High Bending Stiffness Research Articles

Amlodipine accelerates bone healing in a stable closed femoral fracture model in mice.

Calcium channel blockers (CCBs), which are widely used in the treatment of hypertension, have been shown to influence bone metabolism. However, there is little information on whether CCBs also influence the process of fracture healing. Therefore, the effect of the CCB amlodipine on bone healing was studied in a stable closed fracture model in mice using intramedullary screw fixation. Bone healing was investigated by radiology, biomechanics, histomorphometry and Western blot analysis 2 and 5 weeks after fracture healing. Animals were treated daily (post operatively) per os using a gavage with amlodipine low dose (1 mg/ kg body weight, n = 20), amlodipine high dose (3 mg/kg body weight, n = 20) or vehicle (NaCl) (control, n = 20) serving as a negative control. At 2 and 5 weeks, histomorphometric analysis revealed a significantly larger amount of bone tissue within the callus of amlodipine low-dose- and high-dose-treated animals when compared to controls. This was associated with a smaller amount of cartilaginous and fibrous tissue, indicating an acceleration of fracture healing. Biomechanics showed a slightly, but not significantly, higher bending stiffness in amlodipine low-dose- and high-dose-treated animals. Western blot analysis revealed a significantly increased expression of bone morphogenetic protein (BMP)-2 and vascular endothelial growth factor (VEGF). Moreover, the analysis showed a 5-fold higher expression of osteoprotegerin (OPG) and a 10-fold elevated expression of the receptor activator of NF-κB ligand (RANKL), indicating an increased bone turnover. These findings demonstrated that amlodipine accelerated fracture healing by stimulating bone formation, callus remodelling and osteoclast activity.

A high-fidelity numerical study on the propulsive performance of pitching flexible plates

In this paper, we numerically investigate the propulsive performance of three-dimensional pitching flexible plates with varying flexibility and trailing edge shapes. We employ our recently developed body-conforming fluid-structure interaction solver for our high-fidelity numerical study. To eliminate the effect of other geometric parameters, only the trailing edge angle is varied from 45° (concave plate), 90° (rectangular plate) to 135° (convex plate) while maintaining the constant area of the flexible plate. For a wide range of flexibility, three distinctive flapping motion regimes are classified based on the variation of the flapping dynamics: (i) low bending stiffness KBlow, (ii) moderate bending stiffness KBmoderate near resonance, and (iii) high bending stiffness KBhigh. We examine the impact of the frequency ratio f* defined as the ratio of the natural frequency of the flexible plate to the actuated pitching frequency. Through our numerical simulations, we find that the global maximum mean thrust occurs near f*≈1 corresponding to the resonance condition. However, the optimal propulsive efficiency is achieved around f* = 1.54 instead of the resonance condition. While the convex plate with low and high bending stiffness values shows the best performance, the rectangular plate with moderate KBmoderate is the most efficient propulsion configuration. To examine the flow features and the correlated structural motions, we employ the sparsity-promoting dynamic mode decomposition. We find that the passive deformation induced by the flexibility effect can help in redistributing the pressure gradient, thus, improving the efficiency and the thrust production. A momentum-based thrust evaluation approach is adopted to link the temporal and spatial evolution of the vortical structures with the time-dependent thrust. When the vortices detach from the trailing edge, the instantaneous thrust shows the largest values due to the strong momentum change and convection process. Moderate flexibility and convex shape help to transfer momentum to the fluid, thereby improving the thrust generation and promoting the transition from drag to thrust. The increase in the trailing edge angle can broaden the range of flexibility that produces positive mean thrust. The role of added mass effect on the thrust generation is quantified for different pitching plates and the bending stiffness. These findings are of great significance to the optimal design of propulsion systems with flexible wings.

