Modal strain energy-based structural health monitoring validation on rib stiffened composite panels

Structural Health Monitoring (SHM) has reached a high importance in numerous fields of civil and mechanical engineering. Promising damage detection approaches like the Damage Index Method, Gapped Smoothing Technique and Modal Strain Energy Method require the structure's mode shapes [1].Long term modal data acquisition on real life structures requires a computational efficient system based on a measuring method that can easily be installed. Systems using the Random Decrement Method (RDM) are composed of a decentralized network of smart acceleration sensors applied for both, triggering and pure measuring. They allow the reduction of cabling effort and computational costs to a minimum.In order to design a RDM measuring network efficiently, an approved procedure for defining hardware as well as measuring settings is required. In addition, optimal sensor positions have to be defined. However, today those decisions are mostly based on expert's knowledge. In this paper a systematic and analytical procedure for defining the hardware requirements and measuring settings as well as optimal sensor positions is presented. The proposed routine uses the outcome of an Experimental Modal Analysis (EMA).Due to different requirements for triggering and non-triggering sensors in the RDM network a combination of two approaches for sensor placement has to be used in order to find the best distribution of measurement points over the structure. A controllability based technique is used for placing triggering sensors, whereas the Effective Independence (EI) is utilized for the placement of non-triggering sensors.The combination of these two techniques selects the best set of measuring points for a given number of sensors out of all possible sensor positions.Damage detection itself is not considered within the scope of this paper.

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Strain-based health indicators for the structural health monitoring of stiffened composite panels

Journal of Intelligent Material Systems and Structures ◽

10.1177/1045389x20924822 ◽

2020 ◽

pp. 1045389X2092482

Author(s):

Dimitrios P Milanoski ◽

Theodoros H Loutas

Keyword(s):

Structural Health Monitoring ◽

Health Monitoring ◽

Mechanical Load ◽

Elastic Solid ◽

Health Indicators ◽

Element Model ◽

Health State ◽

Structural Health ◽

Stiffened Composite Panels ◽

Stiffened Structures

A common defect of composite-stiffened structures is the disbond at the interface between the two constituents (skin/stringer), as a result of inefficient manufacturing process or foreign object impacts in service. Generally, discontinuities within the volume of an elastic solid medium, subjected to mechanical load, cause anomalies on the strain field in the near vicinity of the discontinuity. Utilizing this observation, this work investigates the effect of artificially induced disbonds in the skin/stiffener interface of an aeronautical-grade generic element. A structural health monitoring methodology is developed, leveraging on numerically simulated strains along the stringer foot which aims to assess the health state of the panel as the size of the disbonds increases. The study is implemented using a parametric finite element model generating various disbond scenarios. Longitudinal strain values are acquired at the exact points where in reality actual fiber Bragg grating sensors will be located. Two types of commonly utilized strain-based health indicators are evaluated, and their drawbacks are revealed and discussed. A new health indicator is proposed that proves its capability to monitor growing disbonds while being both load- and baseline-independent.

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A New Optimal Sensor Placement Strategy Based on Modified Modal Assurance Criterion and Improved Adaptive Genetic Algorithm for Structural Health Monitoring

Mathematical Problems in Engineering ◽

10.1155/2015/626342 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 5

Author(s):

Can He ◽

Jianchun Xing ◽

Juelong Li ◽

Qiliang Yang ◽

Ronghao Wang ◽

...

Keyword(s):

Genetic Algorithm ◽

Structural Health Monitoring ◽

Health Monitoring ◽

Sensor Placement ◽

Adaptive Genetic Algorithm ◽

Optimal Sensor Placement ◽

Modal Assurance Criterion ◽

Modal Strain Energy ◽

Structural Health ◽

Computation Efficiency

Optimal sensor placement (OSP) is an important part in the structural health monitoring. Due to the ability of ensuring the linear independence of the tested modal vectors, the minimum modal assurance criterion (minMAC) is considered as an effective method and is used widely. However, some defects are present in this method, such as the low modal energy and the long computation time. A new OSP method named IAGA-MMAC is presented in this study to settle the issue. First, a modified modal assurance criterion (MMAC) is proposed to improve the modal energy of the selected locations. Then, an improved adaptive genetic algorithm (IAGA), which uses the root mean square of off-diagonal elements in the MMAC matrix as the fitness function, is proposed to enhance computation efficiency. A case study of sensor placement on a numerically simulated wharf structure is provided to verify the effectiveness of the IAGA-MMAC strategy, and two different methods are used as contrast experiments. A comparison of these strategies shows that the optimal results obtained by the IAGA-MMAC method have a high modal strain energy, a quick computational speed, and small off-diagonal elements in the MMAC matrix.

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Damage Localization in Complex Composite Panels Using Guided Wave Based Structural Health Monitoring System

ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 2 ◽

10.1115/smasis2011-5069 ◽

2011 ◽

Author(s):

Yingtao Liu ◽

Seung Bum Kim ◽

Aditi Chattopadhyay ◽

Derek Doyle

Keyword(s):

Structural Health Monitoring ◽

Health Monitoring ◽

Composite Structures ◽

Composite Plates ◽

Guided Wave ◽

Damage Localization ◽

Composite Panels ◽

Time Frequency ◽

Structural Health ◽

Damage Location

Knowledge of the damage location in composite structures is a necessary output for both Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Although several damage localization approaches using a triangulation method and Time-of-Flight (ToF) of guided waves have been reported in literature, the damage localization technique is still not mature for composite structures with complex material properties, varying thickness and complex geometries. This paper investigates the development of a new approach for SHM and damage localization using a guided wave based active sensing system. In contrast to the traditional ellipse method, the proposed method does not require the information of structural thickness, ToF, or the estimation of group velocities of each guided wave mode at different propagation angles, which is one of the main limitations of most current ToF methodologies involving composites. This approach uses time-frequency analysis to calculate the difference of the ToF of the converted modes for each sensor signal. The damage location and the group velocity are obtained by solving a set of nonlinear equations. The proposed method can be used for composite structures with unknown lay-up and thickness. To validate the proposed method, experiments were conducted on both composite plates and stiffened composite panels. Eight piezoelectric (PZT) transducers were surface-bonded on each composite specimen and used in four pairs. The PZT transducers in each pair were bonded close to each other. In the PZT array, one PZT transducer from one PZT pair was used as the actuator and the other three pairs were used as sensors. A windowed cosine signal was used as the excitation signal. The locations of the delaminations in the composite specimens were validated using a flash thermography system. The accuracy of the proposed method in localizing delaminations was examined through comparison with the experimental measurements.

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