Showing papers on "Deflection (engineering) published in 2019"

Continuum Robot Stiffness Under External Loads and Prescribed Tendon Displacements

Abstract: Soft and continuum robots driven by tendons or cables have wide-ranging applications, and many mechanics-based models for their behavior have been proposed. In this paper, we address the unsolved problem of predicting robot deflection and stiffness with respect to environmental loads where the axial displacements of the tendon ends are held constant. We first solve this problem analytically for a tendon-embedded Euler–Bernoulli beam. Nondimensionalized equations and plots describe how tendon stretch and routing path affect the robot's output stiffness at any point. These analytical results enable stiffness analysis of candidate robot designs without extensive computational simulations. Insights gained through this analysis include the ability to increase robot stiffness by using converging tendon paths. Generalizing to large deflections in three dimensions (3-D), we extend a previous nonlinear Cosserat-rod-based model for tendon-driven robots to handle prescribed tendon displacements, tendon stretch, pretension, and slack. We then provide additional dimensionless plots in the actuated case for loads in 3-D. The analytical formulas and numerically computed model are experimentally validated on a prototype robot with good agreement.

Functionally graded graphene reinforced porous nanocomposite curved beams: Bending and elastic stability using a higher-order model with thickness stretch effect

Abstract: Here, the investigation of thick functionally graded graphene platelets reinforced porous nanocomposite curved beams is carried out considering the static bending and elastic stability analyses based on a higher-order shear deformation theory accounting for through-thickness stretching effect. The formulation is general through which different theories can be realized for various structural applications of beam. The governing equations are developed using the Hamilton's principle and are solved by introducing the Navier's solutions. The formulation is firstly assessed considering problems for that results are available in the literature. The performance of various theories is compared here for the selected problems. The structural characteristics of curved beam, constituting of porous metal foam and graphene platelets as nanofillers for reinforcement, are evaluated considering different dispersion patterns for the graphene and porosity, shallowness of the curved beam, thickness ratio, and platelet geometry. The deflection and stress variations in the thickness direction of the beam are also examined.

Analytical study of bending and free vibration responses of functionally graded beams resting on elastic foundation

Abstract: In this investigation, study of the static and dynamic behaviors of functionally graded beams (FGB) is presented using a hyperbolic shear deformation theory (HySDT). The simply supported FG-beam is resting on the elastic foundation (Winkler-Pasternak types). The properties of the FG-beam vary according to exponential (E-FGB) and power-law (P-FGB) distributions. The governing equations are determined via Hamilton\'s principle and solved by using Navier\'s method. To show the accuracy of this model (HySDT), the current results are compared with those available in the literature. Also, various numerical results are discussed to show the influence of the variation of the volume fraction of the materials, the power index, the slenderness ratio and the effect of Winkler spring constant on the fundamental frequency, center deflection, normal and shear stress of FG-beam.

A well-posed Euler-Bernoulli beam model incorporating nonlocality and surface energy effect

Abstract: This study shows that it is possible to develop a well-posed size-dependent model by considering the effect of both nonlocality and surface energy, and the model can provide another effective way of nanomechanics for nanostructures. For a practical but simple problem (an Euler-Bernoulli beam model under bending), the ill-posed issue of the pure nonlocal integral elasticity can be overcome. Therefore, a well-posed governing equation can be developed for the Euler-Bernoulli beams when considering both the pure nonlocal integral elasticity and surface elasticity. Moreover, closed-form solutions are found for the deflections of clamped-clamped (C-C), simply-supported (S-S) and cantilever (C-F) nano-/micro-beams. The effective elastic moduli are obtained in terms of the closed-form solutions since the transfer of physical quantities in the transition region is an important problem for span-scale modeling methods. The nonlocal integral and surface elasticities are adopted to examine the size-dependence of the effective moduli and deflection of Ag beams.

Analytical modeling of ultrasonic surface burnishing process: Evaluation of residual stress field distribution and strip deflection

Abstract: Ultrasonic surface burnishing (USB) process is a promising surface enhancement technique that improves fatigue life of components by exerting work hardening and compressive residual stress of the surface layers. However, USB is a complex process in practice, and there is not an analytical model published to facilitate the design and comprehension of the process. In the present paper an analytical elastic-plastic model was developed to correlate USB process factors to residual stress field (RSF). Also, deformation of strip samples was determined in the analytical approach. Parameters such static force, ultrasonic vibration amplitude, ball material and its diameter as well as ultrasonic vibration frequency were included in the model to find how they influence the residual stress variation and strip deflection. Two types of material constitutive equation i.e. Johnson-Cook (JC) that is sensitive to strain rate as well as Chaboche hardening that is influenced by cyclic loading were considered to find which material behavior is more consistent with experimental results. The experiments have been carried out on two different materials with various initial state of residual stress field (IRSF). It was obtained from the results that residual stress field variation and strip deflection obtained by experiments are consistent well with the values derived from analytical model. Therefore, the model was comprehensively used to find how the USB process factors influence the RSF and strip deflection.

