Linear Bending Research Articles

Strongly Bent Double-Stranded DNA: Reconciling Theory and Experiment.

The strong bending of polymers is poorly understood. We propose a general quantitative framework of polymer bending that includes both the weak and strong bending regimes on the same footing, based on a single general physical principle. As the bending deformation increases beyond a certain (polymer-specific) point, the change in the convexity properties of the effective bending energy of the polymer makes the harmonic deformation energetically unfavorable: in this strong bending regime the energy of the polymer varies linearly with the average bending angle as the system follows the convex hull of the deformation energy function. For double-stranded DNA, the effective bending deformation energy becomes non-convex for bends greater than ~ 2° per base-pair, equivalent to the curvature of a closed circular loop of ~ 160 base pairs. A simple equation is derived for the polymer loop energy that covers both the weak and strong bending regimes. The theory shows quantitative agreement with recent DNA cyclization experiments on short DNA fragments, while maintaining the expected agreement with experiment in the weak bending regime. Counter-intuitively, cyclization probability (j-factor) of very short DNA loops is predicted to increase with decreasing loop length; the j-factor reaches its minimum for loops of ≃ 45 base pairs. Atomistic simulations reveal that the attractive component of the short-range Lennard-Jones interaction between the backbone atoms can explain the underlying non-convexity of the DNA effective bending energy, leading to the linear bending regime. Applicability of the theory to protein-DNA complexes, including the nucleosome, is discussed.

Design optimization of worm gear drive with reduced power loss

In worm gear mechanism, power loss is one of the critical issues, which requires attention from gear designers and researchers. This is due to power loss; the overall efficiency of worm gear drive gets reduced. In this article, Simulated Annealing (SA) is used to minimize the power loss of worm gear drives within the prescribed set of design constraints. Various design constraints included in the design optimization problem are linear pressure, bending strength and deflection of worm. Gear tooth number, coefficient of friction and helix angle are the design variables considered. Results obtained are compared and validated with the results obtained in previous research work found in the literature. It shows that SA is more efficient in attaining optimal design values for worm gear drive for reducing power loss.

Experimental and numerical analysis of wooden sandwich panels with an auxetic core and oval cells

Wood consumption is constantly being rationalized by the production of modern wood-based materials, especially honeycomb plates. Due to the beneficial properties of the auxetics, wooden honeycomb panels with auxetic cores can be used as structural elements. In particularly as walls and partitions in wooden houses, as well as shelves and bodies for cabinet furniture. Thus the aim of this study was to determine rigidity, strength and capacity to absorb energy in novel sandwich honeycomb boards manufactured from beech wood with oval cells of the auxetic core. Samples with honeycomb boards were subjected to uniaxial compression and three-point bending. Based on testing results it was shown that cores of oval cells exhibited auxetic properties and a strong orthotropy. Density of honeycomb panels is below 400 kg/m3, thus they may be classified as lightweight boards. Thanks to a high value of the modulus of linear elasticity and bending strength the designed board is a good substitute for traditional wood-based panels. During bending honeycomb panels with auxetic cores more effectively absorb energy compared to the same panels subjected to axial compression. These investigations provide the foundation for further studies on optimization of the board structure and its applicability in industrial practice.

