Advanced Layered Composite Structures for Underwater Acoustic Applications

The detection of underwater objects is one of the most critical technologies, and there have been constant efforts for developing sophisticated sonar systems in naval warfare. Against such efforts, the countermeasure of hiding underwater vehicles, equipment and weapons is another technological challenge. One of the effective countermeasures against sonic detection for the submarines and other underwater objects, such as naval mines, is to employ composite/hybrid materials to prevent ease of detection. Geometrical forms, shapes and layers, along with the tuning of the acoustical impedance, lead to a considerable decrease of the sonar signals via absorption of the sonic waves. In this study, an original and novel design of multi-layered composite/hybrid structure was developed and underwater acoustic testing procedures of reflection, transmission and scattering were applied in 80 kHz100 kHz frequency range. The findings obtained in this study showed that the multi-layered composite/hybrid materials with porous structure possess much lower values in millivolt than steel plates and might be potential candidates as covering and/or casing materials for underwater mines to reduce the acoustical signature against detection and identification.

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Analysis of High Velocity Impact on Composite Structures

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.617.104 ◽

2014 ◽

Vol 617 ◽

pp. 104-109 ◽

Cited By ~ 4

Author(s):

Milan Žmindák ◽

Zoran Pelagić ◽

Maroš Bvoc

Keyword(s):

Carbon Fibers ◽

Composite Structures ◽

Impact Resistance ◽

Leading Edge ◽

Layered Composite ◽

Bird Strike ◽

Out Of Plane ◽

The Matrix ◽

Composite Wing ◽

Considerable Damage

In the recent years a big focus is subjected to the response of structures subjected to out-of-plane loading such as blasts, impact, etc. not only to homogenous materials, but also to heterogeneous materials, such as composites. Such form of loading can cause considerable damage to the structure. In the case of layered composite materials the damage can have several forms, starting from damage in layers up to delamination and full damage of the construction. This paper describes the investigation of shockwave propagation in composite structures caused by impact loading. The composite consists of carbon fibers in a polymer matrix, in which the fibers are much stiffer then the matrix. Finite element simulations were carried out for a “bird” strike impact on a composite wing leading edge. Results show a good impact resistance and good damping abilities of shockwaves.

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A transmittance-based methodology for damage detection under uncertainty: An application to a set of composite beams with manufacturing variability subject to impact damage and varying operating conditions

Structural Health Monitoring ◽

10.1177/1475921718779190 ◽

2018 ◽

Vol 18 (1) ◽

pp. 318-333 ◽

Cited By ~ 5

Author(s):

Aggelos G Poulimenos ◽

John S Sakellariou

Keyword(s):

Damage Detection ◽

Production Line ◽

Composite Structures ◽

Impact Damage ◽

Parametric Representation ◽

Composite Beams ◽

Operating Conditions ◽

Ratio Test ◽

Detection Characteristic ◽

Testing Procedures

Oftentimes, the complexity in manufacturing composite materials leads to corresponding structures which although they may have the same design specifications they are not identical. Thus, composite parts manufactured in the same production line present differences in their dynamics which combined with additional uncertainties due to different operating conditions may lead to the complete concealment of effects caused by small, incipient, damages making their detection highly challenging. This damage detection problem in nominally identical composite structures is pursued in this study through a novel data-based response-only methodology that is founded on the autoregressive with exogenous (ARX) excitation parametric representation of the transmittance function between vibration measurements at two different locations on the structure. This is a statistical time series methodology within which two schemes are formulated. In the first, a single-reference transmittance model representing the healthy structure is employed, while multiple transmittance models from a sample of available healthy structures are used in the second. The model residual signal constitutes for both schemes the damage detection characteristic quantity that is used in appropriate hypothesis testing procedures with the likelihood ratio test. The methodology is experimentally assessed via damage detection for a population of composite beams which are manufactured in the same production line representing the half of the tail of a twin-boom unmanned aerial vehicle. The damage detection results demonstrate the superiority of the multiple transmittance models based scheme that may effectively detect damages under significant manufacturing variability and varying boundary conditions.

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