Papers by Keyword: Damage Detection

Abstract: Structural Health Monitoring (SHM) is now a fundamental idea in our daily lives. It is related to many disciplines, including Civil Engineering, Aerospace Engineering, Mechanical Engineering, and Marine Engineering, among others. It provides a diagnosis of the structure's state at every moment of its residual life, improves understanding of structural behavior, and detects any change that occurs to any component of it or for the entire structure via some devices (Sensors) that may be wired or wireless, incorporating micro and nanotechnology in their components putting on it or on the part under study. These sensors are data collectors that send data to a laptop or computer for processing via a communication system. These data assist decision-makers in determining the structure's residual life and whether it requires maintenance or rebuilding. The wireless SHM system of a Tahya Masr cable-stayed bridge is developed in this study using Resensys SenSpot^TM Sensors. The following approaches are suggested to achieve the goal. Wireless sensors were used to measure strain and monitor vibration, strain, inclination, tilt, temperature, and humidity. These measurements help to develop a reference data set that can be used to monitor and detect changes in structural behavior that indicate damage. This study successfully assessed the viability of Resensys SenSpot^TM wireless, and it provided a brief overview of vibration- and impedance-based SHM techniques appropriate for the cable-stayed bridge's pylon system. Finally, the Tahya Masr cable-stayed bridge in Egypt served as a successful test site for the smart sensor's applicability.

Abstract: Piezo-chromic oxides are able to mark pressure or strain by a drastic color change. In this paper, CoMoO4 molybdate compound and related thermoset composites were prepared in lab. The distribution of CoMoO4 oxide in the thermoset matrix was first investigated via SEM. Moreover, the effects on the thermal and mechanical properties with the addition of CoMoO4 oxide were further analyzed. The piezo-chromic characteristic for CoMoO4 incorporated thermoset composites were verified with compression test. The color change can be clear visualized at a strain level close to the yield point of the composite blends. This study has the potential to open new directions to piezo-chromic polymeric materials as early damage detector.

Abstract: In-situ monitoring method of FRP (Fiber Reinforced Plastics) by built-in sensors is a key technology for developing future and high-reliable composite structures. The Rayleigh scattering-based distributed optical fiber sensor has high spatial resolution of 1mm and good embeddability into FRP and then it can be considered that the sensor is very suitable to in-situ monitoring of FRP. In the present paper, process monitoring and damage identification of FRP were conducted. In the process monitoring, flow-front of silicon oil impregnating into glass textile during VaRTM (Vacuum-assisted Resin Transfer Molding) process was measured. Comparing to visual observation results, it appeared that the maximum slope position of strain distribution showed flow-front position. In the health monitoring, damage identification of cross-ply GFRP laminates with delamination by the attached distribution optical fiber sensors was carried on. From the results, it was found that the strain varied largely on the delaminated section and then the delamination was detectable from the surface strain distribution measured by the optical fiber sensor.

Abstract: In this work, the applicability of structural health monitoring (SHM) technique for damage detection in two composite mono-stringers representative of composite fuselage are investigated. The two different manufacturing technologies are co-curing and co-bonding of composite mono-stringers to the skin. The panels were then impacted at the foot of the stringer to cause Barely Visible Impact Damage (BVID). Piezoelectric transducers were surface mounted on the mono-stringers, guided wave measurements before and after impact were taken and used for detecting damage based on Weighted Energy Arrival Method (WEAM).

Abstract: It is well known that composite materials are founding increasing applications in the transport field thanks to their high strength to mass ratio. However, their use in primary structures is very challenging because of their high sensitivity to in-service damages and manufacturing defects. As a result, the current adopted damage tolerance approach leads to the oversizing of such structures. Structural health monitoring systems, aimed to the real time damage detection, can provide several benefits in terms of lightweight of the structures, maintenance operations and inspection costs. This paper deals with the use of the Probability Ellipse (PE) method, based on the propagation of ultrasonic guided waves on a composite winglet of a small aircraft. The PE method estimates the probability of the presence of the damage in the monitored area, starting from the knowledge of selected damage indexes for each sensors-path. The winglet, equipped with piezoelectric sensors, usable as both actuating and receiving devices, has been numerically and experimentally investigated under several configurations, varying the actuator location. Sensitivity analysis has been performed to assess the effectiveness of the PE method. The accuracy of the PE method in detecting both location and damaged area is herein discussed.