Intraoperative customization of intramedullary nails – First results

IntroductionIntramedullary nailing is a valuable treatment option for many types of fractures. Furthermore nailing is applicable for osteosynthesis following osteotomy in deformity correction. For intraoperative fine-tuning of alignment in intramedullary (IM) nailing procedures, a bending device for customization of IM nails under sterile conditions was developed. We have performed a retrospective clinical study to analyze and describe the technical requirements, indications and limitations for intraoperative customization of IM nails. Materials and MethodsIn 41 cases of deformity correction with IM nailing, we applied intraoperative sterile bending of IM nails. The patient age ranged from 13 to 64 years. We evaluated the radiological outcome (precision of the intervention) of 31 completed cases, comparing the preoperative planning with the final result on long-standing radiographs (LSR). The diameter of the nails ranged from 8,5mm to 13mm. Cases with fracture or non-union treatment with intraoperative application of the bending device were excluded and analyzed separately. ResultsAll removed implants were examined – none of them showed any signs of material fatigue. The amount of intraoperative bending of the nails was 1° to 12°. A high level of precision was achieved, with a median postoperative axis deviation to the preoperative planning of 3,5mm. In a polio patient with limited bone quality, the implant removal caused an undisplaced cortical crack. There were no other complications. There was uneventful and fast bone healing in all patients. ConclusionsIntraoperative customization of intramedullary nails is a valuable technique for precise alignment control with IM nailing. With this technique, the benefits of IM nailing can be used for a wide range of indications, including deformity correction. The sterile bending device is safe and easy to handle. It is strong enough to bend all commercially available IM nails. Monofocal or linear bending in multiple planes is possible. However, when defining the site of bending, one must consider the removal of the implant in the future.

Evolution of Rheological Behaviors of Styrene-Butadiene-Styrene/Crumb Rubber Composite Modified Bitumen after Different Long-Term Aging Processes.

In this study, a new type of composite modified bitumen was developed by blending styrene-butadiene-styrene (SBS) and crumb rubber (CR) with a chemical method to satisfy the durability requirements of waterproofing material in the waterproofing layer of high-speed railway subgrade. A pressure-aging-vessel test for 20, 40 and 80 h were conducted to obtain bitumen samples in different long-term aging conditions. Multiple stress creep recovery (MSCR) tests, linear amplitude scanning tests and bending beam rheometer tests were conducted on three kinds of asphalt binders (SBS modified asphalt, CR modified asphalt and SBS/CR composite modified asphalt) after different long-term aging processes, including high temperature permanent deformation performance, resistance to low temperature thermal and fatigue crack. Meanwhile, aging sensitivities were compared by different rheological indices. Results showed that SBS/CR composite modified asphalt possessed the best properties before and after aging. The elastic property of CR in SBS/CR composite modified asphalt improved the ability to resist low temperature thermal and fatigue cracks at a range of low and middle temperatures. Simultaneously, the copolymer network of SBS and CR significantly improved the elastic response of the asphalt SBS/CR modified asphalt at a range of high temperatures. Furthermore, all test results indicated that the SBS/CR modified asphalt possesses the outstanding ability to anti-aging. SBS/CR is an ideal kind of asphalt to satisfy the demand of 60 years of service life in the subgrade of high speed railway.

Tilted Disks around Black Holes: A Numerical Parameter Survey for Spin and Inclination Angle

Abstract We conduct a systematic study of the properties of tilted accretion flows around spinning black holes, covering a range of tilt angles and black hole spins, using the general-relativistic magnetohydrodynamics code Athena++. The same initial magnetized torus is evolved around black holes with spins ranging from 0 to 0.9, with inclinations ranging from 0° to 24°. The tilted disks quickly reach a warped and twisted shape that rigidly precesses about the black hole spin axis with deformations in shape large enough to hinder the application of linear bending wave theory. Magnetized polar outflows form, oriented along the disk rotation axes. At sufficiently high inclinations a pair of standing shocks develops in the disks. These shocks dramatically affect the flow at small radii, driving angular momentum transport. At high spins they redirect material more effectively than they heat it, reducing the dissipation rate relative to the mass accretion rate and lowering the heating efficiency of the flow.

