http://bura.brunel.ac.uk/handle/2438/186 2026-06-25T22:24:07Z 2026-06-25T22:24:07Z Marsh, Benedict http://bura.brunel.ac.uk/handle/2438/33450 2026-06-18T13:42:51Z 2025-01-01T00:00:00Z

Title: AI-enabled flaw detection using multi-sensory data fusion Authors: Marsh, Benedict Abstract: This thesis focuses on the challenge of automated flaw detection by developing a method for surface crack detection that uses a data fusion approach. Flaw detection is needed to detect damage that could compromise structural integrity, leading to further consequences. Identification of flaws is important to analyse the severity and then take action to rectify any issues. Automated approaches using AI are needed to reduce cost as well as to speed up identification and increase accuracy. The presented research developed a method that followed a multi-stage approach, where data from multiple sensors are fused into a 3D representation with the use of AI models. Then, detection is done on that representation to identify the cracks so that further analysis can be done to determine the crack severity. Research contributions are from both stages. First, data fusion improvements for RGB images were worked on, and a novel method for fusing depth data from RGB stereo and LiDAR data was developed. Then, a method for crack identification from RGB-D data using a novel synthetic data generation method was developed. Evaluation of the contributions was carried out to demonstrate the improvements due to data fusion with comparisons to other methods. The key findings included: metric evaluations showing the developed enhanced image fusion technique improved RGB image quality. The developed novel stereo and LiDAR data fusion method showed lower error than either input method alone. The evaluation of the developed novel crack segmentation method using synthetic data showed that models can be effectively trained in the absence of extensive real-world data. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2025-01-01T00:00:00Z Yildiz, Ahmet Serhat http://bura.brunel.ac.uk/handle/2438/33449 2026-06-18T13:43:28Z 2026-01-01T00:00:00Z

