ABSTRACT
The present study aimed to enhance the efficiency and efficacy of the Al/Cu joint production process implemented by the company VEMID Ltd., Jagodina, Serbia, by attaining sound joints within a very short welding time. For this purpose, the present study aimed at investigating the accuracy and the quality of the continuous drive friction welding (CDFW) process, as well as the optimum combination of CDFW parameters with highest joint efficiency in terms of investigated properties. The accuracy was estimated through an analysis of temperature-time curves recorded during CDFW using an infrared camera. The quality was evaluated through an investigation of the properties of Al/Cu joints produced using different friction (66.7, 88.9, and 133.3 MPa) and forging (88.9, 222.2, and 355.6 MPa) pressures and a constant total welding time (4 s) and rotational speed (2100 rpm). Thermal imaging with an infrared camera demonstrated that the actual total welding time was 15% longer compared to the nominal value. This was attributed to the slow pressure response of the pneumatic brake system. The relative changes in the maximum surface temperature (TMS) during the CDFW process corresponded to changes in welding pressures, indicating the potential of the thermal imaging method for monitoring and assessing this process. A preliminary investigation demonstrated that Al/Cu joints produced using welding pressures less than 88.9 MPa often displayed the presence of non-joined micro-regions at the Al/Cu interface and a significant thickness of interfacial Al2Cu (up to 1 µm). However, when friction pressure was set at 66.7 MPa, an increase in the forging pressure to 222.2 MPa eliminated the presence of non-joined micro-regions and reduced the thickness of Al2Cu to 0.5 µm on the average level. These Al/Cu joints achieved the highest joint efficiencies in terms of strength (100%) and ductility (61%). They exhibited an electrical conductivity higher than 92% of the theoretical value. A further increase in any welding pressure produced similar or deteriorated properties, accompanied by an increase in the consumption of raw materials and energy. Such turn of events was counterproductive to the original goal of increasing the efficiency and efficacy of the CDFW process.
ABSTRACT
In many industrial processes that include fluid flow, cavitation erosion of different engineering structures (pumps, turbines, water levels, valves, etc.) during their operation is expected. Metallic, ceramic, and composite materials are usual candidates considered for application in such extreme conditions. In this study, the idea is to synthesize refractory ceramic material based on talc with the addition of zeolite for utilization as protective coatings in cavitating conditions. Two talc-based refractories with zeolites from two Serbian deposits were produced. The behaviors of the samples in simulated cavitation conditions were examined by an advanced non-destructive methodology consisting of monitoring mass loss and surface degradation using image analysis compiled with principal component analysis (PCA), interior degradation by ultrasonic measurements, and the microstructure by a scanning electron microscope (SEM). Lower mass loss, surface degradation level, and modeled strength decrease indicated better cavitation resistance of the sample with Igros zeolite, whereby measured strength values validated the model. For the chosen critical strength, the critical cavitation period as well as critical morphological descriptors, Area and Diameter (max and min), were determined. A Young's elasticity modulus decrease indicated that surface damage influence progressed towards interior of the material. It can be concluded that the proposed methodology approach is efficient and reliable in predicting the materials' service life in extreme conditions.
ABSTRACT
PURPOSE: Immature teeth are characterized by short roots, thin root canal walls, and open apices, which makes them prone to fracture. The aim was to investigate whether fiber-post placement had an influence on the fracture resistance of endodontically treated immature teeth. MATERIALS AND METHODS: To simulate immature teeth, the apical third of 20 intact mandibular premolars was resected. After the access cavity was prepared, root canals and apices were enlarged. A 4-mm apical barrier was placed using calcium-silicate based material (Biodentine, Septodont). The teeth were then randomly assigned to two groups (n = 10). Root canals in group 1 were sealed using Acroseal (Septodont, France) and gutta-percha, followed by composite resin for the coronal restoration (Evetric, Ivoclar Vivadent). In group 2, fiber posts (FRC Postec Plus, Ivoclar Vivadent) were luted using self-adhesive composite cement (SpeedCEM Plus, Ivoclar Vivadent), followed by the same coronal restoration. The teeth were then subjected to fatigue and static load testing. RESULTS: The average loads (± SD) that led to tooth fracture were: 401.40 ± 296.83 N in group 1 and 636.20 ± 204.95 N in group 2. Unfavorable fractures were noted in 9 specimens from group 1 and in 7 specimens in group 2. No statistically significant difference in fracture resistance or fracture mode was found between the groups. CONCLUSION: Fiber-post placement had no significant influence on the fracture resistance of endodontically treated immature teeth.
