During selective laser sintering (SLS), the microstructure evolution and local temperature variation interact mutually. Application of conventional isothermal sintering model is thereby insufficient to describe SLS. In this work, we construct our model from entropy level, and derive the non-isothermal kinetics for order parameters along with the heat transfer equation coupled with microstructure evolution. Influences from partial melting and laser-powder interaction are also addressed. We then perform 3D finite element non-isothermal phase-field simulations of the SLS single scan. To confront the high computation cost, we propose a novel algorithm analogy to minimum coloring problem and manage to simulate a system of 200 grains with grain tracking algorithm using as low as 8 non-conserved order parameters. Specifically, applying the model to SLS of the stainless steel 316L powder, we identify the influences of laser power and scan speed on microstructural features, including the porosity, surface morphology, temperature profile, grain geometry, and densification. We further validate the first-order kinetics of the transient porosity during densification, and demonstrate the applicability of the developed model in predicting the linkage of densification factor to the specific energy input during SLS.

Due to many potential promising applications, vibration-based piezoelectric energy harvesters (VPEH) with a clamped circular diaphragm are an intensively studied design in the field of piezoelectric energy harvesters. Nonetheless, their performance still leaves space for improvement, which is the primary target of this article. We define two structural parameters, namely the ratio ϖ ₁ between the bonding area and the piezoceramic diameter as well as the ratio ϖ ₂ between the clamping rim and the substrate diameter, to characterize these structures. A vibration model is developed in order to provide an analytical foundation for the identification of optimal parameters ϖ ₁ and ϖ ₂ . It is verified by finite-element simulations and substantive experiments. The results allow to relate the device performance, including resonance frequency and output power, to ϖ ₁ and ϖ ₂ . This shows that the output rises with increasing ϖ ₂ , and that the maximum output for a given ϖ ₂ always lies in the range ϖ 1 ∈ ( 0.1, 0.2 ) . Based on this observation, an improved harvester structure with a pre-stress of 0.3 N is identified, that exhibits a matched power up to 16.3 mW at 219 Hz. This demonstrates the feasibility to achieve VPEHs with higher outputs and lower eigenfrequency through simultaneous modification of ϖ ₁ and ϖ ₂ , which is highly beneficial for low-frequency energy harvesting.

Modeling and simulation of powder bed fusion (PBF) remain a great challenge due to the sophisticated and interactive nature of underlying physics. A unified scenario considering interactions among the heat transfer, melt flow dynamics and microstructure evolution (noted as “heat–melt–microstructure-coupled processes”) is therefore essential for a thermodynamically consistent description and thus reliable microstructure prediction. In contrast to the state of the art, where either individual aspects are considered or the thermal history is taken as input from separate numerical scheme, we propose in this work a unified non-isothermal phase-field model for the heat–melt–microstructure-coupled processes during PBF. Simulations on a stainless steel 316L powder bed demonstrate that the model can reproduce well-observed features, but also help to discover new in-process phenomena and reveal the mechanism of the defect formation. Based on massive simulation results, we also present the densification map with respect to beam power and scan speed, and have classified the regions of the parameter combination by the distinct resultant morphology.