Papers by Keyword: Damage Detection

Abstract: Detectability of damage using Lamb waves depends on many factors such as size and severity of damage, attenuation of the wave and distance to the transducers. This paper presents a detectability model for pitch-catch sensors configuration for structural health monitoring (SHM) applications. The proposed model considers the physical properties of lamb wave propagation and is independent of damage detection algorithm, which provides a generic solution for probability of detection. The applicability of the model in different environmental and operational conditions is also discussed.

Abstract: A hybrid piezoelectric (PZT)/fibre optic diagnostic system has been developed for damage detection in built up composite structures. The hybrid system uses PZT transducers to actuate the structure and fibre optic (FO) sensors to capture the propagating wave. The diagnostic system will then have the advantages of both PZT and FO sensors. The applicability of the system is then tested for detecting an artificial damage at a skin/stiffener interface of a thick composite structure. The response of the FO sensors is then compared to PZT sensors and presented.

Abstract: Load monitoring and damage identification are important tasks in the field of Structural Health Monitoring and are necessary for assessing the structural integrity and predicting the remaining useful life time. Reconstructing unknown force inputs or system parameters usually involves the solution of an inverse problem which is mostly ill-posed and therefore needs regularization. Using prior information about the desired values is advisable for obtaining meaningful solutions. Damages like for example cracks can often be interpreted as spatial singularities, which cause local stiffness reductions of the observed structures. Damage identification is the task of localizingand quantifying these stiffness reductions. On the other hand, unknown structure excitation usually has also some specia lcharacteristics which can be assumed as known apriori, e.g. spatial concentration for singular forces, short time duration for impact loads or narrow frequency bands for harmonic loads. In this case force reconstruction becomes also a localization and magnitude estimation problem. Thischaracteristic information is used to transform the inverse problem into a sparse recovery task. Inthe last years sparsity constrained regularization of inverse problem has attracted a lot of attention inapplied mathematics, especially in the context of compressive sensing.In this contribution it is shown how sparse solution techniques can be applied in monitoring sys-tems and how this will improve the reconstruction results and additionally reduce the number of required sensors.

Abstract: Probability-based imaging which illustrates a distribution map of probability of damage presence in structures is a diagnostic method well established for damage detection in sensorized structures. Since the quality of the recorded signal is directly linked to the reliability of the diagnostic outcome, the assessment of robustness of the damage detection methodology is of high significance. In this paper, robustness and reliability of the current probability based imaging algorithms have been assessed for detecting BVID in a composite panel. Consequently, a proposed outlier analysis and DI probability distribution damage detection algorithm was shown to improve the reliability of the detection method.

Abstract: In this work the optimal configuration of transducers for damage detection and localization has been investigated. A particular interest is given to three optimization methods: mini-max, average Probability of Non Detection (POND) and ray tracing approach, coupled with genetic algorithm. After optimal configurations have been computed for each technique, they are experimentally tested and compared on a composite panel with one or two damages by generating and receiving Lamb waves signals. Damage detection is carried out with the Probability Based Damage Index Method (PBDIM). It was found that, in most cases, the ray tracing method and the average POND technique give better results, with a good detection of damages in comparison to the minimax POND technique, even if the latter seems numerically better.

Abstract: In this study, an effective method based on wavelet transform, for identification of damage on rotating shafts is proposed. The nodal displacement data of damaged rotor is processed to obtain wavelet coefficients to detect, localise and quantify damage severity. Because the wavelet coefficients are calculated with various scaled indices, local disturbances in the mode shape data can be found out in the finer scales that are positioned at local disturbances. In the present work the displacement data are extracted from the MATLAB model at a particular speed. Damage is represented as reduction in diameter of the shaft. The difference vectors between damaged and undamaged shafts are used as input vectors for wavelet analysis. The measure of damage severity is estimated using a parameter formulated from the distribution of wavelet coefficients with respect to the scales. Diagnosis results for different damage cases such as single and multiple damages are presented.

Abstract: Worldwide, the need for structural retrofit is on the rise and the use of Fibre Reinforced Polymer (FRP) composite material systems is becoming an accepted method for repairs, rehabilitations, and strengthening of deficient structures. The great qualities of the FRP materials, certified in the laboratories and confirmed in the fields have all contributed to propel the material as a very promising one, though more works need to be done to certify the fatigue resistance and durability criteria. This research looked at the experimental investigations of Reinforced Concrete (RC) beams strengthened flexurally with externally-epoxy bonded FRP laminates under four point cyclic loads. Dynamic tests are used to assess damages in the FRP-strengthened RC beams under cyclic loads. 6 RC beams of 150 x 200 mm cross-section and length of 2.20m and were reinforced with four 12mm ribbed longitudinal steel bars. Three types of FRP laminates made of high modulus carbon fibre, high strength carbon fibre and glass fibre were adopted. The results confirm that dynamic-based method is an efficient way of assessing damage evolution in RC beams strengthened with FRP laminates under cyclic loads. The results offered a criterion that can be adopted for quick assessment of the efficiency of FRP composite systems before applying them to civil applications.

Abstract: This paper presents a numerical algorithm technique to detect cracks propagated in concrete beams based on the frequency response curve of the beam determined from vibration testing. Impact tests on simply supported reinforced concrete beams were conducted to measure vibration on the beam. The ICATS software was carried out to capture the Frequency Response Functions (FRFs) data at each load step. Utilizing the FRFs data, a numerical algorithm based on finite different methods was performed to compute the different FRFs between undamage and damage beams based on the mode shape curvature square (MSCS) method. The numerical damage location was defined by subtracting the MSCS undamage to damage of beams. Therefore, the accurate damage location was identified by comparing the numerical and observed experimental results.

Abstract: In this paper a novel concept of the MFC based IDT, Tunable Interdigital Transducer (T-IDT), is presented. The proposed transducer is the extension of the MFC based IDT, where the solid comb electrodes are replaced by series of discrete, stripe electrodes which can be connected independently into the groups and connected to the power source. The span between the centers of the electrodes' groups connected to the same phase are corresponding to the nominal wavelength of the wave excited by the transducer. This makes possible matching to different wavelengths without a need of physical changes of the electrodes’ layout.

Abstract: The paper presents the detection and localization of the induced cracks on small specimens based on a modal analysis. The cracks were induced to cement specimens of dimensions 40 × 40 × 160 mm in three different positions. Their position was detected using different techniques based on natural mode shape changes between virgin and damage states of the specimen. The sensitivity of these techniques to the damage level and position was investigated, compared and then discussed in the conclusion.