Abstract: Thanks to their high damage detection sensitivity and low requested power consumption, guided-waves (Lamb waves) have been increasingly used in the last years to monitor the structural integrity in primary and secondary composite structures. The monitoring of the structural health through the propagation of Lamb waves in composite structures is notoriously complex and, for this reason, the development of a prediction model can be a helpful tool for the improvement of Structural Health Monitoring (SHM) systems. Finite Element Method (FE) appears to be the best candidate for such type of simulation. However, since Lamb waves propagation depends strictly on the local material properties of the medium they propagate through, their numerical characterization is a thorny phase. Real composite components are usually affected by the presence of a large number of voids and defects, which cannot be reproduced in numerical models; this leads to a variability of the mechanical properties of materials, with particular reference to elastic moduli and density. These aspects get really ambitious the development of a well-established FE model. In this paper, a design of experiment (DOE) has been carried out to numerically investigate on the effects of the material properties variability on guided-waves time of flight.

Abstract: Conducting surveys of multi-storey buildings is a laborious task, because large volumes of visual and instrumental research should be carried out. Reduction of labor costs with an increase in the reliability of information about the state of damage and technical condition is an actual scientific and practical task. One of the ways to solve it is to use non-destructive vibration diagnostic methods. The purpose of carrying out diagnostics with the use of vibration based damage detection methods is to search for damages in structural elements that can cause the deviation of the dynamic parameters of a structure from calculated ones. Determination of the dynamic parameters of the structure, in particular natural frequencies and mode shapes of mechanical systems, is one of the most important tasks that allows obtaining integral information about the state of a structure. This article presents the results of calculations for the localization of slabs defects in a multi-storey building with a transverse crack, span L = 4.5 (m), height H = 0.2 (m), with prestressed reinforcement d = 0.05 (m). Vibration based Damage Index method was used to localize the defect. During the study, reliable localization values of the defect area of the slab were obtained, this indicates that the vibration method for determining the damage index with a sufficient degree of accuracy allowed predicting the site of damage to the structure.

Abstract: Piezochromic materials have attracted a great deal of attentions for decades by the virtue of detecting mechanical damage in advance and avoid dangerous failure. However, several vital issues, such as the structure-properties relationship of aggregation-induced emission (AIE), still remain unclear, which impede the discovery of novel piezochromic luminescent materials with excellent properties. Here, the research on the mechanism of AIE polymers will be deeply reviewed, and other types of piezochromic systems will be introduced in order to suggest the future design of novel piezochromic device

Abstract: This work reports on damage detection in a composite plate with an opening. A composite plate with an opening is manufactured and sensorized to investigate the effect of the opening on the wave propagation as well as the reliability of the delay and sum damage detection method in the presence of the opening. The plate was then impacted with a drop mass to cause barely visible impact damage and sensor data are gathered to analyze the diagnosis. The results show that if all the sensors around the opening is used, even though damage can be detected, it cannot be localized accurately. Further investigation shows that by localizing the sensor network to the one close to the damage area (multi-level detection), damage can be both detected and localized reliably. The results of the detection are also compared with the maximum coverage area map to validate the optimal sensor selection strategy.

Abstract: As structural health problems are becoming more and more important, a neural networks model is introduced to detect structural damage. The structural modal flexibility matrix can be accurately constructed by the natural frequency and modal information. All elements of changes in the modal flexibility matrix are looked on as inputs of the networks. Damage locations and extents are both considered with different outputs in the present study. A simply supported truss structure is studied with different damage cases. To localize damage, one case is chosen as location input/target pairs to train the present BP network model. But to identify damage extent, two cases are chosen as extent pairs to train. Although modals of BP neural networks with different outputs are presented for different damage detecting schemes, it is more difficult to ascertain damage extent than location. The results indicate that the present BP neural network modal can effectively detect damage of structures with changes in the flexibility matrix between the intact and the damaged cases.