| Abstract [eng] |
In this work, adhesively bonded dissimilar materials such as aluminium and CFRP which have high interest in aerospace industry because of the joint superior structural characteristics, structure enhancement, and weight reduction were studied. Quality control of the bonding area in such joints is a challenging task due to the absence of a reliable method that can detect adhesive defects with high probability of detection (POD). The aim of the thesis is to develop an advanced technique for the detection of disbonds with improved probability of detection in dissimilar material joints and to measure its performance. First, the existing methods applied for the inspection of layered structures were evaluated. As a result, ultrasonic testing, data post-processing, and calculation of POD were selected to achieve the goal. The fundamentals of wave-disbond interactions in adhesive joints including reverberation, phase change, and reflection magnitudes were investigated. During qualitative evaluation, it was determined that surface/interface curvature of the sample is the major factor influencing the detection of disbonds in adhesive layer. Afterward, a model based on the arrival time of ultrasonic waves was developed to determine time moments of ultrasound reflections from each layer. As a result, the following valuable features were extracted: time of flights and time intervals of the reflected signals, amplitude change, and ratio coefficients of amplitudes at selected time intervals. On the basis of these features, a novel postprocessing algorithm to improve the detectability of disbonds was developed and implemented. As a result, the technique was verified, and it is possible to detect the defect of the size even smaller than 5 mm with 0.88 mm uncertainty. |
