The objective of this work was to analyze the influence of the alkalization and alkalization + silanization (mixed) treatments on the interfacial adhesion and mechanical properties of intralaminar hybrid composites (jute + sisal, jute + curauá, jute + ramie, and jute + glass fiber). Single-fiber tensile tests, fragmentation, and short beam tests were performed. Finally, a SEM analysis was used to study the influence of surface chemical treatments on the morphology of the natural fibers used. SEM images showed that the chemical treatments altered the morphology of the natural fibers. The chemical treatments improved the tensile strength of the fibers studied. It was found that the alkaline treatment is the best suited for jute, ramie, and curauá fibers, while the sisal fiber presented the best results after the mixed treatment. The superficial chemical treatments also affect the interfacial/interlaminar adhesion of the hybrid composites studied here. The best superficial treatments for each type of hybrid composite were: alkaline treatment for jute + ramie and jute + sisal, while for jute + curauá the best results were obtained for the untreated specimens.

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This work has a purpose to evaluate the electrode wear behaviour and the distribution of hardness in a joint welded by resistance spot welding process. The lifetime of electrodes was evaluated by examination of the electrode caps after more than 2000 points with acceptable welds. A microstructural evaluation by optical (OM) and scanning electron microscopy (SEM) was carried out. The microstructure of welded joint is primarily composed of ferrite grains. The microhardness test results indicated a significant increase in hardness in the weld nugget, probably due to the formation of martensite in the fusion zone. The hardness results for the four welding parameters selected at the end of the useful lifetime of the electrode were lower in all regions. The methodology used for parameter selection has highlighted an optimal combination of 200kgf electrodes force and 9 cy welding time (cycles), where more weld points were obtained, thereby increasing the lifetime of the electrode. The cover electrode tends to form brass (Zn + Cu) on the indentation obtained after spot welding, subsequently reducing electrode life. The results indicate the importance of combining welding parameters to reduce the electrode wear.@en