Structural health monitoring (SHM) is being widely evaluated by the aerospace industry as a method to improve the safety and reliability of aircraft structures and also reduce operational cost. Built-in sensor networks on an aircraft structure can provide crucial information regarding the condition, damage state and/or service environment of the structure. Among the various types of transducers used for SHM, piezoelectric materials are widely used because they can be employed as either actuators or sensors due to their piezoelectric effect and vice versa. This paper provides a brief overview of piezoelectric transducer-based SHM system technology developed for aircraft applications in the past two decades. The requirements for practical implementation and use of structural health monitoring systems in aircraft application are then introduced. State-of-the-art techniques for solving some practical issues, such as sensor network integration, scalability to large structures, reliability and effect of environmental conditions, robust damage detection and quantification are discussed. Development trend of SHM technology is also discussed.

Piezoelectric Transducer-Based Structural Health Monitoring for Aircraft Applications.

https://repository.tudelft.nl/islandora/object/uuid%3Ae22dcf36-b9be-4b7a-b7fa-4626e8d5f393/datastream/OBJ/download

Methods for the prediction of fatigue delamination growth in composites and adhesive bonds: A critical review

Acoustic isogeometric boundary element analysis

Piezoelectric sensors are increasingly being used in active structural health monitoring, due to their durability, light weight and low power consumption. In the present work damage detection and characterization methodologies based on Lamb waves have been evaluated for aircraft panels. The applicability of various proposed delay-and-sum algorithms on isotropic and composite stiffened panels have been investigated, both numerically and experimentally. A numerical model for ultrasonic wave propagation in composite laminates is proposed and compared to signals recorded from experiments. A modified delay-and-sum algorithm is then proposed for detecting impact damage in composite plates with and without a stiffener which is shown to capture and localize damage with only four transducers.

https://iopscience.iop.org/article/10.1088/0964-1726/23/7/075007/pdf

Assessment of delay-and-sum algorithms for damage detection in aluminium and composite plates

Sponsored by the U.S. National Science Foundation, a workshop on the boundary element method (BEM) was held on the campus of the University of Akron during September 1–3, 2010 (NSF, 2010, “Workshop on the Emerging Applications and Future Directions of the Boundary Element Method,” University of Akron, Ohio, September 1–3). This paper was prepared after this workshop by the organizers and participants based on the presentations and discussions at the workshop. The paper aims to review the major research achievements in the last decade, the current status, and the future directions of the BEM in the next decade. The review starts with a brief introduction to the BEM. Then, new developments in Green's functions, symmetric Galerkin formulations, boundary meshfree methods, and variationally based BEM formulations are reviewed. Next, fast solution methods for efficiently solving the BEM systems of equations, namely, the fast multipole method, the pre-corrected fast Fourier transformation method, and the adaptive cross approximation method are presented. Emerging applications of the BEM in solving microelectromechanical systems, composites, functionally graded materials, fracture mechanics, acoustic, elastic and electromagnetic waves, time-domain problems, and coupled methods are reviewed. Finally, future directions of the BEM as envisioned by the authors for the next five to ten years are discussed. This paper is intended for students, researchers, and engineers who are new in BEM research and wish to have an overview of the field. Technical details of the BEM and related approaches discussed in the review can be found in the Reference section with more than 400 papers cited in this review.

/pdf/recent-advances-and-emerging-applications-of-the-boundary-rwtzpdh3at.pdf

Recent Advances and Emerging Applications of the Boundary Element Method

A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials

Multiscale modeling of polycrystalline materials: A boundary element approach to material degradation and fracture

A meshless local Petrov-Galerkin (MLPG) method is applied to solve bending problems of shear deformable shallow shells described by the Reissner theory. Both static and dynamic loads are considered. For transient elastodynamic case the Laplace-transform is used to eliminate the time dependence of the field variables. A weak formulation with a unit test function transforms the set of governing equations into local integral equations on local subdomains in the mean surface of the shell. Nodal points are randomly spread on that surface and each node is surrounded by a circular subdomain to which local integral equations are applied. The meshless approximation based on the Moving LeastSquares (MLS) method is employed for the implementation. Unknown Laplace-transformed quantities are computed from the local boundary integral equations. The time-dependent values are obtained by the Stehfest’s inversion technique. keyword: Reissner theory, local boundary integral equations, Laplace-transform, Stehfest’s inversion, MLS approximation, static and impact loads

Meshless Local Petrov-Galerkin (MLPG) Method for Shear Deformable Shells Analysis

Based on the variation of poten- tial energy, the element-free Galerkin method (MFGM) has been investigatedfor structureswith crack on the basis of radial base function interpo- lation. An enriched radial base function is intro- duced to capture the singularities of stress at the crack tips. The advantages of the finite element method are remained in this method and there is a significant improvement of accuracy, particu- larly for the crack problems of fracture mechan- ics. The applicationsof the element-free Galerkin method with enriched radial base functionto two- dimensional fracture mechanics in functionally graded materials have been presented and com- parisonshavebeen madewithnumerical solutions using different numerical approaches. Keyword: element-free Galerkinmethod, func- tionally graded materials, cracks, enriched radial base function, static and dynamic load, stress in- tensity factors.

Meshless Method for Crack Analysis in Functionally Graded Materials with Enriched Radial Base Functions

Multilevel optimization including progressive failure analysis and robust design optimization for composite stiffened panels, in which the ultimate load that a post-buckled panel can bear is maximized for a chosen weight, is presented for the first time. This method is a novel robust multiobjective approach for structural sizing of composite stiffened panels at different design stages. The approach is integrated at two design stages labelled as preliminary design and detailed design. The robust multilevel design methodology integrates the structural sizing to minimize the variance of the structural response. This method improves the product quality by minimizing variability of the output performance function. This innovative approach simulates the sequence of actions taken during design and structural sizing in industry where the manufacture of the final product uses an industrial organization that goes from the material characterization up to trade constraints, through preliminary analysis and detailed design. The developed methodology is validated with an example in which the initial architecture is conceived at the preliminary design stage by generating a Pareto front for competing objectives that is used to choose a design with a required weight. Then a robust solution is sought in the neighbourhood of this solution to finally find the layup for the panel capable of bearing the highest load for the given geometry and boundary conditions.

/pdf/robust-design-and-optimization-of-composite-stiffened-panels-45qyw7cq6d.pdf

M.H. Aliabadi

Papers

A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials

Multiscale modeling of polycrystalline materials: A boundary element approach to material degradation and fracture

Meshless Local Petrov-Galerkin (MLPG) Method for Shear Deformable Shells Analysis

Meshless Method for Crack Analysis in Functionally Graded Materials with Enriched Radial Base Functions

Robust design and optimization of composite stiffened panels in post-buckling