Prediction of Deflection of Shear-Critical RC Beams Using Compatibility-Aided Truss Model

This study proposes a method for predicting the deflection of shear-critical reinforced concrete (RC) beams. Shear deterioration of shear-critical RC beams occurs before flexural yielding. After shear deterioration occurs in the shear-critical RC beams, the deflection caused by shear is greater than the flexural deflection obtained from the elastic bending theory. To reasonably predict the deflection of shear-critical RC beams, it is necessary to evaluate deflections due to shear as well as flexure. In this study, the deflections produced by flexure and shear were calculated and superposed to evaluate the deflection of shear-critical RC beams. The method recommended by ACI 318-19 was employed to calculate the flexural deflection, and a compatibility-aided truss model able to calculate the shear stress and shear deformation at each load stage was used to consider the shear deflection. A comparison of the experimental and analytical results showed that the proposed analytical method can effectively predict the deflection of shear-critical RC beams.

Elastic Flexibility in an Optically Active Naphthalidenimine-Based Single Crystal

Organic single crystals that combine mechanical flexibility and optical properties are important for developing flexible optical devices, but examples of such crystals remain scarce. Both mechanical flexibility and optical activity depend on the underlying crystal packing and the nature of the intermolecular interactions present in the solid state. Hence, both properties can be expected to be tunable by small chemical modifications to the organic molecule. By incorporating a chlorine atom, a reportedly mechanically flexible crystal of (E)-1-(4-bromo-phenyl)iminomethyl-2-hydroxyl-naphthalene (BPIN) produces (E)-1-(4-bromo-2-chloro-phenyl)iminomethyl-2-hydroxyl-naphthalene (BCPIN). BCPIN crystals show elastic bending similar to BPIN upon mechanical stress, but exhibit a remarkable difference in their optical properties as a result of the chemical modification to the backbone of the organic molecule. This work thus demonstrates that the optical properties and mechanical flexibility of molecular materials can, in principle, be tuned independently.

Mathematical model of fuselage oscillations at transonic flight speeds

Ensuring the safety of supersonic aircraft flights and aerospace systems in the transonic range of M flight numbers still remains an urgent scientific and applied problem. This is caused by the peculiarities of the aerodynamic surfaces flow by inhomogeneous (transonic) air and is due to the emergence of various aeroelastic phenomena in these flight modes and the current lack of a generally accepted model of transonic flutter, even for aerodynamic control surfaces. Based on a joint analysis of the conditions for the formation of shock waves on the surface of the aerodynamic profile, changes in the parameters of supersonic flow across the Prandtl-Meyer expansion fan, and the hypothesis of "dynamic curvature of the aerodynamic profile", the approximate laws of interaction of elastic bending vibrations of the fuselage with fluctuations in shock waves were obtained. The obtained regularities are used to substantiate a mathematical model for estimating excited forces and excited bending moments of the fuselage. The analysis of the obtained mathematical model confirms the theoretical possibility of the appearance of fuselage forms of transonic flutter in supersonic aircraft, which was observed in the flight experiment and which is due to the interaction of shock waves with the angular velocity of the fuselage elastic bending vibrations. With the accepted in the article input geometrical data of a fuselage aerodynamic surfaces’ profile, the maximum possible values of fuselage bending moments are obtained using the developed mathematical model. The obtained mathematical model can be used for a preliminary approximate assessment of the transonic flutter fuselage forms characteristics in supersonic aircraft and aerospace systems.

