6 research outputs found
Material elastic waves test exploitation in benefit of composite structure health monitoring
Composite structures suffer from an unsatisfactory behavior to impact damage, which involves conservative designs, high maintenance and repair costs in order to prevent premature failures. These time-consuming operations can be optimized by SHM techniques. In the case study presented, a 48 PZT sensing network has been integrated within two similar composite panels, representative of real aeronautical structures and multi-functional skin concept, approximate size 600mm width and 1650mm length, with substrate made of carbon fiber and thermoset matrix, with two integrated hat stiffeners along the longitudinal direction, and transverse C metallic stiffeners. This sensors network may be used by both active and passive techniques. Passive monitoring consists in the continuous acquisition of high frequency signals during impacts tests on the structure, and thus detecting impact time and location. Active methods require that at least one PZT works as an actuator, thus generating elastic Lamb waves that propagate along the structure. Damage-wave interaction is studied, in such a way that damage detection and location should be possible. The test plan includes different sources of damages from an instrumented impact hammer till air shotgun scenario, taking into consideration BVID levels defined for each part. This paper deals with the analysis of waves traveling through the structure in benefit of event and damage characterization
Environmental effect compensation for damage detection in structures using artificial neural networks and chirplet transform
One of the open problems to implement Structural Health Monitoring techni ques based on guided waves in real structures is the interference of the environme ntal effects in the damage diagnosis problem. This paper deals with the compensation of one of the envir onmental effects, the temperature. It is well known that the guided wave form is modified by temperature variation and causes errors in damage diagnosis. This happens because the waveform has an influence due to temperature changes of the same order tan he damage presence, which makes difficult to separate both effects in order to avoid false positives. Therefore it is necessary to quantify and compensate the temperature effect over the waveforms. There are several approaches to compensate the temperature effect such as Optimal Baseline Selection (OBS) or Baseline Signal Stretching (BSS). In this paper, the experimental data analysis consists on applying the Chirplet Transform (CT) to extract Environmental Sensitive Features (ESF) from raw data. Then, the measure of the environmental condition is related with the ESF training an ANN. The relati onship between the temperature and the ESF is captured by the ANN and then it can be use d to compensate the temperature effect in the guided wave data at a different temperat ure. When the ESF is compensated only the Damage Sensitive Feature (DSF) information is present in the experimental data acquired. Several tests were performed in a range of temperatures under damaged/undamaged conditions and used the experimental data to build and test the models. This method improves the benefits of the OBS(without the need of a big database of baselines, difficult to obtain in complex structures)with the wide range of applicability and simplicity of BSS. Another advantage of this method is its independency from structure arrangement and the type of sensors used for guided waves data acquisition because it is purely data driven. Moreover, it can be used for the simultaneous compensation of a variety of measurable environmental or operation conditions, which affects the guided wavedata acquisition, in example, temperatura and load compensation
Defect detection combining multifrequency ultrasonic guided waves and topological derivative
Ultrasonic guided waves are an attractive alternative to conventional methods.By analyzing these waves, the presence of aws may be detected. Mathematically, this is aninverse problem. A large variety of mathematical methods to solve inverse problems consist inminimizing an instrumental objective function, which gives the difference between the measuredand calculated signals. Among these, the topological derivative describes the sensitivity of theobjective function to in nitesimal inclusions on the material. In this work we investigate thereconstruction of an obstacle buried in an aluminium plate by a non-iterative method based onthe computation of topological derivatives. This is done by extending to the present context someideas by Funes et al. (2016) that gave very good results in the context of the two-dimensionalwave equation. The main purpose is to suitably combine multi-frequency data obtained viapiezoelectric emitters and receivers. In the rst part of the work, the method to detect defectsis described. In the second part, as a proof of the concept, some reconstruction examples areshown
Topological derivative methods for damage detection
This paper deals with the use of the topological derivative as a structural health monitoringmethod, for locating the presence of flaws in an aluminium plate. By minimizing a scalar ob-jective function that measures the least squares difference between the measured and calculatedsignals, flaws can be detected. The topological derivative somehow describes the sensitivity ofthe objective function to localized perturbations of the material properties due to the defectspresence. Here, we reconstruct small defects via the topological derivative by using multi-frequency synthetic data, for several representative configurations of the actuators and sensors,and several defect locations. Among these, some fairly demanding configurations are consideredthat are not accessible to conventional methods, such as actuators and sensors located very closeto the plate boundary and defects located beyond both elongated through-slits and elongatedinclusions of a different material
Defect detection combining multifrequency ultrasonic guided waves and topological derivative
Ultrasonic guided waves are an attractive alternative to conventional methods because the elastic waves emitted at one location travel over along distance. By analyzing these waves, the presence of flaws may be detected. Mathematically, this is an inverse problem. A large varietyofmathematical methods to solve inverse problems consist in minimizing an instrumental objective function, which gives the difference betweenthe measured and calculated signals. Among these, the topological derivative describes the sensitivity of the objective function to infinitesimalinclusions on the material
Material elastic waves test exploitation in benefit of composite structure health monitoring
Composite structures suffer from an unsatisfactory behavior to impact damage, which involves conservative designs, high maintenance and repair costs in order to prevent premature failures. These time-consuming operations can be optimized by SHM techniques. In the case study presented, a 48 PZT sensing network has been integrated within two similar composite panels, representative of real aeronautical structures and multi-functional skin concept, approximate size 600mm width and 1650mm length, with substrate made of carbon fiber and thermoset matrix, with two integrated hat stiffeners along the longitudinal direction, and transverse C metallic stiffeners. This sensors network may be used by both active and passive techniques. Passive monitoring consists in the continuous acquisition of high frequency signals during impacts tests on the structure, and thus detecting impact time and location. Active methods require that at least one PZT works as an actuator, thus generating elastic Lamb waves that propagate along the structure. Damage-wave interaction is studied, in such a way that damage detection and location should be possible. The test plan includes different sources of damages from an instrumented impact hammer till air shotgun scenario, taking into consideration BVID levels defined for each part. This paper deals with the analysis of waves traveling through the structure in benefit of event and damage characterization