Production of titanium-containing metal-ceramic composites based on boron carbide in the nanocrystalline state

ABSTRACTThe results of the study of the production technology, phase composition, structure and physico-mechanical properties of metal-ceramic materials based on boron carbide and their components are presented. Boron carbide was obtained by direct synthesis from chemical elements using amorphous boron and carbon black. By mechanical dispersion, solid reagents were converted into an ultrafine state. Using a chemical method, nanoscale (70–80 nm) boron carbide was synthesised from suspension solutions of amorphous boron and liquid hydrocarbons. Boron carbide-based metal-ceramic composite powder B4C–(Co–Ni–Ti) was obtained by mechanical dispersion of the constituent components. Based on results of studying of the temperature-dependence of wetting angle of boron carbide with Co–Ni–Ti metallic alloy, the compacting modes of metal-ceramic composite powders by plasma-spark sintering and hot pressing have been developed. The influence of the component content of the binder metal (alloy) on some physico-mechanical properties (linear expansion coefficient, hardness, and bending strength) of hardmetal-ceramic materials based on boron carbide was studied. It was found that the optimum content of the metal component in the composite is ∼ 25 wt-%. In the temperature range 300–600°C, the materials obtained are characterised by stable dimensional factors, since in this temperature range the thermal conductivity coefficient does not depend much on temperature. At room temperature, their bending strength is about 1 GPa. A new method of chemical synthesis of nanocrystalline ceramic compositions of boron carbide and titanium diboride using suspension solutions for the preparation of powders and their spark plasma sintering was also developed to obtain a compacted material of composition B4C+30 wt-%TiB2, which has a high hardness of 95 HRA (with maximum microhardness 45.6 GPa) and sufficient strength (with a bending strength of 834 MPa).

Storage, fatigue and low temperature characteristics of plasma treated rubberized binders

Abstract Crumb rubber modified (CRM) asphalt has been increasingly used in highway and airfield pavements due to its great mechanical behavior. However, the poor storage stability limits its application. It has been proved that plasma technology can effectively improve the surface characteristics of polymer. Therefore, this study introduced low temperature plasma (LTP) to modify the surface of crumb rubber for improving its adhesion. In this study, a series of laboratory tests, including hot storage test, linear amplitude sweep (LAS) test and bending beam rheometer (BBR) test, were carried out. Then storage stability, fatigue resistance and low temperature rheological property of LTP treated and untreated CRM binders were explored to evaluate the impact of LTP treatment, rubber content, particle size and binder source. The results indicated that the LTP treated rubberized binders showed enhanced storage stability (except for 20% content) and fatigue property, while its low temperature performance had a slight change. Moreover, the increased rubber content from 10% to 20% had a positive effect on aforementioned properties after LTP treatment. Specially, the critical low temperature tended to increase linearly as CR content increased within the scope of 10–20%. In addition, the fatigue performance increased with a great rubber particle size while the storage stability was on the contrast. Furthermore, after a LTP treatment, the softer crumb rubberized binder showed improved low temperature performance and weakened fatigue resistance.

Refined multiscale model based on the second generation interatomic potential for the mechanics of graphene sheets

Computationally efficient multiscale model based on the refined constitutive law, including second generation reactive empirical bond order potential with dihedral energy term, is employed to investigate the static response of the graphene sheets under transverse and in-plane compressive loads including material nonlinearity through atomic interactions and Green-Lagrange geometric nonlinearity through the strain displacement relations. The bending modulus of the graphene sheet predicted without considering the dihedral energy term in the constitutive law is almost half than those of predicted through first principle calculations. The inclusion of the dihedral energy term predicts bending modulus close to those of through first principle calculations. The atomistic and continuum deformations are coupled through the Cauchy–Born rule. In the present study, the effect of the dihedral energy term on the linear and nonlinear bending and postbuckling response of the graphene sheets under transverse and in-plane compressive loads is investigated in detail. The governing finite element equations for the graphene sheet are derived through the principle of minimum potential energy. The spatial approximation of the graphene sheet at the continuum scale is attained through the finite element method.

