Acoustic-laser Technique Research Articles

Defect detection of FRP-bonded civil structures under vehicle-induced airborne noise

Fiber-reinforced polymer (FRP)-bonded civil structures have been increasingly used in various construction fields, such as building, bridge, and tunnel. To maintain their designed mechanical performance, the integrity of interfacial bonding should be detected on a regular basis. From many recent laboratory studies, acoustic-laser technique is promising to be applied for identifying the presence of delamination or debonding in FRP-bonded civil structures. However, the defect detection performance of this technique towards real infrastructure encounters a challenging problem related to airborne vehicle noise as the number of cars circulating in urban area increases rapidly. In this study, we deal with the effect of vehicle noise on acoustic-laser technique when applying it in defect detection of FRP-bonded structures. Vehicle sound is found to not only raise the noise floor in measured frequency spectrum but also induce noise-related peaks (below 2000 Hz). Noise from a single passing vehicle causes greater reduction in signal-to-noise (SNR) ratio than that from a platoon of vehicle stream. Additionally, detecting large defect is more vulnerable to acoustic interference of vehicle noise than the small one. A quantitative function between the SNR and the noise level is set up to estimate the performance for defect detection in a construction area near the traffic flow. To handle the vehicle noise issue, a de-noising scheme is proposed and demonstrated for practical defect detection in the field.

Interfacial performance of aramid, basalt and carbon fiber reinforced polymer bonded concrete exposed to high temperature

Externally bonding fiber reinforced polymer (FRP) is an effective approach to strengthen/retrofit concrete structures. However, little is known on bond performance of FRP-bonded concrete under high temperature, impeding the application of FRP in buildings potentially subjected to fire. In this paper, the bond performance of aramid, basalt and carbon FRP-concrete subjected to high temperature (80–300 °C) has been investigated through acoustic-laser technique, macroscale fracture tests and microscale characterization. Results have shown that the deterioration percentages of both peel and shear interface fracture toughness of aramid FRP-bonded concrete are largest under high temperature, followed by carbon FRP-bonded concrete and basalt FRP-bonded concrete. The mechanisms behind different bond performance have been revealed with variations of microscale morphology and chemical decomposition. The results and findings can provide a fair comparison of thermal susceptibility and residual bond performance of various FRP-bonded systems, and contribute to designing FRP strengthening/retrofitting systems under high temperature.

Health assessment of tree trunk by using acoustic-laser technique and sonic tomography

An innovative tree defect detection scheme, which combines acoustic-laser technique and sonic tomography, is studied. A new sensor distribution can be adopted based on the near-surface response detected by acoustic-laser technique, and a more reliable image of the tree trunk can be observed by sonic tomography. By using such hybrid detection scheme, the near-surface defects (bark detachment, cracks, decay) can be revealed at the early stages of defect development. The accuracy of defect detection during advanced tree risk assessment is therefore highly improved. As a newly developed detection technique for detecting the near-surface defect in tree trunk, the measurement results of acoustic-laser technique in tree trunk are comprehensively discussed, especially toward the detectable depth beneath the tree surface. The experimental results demonstrated that the acoustic-laser technique can identify the presence of near-surface defects in a tree trunk that are normally overlooked by the conventional sonic tomography measurements with random distribution of sensors.

A novel approach for near-surface defect detection in FRP-bonded concrete systems using laser reflection and acoustic-laser techniques

Two different methods (i.e. laser reflection and acoustic-laser techniques) for defect detection in fiber-reinforced polymer bonded concrete systems are studied. Both the simulation and experimental results demonstrate that laser reflection technique can instantly and economically identify the presence of defect but cannot quantify the defect size. In contrast, acoustic-laser technique is more sophisticated to be used and it enables a reliable measurement of the defect size. A new and economical detection scheme combining these two techniques is established so that a single or multiple defect region can be rapidly recognized by laser reflection technique and the defect size can be predicted by acoustic-laser technique.

Understanding the effect of temperature on the interfacial behavior of CFRP-wood composite via molecular dynamics simulations

Abstract Carbon fiber-reinforced polymer (CFRP) bonding technique can provide an adequate enhancement to wood structures. Varying temperature levels can affect the strengthening by CFRP, particularly the interfacial behavior of CFRP-wood composite, while the fundamental mechanism is still not clear. This research aims to evaluate the temperature effect on interfacial bonding of CFRP-wood composite, and to explore the fundamental mechanism by using molecular dynamics (MD) simulations. After the specimens are conditioned at various temperature levels, the interfacial bonding performance of CFRP-wood composites is evaluated by acoustic-laser technique and shear test. The results indicate that the bonding is strong at low temperature and deteriorates at high temperature. Meanwhile, the fracture energy measured from the shear test and the MD simulation shows a similar trend, which decreases as the temperature level increases. It is found that the constituent materials deteriorate with increasing temperature, as evidenced by the conformational changes of the modeled epoxy-wood interface, which significantly weakens the interfacial bonding. The finding unveiled from our study demonstrates that the long-term exposure to high temperature can significantly deteriorate the CFRP-wood composite and consequently lead to a structural failure ahead of its service life, which should be considered particularly in tropical and subtropical regions.

The Sensitivity of Acoustic-Laser Technique for Detecting the Defects in CFRP-Bonded Concrete Systems

This paper presents an experimental study to evaluate the sensitivity of acoustic-laser technique in defect detection. The technique is particularly useful towards the detection of near-surface defects in fiber reinforced polymer-bonded concrete by vibrating the material with an acoustic excitation and measuring the vibration signals with a laser beam. However, relatively little is known about the sensitivity of acoustic-laser technique. More research work should be conducted to evaluate the effectiveness of the technique when adopted for defect detection. It is also important to investigate the limits of the technique performance with respect to varying operational conditions so as to determine ways of improving the detectability. For this purpose, operational conditions in terms of acoustic excitation and laser beam incidence are investigated for their effectiveness in detecting near-surface defects and a reliable defect detection scheme using our portable equipment is therefore recommended. This work provides a basis for further improving such technique which can be used in other engineering applications including quality control of materials and product development process.

Remote defect detection of FRP-bonded concrete system using acoustic-laser and imaging radar techniques

Two different remote nondestructive testing (NDT) techniques, the acoustic-laser and imaging radar techniques, are studied for near-surface defect detection in fiber-reinforced polymer (FRP) retrofitted systems. In the acoustic-laser technique, the targeted structure is excited by acoustic waves, while vibration data on a measurement point is remotely collected. In the imaging radar technique, radar signals (electromagnetic waves) are remotely emitted toward the target structure and measured when they are reflected from the structure. Three FRP-bonded concrete cylinders with various defect sizes were fabricated for laser and radar measurements. The pros and cons of these two techniques are described with the support of experimental result.