Centre-of-mass motions of two coupled spherical-cap droplets are considered. A model with surface tension and inertia that accounts for finite-amplitude deformations is derived in closed form. Total droplet volume λ and half-length L of the tube that connects the droplets are the control parameters. The model dynamics reside in the phase-plane. For lens-like droplets λ < 1, and for any L there is a single steady state about which the droplets vibrate with limit-cycle behaviour. For λ>1, the symmetric state loses stability (saddle point) and new antisymmetric steady states arise about which limit-cycle oscillations occur. These mirror states – big-droplet up or big-droplet down – are also stable. In addition, there are large finite-amplitude ‘looping’ oscillations corresponding to limit cycles that enclose both steady states in the phase-plane. All three kinds of oscillations are documented in an experiment that sets the system into motion by ‘kicking’ one of the droplets with a prescribed pressure-pulse. Model predictions for frequencies are consistent with observations. Small-amplitude predictions are placed in the wider context of constrained Rayleigh vibrations. A model extension to account for the small but non-negligible influence of viscosity is also presented.

In brazing, the choice of base metal, brazing filler metal (BFM), and braze process conditions involves complex tradeoffs among cost, mechanical strength, corrosion resistance, and others. In this work, the tradeoff between strength and corrosion resistance of 316L stainless steel joints brazed with a newer ''very corrosion-resistant'' Ni-Cr-P-Mo-Si BFM and a more established ''corrosion-resistant'' Ni-Cr-Si-B BFM is quantitatively analyzed. Corrosion tests and microstructural analyses were performed using common practices. Joint strength was evaluated by testing brazed single-lap joints (SLJs) in tension following standardized procedures. However, conventional interpretations were found to be inadequate for quantitative comparisons. Therefore, the SLJ stress state was analyzed in detail and a complete interpretation was developed. Joint strength is shown to be determined by the SLJ geometry, base metal properties, and braze microstructure. This analysis was used to explain the occurrence of different failure modes (fast fracture, peeling, and base metal failure) and to make suggestions for improved methods for conducting and analyzing brazed SLJ tensile tests. The newer BFM is shown to provide significantly better corrosion resistance for a moderate reduction in mechanical strength.

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Planar-flow melt spinning (PFMS) is a single-stage rapid manufacturing/solidification technique for producing thin metal sheets or ribbons. Molten metal is forced through a nozzle onto the substrate where it freezes and is spun as ribbon product. A puddle of molten metal held by surface tension (capillarity) forms between the nozzle and substrate. An important measure of product quality is the uniformity of thickness along and across the ribbon. At small length scales, local thickness changes or surface defects are present that are undesirable. This work examines the cross wave, a well-defined periodic surface defect, seen when casting aluminum-silicon alloys. The presence of the defect is related to processing conditions and puddle dynamics. Motions of the puddle menisci are captured using high-speed video and analyzed for frequency content. A high frequency vibration of both menisci corresponds to the observed frequency of the surface defect. A scaling analysis reveals these motions to be capillary in nature and comparisons are made with two model problems of vibrating capillary liquids.

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