Showing papers on "Bending moment published in 2017"

Interaction Forces of Soft Fiber Reinforced Bending Actuators

Abstract: Soft-bending actuators are inherently compliant, compact, and lightweight. They are preferable candidates over rigid actuators for robotic applications ranging from physical human interaction to delicate object manipulation. However, characterizing and predicting their behaviors are challenging due to the material nonlinearities and the complex motions they can produce. This paper investigates a soft-bending actuator design that uses a single air chamber and fiber reinforcements. Additionally, the actuator design incorporates a sensing layer to enable real-time bending angle measurement for analysis and control. In order to study the bending and force exertion characteristics when interacting with the environment, a quasi-static analytical model is developed based on the bending moments generated from the applied internal pressure and stretches of the soft materials. Comparatively, a finite-element method model is created for the same actuator design. Both the analytical model and the finite-element model are used in the fiber reinforcement analysis and the validation experiments with fabricated actuators. The experimental results demonstrate that the analytical model captures the relationships of supplied air pressure, actuator bending angle, and interaction force at the actuator tip. Moreover, it is shown that an off-the-shelf bend angle sensor integrated to the actuator in this study could provide real-time force estimation, thus eliminating the need for a force sensor.

Exact solutions of inflected functionally graded nano-beams in integral elasticity

Abstract: The elastostatic problem of a Bernoulli-Euler functionally graded nanobeam is formulated by adopting stress-driven nonlocal elasticity theory, recently proposed by G. Romano and R. Barretta. According to this model, elastic bending curvature is got by convoluting bending moment interaction with an attenuation function. The stress-driven integral relation is equivalent to a differential problem with higher-order homogeneous constitutive boundary conditions, when the special bi-exponential kernel introduced by Helmholtz is considered. Simple solution procedures, based on integral and differential formulations, are illustrated in detail to establish the exact expressions of nonlocal transverse displacements of inflected nano-beams of technical interest. It is also shown that all the considered nano-beams have no solution if Eringen's strain-driven integral model is adopted. The solutions of the stress-driven integral method indicate that the stiffness of nanobeams increases at smaller scales due to size effects. Local solutions are obtained as limit of the nonlocal ones when the characteristic length tends to zero.

Out-of-plane behavior of reinforced masonry walls: Experimental and numerical study

Abstract: In the paper, the results of an experimental and numerical study on the out-of-plane bending effectiveness of a modern strengthening technique applied to existing masonry walls are presented. The technique consists in the application, on both wall faces, of a mortar coating reinforced with glass fiber-reinforced polymer (GFRP) meshes. Four point bending tests of full scale masonry samples (1000 width, 3000 mm height) were carried out considering three types of masonry (solid brick, 250 mm thick, rubble stone and cobblestones, 400 mm thick). The performances of plain and reinforced specimens were analysed and compared. It emerged that strengthened specimens are able to resist out-of-plane bending moments almost 4–5 times greater than those of plain specimens; moreover they can overcome deflections more than 25 times higher, due to the presence of the GFRP mesh, which contrasts the opening of cracks. The cracking and the ultimate bending moments of reinforced samples can be analytically predicted using relationships quite close to those used in the design of reinforced concrete beams subjected to combined axial and bending actions. The results of nonlinear static analyses performed on a 2D numerical model were also presented, so to comprehend the mechanical behaviour of reinforced masonry walls. Their agreement with the experimental results proved the reliability of the simulations; moreover, the extension of the 2D model to a 3D one, necessary to analyze the behavior of perforated walls, was also made.

Design, modeling and testing of a novel flexure-based displacement amplification mechanism

Abstract: This paper presents a novel flexure-based displacement amplification mechanism to increase the effective actuation stroke of piezoelectric actuator. The proposed mechanism consists of two L-shape lever-type mechanism and one bridge-type mechanism. The flexure hinges in this mechanism are all loaded in tension and bending, which can solve the potential buckling problems. The symmetrical distribution of the L-shape lever mechanisms can avoid the bending moments and lateral forces at the driving end to protect the piezoelectric actuator. An analytical model based on the stiffness matrix method for the calculations of displacement amplification ratio, input stiffness and natural frequency of the mechanism is constructed and optimal design is performed under certain constraints. The finite element analysis results are then given to validate the design model and a prototype of the amplification mechanism is fabricated for performances tests. The results of static and dynamic tests show that the proposed mechanism is capable of travel range of 288.3 μm with motion resolution of 50 nm, and the working resonance frequencies of the mechanism without and with the actuator mounted are 155 Hz and 178 Hz, respectively. The finite element analysis and the experimental results show that good static and dynamic performances are achieved, which verifies the effectiveness of the proposed mechanism.

Analytical solutions for Euler-Bernoulli Beam on Pasternak foundation subjected to arbitrary dynamic loads

Abstract: In this paper, the dynamic response of an infinite beam resting on a Pasternak foundation and subjected to arbitrary dynamic loads is developed in the form of analytical solution. The beam responses investigated are deflection, velocity, acceleration, bending moment, and shear force. The mechanical resistance of the Pasternak foundation is modeled using two parameters, that is, one accounts for soil resistance due to compressive strains in the soil and the other accounts for the resistance due to shear strains. Because the Winkler model only represents the compressive resistance of soil, comparatively, the Pasternak model is more realistic to consider shear interactions between the soil springs. The governing equation of the beam is simplified into an algebraic equation by employing integration transforms, so that the analytical solution for the dynamic response of the beam can be obtained conveniently in the frequency domain. Both inverse Laplace and inverse Fourier transforms combined with convolution theorem are applied to convert the solution into the time domain. The solutions for several special cases, such as harmonic line loads, moving line loads, and travelling loads are also discussed and numerical examples are conducted to investigate the influence of the shear modulus of foundation on the beam responses. The proposed solutions can be an effective tool for practitioners. Copyright © 2017 John Wiley & Sons, Ltd.

Ultimate load‐carrying capacity of the longitudinal joints in segmental tunnel linings

Abstract: According to the service conditions of operating metro shield tunnels, segment joints are vulnerable locations in tunnel linings In addition, the mechanical performance of segment joints directly determines the bearing capacity of segmental tunnel linings Illustrated with the typical segment joints of the Shanghai Metro rapid transit system, experiments are conducted to investigate the ultimate bearing capacity of the longitudinal joints under different load conditions The failure mechanisms of segment joints are introduced The corresponding analytic model is developed to calculate the bearing capacity of the longitudinal joints during the whole loading process After verification, the proposed model is further employed to compare the mechanical behavior with full section models It is found that the failure mode of positive bending moment joints is similar to that of a large eccentricity stress cross section, while the failure mode of positive bending moment joints is similar to that of a small eccentricity stress cross section What's more, the caulking structure is found to be able to offer the safety margin of structures, which could contribute to the protection of operated subway tunnels

Finite element analysis of undrained stability of cantilever flood walls

Abstract: In this study, new undrained stability solutions of cantilever flood walls in clay were proposed and solved by finite element analysis with a two-dimensional plane strain condition. The analysis considered flood walls in homogeneous and non-homogeneous clay layers, where the latter corresponded to a linear increase in shear strength with depth. Two parametric studies were performed for embedded length ratios and dimensionless strength gradients. Results were summarised in the form of design charts for stability number, normalised maximum shear force and normalised maximum bending moment as a function of those two parameters. Closed-form solutions were proposed for a convenient and accurate evaluation of undrained stability of flood walls in practice, and their applications were demonstrated through a back analysis of a case study.