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Driven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.

N. Sridharan, P.J. WOLCOTT, M.J. Dapino, and S.S. Babu, “Microstructure and mechanical property characterization of aluminum-steel joints fabricated using ultrasonic additive manufacturing,” Science and Technology of Welding and Joining, 22(5), 373-380, 2017.

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The ΔE effect (Young’s modulus variation of magnetostrictive materials) is useful for tunable vibration absorption and stiffness control. The ΔE effect of iron-gallium (Galfenol) has not been fully characterized. In this study, major and minor strain-stress loops were measured under different bias magnetic fields in solid, research grade, ⟨100⟩-oriented, highly-textured polycrystalline Fe81.6Ga18.4 Galfenol. A 1 Hz, constant amplitude compressive stress was applied from −0.5 MPa to −63.3 MPa for major loop responses. Minor loops were generated by simultaneously applying a 4 Hz, 2.88 MPa amplitude sinusoidal stress and different bias stresses ranging from −5.7 MPa to −41.6 MPa in increments of about 7.2 MPa. Bias magnetic fields were applied in two ways, a constant field in the sample obtained using a proportional-integral (PI) controller and a constant current in the excitation coils. The ΔE effect was quantified from major and minor loop measurements. The maximum ΔE effect is 54.84% and 39.01% for constant field and constant current major loops, respectively. For constant field and constant current minor loops, the maximum ΔE effect is 37.90% and 27.46%, respectively. A laminated sample of the same material was tested under constant current conditions. The saturation modulus of this material is 59.54 GPa, or 82.65% of the solid rod’s saturation modulus, due in part to the soft adhesive layers. The minimum modulus calculated from major loops is 36.31 GPa, which corresponds to a 39.02% ΔE effect. A new optimization procedure is presented on the basis of an existing discrete energy-averaged model to incorporate measurement uncertainties. The model was optimized to both major and minor loop data; model parameters with 95% confidence intervals are presented.

Z. DENG, J.J. SCHEIDLER, V. Asnani, and M.J. Dapino, “Quasi-static major and minor strain-stress loops in textured polycrystalline Fe81:6Ga18:4 Galfenol,” Journal of Applied Physics, 120, 243901, 2016.

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Fiber-reinforced asymmetric laminates fabricated at elevated temperatures may exhibit bistability at room temperature. The magnitude of deformation in each shape depends primarily on the curing temperature. This paper presents a novel asymmetric bistable laminate that is fabricated at room temperature and whose stable shapes are analogous to those of a thermally cured fiber-reinforced polymeric composite. The proposed laminate is composed of a stress-free isotropic core layer sandwiched between two asymmetric, mechanically-prestressed, fiber-reinforced elastomeric layers. Its stable shapes can be independently tuned by varying the prestress in each elastomeric layer. The mechanics of the laminate are studied using an analytical laminated-plate model that includes the geometric and material nonlinearities associated with large deformations caused by highly-strained elastomers. The effects of core modulus, core thickness, elastomer-core width ratio, and laminate size are examined through a parametric study. Laminate samples are fabricated in the 90°/core/0° configuration for model validation. The simulated stable shapes of the laminate are in agreement with the measured shapes. The dynamic response of the laminate during shape transition is measured using a motion capture system.

V.S.C. CHILLARA and M.J. Dapino, “Mechanically-prestressed bistable composite laminates with weakly coupled equilibrium shapes,” Composites Part B: Engineering, Vol. 111, pp. 251-260, February 2017.