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[en] Highlights: • Al(ZrTiV)Si phases were found in the studied Al–Si alloy with Zr–V–Ti additions. • The studied alloy achieved up to 40% higher strength up to 200 °C temperature. • Also, the studied alloy was ∼5 times higher ductile than A380. - Abstract: The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al2Cu–Si phase. Whereas the Al15(FeCrMn)3Si2 phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.
[en] Highlights: • The pull of materials across the weld centre line is predominantly from the advancing side. • Mixture of materials only occurred in four regions of the weld. • The finest grain sizes were observed at the top side of the retreating side. • Fragmented grains with high dislocation density and density of Mg2Si phases affected the microhardness. - Abstract: The flow patterns in dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys have been studied. It was observed that material flows (pushes but does not mix) more from the advancing side into the retreating side. Material flow from the retreating side to the advancing side only occurs in the tool shoulder domain, and the pull is greatest at the transition region between the tool shoulder domain and the tool pin domain. It was also observed that materials tend to extrude out only in the thermomechanically affected zone of the retreating side, which was influenced by rotation of both the tool shoulder and the tool pin. The finest grains were present in the regions closest to the tool edge in the retreating side. The volume fraction of recrystallized grains increases down into the deeper part of the nugget from the flow arm region. Microhardness measurements revealed that regions of lowest hardness values were the nugget and the heat affected zone of the AA6082-T6 alloy side. The welding speeds had no influence on the microhardness values per se, but affected the mixing proportions in the flow arm and in the nugget stem.
[en] Highlights: • Prevalent Mode II loading (KII/KI greater than 1) can be made by inclined U-notch. • The formulae proposed for Jcr evaluation, can be applied under prevalent Mode II. • Fracture of Al2014-T6 has been assessed with inclined U-notches under prevalent Mode II. • The mode mixity increases by increasing the notch root radius. - Abstract: In this paper, the J-integral has been evaluated for specimens with inclined U-notches loaded under a prevalent Mode II (i.e. KII/KI ratio greater than 1). Finite element analyses using ABAQUS software have been applied for evaluation of the J-integral. J = Jcr criterion has been used to predict the critical fracture load. The value of Jcr has been determined by means of some useful formulas available in the literature. Some specimens have been produced by aluminum 2014-T6 with inclined U-notches. The aim of selecting aluminum 2014-T6 is that this material has several applications in aerospace industries such as in aircraft for fittings and wheels, as well as applications in machinery, military and weapons industries. The produced specimens have been tested under prevalent Mode II loading. The results of the critical fracture load predicted numerically are in good agreement with the results obtained experimentally for Al2014-T6.
[en] Highlights: • The relationship between arc energy and arc time of Ag/12Ni contacts followed an exponential function. • Regions with arc erosion morphology were found on the surface of Ag/12Ni contacts. • Elemental distribution within the molten pool on Ag/12Ni differs depending on whether the contact was movable or stationary. - Abstract: Ag/Ni electrical contact materials tend to be weld together under high current and/or high temperature, which was a key problem to restrict the usage of Ag/Ni electric contact materials. Arc erosion characteristics of Ag/12Ni electrical contact material after 50,000 operations under direct current 19 V, 20 A and resistive load conditions were investigated. The result indicated that the probability distribution and change trend of arc energy and arc time during 50,000 operations were similar and the relationship between arc time and arc energy followed exponential function. On the one hand, “Crater” type erosion pit, island-like melted silver, pore, crack and coral-like structure spitting were observed on erosion surface of Ag/Ni contact materials. On the other hand, distribution of Ag and Ni element on molten pool of movable contact was different from that of stationary contact. For movable contact, element Ni mainly distributed on melted pool root, whereas element Ag mainly distributed inside of melted pool. For stationary contact, however, element Ni and Ag distributed layer by layer. Furthermore, arc erosion of stationary contact is more serious than that of movable contact.
[en] Highlights: • BaTiO3 was modified with dopamine. • The coated particles improved the dielectric properties of DEs. • Mechanical properties were obtained via the bubble inflation testing system. • A large voltage-induced strain of 78% was achieved by the fabricated DE. - Abstract: In this work, a new soft dielectric elastomer (DE) was fabricated from dopamine coated barium titanate particles and silicone rubber (SR). The results showed that the barium titanate (BaTiO3, BT) was coated by dopamine and the coated particles were highly compatible with SR. In order to achieve a maximum voltage-induced deformation, the minimum secant moduli of DEs were obtained in experimentation at a stretch ratio of approximately 1.6 by applying equi-biaxial tensile strain using the bubble inflation method. Additionally, it was found that the addition of DP-BT into SR led to an increased dielectric constant and decreased dielectric loss tangent for the matrix by comparison with SR/BT composites. Furthermore, the electromechanical properties of the SR/DP-BT composites were greatly improved in terms of voltage-induced deformation (sa), electromechanical energy density (e) and coupling efficiency (K2). A maximum actuated area strain of approximately 78%, which was 30% larger than that of the SR/BT composites, was achieved for the sample having a DP-BT content of 20 wt.%. This strain corresponded to a low dielectric strength of around 53 V/μm, the composite exhibited a maximum energy density of 0.07 MJ/m3 and coupling efficiency of 0.68.
