The ionic polymer–metal composite (IPMC) is a new practical engineering material that, it has a wide range of capabilities in both dry and liquid environments. IPMC is a new candidate for diaphragms in micropump devices, micro and Nano robotic applications. IPMCs are regarded as a capable actuator for transportable applications, however, the unique combination of electrochemical and mechanical properties that they possess, such as back-relaxation, restraint their use in real-life applications. There have a lot of attempts to understand and model the IPMCs properties and build a whole prototype that can be used, with certainty, in different robotic, control, and medical applications, yet, till now, it seems that the dehydration and back-relaxation are still not modeled properly. The Nernst-Plank-Poisson was chosen to be the base model for the IPMC behavior, we were able to create a new model that truly represent the back-relaxation effects that occur in IPMCs, we’ve called the new model as modified NPP model. The modification used captured data from our experimental work Our modified analytical NPP (Nernst-Plank-Poisson) model was the verified using MATLAB & Simulink, which showed that the model, and the controller design for it was able to first compensate the loss of position of the IPMC due to back-relaxation, and then track the desired position input signals with great accuracy. The model and designed controller can be utilized in verity of robotic applications.
In this research, the authors investigated copper (Cu) donor material assisted friction stir welding (FSW) of AA2024-T4 and AA6061-T6 aluminum plates of 6.35 mm thickness. FSW joints were prepared at optimized process parameters at a constant tool rotational rate of 1400 rpm and welding speeds at 1, 2, or 3 mm/s. The Cu donor material of 25% and 50% thickness with respect to the workpiece thickness were selected to assist the FSW joining at the plunge stage. During the welding processes, it was observed that the downward force generated in the FSW process was gradually decreased after introducing Cu donor material. Temperature pro les proved that the inclusion of copper donor material increased the temperature at the beginning of the welding process. Post-weld analysis was characterized in terms of micro-hardness and tensile properties of the welded joints. The experimental results revealed that defect-free joints could be obtained when placing high strength AA2024 alloy at the advancing side with 25% thick donor material. Micro-hardness test results indicated that the hardness decreased from the base metal (BM) to the stir zone across the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). The lowest hardness measurements occurred in the TMAZ and HAZ where tensile failure occurs. The maximum tensile strength improved by 130% with 25% Cu donor material as compared to aswelded condition. SEM Fractography images con rmed mixed modes of brittle and ductile fracture surface with tearing ridges and ner dimples after heat treatment. What Is Your Main Contribution To The Field?The main contribution in this research is on the novel and solid experimental approaches to examine whether donor material can assist friction stir welding (FSW) of dissimilar aluminum alloys. Copper (Cu) was chosen as a donor material due to its good thermal properties. FSW experiments were performed in two different groups: 1) as-welded condition (without Cu donor material) and 2) Cu donor material in assisting different weld con gurations. During the experimentation, it was identi ed that the inclusion of donor material decreases the downward force drastically. It is well known that, when the downward force decreases, the frictional coe cient and contact pressure will reduce, thus it lowers the tool wear. We also studied the temperature pro les using thermocouple in during FSW processes. The temperature measurements con rm that the donor material preheats workpieces in the plunge stage of FSW. The Cu material helps compensate the thermal properties difference between two work pieces, and maintain the equilibrium heat throughout the weldment. The defect-free welding joints were produced when the donor material thickness was 25% of the work piece thickness. Post-weld mechanical testing con rms that the mechanical properties including mechanical strength and micro hardness were not affected after using donor material. This novel idea of FSW assisted by donor material is promising for high volume welding in industrial application...
Post weld heat treated AA6061-T6 alloy resulted from the application of a Cu donor stir assisted (CDSA) friction stir welding (FSW) material was examined for crystal structure and mechanical properties. CDSA FSW samples were tested at a constant tool rotational speed of 1400 rpm and a welding translational speed of 1 mm/s. CDSA samples of 20% and 60% thickness of the AA6061-T6 base alloy were selected to assist the FSW joining at the plunge stage. The FSW AA6061-T6 samples were solid solution treated at 540 °C for one hour, followed by quenching in water at room temperature. The samples were then artificially aged at 180 °C for 6 hours, respectively, followed by air cooling. The samples were tested for microstructure, crystal structure, chemical composition, and mechanical properties using optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation. The microstructure shows the additional grain refinement in the stir zone (SZ) due to recovery and recrystallization with increasing aging time. Examination of the chemical contents of the FSW AA6061-T6 alloy samples using scanning electron microscopy with energy dispersive spectroscopy (EDS) revealed Al (parent material) as the predominant element, while Cu (CDSA) was minimally present as expected. XRD results of the CDSA FSW samples depicted crystal orientations similar to the orientations of the AA6061-T6 alloy. Nanoindentation tests revealed softening effects due to the dissolution of hardening precipitates at the SZ. The hardness of the base metal (BM), left and right regions, is reported as ~ 6.5 GPa, whereas at the SZ, the hardness is ~ 5.5 GPa at a depth of indentation of 4.7 µm.
Friction stir welding of high-strength materials such as steels is the impeded by the lack of the vast heat input needed to start the process. Contact friction is considered the most dominant source of heat generation for FSW steels which tends to cause severe wear conditions of the tool hear. To relieve the extreme wear conditions that occur on the tool heads because of FSW steels, we introduce the non-mixing Cu donor stir material to friction stir welding of aluminum alloys. The elastic properties of the Cu donor assisted friction stir welded aluminum alloys are measured using nanoindentation. The hardness and elastic modulus were measured for two regions, the base metal (BM) and the stir zone (SZ). The measurements were conducted for 20% and 60% Cu non-heat treated (NHT) and heat-treated (HT) samples. The nanomechanical properties were measured using nanoindentation with the continuous stiffness method (CSM) in depth control. The HT samples are softer than the NHT samples as expected. However, the 20% Cu NHT and HT samples depicted the same hardness at the SZ. Similar results were observed for the 60% Cu donor stir samples. It therefore concluded that the SZ is softer than the BM for the 20% and 60% Cu donor stir material as expected. The hardness of the weld at the SZ is similar to the hardness of the Al6061-T6 plate, suggesting that the Cu donor stir material did not impact the hardness properties of the Al6061-T6 plate due to the depletion of the Cu donor stir material during the welding process, an important result of the concept of the donor material. The elastic moduli of the Cu donor stir welded samples vary between 75~85 GPa at a depth of indentation of ~4600 nm, which are different from the elastic moduli of Cu 110 (117.2 GPa) and similar to the elastic modulus of aluminum alloys (68.9 GPa), an important outcome.
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