Effect of the main cable bending stiffness on flexural and torsional vibrations of suspension bridges: Analytical approach

In the design and analysis of suspension bridges, the main cables are conventionally treated as flexible ropes transmitting only tensile loads. Large-span suspension bridges used in new railways require the main cables to be designed with larger cross-sections and higher bending stiffness. The latter can affect the dynamic behavior of the entire bridge. To this end, the analytical expression of the main cable's shape is established in this paper, considering the bending stiffness under the dead loads. According to the D'Alembert principle, the partial differential equations of vibration of the cable in the suspension bridge are derived and solved. Finally, frequencies and mode shapes of the flexural and torsional vibrations of the bridge are calculated considering the main cable bending stiffness. To verify the feasibility of the proposed method, a case study of the Wufengshan Yangtze River Bridge is investigated. The analytical results are compared with the finite element solutions obtained by the ANSYS software, with good agreement achieved. By using the proposed method, the effect of the main cable bending stiffness on the flexural and torsional vibrations of suspension bridges is analyzed. The results show that the cable bending stiffness has a larger effect on flexural vibrations than torsional vibrations. The bridge's frequencies become higher with the increase of cable bending stiffness. Besides, as the order of vibration mode or the ratio of the bending stiffness of cables to the beam increases, the effect of main cable bending stiffness gets greater.

Effect of local stiffeners and warping constraints on the buckling of symmetric open thin-walled beams with high warping stiffness

Local stiffeners affect the behaviour of thin-walled beams (TWBs). An in-house code based on a one-dimensional model proved effective in several instances of compressive buckling of TWBs but gave counterintuitive results for locally stiffened TWBs. To clarify the matter, we investigated TWBs with multi-symmetric double I cross-section, widely used in practical applications where high bending stiffness is required. Several samples were manufactured and stiffened on purpose, closing them over a small portion of the axis at different places. The samples were tested with end constraints accounting for various warping conditions. The experimental and numerical outputs from a commercial FEM code gave a key to overcome the unexpected results by the in-house code, paving the way for further studies.

Bending-wave localization and interaction band gaps in quasiperiodic beams

Aperiodic metamaterials can host topological or localized wave modes, and gradually changing structures are known to induce conversion between elastic wave types. This work describes a family of one dimensional, aperiodic elastic structures that can host localized modes or achieve low-frequency attenuation by varying a single geometrical parameter, i.e., the ratio between the sizes of two interacting periodic structures. Two periodic sets of slits on the top and bottom of a slender beam scatter bending waves. The thickness profile and cross section of beams with a period ratio close to 1 varies slowly, resulting in localized wave modes. The localization happens because of spatially confined band gaps and is only triggered for certain excitation locations, unlike wave localization due to a local defect. If the periods differ more, broad band gaps appear at wave numbers equal to linear combinations of the individual Brillouin zone edges of each set of slits. We call these interaction band gaps, since they result from the interplay between two periodic sets of slits. Low-frequency wave attenuation is achieved while maintaining a high overall bending stiffness.

Non-linear analysis of double skinned composite hollow columns using geopolymer concrete

Abstract This paper investigates the behavior of Doubled skinned (DSCFT) composite hollow columns with steel tubes compressed under concentric axial loads. The DSCFT member is a new type of composite construction, which consists of two concentric steel tubes with geoploymer concrete sandwiched between them. Thus, DSCFT columns have a series of advantages, such as high strength, high bending stiffness, good seismic and fire performance, and also having favorable construction ability. The finite element analysis of the DSCFT circular column is conducted to validate the finite element model. The results obtained from the finite element investigation are compared with the strength values predicted using existing formulations in the analytical investigation. A good correlation was found between the values obtained.

