A New Laser Ultrasonic Inspection Method for the Detection of Multiple Delamination Defects

Abstract

Delamination is one of the most common types of defects for carbon fiber reinforced plastic (CFRP) composites. The application of laser techniques to detect delamination faces difficulties with ultrasonic wave excitation because of its low thermal conductivity. Much of the research that can be found in the literature has only focused on the detection of a single delamination. In this study, aluminum foil was pasted onto the surface of the composite so that it was vulnerable to ablation and could acquire a usable signal. Using a fully noncontact system with laser excitation at a fixed point and a scanning laser sensor, the effects of different aluminum foil sizes and shapes on the wavefield were studied for the composites; we decided to use a rectangle with 3 mm length and 5 mm width for laser excitation experiments. Wavefield characteristics of the composite plates were analyzed with single- and multi-layered Teflon inserts. Taking the time window for standard ultrasonic testing as a reference, the algorithms for localized wave energy with appropriate time windows are presented for the detection of single and multiple defects. The appropriate time window is meaningful for identifying each delamination defect. The algorithm performs well in delamination detection of the composites with one or multiple Teflon inserts.

Multi-mode laser-ultrasound imaging using Time-domain Synthetic Aperture Focusing Technique (T-SAFT)

“…According to previous studies [27] , a focused laser beam can easily cause surface ablation. This problem is more dominant when using a point laser source for which the energy distribution is Gaussian-distributed in space, because when this type of point laser source is focused, the energy density in the central area will be high, leading to ablation excitation.…”

Ultrasound‐Assisted Preparation and Performance Regulation of Electrocatalytic Materials

“…Ultrasonic waves generate a multitude of momentary and hightemperature, high-pressure cavitation bubbles in a liquid medium, sufficient to induce chemical bond rupture and thermal decomposition of organic and inorganic substances within these bubbles. [102][103][104] This facilitates agitation, renewal of non-homogeneous interfaces, and interfacial heat and mass transfer processes. Ample energy is thus provided for the delamination of bulk materials.…”

Guided ultrasonic waves propagation imaging: a review

“…Inspection scanning can be realized using various scanners. An x-y translating stage [11,94,96] can be used, and it is particularly useful when an air-coupled transducer (ACT) is used for inspecting flat specimens. Scanning the specimen instead of the transducer is also possible, as shown in [97].…”

“…A method dedicated to the SSS is pumping more ultrasound energy into the specimen continuously through singlefrequency steady-state generation [42,101] but at the cost of frequency bandwidth reduction. Another method that is only applicable for SSS with fixed-position laser generation is using a sacrifice aluminum foil [96], but the foil must be replaced regularly. Finally, the SNR for SGS can be improved using the diffuse-field concept [118], or measuring the wavefield at the same point using multiple LDVs set at different incident angles [119], or through image synthesizing using multiple receivers at multiple positions [120].…”