[en] Highlights: • Fatigue cycling lowers the Austenite to Martensite transformation stress and the ultimate strength of NiTi alloy. • Lower cyclic frequency fatigue results in higher energy dissipation in NiTi alloy. • Under fatigue exothermic Austenite to Martensite transformation increase sample temperature. - Abstract: The tensile and fatigue behavior of superelastic shape memory alloy (SMA) bars heat-treated at three different temperatures were examined. Low cycle fatigue tests at variable load rates were carried out to determine the effect of stress and frequency on residual strain and energy dissipation in a fatigue cycle. The mechanism of energy dissipation was studied by monitoring the temperature changes in the fatigued samples as a function of applied stress and frequency of testing. Results from the tensile tests revealed that the stress for the Austenite to Martensite transformation decreased from 408 MPa to 204 MPa with an increase in temperature of heat treatment from 300 to 450 °C. The ultimate strength of the SMA increased from 952 MPa to 1115 MPa when the heat treatment temperature was increased from 300 to 450 °C. Fatigue testing prior to conducting the tensile test decreased the ultimate strength of the SMA and also reduced the failure strain. The energy dissipation in fatigue tests was found to decrease as test frequency increased from 0.025 Hz to 0.25 Hz and the change in sample temperature during the test at the lower test frequency was found to be considerably higher than at the higher frequency.
[en] Highlights: • m′ of paired twins distributes in a wide range (− 0.5 to 1) for extruded Mg alloys. • But about 60% of paired twins have the first rank m′ indicating the importance of local strain compatibility. • Simultaneously high SF and high m′ is favorable for twin pair formation in extruded Mg alloys. - Abstract: Recently, geometrical compatibility factor (m′) has been used to characterize local strain compatibility between paired twins formed in rolled Mg alloys with basal texture. High m′ and m′ rank were present in most cases, suggesting that m′ plays an important role in twin pair formation. The present study aims to extend the understanding of the effects of m′ and grain boundary (GB) misorientation angle on twin pair formation in an extruded Mg alloy with basal fiber texture. 106 sets of paired twins were extracted from electron backscatter diffraction (EBSD) data and were analyzed. The results show that m′ of paired twins distributes in a wide range (− 0.5 to 1) in extruded Mg alloys due to the presence of a large fraction of high angle GBs. About 60% of twin pairs have the first m′ rank, implying that m′ is still an important factor for variant selection of paired twins in extruded Mg alloys. The distribution of m′ with SF rank was also analyzed, showing that more than half of twin pairs are located in the left-top corner with m′ > 0.6 and SF either rank one or two, which confirms that simultaneously high SF and high m′ is favorable for twin pair formation in extruded Mg alloys.
[en] Highlights: • Accelerated vibrational fatigue-testing methodology using electrodynamic shaker • Establishment of the high-cycle fatigue curves • Failure criteria defined from the reduction of the strain slope are used. • Comparison of the failure criteria with modal parameter changes - Abstract: This paper presents an original contribution for the establishment of the high-cycle fatigue curves ε–Nf (strain versus cycle number to failure) of low carbon steel under vibratory testing. These curves are obtained thanks to a vibrational fatigue bench composed of an electrodynamic shaker and a closed loop vibration control system. The main advantage of this is the high frequency excitation compared to conventional fatigue systems. Three criteria based on strain gauge measurements are implemented to provide cycle numbers to failure Nf and to plot the fatigue curves. Furthermore, cycle numbers to failure are also assessed from two modal parameters (resonant frequency and loss damping factor) and compared with the results obtained from these three criteria. Some micrographies of fractured samples observed by scanning electron microscope reveal fatigue striations but also intergranular fracture.
[en] Highlights: • Steel z-pinned carbon fiber/Al composites are fabricated by pressure infiltration. • The interlaminar shear strength of the composites is increased by 70%–230%. • An interfacial reaction layer of FeAl3 is identified and characterized. - Abstract: We report that metal z-pin can be used to enhance the interlaminar strength of carbon fiber reinforced aluminum alloy (Cf/Al) composites. The Cf/Al composites incorporated with AISI 321 steel z-pins as interlaminar reinforcement were fabricated by pressure infiltration, resulting in high composite density. The steel pin reacted with the Al alloy matrix and formed a continuous interfacial reaction layer of FeAl3 to provide strong interfacial bonding between the steel pin and Al alloy matrix. Moreover, it has been found that the diameter of the z-pin has a significant influence on the thickness of the interfacial reaction layer. Double-notched interlaminar shear testing showed that the z-pins increased the shear strength of the Cf/Al composite by 70%–230%.