•Effects of hugoniot properties on the jet onset time, velocity and jetting side.•Jet initiates earlier at higher velocity if jetting side has higher shock parameter.•Jet initiates earlier at higher ...velocity if jetting side has higher sound velocity.•Jet initiates later and at lower velocity if jetting side has high density.•Effect of s-parameter and speed of sound is more profound than the density.
Jets are the earliest ejected material from a hypervelocity impact event. Jets comprises of projectile and target's surface material and are ejected at velocities higher than escape velocity for Earth. Effects of Hugoniot properties of the projectile and target material on jet initiation are not well understood. We, therefore, developed a mathematical model that incorporated the limitations imposed by Hugoniot properties on jet initiation for hypervelocity impact. This model analysed the effects of changes in Hugoniot properties of the projectile and target on the jet onset time, jet onset velocity and jetting side (projectile or target). The results reveal that (i) jet initiates earlier and at higher velocity if the jetting side has higher value of shock parameter or higher velocity of sound in the material; (ii) jet initiates later and at lower velocity if jetting side has high density; (iii) effect of s-parameter and speed of sound in material is more profound than the effect of density.
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Predicting formation mode of double emulsion drops in microfluidic emulsification is crucial for controlling the drop size and morphology.
A three-phase Volume of Fluid-Continuum ...Surface Force (VOF–CSF) model was developed, validated with analytical solutions, and used to investigate drop formation in different regimes. Experimental investigations were done using a glue-free demountable glass capillary device with a true axisymmetric geometry, capable of readjusting the distance between the two inner capillaries during operation.
A non-dimensional parameter (ζ) for prediction of double emulsion formation mode as a function of the capillary numbers of all fluids and device geometry was developed and its critical values were determined using simulation and experimental data. At logζ>5.7, drops were formed in dripping mode; the widening jetting occurred at 5<logζ<5.7; while the narrowing jetting was observed at logζ<5. The ζ criterion was correlated with the ratio of the break-up length to drop diameter. The transition from widening to narrowing jetting was achieved by increasing the outer fluid flow rate at the high capillary number of the inner fluid. The drop size was reduced by reducing the distance between the two inner capillaries and the minimum drop size was achieved when the distance between the capillaries was zero.
Sintering is an important consolidation step employed in sinter-based metal additive manufacturing processes. Binder Jetting (BJT) starts with green components with low green density (40–60 %) that ...results in large sintering shrinkages and geometrical shape distortions caused by external forces (e.g. gravity). Consequently, the prediction of the final sintered geometry is crucial during the design process. In this work, a novel sintering simulation framework for gravity-affected sintering of stainless-steel components is presented, including the Rios-Olevsky-Hryha sintering model and the methodology for the identification of the required material parameters. The constitutive law includes material constants to account for the powder packing effects and the delta-ferrite transformation occurring at high temperatures. The material shear viscosity was explicitly related to the equilibrium phase fraction of austenite and delta-ferrite during sintering temperatures. Dilatometry experiments were conducted and followed by the data postprocessing for the model calibration. The calibrated model was incorporated in a FEM code and validated against experimental data from BJT sintered components, showing the remarkably accuracy of the numerical simulations, with small geometric deviations (0.56 mm) related to the assumption of isotropic shrinkage in the model proposed. In parallel, other alternative models were implemented based on different normalized bulk viscosity formulations, which underestimate/overestimate the sintered distortions.
When metallic microparticles impact substrates at high enough velocity, they bond cohesively. It has been widely argued that this critical adhesion velocity is associated with the impact velocity ...required to induce adiabatic shear instability. Here, we argue that the large interfacial strain needed to achieve bonding does not necessarily require adiabatic shear instability to trigger. Instead, we suggest that the interaction of strong pressure waves with the free surface at the particle edges—a natural dynamic effect of a sufficiently rapid impact—can cause hydrodynamic plasticity that effects bonding, without requiring shear instability. We proceed on this basis to postulate and confirm a proportionality between critical velocity and the bulk speed of sound, which supports the viewpoint that shear instability is not the mechanism of adhesion in cold spray.
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This paper demonstrates, for the very first time, 3D printing of pea-based snacks with tunable texture using the binder jetting (BJT) method, pea flour as the print powder, and an aqueous binder ...solution. The binding mechanism was studied by performing both Hele-Shaw cell experiments and confocal microscopy on the printed samples. As the pea flour was exposed to an aqueous binder, the starch granules swelled. These granules remained swollen but were further joined by a network of protein-rich bridges as the sample dried. Inclusion of sugar and post-printing baking tended to strengthen the as-printed samples, and the resultant mechanical properties were on par with commercial snacks that are not 3D printed. By controlling the amount of aqueous binder dispensed from the inkjet print heads, more than one order of magnitude differences in compressive strength and modulus were achieved, demonstrating the exciting potential of using 3D printing for texture modulation of plant-based snacks.
Droplet deposition with material-jetting methods such as thermoplastic 3D printing (T3DP) depends greatly on the rheological properties of the feedstocks. This study investigated the effect of ...particle interactions and the degree of weak flocculation on the shear thinning behaviour, the yield stress and the storage/loss moduli of paraffin-wax-based feedstocks containing 40 vol% of zirconia (3Y-TZP) micron-sized powder. Steric stabilization of the feedstocks was provided by varying the ratios of the surfactants with different chain lengths, i.e., stearic acid (2.4 nm) and Solsperse 3000® (10 nm), which in turn affected the dynamics of the droplet formation and the quality of the layers when jetting non-Newtonian, thermoplastic ceramic feedstocks. The results of the study extend the guidelines for the processing of printable feedstocks used in T3DP additive manufacturing.
•Steric stabilization of ceramic particles can be controlled by using surfactants.•Shorter surfactant chain length leads to higher total attractive potential energy.•Higher total attractive potential energy means higher viscosity and yield stress.•Feedstocks with shear thinning and no yield point are well suited for T3DP.•Interparticle interactions affect the quality of printed droplets and parts.
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