Bending performance of NSTS members based on steel tube connection

This paper proposes a NSTS (new steel tube slab) structure by connecting the longitudinal steel tubes with small steel tubes in transverse, in order to decrease the construction difficulty and improve the bearing capacity of existing NTR (new tubular roof) or STS (steel tube slab) structures. Experimental study on the bending performance and influences of following parameters are carried out: the connection type of the steel tube, the diameter and eccentricity of the small steel tube, and the thickness of the bottom steel plate. The results show that the NSTS members present progressive ductile flexural failure under concentrated load. The connection type has important effect on the mechanical behavior, and the bolts fixed T-shaped plate (B+T) connection method, which provides much higher bending stiffness, is proved to be the most reliable connection type. The increase of small steel tube diameter enhances the bending performance as expected, which also confirms the effectiveness of the B+T connection, while the tube eccentricity presents little impact on the bearing capacity. The bottom steel plate significantly improves the bearing capacity and stiffness and reduces the mid-span deflection. Furthermore, the bending capacity calculation method is proposed and the calculated values show good agreement with the test results. Also, the effect rules of the diameter-thickness ratio of the small tube, the length-diameter ratio of the member and the thickness variety of the bottom steel plate on the bending capacity of NSTS members are further investigated based on the proposed theoretical method.

Investigating the Lifetime of Fibre Ropes

Steel wire ropes have established as transmission, connection and safety elements in transporters such as cranes and elevators, due to their high breaking strength and operational safety as well as out of many years of experience. However, steel wire ropes have disadvantages such as high dead weight, high bending stiffness and sensitivity to corrosion. Increasing requirements on the energy-efficient and resource-saving operation of technical systems demand new materials, technologies and processes. As a result, textile machine elements like HM-HT fibre ropes (high modulus, high tenacity) come into focus of considerations. The aim of the research is to expand the level of knowledge with regard to the state of wear and aging. Another aim is to find out the influencing factors on the lifetime, discard criteria of high-strength fibre ropes and to derive methods for lifetime detection.

Multimaterial direct 4D printing of high stiffness structures with large bending curvature

The emerging direct four dimensional (4D) printing approach is considered as an easy, fast and economical manufacturing strategy that fabricates complex 3D geometries evolving from printed flat patterns in response to external stimuli. However, its implementation to practical engineering applications is impeded by the fact that the existing direct 4D printing methods could not render both the large bending curvature and high loading capacity at the same time. Herein, we report a multimaterial direct 4D printing method to fabricate patterned laminate that consists of covalently bonded elastomer and high-water-content hydrogel. The dehydration induced large volumetric shrinkage (up to 60%) and great modulus escalation (from 100 kPa to 4 GPa) allow the printed flat patterns to evolve into complex 3D structures with large bending curvature (up to 0.7 mm−1) and high bending stiffness (up to 104 MPa m3). To facilitate the structural design, we develop a phenomenological model to describe the dehydration induced shrinkage and stiffening, and implement this model into Euler–Bernoulli beam theory and finite element simulations. Compared with other 3D printing technologies, the proposed multimaterial direct 4D printing approach demonstrates the merits in terms of less building time and high load capacity at both room temperature and high temperature.

Torsional and Transversal Stiffness of Orthotropic Sandwich Panels.

In the present work, an analytical equation describing the plate torsion test taking into account the transverse shear stiffness in sandwich plates is derived and numerically validated. Transverse shear becomes an important component if the analyzed plate or shell is thick with respect to the in-plane dimensions and/or its core has significantly lower stiffness than the outer faces. The popular example of such a sandwich plate is a corrugated cardboard, widely used in the packaging industry. The flat layers of a corrugated board are usually made of thicker (stronger) material than that used for the corrugated layer, the role of which is rather to keep the outer layers at a certain distance, to ensure high bending stiffness of the plate. However, the soft core of such a plate usually has a low transverse shear stiffness, which is often not considered in the plate analysis. Such simplification may lead to significant calculation errors. The paper presents the generalization of the Reissner’s analytical formula, which describes the torsional stiffness of the plate sample including two transverse shear stiffnesses. The paper also presents the implementation of the numerical model of the plate torsion test including the transverse shear stiffnesses. Both approaches are compared with each other on a wide range of material parameters and different aspect ratios of the specimen. It has been proved that both analytical and numerical formulations lead to an identical result. Finally, the performance of presented formulations is compared with other numerical models using commercial implementation of various Reissner–Mindlin shell elements and other analytical formulas from the literature. The comparison shows good agreement of presented theory and numerical implementation with other existing approaches.

