Formulation and experimental validation of space-fractional Timoshenko beam model with functionally graded materials effects

In this study, the static bending behaviour of a size-dependent thick beam is considered including FGM (Functionally Graded Materials) effects. The presented theory is a further development and extension of the space-fractional (non-local) Euler–Bernoulli beam model (s-FEBB) to space-fractional Timoshenko beam (s-FTB) one by proper taking into account shear deformation. Furthermore, a detailed parametric study on the influence of length scale and order of fractional continua for different boundary conditions demonstrates, how the non-locality affects the static bending response of the s-FTB model. The differences in results between s-FTB and s-FEBB models are shown as well to indicate when shear deformations need to be considered. Finally, material parameter identification and validation based on the bending of SU-8 polymer microbeams confirm the effectiveness of the presented model.

Energy Resource for a RFID System Based on Dynamic Features of Reddy-Levinson Beam

Understanding the effect of design parameters on resonant frequency variation is a critically important aspect of piezoelectric energy harvester device design. As a first step in more accurately investigating the performance of a fixture designed for targeted RFID tag communication that also utilizes an energy harvesting application, this paper analyzes the variations in resonant frequency of a higher-order beam based on Reddy-Levinson theory (RLBT) under rotation effects. A long-term goal of this research is to implement an effective energy harvester on the RFID system. Part of the experimental RFID test fixture can be modeled as a beam (or beam element); thus, understanding the resonance frequency variations due to shear deformation and rotation effects is an important first step in obtaining information about the efficacy of the fixture in serving as an energy harvester. Investigating the performance of a beam also provides valuable information about the maximum power, frequency bandwidth, and tuning ability of the device that can be expected from an analogous energy harvester. For the first time, the resonant frequency variation of a rotating thick beam is investigated. Specifically, RLBT is used to verify the effects of shear deformation upon resonant frequency, and a coupled displacement field is utilized to enable tuning the potential piezoelectric energy harvester to low-input excitations by means of constraining translational and rotational movements of the system based on a linear constraint equation. Navier’s method as an analytical-numerical method is adopted to discretize the continuous system and to find resonant frequencies, respectively. Results reveal the significance of beam thickness and rotation effects of the proposed model for the purpose of minimizing energy usage. Current results are compared and verified numerically with available benchmarks to confirm a satisfactory level of accuracy. The proposed model, which is based on a coupled displacement field, can also be used to design other piezoelectric electro-mechanical-systems; e.g., vibration isolators, and vibration controllers. In other words, in an energy-scavenging system, a fundamental understanding of parameters affecting the resonant frequency can be accomplished through the presented analysis. The proposed model highlights the fact that, by adopting a proper speed factor, tuning the piezoelectric energy harvester to low-input excitations is possible. Additionally, it is observed that the rotation effect on the resonant frequency is more severe than effects of slenderness ratio. Finally, in this paper an improved model is proposed to capture the shear deformation effect, particularly for thick-beam energy harvesters, with the capability of tuning to low-input excitations.

Finite Element Model for Prediction of Ground Vehicle Mobility Over Vegetation Covered Terrains

A finite element vegetation model is presented for predicting the dynamic interaction of ground vehicles with vegetation. The purpose of the model is to predict ground vehicle mobility over vegetation covered terrains. The types of vegetation can range from small diameter highly compliant stems to large stiff trees. Those include various types of vegetation such as grass, crops, shrubs/bushes, small trees, and large trees. Mobility measures which can be predicted include maximum safe vehicle speed along a specified path, tire slip, and fuel consumption. The ground vehicles are modeled using high-fidelity multibody dynamics models. The vegetation stems are modeled using an arrangement of thin and/or thick beam finite elements. The thin beam model uses the torsional spring beam formulation for small flexible vegetation and only includes the axial and bending beam responses. The thick beam model includes axial, bending, torsional, and shear beam responses and uses a lumped parameter beam element which connects two rigid body type nodes. The vegetation model includes the effects of normal contact and friction with the vehicle and between stems, stem breaking, and stem aerodynamic forces.

Dynamic analysis of thick beams with functionally graded porous layers and viscoelastic support

This study presents dynamic responses of a composite thick beam with a functionally graded porous layer under dynamic sine pulse load. The boundary conditions of the composite beam are considered as viscoelastic supports. Three layers are considered, and face sheet layers have porous functionally graded materials in which the distribution of material gradation through the graded layer is described by the power law function, and the porosity is depicted by three different distributions (i.e., symmetric distribution, X distribution, and ◊ distribution). The layered composite thick beam is modeled as a two-dimensional plane stress problem. The equation of motion is obtained by Lagrange’s equations. In formation of the problem, the finite element method is used with a 12-node 2D plane element. In the solution process of the dynamic problem, a numerical time integration method of the Newmark method is used. In numerical analyses, influences of stiffness and damping coefficients of viscoelastic supports, material gradation index, porosity parameter, and porosity models on the dynamic response of thick functionally graded porous beam are investigated under the pulse load.