Improved Strategy of Two-Node Curved Beam Element Based on the Same Beam’s Nodes Information

The curved beam with a great initial curvature is the typical structure and applied widely in real engineering structures. The common practice in the current literature employs two-node straight beam elements as the elementary members for stress and displacement analysis, which needs a large number of divisions to fit the curved beam shape well and increases computational time greatly. In this paper, we develop an improved accurate two-node curved beam element (IC2) in 3D problems, combining the curved Timoshenko beam theory and the curvature information calculated from the same beam curve. The strategy of calculating the curvature information from the same bean curve in the IC2 beam element and then transferring the curvature information to the two-node straight beam element can greatly enhance the accuracy of the mechanical analysis with no extra calculation burden. We then introduce the finite element implementation of the IC2 beam element and verify by the complex curved beam analysis. By comparison with simulation results from the straight two-node beam element in the MIDAS (S2-MIDAS) and the three-node curved beam element adopted in the ANSYS (C3-ANSYS), the simulation results of the typical quarter arc examples under constant or variable curvature show that the IC2 beam element based on curved beam theory is a combination of efficiency and accuracy. And, it is a good choice for analysis of complex engineering rod structure with large initial curvature.

Euler–Bernoulli elastic beam models of Eringen’s differential nonlocal type revisited within a $$\mathbf{C }^{0}-$$continuous displacement framework

A theory of the Erigen’s differential nonlocal beams of (isotropic) elastic material is prospected independent of the original integral formulation. The beam problem is addressed within a $$C^{(0)}-$$ C ( 0 ) - continuous displacement framework admitting slope discontinuities of the deflected beam axis with the formation of bending hinges at every cross section where a transverse concentrated external force is applied, either a load or a reaction. Concepts sparsely known from the literature are in this paper used within a more general context, in which the beam is envisioned as a macro-beam whose microstructure is able to take on a size dependent initial curvature dictated by the loading and constraint conditions. Indeed, initial curvature seems to be an effective analytical tool to inject size effects into micro- and nano-beams. The proposed theory is applied to a set of benchmark beam problems showing that a softening behaviour is always predicted without the appearance of paradoxical situations. Comparisons with other theories are also presented.

Elucidating the Mechanical Energy for Cyclization of a DNA Origami Tile

DNA origami has emerged as a versatile method to synthesize nanostructures with high precision. This bottom-up self-assembly approach can produce not only complex static architectures, but also dynamic reconfigurable structures with tunable properties. While DNA origami has been explored increasingly for diverse applications, such as biomedical and biophysical tools, related mechanics are also under active investigation. Here we studied the structural properties of DNA origami and investigated the energy needed to deform the DNA structures. We used a single-layer rectangular DNA origami tile as a model system and studied its cyclization process. This origami tile was designed with an inherent twist by placing crossovers every 16 base-pairs (bp), corresponding to a helical pitch of 10.67 bp/turn, which is slightly different from that of native B-form DNA (~10.5 bp/turn). We used molecular dynamics (MD) simulations based on a coarse-grained model on an open-source computational platform, oxDNA. We calculated the energies needed to overcome the initial curvature and induce mechanical deformation by applying linear spring forces. We found that the initial curvature may be overcome gradually during cyclization and a total of ~33.1 kcal/mol is required to complete the deformation. These results provide insights into the DNA origami mechanics and should be useful for diverse applications such as adaptive reconfiguration and energy absorption.

