An Experimental and Numerical Study on the Free Vibration and Viscoelastic Properties Identification of Sandwich Structures

Abstract

Sandwich structures, known for their high strength-to-weight ratio and excellent mechanical properties, have become integral in various engineering applications. In recent years, there has been a growing interest in utilizing viscoelastic materials as cores in sandwich structures due to their unique mechanical characteristics of viscous and elastic nature. Understanding the free vibration behaviour of sandwich structures with a core of viscoelastic material is of primary importance for several reasons. First and foremost, these structures are prone to dynamic loading conditions in real-world scenarios, such as those experienced during transportation, impact events, or operational conditions in aerospace and automotive applications. Free vibration analysis provides insight into the natural frequencies, mode shapes, damping characteristics and the crucial parameters those govern the dynamic response of these sandwich structures. In the pursuit of a thorough understanding, the present research investigates the critical area of free vibration behaviour of three-layer sandwich structures, with a specific focus on beams, plates and shells. The primary objectives are to combine experimental and numerical methodologies, including the application of artificial neural network (ANN) modelling, to analyze the dynamic characteristics of sandwich structures incorporating a viscoelastic material core. The present study considers a symmetric three-layered sandwich structure with face layers of aluminium and a core layer of natural rubber. The choice of materials in the proposed sandwich structure, specifically aluminium as the face layers and natural rubber as the core layer, has been made to create an elastic-viscoelastic-elastic configuration. In the experimental phase of this study, three-layer sandwich specimens with a viscoelastic core are fabricated, and their modal characteristics are investigated through vibration tests conducted with the impact hammer method. The numerical models are developed using the finite element method (FEM), adopting the first-order shear deformation theory (FSDT) to extract the natural frequencies and modal loss factors of these sandwich structures. The mechanical properties of the viscoelastic core, such as the storage modulus and loss modulus, play a crucial role in determining the dynamic behaviour of the sandwich structures. These properties are often frequency-dependent, necessitating a thorough understanding of the material's viscoelastic nature for accurate modelling and prediction of the structural response. A significant focus of the current research is on the identification of viscoelastic material properties of the core layer in the sandwich structures. This has been achieved through the implementation of inverse techniques. Considering the experimental vibration test results of the sandwich structures, optimization methods are employed to identify the constitutive material properties of the viscoelastic core, ensuring that the numerical models accurately reflect the experimental observations. Cut-outs are common in practical applications, and understanding their influence on structural dynamics is crucial for designing resilient and efficient sandwich structures. The study extends its investigation to explore the impact of cut-outs on the free vibration response of sandwich plates and shells. A parametric study is conducted to analyze the effects of shape, size, and position of the cut-out on the dynamic behaviour of sandwich structures. Furthermore, ANN models are developed to predict the free vibration and damping properties of sandwich plates and shells with cut outs. The developed ANN-based prediction models exhibit excellent agreement with the experimental and numerical results, showcasing their efficacy in capturing the complex relationships of the system parameters. Additionally, a graphical user interface (GUI) is designed using the developed ANN models to provide a user-friendly tool for predicting the modal characteristics of the sandwich structures with cut-outs.