RESUMO
This study developed an experimental system based on Joule heat of sliding-pressure additive manufacturing (SP-JHAM), and Joule heat was used for the first time to accomplish high-quality single-layer printing. The roller wire substrate is short-circuited, and Joule heat is generated to melt the wire when the current passes through. Through the self-lapping experimental platform, single-factor experiments were designed to study the effects of power supply current, electrode pressure, contact length on the surface morphology and cross-section geometric characteristics of the single-pass printing layer. Through the Taguchi method, the effect of various factors was analyzed, the optimal process parameters were obtained, and the quality was detected. The results show that with the current increase, the aspect ratio and dilution rate of a printing layer increase within a given range of process parameters. In addition, with the increase in pressure and contact length, the aspect ratio and dilution ratio decrease. Pressure has the greatest effect on the aspect ratio and dilution ratio, followed by current and contact length. When a current of 260 A, a pressure of 0.60 N and a contact length of 1.3 mm are applied, a single track with a good appearance, whose surface roughness Ra is 3.896 µm, can be printed. Additionally, the wire and the substrate are completely metallurgically bonded with this condition. There are also no defects such as air holes and cracks. This study verified the feasibility of SP-JHAM as a new additive manufacturing strategy with high quality and low cost, and provided a reference for developing additive manufacturing technology based on Joule heat.
RESUMO
Personalised controlled drug delivery systems (CDDSs) can adjust drug concentration levels according to patient needs, which has enormous research prospects in precision medicine. In this study, the topological optimisation method was utilised in the structural design of a hydrogel CDDS to achieve a parameter-based adjustment of the drug average concentration in the hydrogel. A polyacrylamide/sodium alginate dual-network hydrogel was selected as a drug carrier, and tetracycline hydrochloride was used as a model drug. The topological optimisation model of the hydrogel CDDS was developed. The effects of the mesh size, target concentration, and volume factor on the optimised results were investigated. Hydrogel flow channel structures were obtained, which satisfied the different target concentrations. To verify the rationality of the optimisation model, in vitro drug release experiments were carried out. The results show that the hydrogel CDDS can control drug release within 7 days, and the drug release tends to follow zero-order release behaviour. The adjustable average concentration of tetracycline hydrochloride in hydrogel CDDS is recommended in the range of 20.79 to 31.04 mol/m3. This novel method provides a reference for personalised structure design of CDDS in the context of precision medicine.
RESUMO
Nickel-based alloy Inconel 625, produced by the selective laser melting method, was studied experimentally for its mechanical performance under strain rate loading using Hopkinson bars. Both compression and tensile tests were carried out, with the former also being conducted at 500 °C. The strain rate was in the range of 300 to 3500 s-1 at ambient temperature, and 1200 to 3500 s-1 at the elevated temperature, respectively, for compression tests, and 900 to 2400 s-1 for tensile tests. Results show that the alloy has a strong rate sensitivity with the dynamic yield stress at 3500 s-1, almost doubling the quasistatic value. The test results also show that, even though the temperature elevation leads to material softening, the strain rate effect is still evidential with the dynamic compressive yield stress at the rate 103 s-1 and 500 °C still being higher than the quasistatic one at ambient temperature. It is also observed that dynamic tensile strengths are generally higher than those of compressive ones at room temperature.