S. Na

Electromechanical impedance method of fiber-reinforced plastic adhesive joints in corrosive environment using a reusable piezoelectric device

Various nondestructive evaluation techniques exist for structural health monitoring of structures such as acoustic emission, ultrasonic impedance, and impact echo testing. However, these techniques often require expensive and sophisticated hardware with expert operators, limiting their applications to a certain aspect. On the other hand, a relatively new technique known as electromechanical impedance–based structural health monitoring has shown promising results as a local nondestructive evaluation method. To date, only a few numbers of studies have been conducted to develop a reusable lead zirconate titanate sensor for the electromechanical impedance method as majority of researchers have focused on damage detection performance. In this study, a reusable method for the electromechanical impedance method was proposed by using a lead zirconate titanate patch to eliminate the trial-and-error approach to minimize the time requirement for the electromechanical impedance method while reducing the cost for multiple measurements. The proposed reusable device was used to evaluate the damage of the adhesive layer between the fiber-reinforced plastic plates subjected to a corrosive solution while investigating the reliability performance of the device.

A technique for improving the damage detection ability of the electro-mechanical impedance method on concrete structures

To date, a relatively new non-destructive evaluation technique known as the electro-mechanical impedance (EMI) method has shown promising results in local damage detection. However, major issues still exist which are holding back its commercialization. For one, using the EMI method on large concrete structures to detect damage can be very difficult due to the absence of multiple peaks in the impedance signature, resulting in a vague change after subjection to any damage. Such minor variations can increase the uncertainties in damage identification, as other factors may also contribute to the changes in the signature. In this study, a technique is proposed to solve the aforementioned problem to allow a higher threshold value by significantly increasing the sensitivity of the impedance signature when subjected to damage. Experiments have shown that the proposed technique is very effective for concrete, enhancing the damage detection performance of the EMI method.

A multi-sensing electromechanical impedance method for non-destructive evaluation of metallic structures

One of the problems with regard to the electromechanical impedance (EMI) method in the field of structural health monitoring is the relatively high cost requirement of the system. Since the EMI method utilizes a piezoelectric material in small sizes, numerous pieces of equipment are usually required to cover a large area. Thus, in order to compete for the increasing demand for structural health monitoring of components and structures, the technique must be cost effective and large areas need to be rapidly scanned with minimal disruption to the structure’s operation. In this study, a technique is proposed for the EMI method to allow sensing of multiple areas with a single frequency sweep, minimizing both the time and the cost of the method. The principle of the proposed technique is the utilization of different resonance frequencies with the piezoelectric material, allowing one to find the location of the damage. Experiments show exceptional results, bringing the EMI method a step closer for real field application.

Impedance-based non-destructive evaluation of the FRP adhesive joints in corrosive environment with re-usable technique

In this study, a Non-Destructive Evaluation (NDE) method is introduced for evaluating the effects of FRP adhesive joint bond strength subjected to various environmental conditions using electromechanical impedance (EMI) method. The applicability of Fibre Reinforced Plastics (FRP) as a construction material is being globally recognized for their high stiffness and strength to weight ratio and this method proposes a possibility of detecting any strength loss to the adhesive bond without damaging the structure, such as FRP joint itself. PZT (Lead-Zirconate-Titanate) patches were utilized to detect any changes to the bond strength of the FRP adhesive joint exposed to different kinds of environmental conditions by measuring the electrical admittance of the PZT sensors. In addition, a re-usable technique has been introduced with a utilization of magnet to allow multiple sensing of specimens with a single sensor. The results show a possibility of detecting decrease in the bond strength of FRP adhesive using the EMI method.

A preliminary study on the prediction of damaged areas on ordinary concrete and lightweight concrete using electromechanical impedance technique with different frequency ranges

The electromechanical impedance (EMI) method for NDE uses a single piezoelectric material to act as an actuator and a sensor simultaneously, and the EMI method is suitable for structures with complex surfaces. However, this technique still has wide range of problems which needs to be investigated. For one, locating damaged areas on a host structure precisely is known to be extremely difficult as this non-model based technique heavily relies on the variations in the impedance signatures. In this study, an attempt to locate the damaged areas on an ordinary concrete panel and a lightweight concrete panel using bottom ash is carried out by using different frequency ranges. Since the sensing range decreases as the excitation frequency of piezoelectric material increases, one can possibly predict the damaged areas by analyzing the impedance signatures from different frequency ranges. Statistical analysis method such as root mean square deviation (RMSD) is applied to determine the changes of the experimental structures, and the RMSD values of low frequency range and high frequency range are compared to verify the relationship between the frequency range and sensing range. Furthermore, the applicability of this method to locating the damaged areas is investigated on various materials including the lightweight concrete.

A study of reusable electromechanical impedance methods for structural health monitoring of civil structures

Up to date, various studies have been conducted using electro-mechanical impedance (EMI) method on concrete, including monitoring the strength development or to find damage in the structure. Since EMI method utilizes a single piezoelectric material to be used as an actuator and a sensor simultaneously, the method has major advantages compared to other non-destructive testing methods. However the method requires a piezoelectric material to be permanently attached or embedded into a structure. Thus when monitoring multiple structures, the method may become quite expensive. In this study, two re-usable EMI methods conducted by researchers Na et al and Tawie et al are overviewed. The idea of re-usable EMI method is still relatively new, resulting in the reduction of monitoring costs since the same piezoelectric material is used as many times as possible, while ensuring better repeatability and reliability in measurements.

Improvement method for impedance-based nondestructive evaluation on concrete structures using a piezoceramic material

In this study, a relatively new non-destructive evaluation technique known as electro-mechanical impedance (EMI) method has been investigated on concrete structures with large surface area. Although various studies have been conducted on concrete components, a major issue still exists as when using EMI method, damage detection can be very difficult. Due to the property of concrete, only a minor variation in the impedance signature is noticed subjected to damage. Such small change can be hard for one to verify whether the host structure is damaged or not. Since other factors can also change the impedance signature including, temperature changes, humidity and aging of the piezo material, this can increase the uncertainties when differentiating an intact case from a damaged case. In this study, the effect of a technique to enhance the damage detection ability of EMI method is evaluated on concrete structures with the aforementioned problem.