DEVELOPMENT OF AN ULTRASONIC C-SCAN SYSTEM FOR THE DETECTION OF INTERNAL DAMAGES IN COMPOSITE STRUCTURES

• Main Author: Faiziatuzzahria, Yunia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/45646
• Institution: Institut Teknologi Bandung

The application of composite materials in the field of aerospace industry has been increased due to their lightweight, high strength and stiffness, and non-corrosive nature. However, in spite of all their superiorities, composite may suffer from a big diversity of damage types. The barely visible impact damage (BVID) is one of the main concerns in composites as they can reduce the material's compression strength up to 60%. Another continuing concern in composite materials is that the damage evolution has not been fully understood as it has been in the homogenous materials. Hence, a high accuracy damage detection technique is extremely necessary in order to identify the internal damages, keep the structures functioning properly, and in the long run, to avoid catastrophic failures. There are many non-destructive testing (NDT) technique that have been used for the identification and detection of internal damages in composite materials: ultrasonic testing, thermography, shearography, and radiography. Among all those commonly used NDT methods, active ultrasonic testing is the most popular and established one. The ultrasonic testing is based on the detection and the interpretation of the ultrasonic waves reflected by defects. The time interval between one echo to another is called time of flight (TOF). In thin specimen testing, the echo is very closely spaced. Hence, the interpretation requires a suitable signal processing algorithm. The most common algorithm is the Hilbert Transform. This signal processing technique will make the peak finding process and time of flight calculation easier and more accurate. Another important thing to be considered in ultrasonic testing is the coupling mechanism. To provide a uniform coupling mechanism, ultrasonic testing in composite are often done in immersion technique. Not only provides a good coupling mechanism, this technique is also suitable for an automated scanning. In this thesis work, an immersion ultrasonic testing system is built. The system needs main components: transducer driver and immersion tank, signal pulser, and data acquisition system to transfer the raw scanning data. The immersion ultrasonic testing is performed in a 3mm thick hand-lay-up carbon fiber reinforced polymer (CFRP). The tested specimen was made with artificial defects in the form of flat surface hole and aluminum insertion. To enhance the understanding and way of interpreting ultrasonic signals, numerical studies is also performed in this work. The numerical study is carried using a MATLAB toolbox called k-Wave. This toolbox simulates the ultrasonic wave propagation using a pseudo-spectral method. The experimental and numerical study produce A-Scan signals from the tested specimen. The A-Scan result from both numerical and experimental study will be compared to the actual condition. When the damage location can be predicted correctly, the numerical A-Scan then reconstructed to two-dimensional B-Scan and C-Scan images. The reconstruction relies on TOF information of each scan point. Due to instrumentation limitations, the experimental B-Scan and C-Scan cannot be reconstructed. Damage location measured using A-Scan signals from both experimental and numerical study shows good conformity with the actual damage location. For the flat surface hole plate, the maximum error is 5%. However, for the aluminum inserted plate, the experimental A-Scan shows a 11% error. This result mismatch may be caused by the placement of aluminum insertion during the hand lay-up process is not exactly at the center of the plate thickness.