Antonio Lopes Gama

Proposal of New Strain Transducers Based on Piezoelectric Sensors

The high sensitivity of piezoelectric materials to mechanical stress has turned them suitable for use in transducers capable of detecting very slight strains. In this sense, the objective of this paper is the proposal of new configurations of strain transducers based on lead zirconate titanate piezoelectric sensors. Aiming practical applications, for the measurement of dynamic strains in the structures of machines, some transducer prototypes have been developed. For their optimization, the finite-element simulations were performed. The experimental results, obtained with a prototype installed in the bearing house of a rotating machine fault simulator, show the effectiveness of these devices to measure slight dynamic strains. In this way, the measurement of the small dynamic strains in this structure can provide useful information about the machine condition.

Application of Piezoelectric Materials for Monitoring the Growth of Defects in Structures

This paper presents the results of an experimental investigation on the use of piezoelectric materials as a technique for monitoring the growth of defects in structures. The method consists of exciting the structure with piezoelectric actuators while recording the electromechanical responses from sensors placed close to the defect. The piezoelectric sensors detect the damage growth or an incipient defect by monitoring changes in the dynamic strain field, induced by the piezoelectric actuator, near the defect. This technique was evaluated through experiments using an aluminum frame structure. Results show that the piezoelectric active method is capable of detecting small changes in defect depth.

Detection of Shaft Misalignment Using Piezoelectric Strain Sensors

This paper presents preliminary results of a new technique for diagnosing shaft misalignment in rotating machinery. The method is based on the measurement of dynamic strains in the bearing house of the rotating equipment using piezoelectric strain sensors (PSS). The high sensitivity to strain of the PSS allows detection of small dynamic strains in the bearing house of rotating machinery which are closely related to misalignment severity. Tests performed in a machine fault simulator showed that the proposed method has advantages over the conventional diagnosis of misalignment using vibration analysis, particularly at low rotational speed, in which little vibration is produced in terms of acceleration. The method is also useful for distinguishing misalignment from unbalance.

Monitoring Fatigue Crack Growth in Fracture Mechanics Specimens with Piezoelectric Sensors

This paper presents the results of an experimental study on the application of piezoelectric dynamic strain sensors for monitoring the crack growth in fracture mechanics specimens. The performance of the piezoelectric sensors was assessed through fatigue crack propagation tests in three point bend (TPB) specimens and compact tension (CT) specimens. Piezoelectric sensors of lead zirconate titanate (PZT) were placed close to the crack edge of TPB specimens and piezoelectric polyvinilidene fluoride polymer (PVDF) was bonded to the back face of CT specimens. The piezoelectric sensors detect the crack growth by monitoring changes in the dynamic strain field of the specimen. In its simplest mode, the piezoelectric sensors behave like dynamic strain gages, with the main advantage of having a high sensitivity which allows detection of lower strain levels and lower increase in crack length.