Showing papers on "Flexural rigidity published in 2018"

Energy absorbing ability of rectangular self-similar multi-cell sandwich-walled tubular structures

Abstract: Thin-walled tubes (TWTs) have been widely applied as energy absorbers in engineering. The energy absorbing property of rectangular TWTs can be substantially enhanced by changing the ultra-thin solid walls into sandwich walls. Sandwich wall has great bending rigidity and it improves the energy absorption through two aspects: shortening the wave length or improving the plastic bending moment. Competition of these two mechanisms endows the rectangular sandwich-walled tube (SWT) with excellent energy absorbing ability and the best performance is achieved when the two mechanisms appear simultaneously. Mean crushing force (MCF) of the rectangular SWT could be 2.5 times of that of the TWT. The MCF of optimally designed rectangular SWT is even greater than the yield load of the tubular structure.

Structure and dynamics of a self-propelled semiflexible filament

Abstract: We investigate structural and dynamical properties of a self-propelled filament using coarse-grained Brownian dynamics simulations. A self-propulsion force is applied along the bond vectors, i.e., tangent to the filament and their locations are considered in two different manners. In case one, force is applied to all beads of the filament, which is termed as homogeneous self-propulsion. Here, we obtain a monotonic decrease in the flexibility of the filament with Peclet number. Hence, radius of gyration also displays the same trend. Moreover, the radius of gyration of the filament shows universal dependence for various bending rigidities with flexure number. The effective diffusivity of the filament shows enhancement with the active force and it increases linearly with force and bending rigidity. In case two, self-propulsion force is applied only to few bond vectors. The location of active forces is chosen in a periodic manner starting from the tail of the filament and leaving the front end without force. In this case, filament acquires various structures such as rod-like, helical, circular, and folded states. The transition from several states is understood in terms of tangent-tangent correlation, bending energy and torsional order parameter. The helical state is identified through a crossover from exponential to oscillatory behavior of the tangent-tangent correlation. A sudden increase in the bending energy separates a helical to a folded states of the filament.

Elastic buckling and load-resistant behaviors of double-corrugated-plate shear walls under pure in-plane shear loads

Abstract: In this paper, a double-corrugated-plate shear wall (DCPSW) is proposed. It consists of two trapezoidally corrugated plates connected with high-strength bolts. It could be utilized in high-rise buildings as an alternative of the ordinary corrugated plate shear wall (CPSW) to resist lateral shear loads resulting from horizontal seismic or wind effects. In this paper, the elastic buckling behavior of DCPSWs subjected to pure in-plane shear loads is of major concern and is firstly investigated. The DCPSWs are equivalent into orthotropic plates, and accordingly, the rigidity constants, including flexural rigidity constants in the orthotropic directions ( D x and D y ) and the torsional rigidity constant ( H ), are defined and theoretically derived. By comparing the theoretical formulas of the rigidity constants with the results obtained from finite element (FE) eigenvalue buckling analyses, these theoretical formulas are validated to be accurate enough for practical engineering applications. Then, the shear elastic buckling formulas of the DCPSWs are provided by means of FE analyses and numerical fitting technique, and these formulas are validated to be able to conservatively predict the shear elastic buckling loads of DCPSWs with good accuracy. Finally, the shear-resistant behavior of the DCPSWs is investigated via a parametric study of FE models subjected to monotonic shear loads. It is concluded that the normalized aspect ratio could be regarded as a comprehensive design parameter which reflects the ultimate shear resistance of the DCPSW.

Structural behaviour and fracture energy of recycled steel fibre self-compacting reinforced concrete beams

Abstract: Mechanical strength and structural behaviour of Recycled Steel Fibre Self-Compacting Concrete (RSFSCC) were investigated using different Recycled Steel Fibre (RSF) contents (30, 45 and 60 kg/m3) incorporated in three SCC mixes. The corresponding steel fibre volume fraction can be approximated to (0.4%, 0.6% and 0.8%) of the concrete mixtures, respectively. Compressive, splitting, and flexural strengths in addition to water absorption tests were performed to investigate some hardened properties of the tested mixes. The structural behaviour was assessed by determining and calculating flexural stiffness k, flexural toughness I and residual strength factor R for reinforced concrete beams having the dimensions of 100 × 150 × 1000 mm. Fractal dimension D was calculated using Image Processing Technique for all assessed beams to study and quantify the cracks and their tortuosity. It was found that incorporating RSF improved the mechanical properties, strength and structural behaviour of SCC. However, the best strength and behaviour in addition to best cracking resistance were achieved using 60 kg/m3 RSF content. Both first crack and ultimate load capacity were increased with RSF incorporation. The flexural stiffness and toughness in addition to residual strength factor increased with incorporating RSF. In addition, fracture mechanics parameters are determined and discussed.

