Baohui Shi

Although 3D printing enables the flexible manufacturing of ceramic components, the fabrication of complex, large-span ceramic structures usually requires additional supports, leading to high production costs, low efficiency, and increased defect rates. Herein, an ultraviolet (UV)-based in situ photocuring-assisted direct ink writing (DIW) method was developed for shaping alumina-filled photocurable slurries into preceramic composites, which were subsequently debound and sintered into alumina ceramics. The effects of the slurry composition and processing parameters on curing depth and printing accuracy were systematically investigated, and the mechanical properties of the cured and sintered samples were compared. The results showed that the curing depth decreased with increasing photoinitiator and alumina powder content but increased with prolonged UV irradiation time. Due to the increase in viscosity with the increase in alumina content, the flowability of the slurry before solidification decreases, and the printing accuracy increases. The cured composites exhibited good mechanical integrity. After debinding and sintering, the bending modulus and bending strength increased from approximately 125 MPa and 5 MPa for the cured composites to about 200 GPa and 38 MPa for the sintered ceramics, respectively. The linear shrinkage of the sintered sample was around 20%. Using the optimized slurry, various unsupported structures—including discs, solid rectangles, triangular frames, L-shaped brackets, and a 12.5 cm high vase—were successfully printed without any supports. All printed structures exhibited good continuity and integrity, demonstrating the proposed method as a promising route toward the low-cost and efficient manufacturing of alumina ceramic components.

This paper provides a comprehensive understanding of the amplitude- and frequency-dependent characteristics of rubber springs. The dynamic nonlinear inelasticity of rubber is a key academic problem for continuum mechanics and a bottleneck problem for the practical use of rubber structures. Despite intensive efforts witnessed in industrial applications, it still demands an unambiguous constitutive model for dynamic nonlinear inelasticity, which is known as the Payne effect. To this end, three types of rubber springs (shear-type (ST), compression-type (CT) and shear-compression-combination-type (SCCT)) were tested with amplitude and frequency sweeps in different conditions. We investigated and present changes in dynamic stiffness and loss factor with amplitude, frequency and the hysteresis loops of different rubber springs. We also propose a hypothesis and research strategy to study a constitutive model involving multiple factors of hyperelasticity, the Mullins effect, viscoelasticity and the Payne effect, which we hope will provide new ideas for the establishment of a constitutive equation.