Long-Term Deflection Monitoring for Bridges Using X and C-Band Time-Series SAR Interferometry

Abstract: This study aims to monitor the deformation of bridges, namely in the form of long-term deflection and thermal dilation, using multi-temporal interferometric synthetic aperture radar (InSAR) observations. To precisely estimate the vertical and longitudinal displacements, we used the InSAR time-series technique with multi-track stacks of Sentinel-1 SAR dataset and a single-track stack of COSMO-SkyMed SAR data over two extradosed bridge cases; Kimdaejung and Muyoung bridges between 2013 and 2017. The vertical and longitudinal displacements are estimated using multi-track Sentinel-1 SAR data and orientation angle of bridges, and we converted the displacements into thermal dilation and long-term vertical deflection. From COSMO-SkyMed data, we calculated the horizontal thermal dilation and long-term vertical deflection assuming that they dominantly contribute to the horizontal and vertical displacements, respectively. This assumption appeared reasonable based on the comparison with calculations from Sentinel-1 data. The deflection patterns exhibit downward movements at the mid-spans between towers. The results reveal that both bridges have been suffering long-term deflection over the observation period. Thus, this study verifies the potential to monitor the long-term deflection and implies that the bridges need to be monitored periodically.

A new numerical approach and visco-refined zigzag theory for blast analysis of auxetic honeycomb plates integrated by multiphase nanocomposite facesheets in hygrothermal environment

Abstract: The current work suggests a mathematical model for the dynamic response of sandwich plates subjected to a blast load using a numerical method. The sandwich structure is made from an auxetic honeycomb core layer integrated by multiphase nanocomposite facesheets. The facesheets are composed of polymer–carbon nanotube (CNT)–fiber where the equivalent material properties of the multiphase nanocomposite layers are obtained using fiber micromechanics and Halpin–Tsai equations in hierarchy. The top and bottom layers are subjected to magnetic field and the material properties of them are assumed temperature and moisture dependent. The Kelvin–Voigt model is employed to consider the viscoelastic properties of the structure. The sandwich structure is rested on a viscoelastic foundation which is modeled by orthotropic visco-Pasternak medium. Based on refined zigzag theory (RZT), energy method and Hamilton’s principle, the motion equations are derived. A new numerical method, namely differential cubature method (DCM) in conjunction with Newmark method is utilized for obtaining the dynamic deflection of the structure for different boundary conditions. The effects of various parameters such as blast load, viscoelastic foundation, structural damping, magnetic field, volume fraction of CNTs, temperature and moisture changes, geometrical parameters of honeycomb layer and sandwich plate are considered on the dynamic deflection of the structure. The results show that the magnetic field to the facesheets can be considered as effective parameters to control the dynamic deflection. In addition, hygrothermal condition leads to increase of 24% in the dynamic displacement of system.

Buckling and postbuckling of porous cylindrical shells with functionally graded composite coating under torsion in thermal environment

Abstract: This paper investigates the nonlinear buckling and postbuckling of functionally graded porous circular cylindrical shells reinforced by orthogonal stiffeners resting on Pasternak elastic foundations in thermal environment and under torsional load by an analytical approach. Shells are reinforced by closely spaced stringers and rings in which material properties of the shell and the stiffeners are assumed to be continuously graded in the thickness direction. Basing on the classical shell theory with von Karman geometrical nonlinearity and smeared stiffeners technique, the governing equations are derived. Using the Galerkin method with the three-term solution of deflection, the closed form to find critical load and post-buckling response are obtained. The effects of porosity coefficient, material, temperature, dimensional parameters, stiffener and foundation are analyzed.

Thermal deflection and thermal stresses in a thin circular plate under an axisymmetric heat source

Abstract: Motivated by the need to investigate thermal effects on the deflection and stresses in a thin-wall workpiece during machining, the thermal problem is modeled with an axisymmetric input to emulate t...