Reinforcing effect of surface-modified multiwalled carbon nanotubes on flexural response of E-glass/epoxy isogrid-stiffened composite panels

Abstract: The lack of scientific information about the utilization of nanoparticles on grid-stiffened composite (GSC) fabrication was the driving force for the selection of this study. In the present work, GSC panels reinforced with various amounts of surface modified multi-walled carbon nanotubes (MWCNTs) (0–0.5 wt% at a step of 0.1 wt%) have been investigated in terms of their capability to improve the mechanical properties under three-point flexural condition. Out of these specimens, the maximum value of improvement in the flexural stiffness, load bearing capacity, and specific energy absorption was related to the specimen with 0.4 wt% MWCNTs. It would be worth mentioning that in these structures, a considerable energy absorption was observed after the primary failure related to the load peak. The field-emission scanning electron microscopy observations of the fracture surfaces of the nanocomposites clearly indicated that the enhancement in the flexural properties was due to the improvement in the interfacial adhesion between the E-glass fibers and MWCNTs-enhanced epoxy matrix. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Simulation of mechanical parameters of graphene using the DREIDING force field

Abstract: Molecular mechanics/molecular dynamics (MM/MD) methods are widely used in computer simulations of deformation (including buckling, vibration, and fracture) of low-dimensional carbon nanostructures (single-layer graphene sheets (SLGSs), single-walled nanotubes, fullerenes, etc). In MM/MD simulations, the interactions between carbon atoms in these nanostructures are modeled using force fields (e.g., AIREBO, DREIDING, MM3/MM4). The objective of the present study is to fit the DREIDING force field parameters (see Mayo et al. J Phys Chem 94:8897–8909, 1990) to most closely reproduce the mechanical parameters of graphene (Young’s modulus, Poisson’s ratio, bending rigidity modulus, and intrinsic strength) known from experimental studies and quantum mechanics simulations since the standard set of the DREIDING force field parameters (see Mayo et al. 1990) leads to unsatisfactory values of the mechanical parameters of graphene. The values of these parameters are fitted using primitive unit cells of graphene acted upon by forces that reproduce the homogeneous deformation of this material in tension/compression, bending, and fracture. (Different sets of primitive unit cells are used for different types of deformation, taking into account the anisotropic properties of graphene in states close to failure.) The MM method is used to determine the dependence of the mechanical moduli of graphene (Young’s modulus, Poisson’s ratio, and bending rigidity modulus) on the scale factor. Computer simulation has shown that for large linear dimensions of SLGSs, the mechanical parameters of these sheets are close to those of graphene. In addition, computer simulation has shown that accounting for in-layer van der Waals forces has a small effect on the value of the mechanical moduli of graphene.

Design of transverse reinforcement to avoid premature buckling of main bars

Abstract: Summary This paper proposes an enhancement to the current strength and confinement-based design of transverse reinforcement in rectangular and circular reinforced concrete members to ensure that the flexural strength of reinforced concrete sections does not degrade excessively due to buckling of longitudinal bars until the desired level of plastic deformation is achieved. Antibuckling design criteria are developed based on a popular bar buckling model that uses a bar buckling parameter (combining the bar diameter, yield strength, and buckling length) to solely describe the bar buckling behavior. The value of buckling parameter that limits the buckling-induced stress loss to 15% in compression bars at the strain corresponding to the design ductility is determined. For a bar of known diameter and yield strength, the maximum allowable buckling length can then be determined, which serves as the maximum limit for the tie/stirrup/hoop spacing. Lateral stiffness required to restrain the buckling tendency of main bars at the locations of the ties/stirrups/hoops depends on the flexural rigidity of the main bars and the buckling length (equal to or multiple of tie/hoop/stirrup spacing), whereas the antibuckling stiffness (ie, resistance) provided by the ties/stirrups/hoops depends on their size, number, and arrangement. Using the above concept, design recommendations for the amount, arrangement, and spacing of rectangular and circular ties/stirrups/hoops are then established to ensure that the antibuckling stiffness of the provided transverse reinforcement is greater than the stiffness required to restrain the buckling-prone main bars. Key aspects of the developed method are verified using experimental tests from literature.

Stretching and Buckling of Small Elastic Fibers in Turbulence.

Abstract: Small flexible fibers in a turbulent flow are found to be as straight as stiff rods most of the time. This is due to the cooperative action of flexural rigidity and fluid stretching. However, fibers might bend and buckle when they tumble and experience a strong enough local compression. Such events are similar to an activation process, where the role of temperature is played by the inverse of Young's modulus. Numerical simulations show that buckling occurs very intermittently in time. This results from unexpected long-range Lagrangian correlations of the turbulent shear.

Punching Shear Behavior of Two-Way Concrete Slabs Reinforced with Glass-Fiber-Reinforced Polymer (GFRP) Bars.

