Critical Torsional Moment Research Articles

On the torsional buckling moment of cylindrical shells consisting of functionally graded materials resting on the Pasternak-type soil

In this study, the buckling analysis of cylindrical shells made of functionally graded materials (FGMs) under the torsional moment resting on the Pasternak-type soil is performed. After establishing the linear constitutive relations of FGM cylindrical shells within the framework of the modified Donnell type shell theory, the governing equations of FGM cylindrical shells under the torsional moment are derived considering the influence of Pasternak-type soil. Analytical formula for the torsional moment is obtained by choosing the approximation functions that satisfies the boundary conditions in an integral sense. From the obtained formula, the formulas for the critical torsional moment in the presence of Winkler soil and absence of soils are obtained as a special case. Variations of critical torsional moment for different soil coefficients, volume fraction ratio and shell characteristics are investigated in detail. Keywords: functionally graded materials; cylindrical shell; buckling; critical torsional moment; Pasternak-type soil.

The mechanical behavior of thermally enhanced polypropylene concrete

This article presents the investigation of the change of mechanical properties of reinforced and non-reinforced beams produced by using a constant amount of polypropylene (PP) instead of 50% of fine aggregates by volume as a result of exposure to high temperatures (170° C) for different periods (1, 3, and 5 h) of time. The thermal enhancement procedure is applied after the 28 days of curing period. Bending, shear and torsion tests were applied to the beams. In this study, torsional moment capacity, flexural, and shear strengths were evaluated according to the American Concrete Institute (ACI318-19) and Eurocode-2 standards. These theoretical values are compared with experimental results. The polypropylene aggregate, which is used instead of fine aggregates in reinforced or non-reinforced groups, caused a decrease in flexural and shear strength compared to the control samples. The ductile fracture tendency was increased with the exposure time of PP containing samples to high temperatures. The ultimate torsional moment and critical torsional moment are reduced except for the samples that have been heat-treated for 3 h in groups with and without reinforcement. The results show that none of the existing formulas according to the relevant standards is adequate for prediction of torsional moment, flexural and shear strengths of the beams with PP concrete.

Betonarme Kirişlerin Deneysel ve Teorik Burulma Momenti Değerlerinin Karşılaştırılması

The experimental investigation effect on the torsional behavior of web spacing, concrete class and concrete type of reinforcement concrete beams constitute basis of this work. The compressive strength of concrete, 20 MPa and 40 MPa, the type of concrete, conventional concrete and self-compacting concrete, web spacing of 80 mm and 100 mm, was determined the main parameters of this work. 12 unit of conventional concrete beams and 8 unit of self-compacting concrete beams of 250x300x1500 mm was manufactured. The torsional moment capacities and corresponding rotation angle values, the critical torsional moment values and corresponding critical rotation angles, torsional cracks of the beam samples that subjected to the torsion was measured experimentally. The torsional moment capacity results that were measured experimentally were compared with the elastic, plastic and skew-bending theories. The most closed results were get to the skew-bending theory. The graphic of torsional moment capacity- unit rotational angles were plotted. The low web spacing, high concrete class and self-compacting concrete type that have a positive effect on the torsional behavior was determined experimentally in this study. Experimental critical torsion values were compared with empirical values obtained from related studies.

Size-Dependent Torsional Buckling of Carbon Nano-Peapods Based on the Modified Couple Stress Theory

Using the modified couple stress theory and the shell model, this paper investigates the torsional instability of carbon nano peapods (CNPs), which are the hybrid structures made by inserting C[Formula: see text] fullerenes into CNT. Based on the modified couple stress theory as a higher order elasticity theory and using the first-order shear deformation shell theory, the equilibrium equations are derived through the principle of the minimum potential energy. The critical torsional moment is determined for the (10,10) CNT and the C[Formula: see text]@(10,10) CNP, and compared with that of MD simulations in the literature. Then, the increase in critical torsional moment is represented with the increase in the length scale parameter in both (10,10) CNT and C[Formula: see text]@(10,10) CNP based on the modified couple stress theory. Besides, by comparing the critical torsional moment in the C[Formula: see text]@(10,10) CNP and the (10,10) CNT, 100 percent increase in buckling resistance due to the presence of C[Formula: see text] fullerene is exhibited as well. In addition, the CNP surrounding is modeled as Pasternak foundation, and the effects of Pasternak stiffness are shown on the critical torsional moment.