Determination of parameters of pipeline repair with initial curvature

Ремонт трубопровода часто предусматривает его подъем трубоукладчиками, что предполагает перемещение заполненной трубы в вертикальной и горизонтальной плоскостях. Для обеспечения безопасности проведения ремонтных работ необходима оценка напряженно-деформированного состояния ремонтируемого участка. Известна методика определения технологических параметров ремонта при перемещении прямолинейного трубопровода. Однако почти всегда трубопровод имеет начальную кривизну оси. В этой связи разработана методика определения технологических параметров ремонта участков подземного трубопровода с начальной кривизной оси. Проведен сравнительный анализ параметров ремонта методом изменения положения трубопровода с начальной кривизной и прямолинейного трубопровода. Приведены основные положения методики расчета. Рассмотрены случаи изгиба трубопровода в вертикальной плоскости выпуклостью вниз (вогнутая кривая) и выпуклостью вверх (выпуклая кривая), а также деформирование при разрезке. Исследована зависимость параметров ремонта от знака начальной кривизны участка трубопровода. Методика может быть использована при планировании ремонтных работ для определения нагрузок на крюки трубоукладчиков, расстояния между трубоукладчиками, высоты подъема (дозаглубления) трубопровода, протяженности ремонтируемого участка (участка вскрытия траншеи), а также для расчета вертикального перемещения и угла поворота торца реза при установлении геометрических параметров кривой вставки. Pipeline repairs often involve lifting by pipe-layers, which involves moving the filled pipe in both vertical and horizontal planes. To ensure the safety of repair work, it is necessary to assess the stress-strain state of the repaired area. There is a technique for determining the technological parameters of repair when moving a straight pipeline. However, the pipeline almost always has an initial axis curvature. Accordingly, an urgent scientific and practical task is to assess the influence of pipeline initial curvature on technological parameters of repair. For this purpose, a method has been developed for determining the technological parameters of repairing sections of an underground pipeline with initial axis curvature. A comparative analysis of the repair parameters by changing the position of pipeline with initial curvature and straight pipeline is carried out. Then the main provisions of the calculation method are given. Cases of pipeline bending in the vertical plane with a downward convexity (concave curve) and upward convexity (convex curve), as well as deformation during cutting, are considered. The dependence of repair parameters on initial curvature sign of the pipeline section is investigated. The technique can be used when planning repair work to determine pipe-layer hook loads, the distance between pipe-layers, the height of the pipeline rise (additional deepening), length of the section to be repaired (trench opening section), as well as for calculating the vertical displacement and angle of rotation of the cut end when establishing geometric parameters insertion curve.

Elucidating the Mechanical Energy for Cyclization of a DNA Origami Tile

ABSTRACTDNA origami has emerged as a versatile method to synthesize nanostructures with high precision. This bottom-up self-assembly approach can produce not only complex static architectures, but also dynamic reconfigurable structures with tunable properties. While DNA origami has been explored increasingly for diverse applications such as biomedical and biophysical tools, related mechanics are also under active investigation. Here we studied the structural properties of DNA origami and investigated the energy needed to deform the DNA structures. We used a single-layer rectangular DNA origami tile as a model system and studied its cyclization process. This origami tile was designed with an inherent twist by placing crossovers every 16 base-pairs (bp), corresponding to a helical pitch of 10.67 bp/turn which is slightly different from that of native B-form DNA (10.5 bp/turn). We used molecular dynamics (MD) simulations based on a coarse-grained model on an open-source computational platform, oxDNA. We calculated the energies needed to overcome the initial curvature and induce mechanical deformation by applying linear spring forces. We found that the initial curvature may be overcome gradually during cyclization and a total of ~33.1 kcal/mol is required to complete the deformation. These results provide insights into the DNA origami mechanics and should be useful for diverse applications such as adaptive reconfiguration and energy absorption.

Hygrothermal environment effect on the critical buckling load of FGP microbeams with initial curvature integrated by CNT-reinforced skins considering the influence of thickness stretching

Due to the need for structures with refined properties to bear against different loading conditions, recently, carbon nanotubes (CNTs) have been used widely to reinforce them. The extremely high stiffness of CNTs makes them significant as one of the best reinforcements to improve the mechanical behaviors of structures. This work focuses on microbeam buckling response with an initial curvature that includes three layers. The mid-layer that is known as the core is constituted of functionally graded porous (FGP) materials and two CNT-reinforced composite skins are bonded to the core to integrate it. The whole structure is affected by the hygrothermal environment and springs and shear layers are put below it. For the first time, for such a structure, a refined shear deformation theory (RSDT) as a higher-order theory that considers thickness stretching effect in polar coordinates is used that presents more accurate results, especially for deeply curved beams. Modified couple stress theory (MCST) in combination with the virtual displacement principle is utilized to establish the governing equations. The obtained results demonstrate the significance of porosity percentage and CNTs’ addition to the skins on the critical nanotubes buckling load. Also, the different behaviors of the microstructure at various temperatures are analyzed and discussed in detail.