ON THE BUCKLING AND VIBRATIONAL RESPONSE OF CARBON NANOTUBES WITH SPIRAL DEFORMATION

Perfect and spiral models of carbon nanotubes (CNTs) have been simulated based on the finite element method and their vibrational and buckling behavior has been investigated. In order to evaluate their natural frequency and critical buckling load, computational tests have been conducted. It has been concluded that the existence of any geometrical modification in the configuration of perfect CNTs results in a remarkable reduction in the natural frequency and critical buckling load of CNTs. It has been also revealed that the analytical solutions are in good agreement with the finite element simulation results in the cases of perfect and spiral CNTs

Dynamic analysis of aircraft landing gear

Landing gear dynamics, especially shimmy and break-induced vibrations, is one of the problems faced today by the aircraft community. Landing gear vibration may lead to fatal accidents due to excessive wear; it can also shorten the gear life, and affect comfort to the pilot and passengers. Among the most important reasons for landing gear vibrations are unsuitable combination of structural stiffness, damping, and pneumatic tire characteristics furthermore an unlucky combination of brake system design with the tire physics can produce a serious vibration problem. Many available computer-aided engineering tools and software have made it possible to test some of the problems in the design phase by simulating the landing gear impact and ground maneuvers. In this study, it has been conducted to simulate the simplified model of aircraft Eagle-150 in MSC. ADAMS software and work on the simulation of such an unstable and complex phenomenon during landing position and also aircraft ground maneuver in order to detect vibrations in aircraft landing gear. It has also been tried to study the effect of important parameters that may affect the instability and comfort a simple simulated model of aircraft and its landing gear was prepared using ADAMS for this purpose. An adequate model of aircraft and landing gear is an important aspect of analysis in order to understand the behavior of an aircraft during landing and ground maneuver. Effect of various parameters on landing gear vibration is also one the purposes of this study

Advances in mechanical analysis of structurally and atomically modified carbon nanotubes and degenerated nanostructures: a review

In the past few years, numerous research activities concerning the mechanical behavior of defected and imperfect carbon nanotubes have been conducted. It is reported that the superlative mechanical properties of these nano-structures, i.e. high stiffness, high strength and vibrational response, would be affected by existing or introducing defects and impurities in the structure of the nanotubes. Such defects may results from manufacturing routes or introduced on purpose to tailor certain physical properties. This review attempts to categorize and highlight the advanced breakthroughs and recent studies employed to investigate the mechanical properties, e.g. stiffness, buckling behavior and vibrational response of structural and atomically modified carbon nanotubes. The presented studies cover the mechanical behavior of nanotubes, both theoretically and experimentally which allowed a realistic prediction of the mechanical behavior of defected tubes in a closer form to those found in reality. It was concluded that any type of imperfection, either atomic or structural modification, influences the mechanical behavior of nanotubes and reduces the stiffness and structural stability, as well as vibrational response of these nano-structures. The present review includes: (i) a brief introduction to atomic and structural modification of nanotubes; (ii) a review of mechanical analysis of atomically and structurally modified models in two separate sections; and (iii) a detailed conclusion on the discussed studies and present the potential progress

On the eigenmodes and eigenfrequencies of low-dimensional degenerated carbon structures: obtaining natural frequencies of ideal and structurally defected systems

We concentrated on evaluating the vibrational response of ideal and defected degenerated carbon nanostructures under the influence of different boundary conditions. In addition, an attempt has been made to investigate the relative deviation of the natural frequency of imperfect systems and to study the effect of defected regions on vibrational stability of the particles. It has been found that a single and pinhole vacancy defect have the least and the most impact on the natural frequency of nanostructures. Furthermore, the effect of CNT diameter on natural frequencies of low-dimensional systems has also been investigated in this research

On the influence of atomic moifications on the structural stability of carbon nanotube hybrids: numerical investigation

Connected carbon nanotubes (CNTs) with parallel longitudinal axes and with bending angles were simulated by a commercial finite element package and their buckling behavior was investigated by performing several computational examinations. In addition, the effect of defects on the structural stability of these heterojunctions was analyzed. For this purpose, two different nanotube hybrids (straight and kink heterojunction) were constructed in their perfect forms. In the second phase, three most likely atomic defects, i.e., impurities (doping with Si atoms), vacant sites (carbon vacancy) and introduced perturbations of the ideal geometry in different amounts to the perfect models, were simulated. To conclude our study, the buckling behavior of imperfect heterojunctions was numerically evaluated and compared with the behavior of the perfect ones. It was concluded that the existence of any type of defects in the configuration of nanotube hybrids leads to a lower critical load and as a result, lower buckling properties. This study provides a better insight into the prediction of straight and kink heterojunction CNTs behavior

Numerical simulation of the vibration behavior of curved carbon nanotubes

Several zigzag and armchair single-walled carbon nanotubes (CNTs) were modeled by a commercial finite element package and their vibrational behavior was studied. Numerous computational tests with different boundary conditions and different bending angles were performed. Both computational and analytical results were compared. It was shown that the computational results are in good agreement with the analytical calculations in the case of straight tubes. In addition, it was concluded that the natural frequency of straight armchair and zigzag CNTs increases by increasing the chiral number of both armchair and zigzag CNTs. It was also revealed that the natural frequency of CNTs with higher chirality decreases by introducing bending angles. Nevertheless, the influence of increasing bending angle on the natural frequency of armchair and zigzag CNTs with lower chiral number is almost negligible