Kalyan S. Nadella

Numerical simulation of wave propagation in composite plates

Composite structures are being extensively used in modern industrial applications due to their superior physical attributes, thus necessitating the need for structural health monitoring (SHM) systems to ensure their structural integrety. Guided wave (GW)-based methods are an obvious choice because of their ability to travel long distances through the thickness of the composite structures. In this work, local interaction simulation approach (LISA), a finite difference (FD)-based numerical method, is used to study the GW propagation characteristics in laminated composite plates. The iterative equations, which form the core of the LISA method, have been derived for orthotropic materials with in-plane rotation. Simulation results for uni-ply and quasi-isotropic graphite/epoxy laminates are used to demonstrate the capabilities of the advanced equations.

Hybrid Global Matrix/Local Interaction Simulation Approach for Wave Propagation in Composites

This paper presents a hybrid approach to model guided wave propagation in composite laminates. The global matrix approach is used to determine the displacement field surrounding a piezoelectric actuator. The displacement field is then enforced in a specified region of a numerical model that employs the local interaction simulation approach. This hybrid approach improves upon previous local interaction simulation approach methods that prescribe in-plane displacements within the actuator profile to model actuation. Additionally, it circumvents the problem of modeling nonrectangular actuators in the Cartesian discretization in the local interaction simulation approach. Results show that the hybrid model outperforms previous local interaction simulation approach models when considering actuation from circular, square, and composite long-range variable-direction emitting radar actuators. The hybrid model produces wave propagation time histories that closely match the baseline global matrix method and successfu...

Characterization of guided-wave propagation in composite plates

The increasing use of composite materials in multiple engineering applications has emphasized the need for structural health monitoring (SHM) technologies capable of detecting, locating, and classifying structural defects in these materials. Guided wave (GW) methods offer an attractive solution for SHM due to their tunable sensitivity to different defects and their ability to interrogate large structural surfaces. The complications associated with the material anisotropy and directionality in composites result in an increased need for accurate and efficient simulation tools to characterize GW excitation and propagation in these materials. This paper presents a theoretical model based on three-dimensional elasticity to characterize GW excitation by finite-dimensional transducers in composite laminates. The theory uses an eigenbasis expansion for a bulk transversely isotropic material combined with Fourier transforms, the global matrix approach, and residue theory to find the displacement field excited by an arbitrarily shaped finite-dimensional transducer. Experimental results obtained in a cross-ply composite laminate are used to assess the accuracy of the theoretical solution.

Simulation of Guided Wave Propagation in Isotropic and Composite Structures using LISA

This paper presents a local interaction simulation approach (LISA) numerical method to examine the guided wave propagation in plate and sandwich structures. The method is based on recursive iterative equations, derived from the elastodynamic equilibrium equations. Derivation of the iterative equations with varying spatial discretizations is presented for a generalized orthotropic medium in non-principle axis frame. The new iterative equations have the capability to model generic laminated composite plates and sandwich composite structures. The results address some of the propagation aspects in isotropic plates, laminated composite plates, and simple composite foam core sandwich.

Effect of piezoelectric actuator modeling for wave generation in LISA

The local interaction simulation approach (LISA), a finite difference based numerical method, has been proven to be efficient in modeling guided wave (GW) propagation in isotropic and composite laminated structures. Recently, the LISA framework has been augmented to incorporate the piezoelectric material directly in the formulation so to more accurately model the transducer effects in the GW generation. This paper presents a study to assess the importance of the actuation modeling from surface-mounted piezoelectric actuators in LISA. Actuation modeling includes the prescribed displacements (either in plane or out of plane) that are commonly found in the literature, as well as the direct modeling of the piezoelectric material of the actuator with prescribed electric potentials. The study is carried out both for isotropic and composite laminated substrates. Numerical and experimental results are used to characterize the quality of the actuator modeling options.

Piezoelectric coupled LISA for guided wave generation and propagation

Recently there has been an increased utilization of composite structures in aerospace and other industries due to their superior physical attributes compared to traditional metallic structures. This has spurred the need for structural health monitoring (SHM) systems to support structural integrity. Guided wave (GW) based techniques for health monitoring have shown to be reliable and promising. The local interaction simulation approach (LISA), a finite difference based numerical method, has been proven to be efficient in modeling GW propagation in isotropic and composite plate structures. Piezoelectric actuators are traditionally used to generate GW in structures. In this work, iterative equations which form the basis of the LISA method are derived for a generic orthotropic laminated structure with a piezoelectric actuator on top. The piezoelectric actuator is modeled by considering the coupled electromechanical equations.

Hybrid Global Matrix/Local Interaction Simulation Approach for Wave Propagation Simulation in Composite Laminates

This paper presents a hybrid approach to model guided wave propagation in composite laminates. The global matrix approach is used to determine the displacement field surrounding a piezoelectric actuator. The displacement field is then enforced in a specified region of a numerical model that employs the local interaction simulation approach (LISA). This LISA Hybrid approach circumvents the problem of modeling non-rectangular actuators in the Cartesian discretization in LISA by using the global matrix method to characterize the actuator’s influence on a cut-out region surrounding it. Results show the LISA Hybrid model outperforms previous LISA models that enforce in-plane displacements on the surface of the plate. The LISA Hybrid model produces wave propagation time histories that closely match the baseline global matrix method and successfully capture directional effects resulting from the anisotropic nature of composite plates. Results for aluminum, cross-ply, unidirectional, and quasi-isotropic plates show dependence on the in-plane discretization size, but that dependence is less pronounced for the cross-ply case.

Local interaction simulation of guided-wave propagation in composite plates

Composite structures are being extensively used in the modern industries because of their superior strength to weight ratio, high stiffness, and long fatigue life. The ability to tailor the material properties along different directions also increases the avenues of composites material application. The ever-increasing demand for composite structures and the need to ensure the structural integrity necessitates the development of sustainable and efficient structural health monitoring (SHM) systems. Guided wave (GW) methods offer an attractive solution for SHM due to their tunable sensitivity to different defects and their ability to interrogate large structural surfaces. Because of the anisotropy present in the composite materials, the development of the SHM methods is significantly more complex and challenging than in the case of isotropic materials. This paper presents numerical simulations based on the local interaction simulation approach (LISA) to characterize the propagation of GW in laminated composite plates.