Generalization of the Thin Plate Bending Equation under the Action of Gas

The transverse distributed load on an elastic thin plate in a gas environment is determined. Different values of the pressure of the medium on both surfaces form both the pressure difference and the transverse unbalanced force depending on the average pressure and curvature of the mid-surface. It is shown that in the general case both of these components of the transverse force should be taken into account. With a small ratio of the average pressure to the elastic modulus of the plate material and a large relative thickness, the influence of the second load component is small. With a small relative thickness of the plate and a large ratio of the average medium pressure to the elastic modulus of the material, the influence of the second component of the transverse bending load becomes comparable to the bending stiffness of the plate. Linear bending and plate stability are considered.

Buckling of an Oscillating Rod Under Longitudinal Impact

The dynamics of a thin rod under the action of compressive force is considered. The compressive force increases abruptly and then remains constant. The compression of the rod is assumed to take place instantly throughout its length. The motion of the rod is studied, depending on the magnitude and time of action of the compressive force defined by the phase of the initial free oscillation of the rod. Only the initial stage of the process is investigated, for which the linear bending theory is valid. The friction forces are not taken into account. An essential relationship is shown to exist between the dynamics of the rod and the initial conditions determined by the phase of the bending oscillations at the instant of impact. Relatively weak impact leads to excitation of the bending oscillations. Rearrangement of harmonics develops with time under specified initial maximum deflection from a straight line and zero velocity. The fastest buckling takes place at some initial deflection with the velocity directed toward the increasing bend.

Electrical contacts of coplanar 2H/1T′ MoTe2 monolayer

Contact resistance plays a crucial role in determining the performance of nanodevices. The phase contact of 2H/1T′ MoTe2 has driven significant interest for its potential in dealing with this issue. Using first-principles calculations, this work reports on the electronic and contact properties of coplanar 2H/1T′ MoTe2 interfaces down to monolayer limits. Twelve interface structures are investigated, two of them are expected to be the most energy-favored structures depending on the chemical condition; we name them as (0°, 30°) and (0°, −30°). For all the interfaces, the quality of electrical contact is evaluated by analyzing the Schottky barrier height (SBH), the interfacial states, and charge transfer at the phase boundaries. The SBH changes greatly between different interfaces. Especially, as the electrical contact of (0°, 30°) is ohmic with a small SBH of 0.03 eV for hole, the electrical contact of (0°, −30°) is Schottky with the Fermi level located near the midgap. All the interfaces introduce very tiny and thin midgap states in the 2H sides, these states cause the Fermi level to be partly pinned. Besides, linear band bending is found in these coplanar phase contacts due to interface polarity. Our results suggest that the control of interfacial morphology is a key factor for the device applications.

Bending of biomimetic scale covered beams under discrete non-periodic engagement

Covering elastic substrates with stiff biomimetic scales significantly alters the bending behavior via scales engagement. This engagement is the dominant source of nonlinearity in small deflection regime. As deformation proceeds, an initially linear bending response gives way to progressive stiffening and thereafter a geometrically dictated ‘locked’ configuration. However, investigation of this system has been carried out until date using assumption of periodic engagement even after scales contact. This is true only under the most ideal loading conditions or if the scales are extremely dense akin to a continuum assumption on the scales. However, this is not true for a practical system where scales are more discrete and where loading can alter periodicity of engagement. We address this nonlinear problem for the first time in small deflection and rotation regime. Our combined modeling and numerical analysis show that relaxing periodicity better represents the geometry of discrete scales engagement and mechanics of the beam under general loading conditions and allows us to revisit the nonlinear behavior. We report significant differences from predictions of periodic models in terms of predicting the behavior of scales after engagement. These include the difference in the angular displacement of scales, normal force magnitudes along the length, moment curvature relationship as well as a distinct nature of the locking behavior. Therefore, non-periodicity is an important yet unexplored feature of this problem, which leads to insights, absent in previous investigations. This opens way for developing the structure-property-architecture framework for design and optimization of these topologically leveraged solids.