Tuning the Shear Modulus of Single-Walled Carbon Nanotube by Feeding Van Der Waals Molecules

Torsional buckling of single-walled carbon nanotubes filled with light weight molecular via molecular dynamics is reported. The model accounts for the deformation of CNTs, and interactions among gas molecules; between gas and carbon atoms. The effect of particle loading is predicted to significantly change CNT’s critical torsional moment and stiffness. This is therefore an approach by which the torsional mechanical properties and oscillation frequencies of carbon nanotubes may be tuned. Importantly, the predicted changes in torsional siffness are unique relative to conventional linear elastic materials and are indicative of nonlinear oscillations due to nonlinear mechanical effects. CNTs subjects to large deformations reversibly switch into different morphological patterns. Each shape change corresponds to an abrupt release of energy and a singularity in the stress-strain curve. At higher torsional angle, van der Waals (VDW: He, Ar, H2) molecules reveal a stability effect on carbon nanotubes.

Mechanical response of hydrogen-filled single-walled carbon nanotubes under torsion

Molecular dynamics simulations are performed to investigate the torsional buckling behavior of single-walled carbon nanotubes (SWCNTs) filled with hydrogen gas. The simulation model accounts for both the mechanical deformation of the SWCNT and the interactions among the hydrogen and carbon atoms. It is found that the critical torsional moment and stiffness of the SWCNT are both significantly dependent on the hydrogen molecule storage density. Importantly, the change in torsional stiffness differs from that of conventional linear elastic materials as a result of the nonlinear oscillatory response due to nonlinear mechanical effects. It is shown that under large deformations, the SWCNT switches reversibly between different morphological patterns. Each change in pattern corresponds to an abrupt release of the strain energy and a singularity in the stress–strain curve. It is shown that at higher hydrogen storage densities, the hydrogen molecules exert a stabilizing effect on the SWCNT. The degree of torsional stability is determined principally by the distribution of the hydrogen molecules within the SWCNT. Finally, it is shown that the torsional deformation of the SWCNT is characterized by a stick-slip phenomenon.

Torsional instability of carbon nano-peapods based on the nonlocal elastic shell theory

In this paper a shell formulation is proposed for analyzing the torsional instability of carbon nano-peapods (CNPs), i.e., the hybrid structures composed of C60 fullerenes encapsulated inside carbon nanotubes (CNTs), based on the nonlocal elasticity theory. The nonlocal elasticity theory, as a well-known non-classical continuum theory, is capable to capture small scale effects which appear due to the discontinuities in nano-structures. Based on the derived formulation, the critical torsional moments for a pristine (10,10) CNT and C60@(10,10) CNP are investigated as case studies. The results for the (10,10) CNT are compared with those of the available molecular dynamics simulations in the literature, and accordingly the appropriate value of the small scale coefficient appearing in the constitutive equations of the nonlocal theory is estimated for CNTs. Then, the critical torsional moment for the C60@(10,10) CNP is predicted. It is observed that the presence of the encapsulated C60 fullerenes inside the (10,10) CNT causes an increase in the torsional instability resistance of the CNT more than 100%.

Torsional behaviour of carbon nanotubes with abnormal interlayer distances

Atomistic simulations are performed to investigate the torsional behaviour of abnormal double-walled carbon nanotubes (DWCNTs) with an interlayer distance of less than 0.34 nm and carbon nanowires (CNWs) made of linear carbon-atom chain (C-chain) encapsulated inside single-walled carbon nanotubes (SWCNTs) subject to torsional motion. The interaction between atoms is modelled using the second-generation reactive empirical bond-order potential coupled with the Lennard-Jones potential. These simulations indicate that the effect of the van der Waals (vdW) interaction is more significant for abnormal DWCNTs than for normal DWCNTs. The critical torsional moments of abnormal DWCNTs are considerably enhanced compared with those of corresponding normal DWCNTs. It is worth noting that the critical torsional moment does not always increase with a decrease in the interlayer distance of DWCNTs. Numerical results also show that the torsional behaviours of CNWs are influenced dramatically by the radius of CNWs. Compared with those of corresponding SWCNTs, the critical torsional moment and the critical torsional angle of CNW increase in CNWs of radius less than 0.4 nm and decrease in (6, 6) and (11, 0) CNWs with large radius.

