the valve, roughly between 0.003 and 0.04 in normalized term. We further develop a one-dimensional unsteady flow model based on the momentum and mass conservation equations to replace the 3-D flow in the FSI simulation. The new flow model incorporates pressure loss across the valve as well as the leaflet motion. Comparison with the 3-D results shows that the reduced flow model is able to produce a reasonable 3-D deformation sequence of the leaflets, opening area and flow rate, especially in the cases of low bending rigidity.

Optimization of bending and shear rigidities of woven fabrics using desirability function

Banding and shear properties influence the drape and handle characteristics of woven fabrics. As bending and shear rigidities of woven fabrics generally have high degree of association, it is difficult to design a woven fabric having low bending rigidity and high shear rigidity or vice versa. This paper deals with the optimization of bending and shear rigidities of woven fabrics using the desirability function approach. Low stress mechanical properties such as bending rigidity and shear rigidity have been combined to represent ‘the overall desirability’ which is varying from 0 to 1. The overall desirability has been maximized against the target values of shear and bending rigidities. It was possible to attain overall desirability of 0.684 resulting from individual desirability of 0.662 and 0.707 for banding and shear rigidities, respectively. Experimental validation confirms that the applied method can be effectively used to optimize the woven fabric mechanical properties at low stress region.

Mechanomodulation of Lipid Membranes by Weakly Aggregating Silver Nanoparticles.

Silver nanoparticles (AgNPs) have wide-ranging applications, including as additives in consumer products and in medical diagnostics and therapy. Therefore, understanding how AgNPs interact with biological systems is important for ascertaining any potential health risks due to the likelihood of high levels of human exposure. Besides any severe, acute effects, it is desirable to understand more subtle interactions that could lead to milder, chronic health impacts. Nanoparticles are small enough to be able to enter biological cells and interfere with their internal biochemistry. The initial contact between the nanoparticle and cell is at the plasma membrane. To gain fundamental mechanistic insight into AgNP-membrane interactions, we investigate these phenomena in minimal model systems using a wide range of biophysical approaches applied to lipid vesicles. We find a strong dependence on the medium composition, where colloidally stable AgNPs in a glucose buffer have a negligible effect on the membrane. However, at physiological salt concentrations, the AgNPs start to weakly aggregate and sporadic but significant membrane perturbation events are observed. Under these latter conditions, transient poration and structural remodeling of some vesicle membranes are observed. We observe that the fluidity of giant vesicle membranes universally decreases by an average of 16% across all vesicles. However, we observe a small population of vesicles that display a significant change in their mechanical properties with lower bending rigidity and higher membrane tension. Therefore, we argue that the isolated occurrences of membrane perturbation by AgNPs are due to low-probability mechanomodulation by AgNP aggregation at the membrane.