Priyambada Nayak

Piezoelectric energy harvesting is a promising approach for powering nano- to microwatt-scale electronic devices using ambient vibrations. While most conventional energy harvester designs consider uni-directional excitation, real-world environments often involve multi-directional excitations. In this work, the dynamic and electrical response of a piezoelectric energy harvester (PEH) beam is investigated under bidirectional excitation. Experimental setup is developed such that transverse excitation to the energy harvester is provided by an electrodynamic shaker and axial excitation applied through a smart miniature shaker. A coupler is incorporated into the assembly to transmit axial motion from a miniature shaker to the energy harvester, which introduces an additional resonance mode that modifies the system’s response. The coupler is therefore included in the simulation models. The findings demonstrate that when bidirectional excitation is precisely tuned, can alter system dynamics and significantly improve the energy harvesting potential. It is observed that the voltage improvement compared to unidirectional excitation is 181.15% at the axial /transverse frequency ratio (A/T ratio) = 1.0 and 365.17% at the A/T ratio = 2.0. This work underscores the need to consider both structural interactions and multi-axis vibration inputs when designing and optimizing PEH systems for real-world applications.

Several additive manufacturing processes are capable of fabricating three-dimensional parts with complex distribution of material composition to achieve desired local properties and functions. This unique advantage could be exploited by developing and implementing methodologies capable of optimizing the distribution of material composition for one-, two-, and three-dimensional parts. This paper is the first effort to review the research works on developing these methods. The underlying components (i.e., building blocks) in all of these methods include the homogenization approach, material representation technique, finite element analysis approach, and the choice of optimization algorithm. The overall performance of each method mainly depends on these components and how they work together. For instance, if a simple one-dimensional analytical equation is used to represent the material composition distribution, the finite element analysis and optimization would be straightforward, but it does not have the versatility of a method which uses an advanced representation technique. In this paper, evolution of these methods is followed; noteworthy homogenization approaches, representation techniques, finite element analysis approaches, and optimization algorithms used/developed in these studies are described; and most powerful design methods are identified, explained, and compared against each other. Also, manufacturing techniques, capable of producing functionally graded materials with complex material distribution, are reviewed; and future research directions are discussed.

Although some conventional manufacturing technologies are capable of producing functionally graded materials, only a few additive manufacturing processes are able to build functionally graded materials with complex distribution of material composition. To exploit this unique advantage, we have developed a new methodology capable of optimization of material distribution for three-dimensional parts for any given conditions. Representation of material distribution was done through a new technique by extending the nonuniform rational basis spline surfaces to four-dimensional space. Mori–Tanaka, Levin, and Tamura–Tomota–Ozawa models were employed for the estimation of effective material properties of functionally graded structures. Subroutines were developed in a commercial finite element software to enable the analysis of parts made from functionally graded material. A constrained particle swarm optimization method was selected and implemented to optimize the material composition distribution taking into account the additive manufacturing limitations. As a case study, the material distribution optimization of a functionally graded femur bone plate under thermomechanical loading was considered. The objective was to maximize the safety factor; i.e. the ratio of local yield strength of the functionally graded plate over the von Mises stress. The results showed significant improvement compared to nonoptimal part and demonstrated the efficacy of the proposed methodology.

The aim of this study is to investigate the growth of yield front in post-elastic domain of a thermo-mechanically loaded non-uniform bar with clamped ends. The problem is solved through an extension of the variational method in post-elastic regime. It is assumed that yield stress is the only physical parameter dependent on temperature variation of the bar and all other material properties remain constant corresponding to the value at ambient temperature. The bar is axisymmetric, and during thermal loading, its plane cross sections remain plane maintaining axisymmetry. This analysis of the energy-based variational formulation is carried out by Galerkin’s principle, using a linear combination of sets of orthogonal coordinate functions which satisfy prescribed boundary conditions. The approximate solution additionally needs an iterative technique to find the growth in yield front for the type of prescribed temperature field. The solution algorithm is actualized with the assistance of MATLAB^® computational simulation software. Uniform, linear and parabolic types of temperature distribution over the length of the bar are assumed, and some numerical results in dimensional form are presented and discussed for a clamped-clamped mild steel bar. The temperatures corresponding to onset of yielding and total collapse are considered as markers of yield limit and collapse loads. The temperatures and limit load factors for different bar geometries and temperature distributions are provided. The results reveal that the thermo-elasto-plastic deformation of clamped bar is significantly influenced by the effect of geometry parameters and by the nature of thermal load.

In this study, the influence of thermo-mechanical loading on stresses and deformation states in a rotating disk with varying thicknesses has been evaluated based on a variational principle considering the radial displacement field as unknown. The solutions till the elastic limit yield stress of the material are attained with the assumption of plane stress condition. MATLAB® computational simulation software is used to implement the solution algorithm. The analysis is accomplished for different disk geometries as well as temperature distribution profiles. Limit angular speed of the disks is calculated under thermo-mechanical loading and accounted for in dimensional mode as limit peripheral speed and dimensionless form as normalized limit angular speed. The influence of temperature on yield stress and subsequently on the limit peripheral speed is also studied for any given temperature distribution and results are furnished in dimensional form. The effects of temperature field on other material properties are also studied. The results of some reduced problems are validated with those available in literature and very good agreement is observed. The new results, furnished graphically as design monograms, might prove helpful for the practicing engineers.Keywords: Rotating disks, Variational method, Thermo-elastic stresses

The present paper evaluates the axial strain and stress of a thermo-mechanically loaded non-uniform bar by using a numerical method based on a variational principle. The solutions are obtained up to the elastic limit of the material based on the assumptions that material properties are independent of temperature variation and plane cross-sections remain plane maintaining axisymmetry. This approximation is carried out by Galerkin's principle, using a linear combination of sets of orthogonal co-ordinate functions which satisfy prescribed boundary conditions. The solution algorithm is implemented with the help of MATLAB^® computational simulation software. Some numerical results of thermoelastic field are presented and discussed for different bar materials such as mild steel, copper, aluminium alloy 6061 (Al alloy 6061), aluminium alloy 7075 (Al alloy 7075) and diamond. The effect of geometry parameters like aspect ratio, slenderness ratio and the type of taperness is investigated and the relevant results are obtained in dimensional form. The term bar used in this paper is in generic sense and hence the formulation is applicable for all one dimensional elements, e.g., rods, pipes, truss members, etc.