Performance characteristics of collapsible CaO-SiO2 based ceramic core material via layered extrusion forming

An additive manufacturing method, named layered extrusion forming (LEF), was adopted to fabricate collapsible ceramic cores. Green samples were first fabricated using CaCO3 and SiO2 powders as precursor materials and aqueous polyethylene glycol solution-silica sol as a composite binder and then calcined at 1100 °C − 1300 °C for 2 h. The effect of CaO-SiO2 molar (C/S) ratio on the performance characteristics of green and sintered samples was investigated. The results showed that the slurries exhibited a pseudoplastic behavior for different C/S ratios, and the linear shrinkage of the green samples showed a slight increase with decreasing C/S ratio. After sintering, the reduction of C/S ratio obviously decreased linear shrinkage and bending strength, whereas strengthened the hydration resistance. The microstructure analysis demonstrated that the porosity was increased with decreasing C/S ratio, thereby weakening the bending strength. The ceramic cores samples were constituted by Ca2SiO4 and CaO phases. The existence of the Ca2SiO4 improved the hydration resistance, leading to relative lower collapsibility. The sintered samples with a C/S ratio of 2.45 obtained a superior collapsibility in water, especially in the higher water temperature, which is significant for industry applications.

Free vibration analysis of functionally graded rotating conical shells in thermal environment

Due to the wide applications of functionally graded shells in high temperature conditions, the study of dynamic behavior of these structures in thermal conditions is of the key importance. The vibration of rotating functionally graded conical shells with temperature-dependency of material properties is studied in this paper. The Donnel shell theory is employed to extract governing equations including initial thermomechanical stresses as well as centrifugal forces, Coriolis forces, and initial hoop tensions due to rotation. The initial thermomechanical stresses are obtained from the nonlinear heat conduction equation with temperature-dependent thermal conductivity for temperature distribution and linear bending equations for initial deflections. The method of generalized differential quadrature is employed to solve the problem. The obtained results are compared with the available literature and finally, the effects of angular velocities, thermal conditions, volume fraction index, semi-vertex angles and lengths of the cone on frequency are investigated.

Vibration signatures of a rotor-coupling-bearing system under angular misalignment

Forces and moments arise in flexible couplings while accommodating misalignments. These efforts are exerted on the coupled shafts, influencing the rotor dynamics and giving rise to vibration patterns, which are of interest for investigations focusing on malfunction signatures and, consequently, on fault identification and diagnosis. This work proposes the comparison between two approaches for modeling the forces and moments generated by a metallic disc coupling under angular misalignment. The first is a well-established model based on the linear bending flexure of the disc packs, and assuming the misalignment efforts are the sum of the first four harmonic components. In the second approach, a structural analysis of the coupling is conducted through finite element method, where the cyclic nature of coupling efforts is captured by the application of consecutive shaft spin angles. Steady state responses are simulated and then both orbit shapes and displacements spectrum are analyzed in order to highlight harmonic components rising due to misalignment. Finally, test rig measurements are compared to predicted results by the theoretical approach presented in this work.

Two-scale constitutive modeling of a lattice core sandwich beam

Constitutive equations are derived for a 1-D micropolar Timoshenko beam made of a web-core lattice material. First, a web-core unit cell is modeled by discrete classical constituents, i.e., the Euler–Bernoulli beam finite elements (FE). A discrete-to-continuum transformation is applied to the microscale unit cell and its strain energy density is expressed in terms of the macroscale 1-D beam kinematics. Then the constitutive equations for the micropolar web-core beam are derived assuming strain energy equivalence between the microscale unit cell and the macroscale beam. A micropolar beam FE model for static and dynamic problems is developed using a general solution of the beam equilibrium equations. A localization method for the calculation of periodic classical beam responses from micropolar results is given. The 1-D beam model is used in linear bending and vibration problems of 2-D web-core sandwich panels that have flexible joints. Localized 1-D results are shown to be in good agreement with experimental and 2-D FE beam frame results.