The Mechanism of Bending in Co-Crystals of Caffeine and 4-Chloro-3-Nitrobenzoic Acid

<p>In a recent study, Dey <i>et al.</i>¹ propose a mechanism of elastic bending in co-crystals of caffeine, 4-chloro-3-nitrobenzoic acid and methanol (<b>1</b>) in which mechanical interlocking is proposed to allow for the reversible flexibility observed. We have now determined the mechanism to atomic resolution using micro-focused synchrotron radiation,² which is different to that previously reported. When subjected to strain the inter-molecular distances change and hydrogen-bonded dimers rotate over two orthogonal directions to allow the compression and expansion producing flexibility. </p>

The Mechanism of Bending in Co-Crystals of Caffeine and 4-Chloro-3-Nitrobenzoic Acid

<p>In a recent study, Dey <i>et al.</i>¹ propose a mechanism of elastic bending in co-crystals of caffeine, 4-chloro-3-nitrobenzoic acid and methanol (<b>1</b>) in which mechanical interlocking is proposed to allow for the reversible flexibility observed. We have now determined the mechanism to atomic resolution using micro-focused synchrotron radiation,² which is different to that previously reported. When subjected to strain the inter-molecular distances change and hydrogen-bonded dimers rotate over two orthogonal directions to allow the compression and expansion producing flexibility. </p>

Protocol for mapping the spatial variability in cell wall mechanical bending behavior in living leaf pavement cells

An integrated, experimental-computational approach is presented to analyze the variation of elastic bending behavior in the primary cell wall of living Arabidopsis thaliana pavement cells and to measure turgor pressure in the cells quantitatively under different osmotic conditions. Mechanical properties, size and geometry of cells and internal turgor pressure greatly influence their morphogenesis. Computational models of plant morphogenesis require values for wall elastic modulus and turgor pressure but very few experiments were designed to validate the results using measurements that deform the entire thickness of the cell wall. Because new wall material is deposited from inside the cell, full-thickness deformations are needed to quantify relevant changes associated with cell development. The approach here uses laser scanning confocal microscopy to measure the three-dimensional geometry of a single pavement cell, and indentation experiments equipped with high magnification objective lens to probe the local mechanical responses across the same cell wall. These experimental results are matched iteratively using a finite element model of the experiment to determine the local mechanical properties, turgor pressure, and cell height. The resulting modulus distribution along the periclinal wall is shown to be nonuniform. These results are consistent with the characteristics of plant cell walls which have a heterogeneous organization. This research and the resulting model will provide a reference for future work associated with the heterogeneity and anisotropy of mechanical properties of plant cell walls in order to understand morphogenesis of the primary cell walls during growth and to predict quantitatively the magnitudes/directions of cell wall forces.One sentence summaryThe distribution of elastic modulus of the periclinal cell walls of livingArabidopsis epidermis is nonuniform as measured by bending the entire thickness of the wall.HighlightsExperimental characterization of the spatial distribution of elastic bending behavior across the periclinal wallQuantification of the turgor pressure of the living plant epidermal cells validated with osmotic treatmentsQuantification of the effect of cell geometry on the measured mechanical responseGraphical abstract

ELASTIC BENDING OF A DRILL STRING IN AN ELLIPTICAL WELL WITH GEOMETRIC IMPERFECTIONS

The problem is posed of determining the resistance forces and internal forces in the drill string during drilling and when performing tripping operations in a curved well. The object of the study is the geometry of the centerline of deep inclined well trajectories. The aim of the work is to formulate and solve new problems of structural mechanics about nonlinear deformation of drill strings in directional wells. To study the mechanics of elastic bending of drill strings in directional wells, the methods of structural mechanics of flexible curved rods were used; methods of differential geometry and theory of surfaces; numerical Runge-Kutta method. The study of the influence of geometric imperfections of the borehole centerline on the forces of contact interaction between the drill string and the borehole wall has been carried out. The case is considered when geometric imperfections have the form of a localized spiral of variable radius. KEY WORDS: OIL AND GAS WELLS, CURVED TRAJECTORY, DRILLING COLUMN, RESISTANCE FORCES.

Intense Red Emissive Organic Crystals with Elastic Bending Ability and Optical Waveguiding Behaviour

Orange (Cry-1O) and red (Cry-1R) emissive crystals with mechanical brittleness and elasticity, respectively, were obtained by modifying the crystallization conditions based on a green emissive molecule. Light transducing capability of...