Abstract: This study investigated the punching shear behavior of full-scale, two-way concrete slabs reinforced with glass fiber reinforced polymer (GFRP) bars, which are known as noncorrosive reinforcement. The relatively low modulus of elasticity of GFRP bars affects the large deflection of flexural members, however, applying these to two-way concrete slabs can compensate the weakness of the flexural stiffness due to an arching action with supporting girders. The test results demonstrated that the two-way concrete slabs with GFRP bars satisfied the allowable deflection and crack width under the service load specified by the design specification even in the state of the minimum reinforcement ratio. Previous predicting equations and design equations largely overestimated the measured punching shear strength when the slab was supported by reinforced concrete (RC) girders. The strength difference can be explained by the fact that the flexural behavior of the supporting RC beam girders reduces the punching shear strength because of the additional deflection of RC beam girders. Therefore, for more realistic estimations of the punching shear strength of two-way concrete slabs with GFRP bars, the boundary conditions of the concrete slabs should be carefully considered. This is because the stiffness degradation of supporting RC beam girders may influence the punching shear strength.

Hybrid bio-composites reinforced with sisal-glass fibres and Portland cement particles: A statistical approach

Abstract: The hybrid configuration of bio-reinforced composites has established a new extended boundary for the development of pro-ecological technologies due to light weight, moderate specific strength, low cost, environmental benefits, and potential applications of natural components. This work investigates the physical and mechanical properties of hybrid composites made of sisal/glass fibres and Portland cement inclusions. A full factorial design was generated to identify the effects of the stacking sequence and cement particles on the flexural strength, flexural stiffness, apparent density, apparent porosity and water absorption of the composites. The significant contributions of these main factors and their interactions were determined via Design of Experiments (DoE) and Analysis of Variance (ANOVA). The fracture features and damage mechanisms of hybrid composite were also reported. The inclusion of cement microparticles led to an increased apparent porosity, as well as enhanced water absorption, flexural stiffness and flexural strength of the hybrid composites. The mechanical properties were strongly dependent on the fibre stacking sequence, which accounts for approximately 98% of the effects observed. Moreover, the stacking sequence affected the damage mechanism of the bio-composites. Finally, the replacement of glass fibres by unidirectional sisal reinforcements may potentially improve the specific properties in structural applications with an environmental sustainable footprint.

Three-dimensional Architecture Enabled by Strained Two-dimensional Material Heterojunction

Abstract: Engineering the structure of materials endows them with novel physical properties across a wide range of length scales. With high in-plane stiffness and strength, but low flexural rigidity, two-dimensional (2D) materials are excellent building blocks for nanostructure engineering. They can be easily bent and folded to build three-dimensional (3D) architectures. Taking advantage of the large lattice mismatch between the constituents, we demonstrate a 3D heterogeneous architecture combining a basal Bi2Se3 nanoplate and wavelike Bi2Te3 edges buckling up and down forming periodic ripples. Unlike 2D heterostructures directly grown on substrates, the solution-based synthesis allows the heterostructures to be free from substrate influence during the formation process. The balance between bending and in-plane strain energies gives rise to controllable rippling of the material. Our experimental results show clear evidence that the wavelengths and amplitudes of the ripples are dependent on both the widths and thick...

Stability and free vibration analysis of tapered sandwich columns with functionally graded core and flexible connections

Abstract: In this study, the buckling and free vibration behavior of tapered functionally graded material (FGM) sandwich columns is explored. The connections are considered to be semi-rigid. The core material is functionally graded along the beam depth according to the simple power law form. Euler–Bernoulli beam theory and the Ritz method will be employed to derive the governing equations. Legendre polynomials are chosen as auxiliary functions. After reducing the order of Euler’s buckling equation, an Emden–Fowler differential equation will be obtained. To reach a closed-form solution, the flexural rigidity of the column will be approximated with an exponential function by enforcing least-squares method. Non-dimensional natural frequencies and critical buckling loads will be presented for various cross-sectional types. The effects of FGM power, taper ratio, and spring rigidities on the critical buckling loads, and natural frequencies will be also investigated. Numerical results for various boundary conditions and configurations reveal the high accuracy of authors’ scheme.

Bending Rigidity of 2D Silica

Abstract: A chemically stable bilayers of SiO_{2} (2D silica) is a new, wide band gap 2D material. Up till now graphene has been the only 2D material where the bending rigidity has been measured. Here we present inelastic helium atom scattering data from 2D silica on Ru(0001) and extract the first bending rigidity, κ, measurements for a nonmonoatomic 2D material of definable thickness. We find a value of κ=8.8 eV±0.5 eV which is of the same order of magnitude as theoretical values in the literature for freestanding crystalline 2D silica.