Estudo da energia de fratura em modo misto de juntas coladas para diferentes tratamentos superficiais no substrato metálico

Abstract

This academic work aims to analyze the mechanical performance of fracture in bonded metal joints under combined tensile (Mode I) and shear (Mode II) loading conditions, known as mixed mode. To achieve this objective, a new mechanical device was developed in the Materials Analysis Laboratory (LAA). This device, integrated with a universal testing machine, allows for varying the ratio between Mode I and Mode II loadings. This approach aims to provide a more comprehensive understanding of the fracture behavior in bonded joints subjected to different loading conditions. Subsequently, fracture tests are conducted on the bonded metal joints, employing different surface treatments. The experimental results from these tests are then used to develop failure envelopes associated with each surface treatment variant. Through this construction, a comparative analysis is performed to examine disparities in the mechanical properties and fracture patterns of the bonded joints, considering different surface treatment approaches. Metallic joints bonded with NVT epoxy adhesive were manufactured in a mold, incorporating two distinct surface treatment methods, namely blasting and MBX, and then subjected to tests on the new device designed for mixed mode evaluation. Finally, the obtained results are thoroughly analyzed, considering that the discussion covers the evaluation of the fracture energy of the bonded joints, using the Compliance-Based Beam Method (CBBM) to construct the failure envelope. This method is independent of crack propagation monitoring, focusing solely on the load P controlled by the universal testing machine, and deformations in Mode I ( ) and Mode II ( ), monitored by LVDTs installed on the device. The results reveal that the developed device is effective in testing the bonded joint in mixed mode, covering various ratios between Modes I and II. Furthermore, the results of joints with surfaces treated by blasting and MBX clearly demonstrate the influence of these surface treatments on fracture resistance and energy dissipation of the adhesive material, providing insights for optimizing material bonding processes and emphasizing the importance of careful selection of surface treatments in the application of NVT adhesive.