A systematic printability study of direct ink writing towards high-resolution rapid manufacturing

Direct ink writing(DIW)holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials,simple operation,and ease of rapid prototyping.Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects,the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood.To tackle this issue,we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating.Hybrid non-Newtonian fluid inks were first prepared,and their rheological properties were measured.Then,finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks.The obtained optimal process parameters(ink rheology,applied pressure,printing speed,etc)were also validated by experiments where high-resolution(<100μm)patterns were fabricated rapidly(>70 mm s^(-1)).Finally,as a process research demonstration,we printed a series of microstructures and circuit systems with hybrid inks and silver inks,showing the suitability of the printable process parameters.This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution,high-precision samples.

Dynamics response analysis of airborne external storage system with clearance between missile-frame

Considering the aircraft and its external components are subjected to complex and variable aerodynamic loads during the working process,the missile-frame clearance system of the airborne external missile is investigated.The random vibration characteristics of the airborne external components are analyzed by finite element method.The finite element model is optimized with reference to the test results,and the effects of different clearance on the dynamic response of the missile-frame system are compared.The result shows that the frequency response curves of the same position and the resonant peak frequencies are consistent under different clearances.The acceleration response at both ends of the missile is large and the amplitude near the center of mass is gentle.The results can be used to predict reasonable missile-frame clearance and make guidance to the structural design and reliability analysis of the missile-frame system.

Physical clogging experiment of sand gravel infiltration with Yellow River water in the Yufuhe River channel of Jinan, China

To make sense of physical clogging during Yellow River water spreading in the strong leakage zone of the Yufuhe River,a laboratory sand column experiment was undertaken and the heterogeneous sand gravel with a uniformity coefficient of 25.2 from the Yufuhe River was used as an infiltration medium.Under either the condition of raw sand or washed sand,physical clogging tests were conducted with constant hydraulic heads of 10 cm and 30 cm and inflow suspension concentrations of 200 mg/L,500 mg/L,and 1000 mg/L.The fine particles in the suspension and in the raw sand were considered exogenous and endogenous particles,respectively.Rapid clogging was observed in the porous medium when the inflow concentrations of the exogenous particles were high,and increased hydraulic head led to serious clogging.This result indicated that the Yufuhe River has a strong recharge capability with respect to clogging.The analysis of particle content shows that endogenous fine particles(diameter 1–10 mm and 50–74 mm)had less mobility and generally accumulated in the sand column,whereas particles with diameter 10–50 mm had greater mobility in the sand column.And the distribution of exogenous fine particles size after movement is relatively uniform in the sand column.Field observations indicated that the filtration effect of the aquifers have greatly improved the water quality of recharge water in the strong leakage zone of the Yufuhe River,and test data of turbidity also verified the results of the sand column experiments.