Variable Rigidity Module with a Flexible Thermoelectric Device for Bidirectional Temperature Control.

Dynamic stiffness tuning is a promising approach for shape reconfigurable systems that must adapt their flexibility in response to changing operational requirements. Among stiffness tuning technologies, phase change materials are particularly promising because they are size scalable and can be powered using portable electronics. However, the long transition time required for phase change is a great limitation for most applications. In this study, we address this by introducing a rapidly responsive variable rigidity module with a low melting point material and flexible thermoelectric device (f-TED). The f-TED can conduct bidirectional temperature control; thereby, both heating and cooling were accomplished in a single device. By performing local cooling, the phase transition time from liquid to solid is reduced by 77%. The module in its rigid state shows 14.7 × higher bending stiffness than in the soft state. The results can contribute to greatly widening the application of phase transition materials for variable rigidity.

Comparison of the mechanical properties of biodegradable and titanium osteosynthesis systems used in oral and maxillofacial surgery

To guide the selection of osteosynthesis systems, this study compared the mechanical properties of biodegradable and titanium osteosynthesis systems. SonicPins Rx and xG were subjected to pull-out tests. Additionally, 15 biodegradable (Inion CPS 2.0 and 2.5 mm; LactoSorb 2.0 mm; Macropore 2.0 mm; Polymax 2.0 mm; BioSorb FX 2.0 mm; ResorbX 2.1 mm; Osteotrans-MX 2.0 mm with plate thicknesses 1.0 and 1.4 mm; SonicWeld Rxplate/Rxpins, xGplate/Rxpins and xGplate/xGpins 2.1 mm without and with tapping the burr hole) and six titanium (CrossDrive (2006), CrossDrive (2018), MaxDrive; all 1.5 and 2.0 mm) straight, four-hole osteosynthesis systems were evaluated. All systems were subjected to tensile, bending and torsion tests. Pull-out loads of the SonicPins were comparable (P = 0.423). Titanium systems’ tensile loads were higher than biodegradable systems (P < 0.001). CrossDrive (2018) and MaxDrive systems’ tensile and torsional stiffness were lower, accompanied with higher ductility, than corresponding CrossDrive (2006) systems (P < 0.001). Bending stiffness of 1.5 mm titanium systems was comparable to, and of the 2.0 mm systems higher than, all biodegradable systems (P < 0.001). Regarding biodegradable systems, Inion CPS 2.5 mm had highest tensile load and torsional stiffness, SonicWeld 2.1 mm highest tensile stiffness, and BioSorbFX 2.0 mm highest bending stiffness (P < 0.001). On the basis of the results of this study, the CrossDrive (2018) and MaxDrive 1.5 mm titanium systems are recommended for midface fractures (e.g., zygomatic or maxillary fractures) and osteotomies (e.g., Le Fort I osteotomy), and the CrossDrive (2018) and MaxDrive 2.0 mm titanium systems for mandibular fractures and osteotomies when a titanium osteosynthesis system is used. When there is an indication for a biodegradable osteosynthesis system, the SonicWeld 2.1 mm or BioSorbFX 2.0 mm are recommended for midface fractures and osteotomies, and the Inion CPS 2.5 mm biodegradable system for mandibular osteotomies and non-load bearing mandibular fractures, especially when high torsional forces are expected (e.g., mandibular symphysis fractures).

Design of Continuum Robot With Variable Stiffness for Gastrointestinal Stenting Using Conformability Factor

Stent placement in the gastrointestinal tract has emerged as an effective method of therapy for intestinal obstruction. In fluoroscopic guided stenting, clinicians first insert a hyper-elastic guidewire, and a stent introducer loaded with a compressed stent is passed along the guidewire to the desired deployment site. However, the high bending stiffness of the loaded stent introducer tends to straighten the inserted guidewire at the tortuous region. To overcome this issue, tubes of various stiffnesses are repeatedly inserted and removed. To optimize the mechanical properties of the devices for successful GI stenting, the interaction between the device and the environment should be considered as a key factor. In this study, conformability factor, a new index that abstracts the physical interaction for GI stenting was proposed. Based on the conformability factor, we proposed design requirements for variable stiffness continuum robots for GI stenting. The in vitro stent deployment experiment result shows that the proposed instrument can successfully deploy the loaded stent introducer without exchanging multiple tubes.

