An Adaptive Wood Composite: Theory

A theoretical model is presented for the steady-state and transient behavior of adaptive wood composite plates composed of layers of wood and other piezoelectric materials. Effects of the mechanical, electrical, temperature, and moisture fields are studied simultaneously using a discrete-layer model of the governing equations. These are solved using the finite element method. The computational model employs a one-dimensional Lagrange linear interpolation function in the through-thickness direction and two-dimensional quadratic finite element for the in-plane approximations, treating the displacements, potential, temperature, and moisture as the nodal unknowns. Representative examples of adaptive wood composites are modeled and potential applications are discussed

Layerwise mechanics and finite element for the dynamic analysis of piezoelectric composite plates

Laminate and structural mechanics for the analysis of laminated composite plate structures with piezoelectric actuators and sensors are presented. The theories implement layerwise representations of displacements and electric potential, and can model both the global and local electromechanical response of smart composite laminates. Finite-element formulations are developed for the quasi-static and dynamic analysis of smart composite structures containing piezoelectric layers. Comparisons with an exact solution illustrate the accuracy, robustness and capability of the developed mechanics to capture the global and local response of thin and/or thick laminated piezoelectric plates. Additional correlations and numerical applications demonstrate the unique capabilities of the mechanics in analyzing the static and free-vibration response of composite plates with distributed piezoelectric actuators and sensors

Artificial Crack in Steel: An Ultrasonic-Resonance-Spectrscopy and Modeling Study

The problem of detecting and characterizing cracks in solids is a major research area involving contributions from mathematics, physics, mechanics, and materials science

Mode-selective resonance ultrasound spectroscopy of a layered parallelepiped

The resonance frequencies of mechanical free vibration of a three-layer material calculated by a discrete-layer model and measured by acoustic-resonance methods were compared. The material was composed of an aluminum parallelepiped sandwiched by two stainless-steel parallelepipeds. The discrete-layer model developed here used linear Lagrange basis functions through the layered dimension and continuous global power-series basis functions in the plane perpendicular to the layer thickness. Using such a basis function for the layer-thickness direction allows discontinuity in the elastic properties across the interface between dissimilar layers. The resonance frequencies were measured using two methods: mode-selective electromagnetic acoustic resonance (EMAR) and resonance ultrasound spectroscopy (RUS). The measurements agreed with the calculations typically within 1%. The EMAR method allows the selective detection of vibrational modes possessing particular displacement patterns. This selectivity was supported by the model calculation. Thus, using the EMAR method makes mode identification clear and this is essential for developing and improving the model calculation of such a complicated structure. Internal friction was also measured by the two acoustic methods, which reveals the mechanical-contact effect on the internal-friction measurement in the RUS method.Ogi H., Heyliger P., Ledbetter H., et al. Mode-selective resonance ultrasound spectroscopy of a layered parallelepiped. Journal of the Acoustical Society of America, 2000, 108(6), 2829. https://doi.org/10.1121/1.1323722

Elastic Field and Frequency Variation in Extendable Wind Turbine Blades

The behaviors of tip displacement, maximum stress, and natural frequency of vibration as a function of blade length are investigated for extendable wind turbine blades. A three-dimensional linear elasticity finite-element model of the blade is used along with a typical profile and representative material properties. The quasi-linear response and free vibration behavior are investigated for a sequence of blade geometries. These estimates are intended to give approximate measures of expected changes in the elastic and dynamic field as the operating length changes and provide preliminary guidelines for this novel class of structure

Artificial Crack in Steel: An Ultrasonic-Resonance-Spectrscopy and Modeling Study

The problem of detecting and characterizing cracks in solids is a major research area involving contributions from mathematics, physics, mechanics, and materials science.</p