Title: The multi-sensor fusion of camera and LiDAR with semantic 3D depth sensing for enhanced perception in autonomous driving systems Authors: Yildiz, Ahmet Serhat Abstract: The development of autonomous driving technology depends on the precise perception of the environment and effective object detection and classification, tracking, essential for safe navigation and decision-making. However, existing multi-sensor fusion methods focus on generating dense depth maps by combining camera and LiDAR data, where distance is represented using colour values. In these depth maps, object shapes are often unclear and small or partially occluded objects are difficult to detect. As a result, it is challenging to accurately detect an object and extract object’s specific distance information. Therefore, this research focuses on detecting specific important objects and directly extracting their distance information from a sparse depth map combined in a more efficient and reliable way. This thesis explores multi-sensor fusion strategies, specifically fusing camera and LiDAR data, to enhance the perception capabilities of autonomous driving systems. While LiDAR sensors provide accurate depth measurements, their limited resolution restricts detailed scene understanding. Conversely, cameras provide much semantic information, but lack depth precision. This research addresses sensor limitations by integrating YOLOv8, a state-of-the-art object detection framework, with LiDAR point cloud data using precise camera–LiDAR projection utilising calibrated transformation matrices. The system is evaluated using the KITTI object detection benchmark, demonstrating improved range resolution and detection robustness under complex driving conditions. This work presents three main contributions: CNN-based traffic sign classification, camera-LiDAR fusion with depth enhancement and projection, and novel depth estimation techniques for distance measurement. Firstly, a Convolutional Neural Network (CNN) model is developed, trained, and implemented on the German Traffic Sign Recognition Benchmark (GTSRB) to achieve reliable classification of traffic signs under varying real-world conditions. The CNN architecture has several convolutional layers with activation functions (including ReLU, Leaky ReLU, and GELU), and each one is followed by a max-pooling layer that systematically reduces the spatial dimensions while keeping important features. After that, the extracted features are subsequently sent to fully connected (FC) layers for classification purposes. The network utilises the Adam optimiser with categorical cross-entropy loss and employs regularisation methods. The study evaluates and compares the performance of different activation functions to analyse their impact on recognition accuracy and model robustness. The final model does a great job of classifying traffic signs in the GTSRB test set, offering a dependable vision input source for further perception tasks in autonomous driving systems. Secondly, this study introduces a complete camera–LiDAR fusion framework that improves depth perception by using calibration data and transformation matrices, which include both intrinsic and extrinsic parameters, to project 3D LiDAR point clouds onto 2D camera images. Using homogeneous coordinate transformations, and matrix multiplication, the projection pipeline carefully maps LiDAR points onto the image plane, creating a sparse depth map that matches the RGB data. LiDAR sensors are naturally sparse and have low resolution, especially in systems with fewer vertical beams. To address this problem, the interpolation method was used to make the depth map denser and emulate higher-resolution point distributions. This upsampling process was used on both bounding box and segmentation mask regions to evaluate the efficacy of various spatial priors. The study provides a foundation for future perception pipelines in autonomous driving systems. Thirdly, a novel distance estimation method is proposed based on fused cam-era–LiDAR data. Several depth extraction techniques are introduced and evaluated, including Point-by-Point (PbyP), Complete Region Depth Extraction (CoRDE), Central Region Depth Extraction (CeRDE), and Grid Central Region Depth Ex-traction (GCRDE). These methods are tested across various object categories (e.g., cars, trucks, bicycles) and occlusion levels (0 to 3) using metrics such as extraction time, accuracy, and Root Mean Square Error (RMSE). Results show that segmentation mask-based methods, especially CeRDE and GCRDE, achieve higher depth estimation accuracy and lower RMSE, particularly for large and occluded objects. However, bounding box methods like PbyP and CoRDE maintain faster processing times, favoring real-time applications. GeRDE provides a balanced solution, offering both high accuracy and computational efficiency. Overall, this thesis contributes to the field of autonomous driving systems perception by demonstrating that deep learning-enhanced sensor fusion and optimised depth extraction can significantly improve the performance and reliability of perception systems under complex real-world conditions. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2026-01-01T00:00:00Z Sui, Wanxin http://bura.brunel.ac.uk/handle/2438/33441 2026-06-18T13:45:15Z 2026-01-01T00:00:00Z

Title: Data privacy preservation and uncertainty estimation in machine learning Authors: Sui, Wanxin Abstract: This thesis addresses the challenges of data privacy in the field of ma-chine learning, with a focus on privacy threats and uncertainty estimation in decentralized learning environments. As data grows exponentially and ma-chine learning models are widely adopted, the challenge of effectively using data while ensuring privacy protection has become paramount. To tackle this issue, the thesis proposes a task-adaptive privacy protection method that combines differential privacy and local differential privacy techniques, dynamically adjusting the noise level to maximize model utility while ensuring privacy protection. Additionally, this thesis explores privacy attacks in decentralized learning, including reconstruction attacks on Decentralized Gradient Descent (D-GD) and Gossip averaging protocols, and proposes cor-responding defense strategies. To improve model robustness, a normalizing flow-based uncertainty estimation method is introduced to detect anomalous predictions and apply additional privacy measures. Experiments demonstrate the effectiveness of these methods in various application scenarios, including real estate valuation and breast cancer detection. Ultimately, this thesis proposes a multi-layer defense mechanism that combines privacy protection and uncertainty estimation, offering stronger privacy protection and model robustness in complex decentralized learning scenarios. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

2026-01-01T00:00:00Z Teyeb, Ahmed http://bura.brunel.ac.uk/handle/2438/33216 2026-04-26T09:58:59Z 2026-01-01T00:00:00Z

