Showing papers on "Flexural rigidity published in 2019"

Bending of Multilayer van der Waals Materials

Abstract: Out-of-plane deformation patterns, such as buckling, wrinkling, scrolling, and folding, formed by multilayer van der Waals materials have recently seen a surge of interest. One crucial parameter governing these deformations is bending rigidity, on which significant controversy still exists despite extensive research for more than a decade. Here, we report direct measurements of bending rigidity of multilayer graphene, molybdenum disulfide (MoS_{2}), and hexagonal boron nitride (hBN) based on pressurized bubbles. By controlling the sample thickness and bubbling deflection, we observe platelike responses of the multilayers and extract both their Young's modulus and bending rigidity following a nonlinear plate theory. The measured Young's moduli show good agreement with those reported in the literature (E_{graphene}>E_{hBN}>E_{MoS_{2}}), but the bending rigidity follows an opposite trend, D_{graphene}

Bending rigidity of charged lipid bilayer membranes

Abstract: We experimentally investigate the effect of lipid charge on the stiffness of bilayer membranes The bending rigidity of membranes with composition 0-100 mol% of charged lipids, in the absence and presence of salt at different concentrations, is measured with the flicker spectroscopy method, using the shape fluctuations of giant unilamellar vesicles The analysis considers both the mean squared amplitudes and the time autocorrelations of the shape modes Our results show that membrane charge increases the bending rigidity relative to the charge-free membrane The effect is diminished by the addition of monovalent salt to the suspending solutions The trend shown by the membrane bending rigidity correlates with zeta potential measurements, confirming charge screening at different salt concentrations The experimental results in the presence of salt are in good agreement with existing theories of membrane stiffening by surface charge

Influence of infill properties on flexural rigidity of 3D-printed structural members

Abstract: This paper characterises the flexural properties of relatively slender structural members (beams) manufactured using a FDM-based 3D printer. The primary goal is to assess the influence of infill pr...

Flexural rigidity of cold-formed steel built-up members

Abstract: Cold-formed steel (CFS) built-up members are formed by connecting several single members by fasteners. This paper presents experimental, numerical and analytical studies on the effect of fastener configurations on the flexural rigidity of built-up sections. In this research, two zinc-coated steel C-sections are connected back-to-back to form a double-web built-up I-section, which is subject to weak-axis bending. A closed-formed expression for the flexural rigidity of built-up sections as a function of fastener stiffness, number and position of fasteners, and section geometry is then derived. This is validated against the tests and finite element modelling, and can be adapted more generally to determine the stiffness and global strength of CFS built-up members in bending.

Flexural Behavior of Sprayed Lightweight Composite Mortar-original Bamboo Composite Beams: Experimental Study

Abstract: To study the flexural behavior of a composite beam, original single and double bamboo beams (SBBs and DBBs, respectively) and sprayed lightweight composite mortar-original bamboo composite beams (SCBs and DCBs) were designed and subjected to a four-point bending test based on the moisture content of the original bamboo. The failure modes, bearing capacity, and initial flexural rigidity of all of the beams were analyzed. Also, the strengthening effect of the lightweight composite mortar on the flexural behavior was studied. The results showed that a higher moisture content in the bamboo degraded the anti-slip property of the bond interface between the lightweight composite mortar and bamboo. The moisture content of the bamboo should be kept at approximately 20% before spraying. The initial flexural rigidity and bearing capacity of the DBBs were approximately 2.5 times and twice that of the SBBs, respectively. The initial flexural rigidities of the SCBs and DCBs were approximately 3.8 and 5.7 times that of the SBBs and DBBs, respectively. The ultimate load bearing capacity of the composite beams was approximately 1.5 times that of the original bamboo beams. It was shown that the lightweight composite mortar had a remarkable strengthening effect on the flexural behavior of the original bamboo.

