Guided ultrasonic wave array have found many applications in detection and localization of damage in structural health monitoring (SHM) and non-destructive testing (NDT) of plate-like structures. For accurate and reliable monitoring of large structures by array systems, a high number of actuator and sensor elements are often required. In this paper, A minimum redundancy sparse array is adopted to realize high resolution and accurate damage imaging in carbon fiber reinforced polymer (CFRP) laminates, considering the energy skew effect and dispersion of Lamb wave. The Lamb wave wavenumber curve of A0 mode with its geometric relationship is used to calculate the skew angle. In order to avoid the dispersive phenomenon, the array beam-forming and imaging algorithm is presented in frequency domain by applying phase delay to each frequency component. A cross-shaped sparse array is designed according to minimum redundancy linear array. In the experiment, a PZT is used to generate Lamb waves, and a scanning laser doppler vibrometer (SLDV) is used to receive signals by arranging the scanning points in a sparse array. Experimental Results indicated that the proposed sparse array combined with imaging algorithm can locate defects of CFRP laminates with high accuracy while decreasing the processing costs and the number of required transducers. This method can be utilized in critical structures of aerospace where the use of a large number of transducers is not desirable.
Oil lubrication plays an important role in a variety of mechanical equipment. The traditional purification method is difficult to remove the tiny impurity size of 5-15 μm. Three different types of the transducers and its preparation methods were used in the experiment. The phenomenon that the impurity particles in viscous fluid by the acoustic radiation force was moved the wave node position and focused on the center line was observed by the super-depth microscope. The influence factors of the produced SSAW, particle force condition and movement track were analyzed. The experimental results show that the interdigital transducer can be used to generate SSAW, so as to achieve the separation effect of oil and suspended particles.
This paper presents a novel fabrication method of PZT micro-fibers using activated carbon template with the aim of
manufacturing PZT/epoxy 1-3 composites. Porous carbon was first prepared by chemical activation technology. The pore
diameter formed in an activated carbon template is of several microns and lengths are up to several millimeters. These
pores provide a basic platform to grow PZT fibers inside. Then the carbon template is removed at high calcination
temperatures to form PZT micro-fibers. Subsequently, thermo-gravimetric analysis (TG) and differential scanning
calorimetry (DSC) were performed to analyze the process of removing the template as temperature changing. For
manufacturing 1-3 piezo-composites, the PZT fibers were carefully aligned in one direction and infiltrated by epoxy resin.
Based on the observation from X-ray diffraction (XRD) the fibers show a pure pervoskite phase at low sintering
temperature of 950°C. The fibers embedded orderly in the epoxy matrix are smoothly distributed and straightened which
were observed using a scanning electron microscopy (SEM). The diameter of fibers is around several microns with the
length up to a few millimeters, matching well with pores in the template. The new micro-fiber composite material can be
potentially used in a sensor with high directivity in structural health monitoring.
The directivity function of orthotropic piezoelectric composite materials (OPCM) ultrasonic linear array is deduced by
constructing a mathematic model of acoustic field on a new OPCM ultrasonic phased array actuator/sensor, which is
based on the 1-1 mode OPCM. By calculating scatter feature of acoustic field in space and analyzing the effects of
change in structure type and dimension on main lobe and side lobe of array, optimal array parameters of new OPCM
ultrasonic phased array actuator/sensor, such as operating frequency, array interval, array width and array number are
obtained. The developed OPCM actuator/sensor elements are applied in detecting the simulated damage in aluminum
plate. The testing results show that the damage detection precision is further improved by using OPCM ultrasonic
phased array actuator/sensor.
This study focuses on a signal processing method of damage detection for concrete beams. On the surface of the concrete
beam, two sensors are respectively used to excite/receive stress wave signals and catch the reflection information from
the damages inside. In order to improve the signal to noise ratio, wavelet method is adopted to pre-process the raw
signals. Afterwards, the pre-processed signals are interpreted by a prestack migration technique, which is the reverse
problem of the wave propagation, and lead to the profile image of the concrete beam. Results show that with the help of
wavelet de-noising method, the prestack migration method can display the locations and dimensions of the damages very
well. It is also shown that the present method is more suitable for the incline damage than the horizontal stacking method.
Moreover, by comparing the results with different sensor intervals, we analyzed the relatives between the sensor
intervals and the resolutions of the profile imaging.