Title: Investigation of the use of power ultrasound to improve manufacturing processes in fluid phase Authors: Teyeb, Ahmed Abstract: Advanced manufacturing techniques play a crucial role in ensuring the efficiency and reliabil-ity of electric vehicle (EV) battery packs. In particular, the assembly of busbars and connect-ors—key components for current distribution—relies on joining dissimilar metals like copper and Aluminum. Aluminium-Copper (Al-Cu) alloys are often selected as best choice due to the combination of lightweight and effective conductivity. However, conventional joining methods of these metals often lead to the formation of brittle intermetallic compounds, compromising electrical performance and mechanical integrity. Despite the progressive interest in ultrasonic vibration–assisted laser welding for joining dissimilar metals in EV busbars and connectors, there remains a restriction in foundational understanding of how ultrasonic frequency, ampli-tude, and energy coupling interact with laser–material dynamics to control melt pool physics, intermetallic compound formation, and joint integrity. There is a rare integration of systematic transducer design and tuning with welding process optimization by existing studies, leaving the relationship between transducer characteristics and weld quality largely unexplored. Con-sequently, there is a critical knowledge gap in establishing quantitative, process–structure–property relationships that link ultrasonic transducer parameters to mechanical, electrical, and metallurgical performance of dissimilar-metal laser welds in EV applications. Therefore, this study addresses the use of ultrasound vibration-assisted laser welding as a manufacturing tech-nique, to join dissimilar metals such as Al-Cu, particularly for electric vehicles (EV) battery assembly. The research considers both theoretical and experimental approaches to the mecha-nism involved in formation of cavitation microbubbles and the effects of these agitated mi-crobubbles on the process-structure-property relationship arising from the integration of high-power ultrasonic vibration technology with laser welding. Owing to optimal cavitation bubble formation at ultrasonic frequencies between 20 kHz and 40 kHz – ranges widely adopted in industry for both performance and safety – the study presents the design and development of different transducer types operating at varying frequencies of 20, 28, and 40 kHz. Considera-tion of different experimental setups and varying sets of processing parameters, like transducer angle, transducer distance from metal plate, electrical impedance, and are put in place, to obtain optimal displacement and acceleration amplitudes. The initial section of the work focuses on comprehensive review of metal joining processes; the advancements and challenges associated with EV batteries in recent times and introduces power ultrasound in industrial applications. Also, it delves into the theoretical modelling of formation and collapse of microbubbles caused by the introduction of ultrasonic waves into the solidifying phase of the weld pool. In addition, experimental investigation of structural vibra-tion of lap and butt joints is discussed. Furthermore, the latter section elucidates the mechanical and microstructural analyses of ultra-sonic vibration-assisted laser welded joints. Results showed that the application of high-inten-sity ultrasound significantly disrupted epitaxial dendrite growth, refined grain structure, mini-mized plasma cloud formation, and altered the shape of intermetallic compounds from linear to spherical. The mechanical strength of vibration-assisted joints welded at 28 kHz and at weld-ing speed of 40 mm/s showed a significant increase of 24.5% against the non-vibration-assisted counterpart. The application of high-intensity ultrasound significantly improved weld quality by straightening the weld profile, reducing differential weld width-to-root by 14 - 62%, refining grain structure, and reducing defects such as spatter and plasma cloud formation. Also, SEM results showed that the ultrasonic-assisted laser welded joint was characterized by smaller in-termetallic formations and appeared mostly in the shape of spheres. Furthermore, it was ob-served that the volume density of the secondary phases within the grain boundaries reduced with the application of ultrasonic vibration. The pull test results indicated an approximate 10% increase in load capacity and a 27% increase in extension when vibration was introduced, com-pared to welds produced without vibration. This demonstrates that vibration-assisted welding enhances joint strength and ductility, contributing to improved mechanical performance and reliability of the weld. Overall, the study provides an innovative methodology to address critical issues in industrial and manufacturing processing of dissimilar metals, mitigating the detrimental effects of the formation and presence of hard, brittle intermetallic compounds associated with Al-Cu alloys. This method is highly effective in contemporary material processing of busbars and connectors of EV batteries. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London

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