DARLING: a device for assessing resistance to lodging in grain crops

Abstract: Stalk lodging (breakage of plant stems prior to harvest) is a major problem for both farmers and plant breeders. A limiting factor in addressing this problem is the lack of a reliable method for phenotyping stalk strength. Previous methods of phenotyping stalk strength induce failure patterns different from those observed in natural lodging events. This paper describes a new device for field-based phenotyping of stalk strength called “DARLING” (device for assessing resistance to lodging in grains). The DARLING apparatus consists of a vertical arm which is connected to a horizontal footplate by a hinge. The operator places the device next to a stalk, aligns the stalk with a force sensor, steps on the footplate, and then pushes the vertical arm forward until the stalk breaks. Force and rotation are continuously recorded during the test and these quantities are used to calculate two quantities: stalk flexural stiffness and stalk bending strength. Field testing of DARLING was performed at multiple sites. Validation was based upon several factors. First, the device induces the characteristic “crease” or Brazier buckling failure patterns observed in naturally lodged stalks. Second, in agreement with prior research, flexural rigidity values attained using the DARLING apparatus are strongly correlated with bending strength measurements. Third, flexural stiffness and bending strength values obtained with DARLING are in agreement with laboratory-based stiffness and strength values for corn stalks. Finally, a paired specimen experimental design was used to determine that the flexural data obtained with DARLING is in agreement with laboratory-based flexural testing results of the same specimens. DARLING was also deployed in the field to assess phenotyping throughput (# of stalks phenotyped per hour). Over approximately 5000 tests, the average testing rate was found to be 210 stalks/h. The DARLING apparatus provides a quantitative assessment of stalk strength in a field setting. It induces the same failure patterns observed in natural lodging events. DARLING can also be used to perform non-destructive flexural tests. This technology has many applications, including breeding, genetic studies on stalk strength, longitudinal studies of stalk flexural stiffness, and risk assessment of lodging propensity.

Bending performance of glubam beams made with different processes

Abstract: This article presents experimental testing results designed to obtain physical and mechanical properties of glued laminated bamboo (glubam) beams. Two types of glubam beams made with different pre-...

Size-dependent electro-thermo-mechanical analysis of multilayer cantilever microactuators by Joule heating using the modified couple stress theory

Abstract: The size-dependent electro-thermo-mechanical responses of multilayer cantilever microactuators by Joule heating is investigated. An analytical expression of the deflection of three-layered cantilever microactuators subjected to non-uniform temperature variations and mechanical loading is derived by using the modified couple stress theory and the two-variable method. The predicted result is in good agreement with the experimental data. Compared with the results from the classical beam theory, the influence of the size-dependency on the deformation, equivalent bending rigidity and average thin film stress are discussed. The results reveal that the equivalent bending rigidity of multilayer cantilever microactuators predicted by the present model is larger than that from the classical beam model, which decreases the size-dependent bending response of the microactuator. In addition, the size-dependent average stresses of thin film is more likely to produce mechanical failure. The current study is helpful for the design of micro/nano-actuators.

Continuously Variable Stiffness Mechanism Using Nonuniform Patterns on Coaxial Tubes for Continuum Microsurgical Robot

Abstract: Variable stiffness enables the safe and effective operation of the minimally invasive surgical instruments. In this article, we propose a continuously variable stiffness mechanism of the scalable tubular structure. The mechanism consists of multiple coaxial nitinol tubes, and each tube has an anisotropic distribution of flexural stiffness created by nonuniform through-hole patterning. The stiffness of the mechanism is varied by relative rotation and translation among the tubes, resulting in flexural stiffness difference up to 7.2 times in the direction of load. Its flexural stiffnesses along principal axes are independently controlled by the suggested counterrotation algorithm. The stiffness change is validated through analytical modeling, FEM simulation, and the experiments. Thanks to its physically embodied intelligence, the mechanism has a simple scalable structure and the response time is immediate. We applied this mechanism to control the stiffness of the steerable needle. Varying the stiffness grants the additional degree of freedom to control the needle's trajectory, which can expand the workspace of the steerable needle.

Boson peak, elasticity, and glass transition temperature in polymer glasses: Effects of the rigidity of chain bending.

Abstract: The excess low-frequency vibrational spectrum, called boson peak, and non-affine elastic response are the most important particularities of glasses. Herein, the vibrational and mechanical properties of polymeric glasses are examined by using coarse-grained molecular dynamics simulations, with particular attention to the effects of the bending rigidity of the polymer chains. As the rigidity increases, the system undergoes a glass transition at a higher temperature (under a constant pressure), which decreases the density of the glass phase. The elastic moduli, which are controlled by the decrease of the density and the increase of the rigidity, show a non-monotonic dependence on the rigidity of the polymer chain that arises from the non-affine component. Moreover, a clear boson peak is observed in the vibrational density of states, which depends on the macroscopic shear modulus G. In particular, the boson peak frequency ωBP is proportional to [Formula: see text]. These results provide a positive correlation between the boson peak, shear elasticity, and the glass transition temperature.