FE analysis and experimental determination of a shaft deflection under three-point loading

Increasing industrial demand for new products including advanced production technology leads to substantial natural resources consumption. Furthermore, huge environmental pollution and emerging environmental legislation motivate the machine tools industry as one of the major resource consumers on a global scale to develop methods for more sustainable use of the Earth's resources. Machine tools re-engineering concerning design and failure analysis is an approach by which outdated machines are upgraded and restored to like-new machines. To evaluate the mechanical failure of the used machine components and to ensure their reliable future performance, it is essential to make material, design, and surface investigations. In this paper, an experimental approach based on the principle of a three-point bending test is presented to evaluate the shaft elastic behavior under loading. Moreover, finite element analysis and numerical integration method are used to determine the maximum linear deflection and bending stress of the shaft. Subsequently, a comparison between the results is made. In conclusion, it was found that the measured bending deflection and stress were well close to the admissible design values. Therefore, the shaft can be used again in the second life cycle. However, based on previous surface tests conducted, the shaft surface needs re-carburizing and refining treatments to ensure the reliable performance of the surface.

Effect of the Addition of the Waste Generated from the Feldspar Mining on the Obtainment of Ceramic Brick

TheNossa Senhora do Carmomining company, located at the southern of Santa Catarina (SC), Brazil, explores a large amount of feldspar to the ceramic market. As a result, waste is inevitable in the production and processing of the feldspar mineral, which results in an environmental impact. Therefore, this study aims to evaluate the effect of the addition of the waste coming from the feldspar mining in the composition of ceramic bricks. In this way, the waste and a clay mineral were characterized. The waste (0, 5, 15 and 25 wt%) was added to a composition of clay brick based on a standard clay fromMorro da Fumaça, Santa Catarina, Brazil. Specimens were extruded and sintered at temperatures of 1123, 1223, and 1323 K. The technological properties assessed in this study were linear shrinkage, water absorption and bending strength. The data were assessed by analysis of variance. The results showed the feasibility of adding 15 and 25 wt% of waste to the brick composition. All technological properties were improved when compared to pure samples, except for linear shrinkage. The analysis of variance showed significant and reproducible effects for the water absorption results. The results for linear shrinkage and bending strength showed no statistical significance.

Structural Reliability Analysis of Container Ships under Combined Wave and Whipping Loads

A practical methodology for structural reliability assessment of ultra large container ships is proposed in the article. The commonly used limit state function for structural reliability analysis of oil tankers and bulk carriers was extended to take into account the whipping response due to the bow flare slamming. The ultimate vertical bending moment capacity of hull girder was considered as a fundamental safety variable in the limit state function, whereas the stochastic model of the loads consists of static still-water bending moments (SWBMs), low-frequency rigid body vertical wave bending moments and high-frequency whipping bending moments. The stochastic model of SWBM for one of the studied ships was obtained from actual bending moments recorded by the onboard loading computer in 2 years of operation. Linear vertical wave bending moment was calculated by a 3D panel seakeeping code, using International Association of Classification Societies (IACS) recommendation No. 34 for the computation of extreme global wave loads. The nonlinear correction of linear wave bending moment was obtained from the recent IACS Unified Requirement S11A for longitudinal strength of container ships. Impulsive loading was modeled by von Karman added mass variation method, whereas transient dynamic hull girder response was analyzed by Timoshenko beam finite elements. Load combinations between extreme still-water and vertical wave bending moments, and between extreme low- and high-frequency vertical wave bending moments are considered. The structural reliability analysis of two container ships of different sizes was performed using the first-order reliability method, to observe differences in safety levels due to different ship sizes. Safety indices are compared with the International Maritime Organization recommendations for double-hull oil tankers to have credible basis for assessing the obtained results. An extensive sensitivity and parametric study was performed, accounting for various operational, environmental, and modeling uncertainties, as well as for corrosion degradation. The presented study may be useful for classification societies in further development of recently introduced IACS Unified Requirements for longitudinal strength of container ships.