Xinliang Mei

Four-dimensionally (4D) printing technology effectively demonstrates the advantages of portability, foldability, and improved mechanical properties in origami structures. This study highlights the significance of printing process parameters and origami hinge structures in ensuring rapid and complete deployment of origami structures. Polylactic acid based semicrystalline shape memory polymer was utilized to produce 4D printed origami structures. Through response surface analysis methods and bending tests, optimal printing parameters were determined, including layer thickness of 0.31 mm, extrusion speed of 17 mm s⁻¹, and infill percentage of 71%. Additionally, the study designed a U-shaped hinge and analyzed its recovery mechanism through micromorphology of bending hinges and recovery experiments.

Shape memory polymers are attractive smart materials that have many promising applications in a wide variety of fields. Here the multi-walled carbon nanotube (MWCNT) was used to adjust the performance of crosslinked poly(vinyl alcohol) (PVA), which had acetal reaction with glutaraldehyde (GA). The thermal degradation, mechanical strength and shape recovery properties of PVA/MWCNT/GA membranes were investigated by thermogravimetry, differential scanning calorimetry, x-ray scattering, dynamic mechanical analysis, tensile test and thermal-stimulus shape memory recovery measurements. The MWCNT embedded in the crosslinked PVA matrix accelerated the breaking of C–O bonds. The mechanical strength and shape recovery properties of PVA/MWCNT/GA composites were tunable. As the MWCNT loading increase in crosslinked PVA matrix, the yield strength increased from 3.85 MPa to 10.21 MPa, breaking elongation decreased from 230% to 50%, the 100% shape recovery time decreased from 27 s to 16 s, respectively.

Nickel iodate tetrahydrate (Ni(IO₃)₂·4H₂O) particles with different morphology and size were synthesized by precipitation method (PM) and electrospray precipitation method (EPM). The electrospray was used in chemical precipitation to synthesize nanoscale metal iodate particles with a narrow size distribution. The thermal decomposition mechanism of Ni(IO₃)₂·4H₂O at different heating rates, ignition, and combustion of Al/Ni(IO₃)₂·4H₂O nanothermites was studied by thermogravimetry–differential scanning calorimetry–mass spectrometry, T-jump and time-of-flight mass spectrometry, T-jump equipped with high-speed camera, and combustion cell test. The Al/Ni(IO₃)₂·4H₂O prepared by EPM had a lower ignition temperature (587 ± 14°C) and a shorter burn time (159 µs). The ignition processes of Al/Ni(IO₃)₂·4H₂O nanothermites prepared by EPM and PM were solid–solid and gas–liquid reactions, respectively. The rate-determining step of their combustion processes was the burning of aluminum powder and the decomposition of Ni(IO₃)₂· 4H₂O, respectively.

The traditional machine tool design method with metal materials makes large-scale moving structures very heavy, which seriously impacts dynamic performance and results in significant energy consumption. Using sandwich structures of composite materials to replace metal materials is an important strategy for lightweight large-scale moving structures. However, this kind of substitution is generally believed to be difficult because foam-filled sandwich structures usually show nonlinear characteristics and must balance the moving mass, material costs, and structural stiffness. In the present study, we proposed a design optimization approach for a large-scale moving framework in a large 5-axis machining center (L5AMC) considering large dimensions in the x, y, and z work space and high machining speed with the aim of minimizing the displacements of the milling head. An improved approach, named the 3-step design optimization, was executed to obtain the optimum framework structures to solve the contradiction between the moving mass, material costs, and structural stiffness. This approach was based on multi-objective optimization and finite element analysis. The structural stiffness of the framework after optimization increased by 89% compared with before optimization although the mass increased by 6% and the material costs increased by 9%. A finite element simulation under four given operational loads showed that the displacements of the milling head were all less than the design requirement of 0.25 mm. The results indicated that the proposed 3-step design optimization approach for the optimal design of a large-scale moving framework was feasible and successful. A 40 m × 6 m × 4 m L5AMC prototype was manufactured, and the actual verification results indicated that the large-scale moving framework fully met the design requirements of the L5AMC and reduced energy consumption.