Size-dependent static bending of flexomagnetic nanobeams

Abstract: The present paper presents a Bernoulli–Euler flexomagnetic (FM) nanobeam model, which considers the effects of flexomagneticity, piezomagneticity, and the surface elasticity. Differential control equations and corresponding magnetic boundary conditions are derived to investigate the influences of direct and converse FM couplings over the magnetic-elastic response. Size-dependent theoretical solutions for the static bending deformation of the cantilever, simply supported, and clamped nanobeams subjected to concentrated or uniformly distributed load are derived. Numerical simulations demonstrate that the flexomagneticity effect plays the role of the scale-dependent enhancement of the bending rigidity, which is independent of boundary conditions. But for the residual surface stresses, softening or stiffening the beam depends on boundary conditions.

Investigations on sustainable honeycomb sandwich panels containing eucalyptus sawdust, Piassava and cement particles

Abstract: A full factorial design is performed to investigate a sandwich structure consisted of Piassava fibre laminates as face sheets and epoxy-based honeycomb cores containing eucalyptus sawdust and cement particles. A three-point bending test is used to evaluate the composite structure. The composite setup which achieves higher flexural modulus and strength is used as honeycomb core material. Finite element models are developed to predict the failure and the elastic flexural properties of the sandwich panels. The validated FE model is used to perform a parametric analysis identifying the effect of geometric variations on the flexural performance. The results reveal that the constructive parameters significantly affect the core shear stress, facing stress, flexural stiffness and strength in different ways and intensities.

Steel modules of composite plate shear walls: Behavior, stability, and design

Abstract: Concrete-filled composite plate shear walls (CPSW) consist of a concrete (infill) wall sandwiched between two steel plates that are connected to each other using ties and anchored to the concrete infill using these embedded ties or shear connectors. Steel modules consisting of plates, ties and shear connectors are prefabricated in the shop, transported to the field, and assembled first. The erected modules serve as falsework for construction activities and stay-in-place formwork for concrete casting. This is a primary advantage and appeal of this system. However, there is a lack of knowledge regarding the structural behavior of empty steel modules (before and during concrete casting). This paper presents the results of analytical, numerical, and experimental investigations conducted to evaluate: (i) the structural behavior of empty steel modules under their own self-weight, (ii) the stability and axial load capacity of steel modules for construction loads and activities, and (iii) the effects of concrete casting (hydrostatic pressure) in terms of the deflections and stresses induced in the steel plates. The results indicate that the effective shear stiffness of the empty modules governs their structural behavior as well as their stability. The effective shear stiffness can be estimated using the finite element method (verified using test results), or conservatively using mechanics-based equations presented in this paper. The effective shear stiffness is governed by plate slenderness, defined by the tie spacing and plate thickness, and the relative flexural rigidity of the steel plates and the connecting ties. These parameters can be designed to limit the flexibility and the critical buckling stress of the empty modules. The paper also provides equations for calculating the out-of-plane displacement and stresses induced in the steel plates by the concrete casting hydostatic pressure.

First-principles study of mechanical and electronic properties of bent monolayer transition metal dichalcogenides

Abstract: The mechanical and electronic properties of transition metal dichalcogenide (TMD) monolayers corresponding to transition groups IV, VI, and X are explored under mechanical bending from first principles calculations using the strongly constrained and appropriately normed (SCAN) meta-GGA. SCAN provides an accurate description of the phase stability of the TMD monolayers. Our calculated lattice parameters and other structural parameters agree well with experiment. We find that bending stiffness (or flexural rigidity) increases as the transition metal group goes from IV to X to VI, with the exception of ${\mathrm{PdTe}}_{2}$. Variation in mechanical properties (local strain, physical thickness) and electronic properties (local charge density, band structure) with bending curvature is discussed. The local strain profile of these TMD monolayers under mechanical bending is highly nonuniform. The mechanical bending tunes not only the thickness of the TMD monolayers, but also the local charge distribution as well as the band structures, adding more functionalization options to these materials.