Adhesion between metal and composite is key to fiber-metal laminates (FML). CMT (Cold Metal Transfer) welding has been used for hybrid joints that couple metal pin anchoring with adhesive bonding, but this concept has not been extended to FML panels yet. The objective of this work was to employ metal pins deposited by CMT PIN in FML panels. Panels with different pin deposition patterns were compared with panels without pins in terms of impact energy dissipation and damage characterization, and damage tolerance by means of compression and buckling tests after impact. The pins did not make the FML panels more brittle and the change in deposition pattern did not change the capacity to dissipate impact energy. The pins increased the maximum permanent deformation of the panels after impact, especially if less spaced. The in-plane damage areas were larger in the panels with pins, corroborating the damage depth profile results and their connection with impact energy dissipation. The compression and buckling tests indicated that the pins have potential to improve damage tolerance of FML panels, since a lesscatastrophic behavior was observed. Pin anchoring seems to retard propagation of debonding between metal sheets and composite and hold back delamination within the composite.
One of the biggest concerns in automated (mechanized) welding of root passes is the robustness of bead geometry in response to utilized parameters and operational conditions. Skilled welder is able to control the weld pool from visual information, regardless of variation in the root opening (gap) and/or misalignment in the groove. However, there is no sensor and actuator capable of mimicking the ability of the welder to identify the condition of the pool and move the arc to face anomalies present in automated (mechanized) welding. One solution to avoid the typical problems of the root pass (burn-through, for example) is the use of backing.However, this feature increases the cost and production time. Thus, to accomplish automatic welding of root passes it would be necessary to develop a process/technique robust enough to maintain a stable pool even with geometric variations (high-low and misalignment of the joint faces) on the grooves. Then, pipe welding could be carried out with less time and cost.Thus, the objective of this work is to innovatively develop and evaluate, in an original manner, a GMAW technique based on the control of the type of current and torch motion, in order to prevent the collapse of the weld pool under different geometric tolerances of joint preparation. For this, a particular welding power source controlled by motion sensors for synchronizing a type of operating mode of the process with the position of the arc in the joint (sides and center of the groove) was used. To allow a better distribution of heat in the joint, a welding pass was made on the sides of the groove with DCEP polarity pulsed (more heat input) and a central pass was performed with DCEN polarity in constant current mode or Short Circuit Controlled DCEN polarity (less heat input and arc pressure). The evaluation of this process involved verification of parameters affecting weld bead visual quality and process stability. The results show the feasibility of the technique for enabling automatic welding of root passes in the flat position with variations of the root opening (gap) of ± 0.5 mm and with high-low up to 3 mm.
Fiber-metal laminates (FMLs) are key to modern composite structures and metal-composite coupling is crucial to improve their effectiveness. Cold-metal transfer (CMT) PIN welding, in correlated efforts, has been successfully explored as a metal-composite hybrid joining approach. This work proposes a novel development on FMLs, which consists of introducing metal pins welded by CMT PIN for anchoring their metal and composite layers together. Thus, miniaturized FML panels with different pin deposition spacing and patterns are evaluated with emphasis in drop-weight testing followed by buckling and by means of Iosipescu shear test as complement. They are also subjected to cosmetic and preliminary modal analyses. Besides not adding significant weight, the pins does not make the panels more brittle and their distribution does not imply significant effect in the capacity that the panels have to dissipate impact. The panels with pins exhibit a less catastrophic trend, indicating damage tolerance improvement as significantly higher loads at longer axial displacements in buckling test after impact are achieved. The anchoring effect of the pins is confirmed throughout the shear test results. The pins also significantly increase the damping factor of the panels and the changes in their metal surfaces by the CMT PIN process are considered as irrelevant.
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