RESUMO
The present paper provides a solution to enhance the reliability of bonding. The effect of the nonwoven carbon tissue (NWCT) composite adhesive layer on the bonding strength and reliability of aluminum alloy of single lap joints (SLJ) was investigated by embedding NWCT into the epoxy adhesive layer. The bonding strength, Weibull distribution, metallography of cross section, and fracture surface morphology of NWCT specimens were investigated. The results showed that the average bonding strength and Weibull characteristic strength (WCS) of NWCT-reinforced specimen were 16.78 and 17.17 MPa, which increased by 70.2 and 66.7%, respectively, compared with the neat specimen, and the Weibull modulus increased from 11.46 to 22.83, which indicated that NWCT specimens had higher bonding reliability. The mechanism of microcrack formation was obtained by analyzing the cross section of specimen loaded 95% WCS without macroscopic damage. The metallographic section showed that the microcrack of the neat specimen originated from the adhesive-aluminum interface, while the microcracks of the NWCT specimen originated from the interface between short carbon fibers (SCF) and adhesive. Typical failure modes were gained from visual observation and SEM. The failure mode of the neat specimen included more Al-adhesive interface failure, while the NWCT specimen included more internal failure of adhesive-SCFs with the fracture, pullout, peeling, and slippage of SCFs improving the toughness and bonding strength of the adhesive layer. The bridging effect of SCFs in the adhesive layer reinforced by NWCT can even the load and release the stress to improve the bonding reliability.
RESUMO
A temporary confinement of the quaternary tetramethylammonium tetrafluoroborate (TMA BF4) salt among polyamide molecules has been used for the preparation of aliphatic polyamide nylon 6,6 fibres with high-modulus and high-strength properties. In this method, the suppression or the weakening of the hydrogen bonds between the nylon 6,6 segments has been applied during the conventional low-speed melt spinning process. Thereafter, after the complete hot-drawing stage, the quaternary ammonium salt is fully extracted from the drawn 3 wt.% salt-confined fibres and the nascent fibres are, subsequently, thermally stabilized. The structural developments that are acquired in the confined-nylon 6,6 fibres are ascribed to the developments of the overall fibres' properties due to the confinement process. Surprisingly, unlike the neat nylon 6,6 fibres, the X-ray diffraction (XRD) patterns of the as-spun salt-confined fibres have shown diminishing of the (110)/(010) diffraction plane that obtained pseudohexagonal-like ß' structural phase. Moreover, the ß' pseudohexagonal-like to α triclinic phase transitions took-place due to the hot-drawing stage (draw-induced phase transitions). Interestingly, the hot-drawing of the as-spun salt-confined nylon 6,6 fibres achieved the same maximum draw ratio of 5.5 at all of the drawing temperatures of 120, 140 and 160 °C. The developments that happened produced the improved values of 43.32 cN/dtex for the tensile-modulus and 6.99 cN/dtex for the tensile-strength of the reverted fibres. The influences of the TMA BF4 salt on the structural developments of the crystal orientations, on the morphological structures and on the improvements of the tensile properties of the nylon 6,6 fibres have been intensively studied.
RESUMO
A reversible confinement of ionic liquid (IL) among the amide segments has been carried out for the preparation of high-modulus and high-strength aliphatic semicrystalline nylon 6 fibers. In this research work, the suppression or the weakening of the hydrogen bonds during the conventional low-speed melt spinning process is followed by a hot-drawing stage and a subsequent IL extraction of the IL out of the 2% wt IL-confined fibers and an immediate thermal stabilization process for the improvement of the properties of the pristine nylon 6 fibers. The resulted crystal structural developments of the IL-confined fibers are attributed to ultimate molecular orientations, which have contributed to the developments of the overall fiber properties. Here, the influences of the IL on the γ and the α crystal phases, the γ-α transition, the morphological properties, and the tensile properties are investigated. The FTIR reported, experimentally, additional peaks at 1237 cm-1 for the γ crystal phase and at 1417 and 1476 cm-1 for the α crystal phase, in conformity with the theoretical computations. The XRD demonstrated that the conventional low-speed melt spinning can successfully be used to prepare as-spun IL-confined fibers having highly improved properties. The so prepared as-spun IL-confined fibers are found to have a γ phase structure that has a small crystal size and high crystal perfections. Fortunately, the γ-to-α crystal phase transition for the IL-confined nylon 6 fibers can be acquired during the hot-drawing stage (stress-induced phase transformation). Furthermore, the IL extraction process followed by a thermal stabilization process, interestingly, has led to significant increases in both of the tensile strengths and the tensile moduli of the reverted nylon 6 fibers. The values that are found are 8.46 cN/dtex for the tensile strength and 39.09 cN/dtex for the tensile modulus. The structure-property relationships between the IL-confined and the reverted nylon 6 fibers have also been discussed.