Flutter analysis of a sandwich composite beam using an analytical method

In this paper, the aeroelastic behavior of a composite wing is investigated in the compressible flow using the analytical method. The composite wing is simulated as a thin-walled single-cell closed cross-section beam with circumferentially asymmetric stiffness (CAS) configuration. The best layup configuration for the maximum flutter speed is determined by analyzing four layups configuration where the fiber orientation angle varies within the range of 0–90 degrees. Moreover, an included foam layer between composite layers resulted in higher bending stiffness and improved stability characteristics of the wing. It was shown that there is a significant improvement in the flutter speed for [Formula: see text] layup. Numerical results demonstrate the advantages of foam filled model over the model without foam in terms of the flutter speed to the weight ratio.

Bending behavior of sandwich beam with tailored hierarchical honeycomb cores

It is challenging to maintain the lightweight performance of sandwich structure while at the same time to obtain high bending stiffness and strength. In this study, sandwich beams with hierarchical honeycomb cores were proposed. Corresponding mechanical responses bsubjected to three-point bending load were explored and compared with that of the sandwich equipped with conventional honeycomb core by means of numerical simulation. Theoretical solutions of equivalent bending stiffness coincide well with numerical results. Scaling effect of vertex cell and cell size on the hierarchical honeycomb sandwich was investigated. Two tailored hierarchical patterns were proposed by replacing the hexagonal vertex cells with circular and square cells. Compared with the conventional counterpart, the hierarchical sandwich beams offer higher load-bearing capacity. Distinctions of bending strength of each configuration demonstrate different influences of tailored hierarchical cores on enhancing bending resistance ability. There are more local interactions of cells for hierarchical structures. The local improvement promotes more cells to withstand load and the whole sandwich beam can be globally strengthened.

Modeling the deformation behavior of polymer sandwich structures with inhomogeneous core

Polymer sandwich structures become widely used in the transportation industry due to their high bending stiffness and strength combined with low weight. In the conceptual design phase, it is essential to model the mechanical behavior of the sandwich properly in full-vehicle scale in order to analyze different design variants effectively. In this paper, a finite element modeling method is shown. The method is introduced on a sandwich structure with glass fiber reinforced, vinyl-ester matrix composite face-sheets and a PET foam as core material with an inhomogeneous structure. To model the sandwich panel with layered shells, where the core material is a single layer, equivalent stiffness constants of the inhomogeneous core are needed. To determine these constants, a detailed finite element model was created and virtual tensile and shear tests were performed. On the other hand, an analytical method was also shown. By applying the Voigt- and Reuss-rule on the inhomogeneous core, the needed stiffness constants can also be determined properly. Results of the two methods were compared and they showed a good correlation. Validation of the model was performed via comparing the results of the 4-point bending experimental tests and the simulation results.

Influence of core and matrix modifications on the mechanical characteristics of sandwich composites

Sandwich composites are increasingly being used for a variety of applications owing to excellent properties like high bending strength and stiffness, low strength-to-weight ratio and excellent damping and acoustic properties. However, there are certain issues faced while using sandwich structures for structural applications which includes debonding of face sheets from core, matrix cracking and core shear failure. In the current work, an effort is made to enhance the mechanical characteristics of sandwich composites by altering poly vinyl chloride (PVC) foam core and adding multi-walled carbon nanotubes (MWCNT) to epoxy resin used as the matrix. Four different configurations of sandwich laminates were fabricated using vacuum bagging process: (1) plain core and neat epoxy resin (2) core with blind holes and neat epoxy resin (3) core with blind holes and epoxy resin with MWCNT (4) core with through holes and epoxy resin with MWCNT. Flexural and compression tests were carried out on these sandwich specimens according to American Society for Testing Materials (ASTM) standards. Sandwich specimens with through holes in the core and resin mixed with MWCNT exhibited better mechanical characteristics compared to the other sandwich laminates. Type 4 sandwich specimens were able to withstand 12% and 16% more flexural and compressive loads respectively compared to conventional sandwich specimens.

