Himadri Samajder

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• Schaal, C., Zhang, S., Samajder, H., & Mal, A. K. (2017).

  An analytical study of the scattering of ultrasonic guided waves at a delamination-like discontinuity in a plate:

  . Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 231(16), 2947-2960. doi:10.1177/0954406217700176
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  Interface delaminations between individual plies in a composite, or disbonds of face sheets in honeycomb structures often remain undetected. Using guided ultrasonic waves (Rayleigh and Lamb waves) ...
• Schaal, C., Samajder, H., Baid, H., & Mal, A. K. (2016).

  Corrigendum to ''Rayleigh to Lamb Wave Conversion at a Delamination-Like Crack''

  . Journal of Sound and Vibration, 360, 320-320. doi:10.1016/j.jsv.2015.06.041
• Schaal, C., Samajder, H., Baid, H., & Mal, A. K. (2015).

  Rayleigh to Lamb wave conversion at a delamination-like crack

  . Journal of Sound and Vibration, 353, 150-163. doi:10.1016/j.jsv.2015.05.016
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  Abstract Composite structures require careful monitoring to detect and characterize hidden defects at an early stage of their development so that preventive measures can be taken before the structure loses its load carrying capacity and suffers from catastrophic failure. Ultrasonic guided waves offer an attractive tool for inspecting relatively large plate-like structural components due to the waves׳ large propagation range and sensitivity to defects in their propagation path. Since such waves are affected by geometrical structural features (e.g. stringers) as well as defects (e.g. delaminations), the application of guided waves in real structures requires a good understanding of their interaction with the aforementioned discontinuities. In this paper, a detailed study of the interaction of Rayleigh surface waves with defects in a thick aluminum plate is carried out using numerical simulations and laboratory experiments. The simple aluminum plate is used to demonstrate and analyze the basic characteristics of the interaction phenomena, which are shown to partially result in Lamb wave conversion. Furthermore, the agreement between simulated waveforms and those obtained from experiments are shown, indicating the possibility of applying the techniques to more realistic structures and their use in damage detection systems.
• Schaal, C., Zhang, S., Samajder, H., & Mal, A. K. (2015).

  Analytical Investigation of the Interaction of Rayleigh and Lamb Waves at a Delamination-like Discontinuity in a Thick Plate

  . Structural Health Monitoring-an International Journal. doi:10.12783/shm2015/225
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  In this paper, an analytical framework to analyze the scattering of an incident ultrasonic Rayleigh wave at a delamination-like discontinuity located near the surface of a thick plate is developed. It is assumed that the waves are generated and received using a pitch-catch setup, in which a pair of movable transducers is placed on the surface of the plate. It can be shown that the incident Rayleigh wave is converted into Lamb waves propagating in the thin layer above the defect, and a Rayleigh wave propagating below it. The Rayleigh to Lamb wave conversion at the delamination is quantified in terms of the scattering coefficients. The results from the analytical solutions are compared with those from numerical simulations for a thick aluminum plate, revealing good agreement between them. doi: 10.12783/SHM2015/225
• Ricci, F., Samajder, H., Baid, H., & Mal, A. K. (2013).

  NDE of composite structures using ultrasonic guided waves

  . Proceedings of SPIE, 8695. doi:10.1117/12.2009845
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  Composite structures require a rigorous program of nondestructive inspection and maintenance to detect and characterize hidden defects at an early stage of their occurrence so that preventive measures can be taken before the structure loses its load carrying capacity or suffers from catastrophic failure. Current methods for defects detection in large aircraft and aerospace structures are slow, labor intensive and costly. This is especially true for composite structures where conventional techniques are often ineffective. Ultrasonic guided waves offer an attractive complementary tool for improving inspection techniques in relatively large plate-like structural components due to their large propagation range and sensitivity to defects in their propagation path. Since the waves are affected by the geometrical structural features (e.g. stringers) as well as harmful defects (e.g. delaminations), the application of guided waves in the NDE or SHM of real structures requires a good understanding of these interaction effects. This will help identify the defects from their distinguishing features in the signal in structural components with complex geometry. In this paper a detailed study of the interaction of guided waves with defects in an aluminum plate and a honeycomb composite sandwich structure is carried out using numerical simulations and laboratory experiments. The simpler aluminum plate is used for model validation and understanding the basic characteristics of the interaction phenomena. The agreement between the simulated waveforms and those measured from the experiments are found to be excellent in both cases indicating the possibility of applying guided wave based techniques to more realistic structures.
• Samajder, H., Baid, H., Ricci, F., & Mal, A. K. (2013).

  Lamb Waves in a Honeycomb Composite Sandwich Plate

  . Proceedings of SPIE, 8695. doi:10.1117/12.2010087
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  Composite materials are being used increasingly in advanced aircraft and aerospace structures. Despite their many advantages including high strength to weight ratio, formability and low coefficient of thermal expansion, composites are often susceptible to hidden damage that may occur during their manufacturing and/or service of the structure. Safe operation of composite structures requires careful monitoring of the initiation and growth of such defects before they grow to a critical size resulting in possible catastrophic failure of the structure. Ultrasonic methods using guided waves offer a reliable and cost effective method for defects monitoring in advanced structures due to their long propagation range and their sensitivity to defects in their propagation path. In this paper some of the useful properties of guided Lamb type waves are investigated in an effort to provide the knowledge base required for the development of viable defects monitoring systems in composite structures. Some of our recent research in this area is presented in this paper. The research includes laboratory experiments using a pitch catch method in which a pair of moveable transducers are placed on the outside surface of the structure for generating and recording the wave signals. The recorded signals are analyzed to construct the dispersion and other relevant properties of the guided waves. Theoretical simulations using analytical and numerical methods are carried out and compared with the experimental results. The specific cases considered include an aluminum plate, a woven quasi-isotropic composite panel and an aluminum honeycomb panel with woven composite face sheets. The agreement between the experimental and theoretical results are shown to be excellent in certain frequency ranges, but not for others, providing a guidance for the design of effective inspection systems.
• Idesman, A., Samajder, H., Aulisa, E., & Seshaiyer, P. (2009).

  Benchmark problems for wave propagation in elastic materials

  . Computational Mechanics, 43(6), 797-814. doi:10.1007/s00466-008-0346-3
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  The application of the new numerical approach for elastodynamics problems developed in our previous paper and based on the new solution strategy and the new time-integration methods is considered for 1D and 2D axisymmetric impact problems. It is not easy to solve these problems accurately because the exact solutions of the corresponding semi-discrete elastodynamics problems contain a large number of spurious high-frequency oscillations. We use the 1D impact problem for the calibration of a new analytical expression describing the minimum amount of numerical dissipation necessary for the new time-integration method used for filtering spurious oscillations. Then, we show that the new numerical approach for elastodynamics along with the new expression for numerical dissipation for the first time yield accurate and non-oscillatory solutions of the considered impact problems. The comparison of effectiveness of linear and quadratic elements as well as rectangular and triangular finite elements for elastodynamics problems is also considered.