Structural Health Monitoring and Resonance Frequency Analysis of Internal Damage In Isotropic Laminated Plates

Abstract

Composite plates are a structural solution that enhances material stiffness and reduces structural weight. For instance, the introduction of glass fiber-reinforced materials in wind turbine blades improves tensile strength in specific directions, thereby reducing system weight and increasing power generation efficiency. Additionally, composite plates enhance structural rigidity due to the directional nature of the interlayer fibers. However, the anisotropic nature of composite materials can lead to internal damage when external stresses are not aligned with the fiber distribution. In practical systems, forces act in various directions, posing fatigue and damage risks to the inner layers of composite plates. The objective of this study is to initially assume isotropic properties for all plates to simplify the complexity of theoretical validation. By applying Kirchhoff's plate theory, internal force equilibrium equations are established for intact and damaged plates. Subsequently, the force equilibrium equations for all plates are summed to derive the governing equation for out-of-plane displacements of isotropic plates. Neglecting material damping coefficients, the out-of-plane motion of plates is assumed to follow harmonic motion, and the resonant frequency of the structure is calculated and compared with that of a damaged structure. Through this research, a better understanding of the impact of structural integrity and internal damage on resonant frequency response can be achieved. Further investigations will focus on exploring the effects of different stacking sequences and proposing methods to calculate the influence of resonance frequencies for various plate configurations. This will contribute to improving the design and analysis of laminated structures, providing more accurate and reliable guidance to ensure structural safety and performance.