Cross-Sectional Performance of Hollow Square Prisms with Rounded Edges

Hollow-section columns are one of the mechanically superior structures with high buckling resistance and high bending stiffness. The mechanical properties of the column are strongly influenced by the cross-sectional shape. Therefore, when evaluating the stability of a column against external forces, it is necessary to reproduce the cross-sectional shape accurately. In this study, we propose a mathematical method to describe a polygonal section with rounded edges and vertices. This mathematical model would be quite useful for analyzing the mechanical properties of plants and designing plant-mimicking functional structures, since the cross-sections of the actual plant culms and stems often show rounded polygons.

Bending behavior of optimally graded 3D printed cellular beams

Periodic cellular materials can substantially improve the stiffness-to-weight ratio of structures. This improvement depends on the geometry of periodic cells. This article presents the idea of enhancing the bending stiffness of an architected cellular beam by an optimum distribution of relative density through its length and/or across its thickness. We employ a hybrid-homogenized model to expedite the computational evaluation of the bending performance of the graded cellular beams. Detailed finite element analysis (FEA) and experimental bending tests on specimens 3D printed by stereolithography validate the hybrid-homogenized modeling approach. The hybrid-homogenized model facilitates transforming the general optimization problem into a shape optimization process with the relative density of unit cells as design variables. The teaching-learning-based optimization (TLBO) algorithm is used to obtain the optimum relative density distribution, which maximizes the bending stiffness. The optimization results show a substantial increase in bending stiffness; as high as 43%, 155%, and 182% for a cellular beam graded through the length, across the thickness, and in both directions, respectively. It is found that varying the relative density of cells across the beam thickness is more effective than variation through the length. Detailed FEA and experimental bending tests corroborate the optimization findings and confirm the practicality of such graded designs for developing advanced lightweight structures. Investigating the effect of cell architecture also reveals that optimally graded cellular beams have a potential to outperform uniform cellular beams made out of ideal unit cells (Voigt bound for elastic properties) by reaching bending stiffness-to-density ratios greater than one. The relatively simple graded cellular designs are beneficial in applications where high bending stiffness and low density are essential. Recent advances in additive manufacturing promise extending the presented grading strategy for polymeric, composite, and metallic 3D printed cellular materials to fabricate high performance lightweight structural elements at a relatively low cost.

Effect of Fillet Radii on Moment Carrying Capacity of Sinusoidal Web Opening Castellated Steel Beams in Comparison with Hexagonal Web Openings

In recent times, the use of castellated beams with various web openings for structures like high-rise building and industrial structure has turned out to be extensive. It offers an increase in depth of section without any extra weight, high strength-to-weight ratio, lower maintenance and painting cost. The most important advantage of the castellated beam is its higher bending stiffness, simplicity of service facility and beautiful appearance. The aim of this research paper is to offer a new web opening shape as a sinusoidal opening to avoid failure of the castellated beam due to shear stress concentration at the corner of the opening and also to study the maximum moment carrying capacity and deflection of castellated beams. In this research, 15 beams were fabricated. Four models of castellated beams were considered for experimentation. This research is focussed on hexagonal and sinusoidal openings of a castellated beam subjected to flexural loading. The variables were considered are fillet radii for sinusoidal openings with one-fourth, one-sixth and one-eighth of hexagonal opening. All the beams were analysed by the finite element method using ANSYS software, and the results were compared with experimental outcomes. The experimental results for maximum moment carrying capacity and deflection show good agreement with the corresponding value observed in ANSYS software. The experimental results show that castellated beam with fillet radius one-fourth of opening has 20.78% more moment carrying capacity and 11.51% less deflection compared to hexagonal opening. The outcomes consider relevant for practical applications.