Papers by Author: Hang Yin Ling

Abstract: In this paper, fiber Bragg grating (FBG) sensor and piezoelectric (PZT) actuator are used to develop a hybrid system for the evaluation of delamination in glass fiber-reinforced epoxy (GF/EP) composite laminates. The surface-bonded PZT actuator generates ultrasonic Lamb wave in the composite laminates, while the FBG sensor, which is embedded in the composite laminates, captures the Lamb wave signal. Wavelet analysis is introduced to extract signal spectrographic characteristics in the time-scale domain appropriately. Since the propagation characteristics of Lamb wave is altered by the existence of damage in the composite laminates, delamination information can be obtained from the received signal. With the assistance of a signal generation and an acquisition system, this methodology enables active sensing and non-destructive evaluation of delamination in the composite laminates. Experiments have been carried out with GF/EP composite beams to examine the feasibility of the proposed detection technique. The acquired and processed Lamb wave signals corresponding to different delamination sizes are compared.

Abstract: This paper demonstrates the use of ultrasound (US) indentation technique for estimating the mechanical properties of tissue- mimicking phantom composites. A tissue-mimicking phantom composite is used to simulate two-layer soft tissue in human. Investigation on the mechanical properties of the phantom composites is extremely important for the understanding of the viscoelastic behaviours of soft tissues and the validation of our proposed US indentation system. The hand-held indentation probe embedded with a US transducer and a load cell together with a US pulser/ receiver. The output of the whole indentation process can be illustrated as force-deformation curves. The mechanical properties of the phantom composites can be estimated by analyzing the force-deformation curves using genetic algorithm (GA).

Abstract: In recent years, embedded fibre-optic sensors as structural health monitoring devices have been widely used in both civil and aerospace engineering applications. Their small physical size and ability to immunize electromagnetic interference make them ideal sensing devices, which provide highly accurate and reliable strain and temperature measurements for structures. This paper presents a new designed temperature-compensated fibre-optic Bragg grating (TCS) strain sensor for imbedding into cement-based materials to measure their mechanical and thermal strains individually or simultaneously. However, the residual stress generated due to the constrained boundary of a steel tube that is used to protect the sensor, will influence the accuracy of measurement. Therefore, a theoretical model that is used to estimate this stress at different temperature conditions is discussed.

Abstract: A comparison of strain measurement results, from an embedded fibre-optic Bragg grating (FBG) sensor and surface mounted strain gauge, at different vibration frequency ranges and using a clamped-clamped glass fibre composite beam, is presented. It is shown that the FBG sensor is able to precisely measure the peaks at the first-two natural frequency modes compared with the spectrum captured from the strain gauge. The results also demonstrate that the strains measured from the FBG sensor agreed well with the strain gauge at frequencies below 100 Hz. Beyond this value, the actual strain on the beam surface was less than 3µe, and the data extracted from the strain gauge are no longer valid. For a clamped-clamped structure, the longitudinal strain of the beam correlates to its vibration amplitude and excitation frequency. Increasing the frequency results in decreasing the longitudinal strain of the beam and erroneous measurements from the strain gauge resulted. This study provides important information on the feasibility of using embedded FBG sensors as vibration monitoring devices to measure mechanical performance of composite structures.