Molecular dynamics study of effects of sp3 interwall bridging upon torsional behavior of double-walled carbon nanotube

Atomistic simulations are performed to investigate the torsional behavior of double-walled carbon nanotubes (DWCNTs) with and without some interwall sp3 bonds subject to torsion motion. The interaction between atoms is modeled using the second-generation reactive empirical bond-order potential coupled with the Lennard–Jones potential. These results show that the critical buckling moment is increased to 97% for the ( ( 5 , 5 ) , ( 10 , 10 ) ) DWCNT in comparison with the ( 10 , 10 ) SWCNT. They also indicate that the critical torsional moment and critical torsion angle of DWCNT can be obviously increased by addition of interwall sp3 coupling to provide an effective channel for load transfer of constituent outer and inner tubes. The influences of the distribution density and location of sp3 bonds on the torsional behavior of DWCNTs are also studied. For three types of distribution density, i.e., 2.63 / nm , 3.68 / nm and 6.84 / nm , the increased magnitude of the critical torsional moments [respectively the critical torsional angles] of DWCNTs are 25.5%, 36.7% and 85.2% [respectively 32.7%, 51.9% and 103.8%]. The results also show that the torsional behavior depend strongly on the location of sp3 bonds.

Tuning the torsional properties of carbon nanotube systems with axial prestress

The effects of tensile or compressive prestress on the torsional responses of carbon nanotubes are examined using classical molecular dynamics simulations. Prestressing the nanotubes is predicted to significantly change their critical torsional moment and stiffness. This is therefore an approach by which the torsional mechanical properties and oscillation frequencies of carbon nanotubes may be tuned. Importantly, the predicted changes in torsional stiffness are unique relative to conventional linear elastic materials and are indicative of nonlinear oscillations due to nonlinear mechanical effects.

Torsional stiffening of carbon nanotube systems

The torsional responses of hollow and filled carbon nanotubes under a combination of tension and torsion are examined using classical molecular dynamics simulations. The critical torsional moment and shear modulus are predicted to significantly increase as a result of coupling between tension and torsion. In particular, the simulations predict that the torsional responses under this type of combined loading are beyond the linear responses of the nanotubes. Importantly, the coupling effect between tension and torsion also increases the torsional stiffness and oscillation frequency of the nanotubes.

탄소나노튜브 다발의 압축 및 비틀림 좌굴 거동

The compressive and torsional buckling behavior of carbon nanotube bundles at room temperature is examined with classical molecular dynamics simulation. The critical compressive load and stiffness of a single carbon nanotube in the bundle are found to be similar to those of individual carbon nanotubes. However, the critical torsional moment and stiffness of a single carbon nanotube in the bundle are found to be higher than those of individual carbon nanotubes. In addition, this study demonstrates that van der Waals interactions between the nanotubes in the bundle significantly affect the critical compressive load of the nanotube bundle.

Crazing and fatigue of poly(methyl methacrylate) due to case II diffusion of methanol

Static torsion and dynamic fatigue tests were performed on poly(methyl methacrylate) in methanol at room temperature using solid cylindrical specimens which had previously been soaked in methanol for various periods. Presoaking for times in the range 8–96 h brought about dramatic increases in both the critical torsional moment for crazing and the fatigue lifetime. The latter, for instance, attained a value 10 4 times that of the specimen without presoaking. Presoaking for longer times, however, allowed shear flow to occur prior to crazing, and contributed less to the increase in fatigue life. These results are explained in terms of both the softening of matter and the generation of internal compressive stress in the swollen surface layer following the case II diffusion of methanol.