Search

In fusion‐based metal additive manufacturing (MAM), the high‐intensity energy input leads to serious evaporation, but how evaporation induces composition evolution and variation and further impacts microstructure and mechanical properties remain a knowledge gap. Here a model integrating composition evolution with molten pool dynamics is developed to reproduce temperature‐ and composition‐dependent evaporative losses and subsequent transport during laser melting. Together with comprehensive experimental characterizations and tests, the simulation results illustrate varying evaporation rates of different elements altering compositions, resulting in a 3D cirrus‐shaped concentration distribution, which significantly impacts the mechanical properties. The simulations reproduce the detailed composition evolution from surface evaporation to molten pool transport and reveal underlying mechanisms relating the composition, temperature, fluid flow, and cracking, which is challenging to observe experimentally. This study elucidates the critical role of evaporation‐induced composition evolution in determining microstructure and mechanical properties. In future alloy design for MAM, integrating initial composition and manufacturing parameters is imperative, where composition evolution simulation offers valuable guidance. [ABSTRACT FROM AUTHOR]

High voltage circuit breakers are important equipment in power systems, and the valve motion of the chambers plays a role in the arc extinguishing performance of high-voltage circuit breakers. Therefore, in this paper, a 145 kV auto-expansion SF6 circuit breaker is taken as the research object, and a two-dimensional axisymmetric magnetohydrodynamic arc model considering valve motion process is established. The influence of different short circuit breaking conditions on the valve motion was studied. The results show that the backflow phenomenon of ablated steam is the main reason for the closure of the non-return valve, which plays an important role in opening the pressure relief valve. The closing time of the non-return valve is about 0.4 ms faster at a short circuit current of 40 kA than at a short circuit current of 36 kA. [ABSTRACT FROM AUTHOR]

The C4F7N/CO2 mixed gas is most expected to replace SF6 in high-voltage power equipment, and the generation of free metal particles in gas-insulated equipment is unavoidable and highly susceptible to inducing insulation failures. In this paper, the effects of flaky, spherical, and mixed shape aluminum particle defects on the breakdown characteristics of C4F7N/CO2 mixed gas are investigated and compared to those of SF6 under the same conditions. The experimental results show that the effect of particle defects on the insulating properties of C4F7N/CO2 gas mixtures is visualized by the fact that particle defects reduce the breakdown voltage of C4F7N/CO2 gas mixtures, increase their stochasticity, and reduce the enhancement of the insulating properties of C4F7N/CO2 gas mixtures by increasing the air pressure. The greater the number of particles, the greater is the degree of influence. Comparison of the SF6 and C4F7N/CO2 gas mixtures reveals that, in the case of flake defects, increasing the air pressure improves the insulation performance of the SF6 gas better than that of the C4F7N/CO2 gas mixture. Under the condition of the same number of particles, the larger the proportion of spherical particles in the hybrid particles, the smaller is the influence of metal particles on the C4F7N/CO2 mixed gas and on SF6 gas. [ABSTRACT FROM AUTHOR]

Background: This study aimed to analyze the trends of Parkinson’s disease (PD) mortality rates among Chinese residents from 2004 to 2021, provide evidence for the formulation of PD prevention and control strategies to improve the quality of life among PD residents. Methods: Demographic and sociological data such as gender, urban or rural residency and age were obtained from the National Cause of Death Surveillance Dataset from 2004 to 2021. We then analyzed the trends of PD mortality rates by Joinpoint regression. Results: The PD mortality and standardized mortality rates in China showed an overall increasing trend during 2004–2021 (average annual percentage change [AAPC] = 7.14%, AAPCASMR=3.21%, P < 0.001). The mortality and standardized mortality rate in male (AAPC = 7.65%, AAPCASMR=3.18%, P < 0.001) were higher than that of female (AAPC = 7.03%, AAPCASMR=3.09%, P < 0.001). The PD standardized mortality rates of urban (AAPC = 5.13%, AAPCASMR=1.76%, P < 0.001) and rural (AAPC = 8.40%, AAPCASMR=4.29%, P < 0.001) residents both increased gradually. In the age analysis, the mortality rate increased with age. And the mortality rates of those aged > 85 years was the highest. Considering gender, female aged > 85 years had the fastest mortality trend (annual percentage change [APC] = 5.69%, P < 0.001). Considering urban/rural, rural aged 80–84 years had the fastest mortality trend (APC = 6.68%, P < 0.001). Conclusions: The mortality rate of PD among Chinese residents increased from 2004 to 2021. Male sex, urban residence and age > 85 years were risk factors for PD-related death and should be the primary focus for PD prevention. [ABSTRACT FROM AUTHOR]

One of the most essential tasks in probabilistic damage tolerance assessment is to describe the scatter in crack growth accurately. This study proposes a stochastic model of the crack growth rate, which calculates the critical parameters of a random distribution accurately by combining the Markov chain and data fitting algorithms. The proposed method is validated by the crack growth test data of Ni‐based superalloy GH4710Li at 550°C. The validation results show that the proposed method is a robust and efficient stochastic model for the crack growth rate. [ABSTRACT FROM AUTHOR]

ABSTRACT A combined high and low cycle fatigue (CCF) life prediction model, considering creep, low‐cycle fatigue (LCF), high‐cycle fatigue (HCF) at the maximum LCF nominal stress (HLCF) damages, and the interaction damage between LCF and HLCF, is proposed. The proportions for these four types of damage in total CCF damage are quantified. Compared with the existing CCF models, the CCF model proposed in this paper considers creep damage in CCF and has higher accuracy. The escalation in HCF stress amplitudes leads to reduced CCF life owing to the augmentation of HLCF and interaction damages. The increase in the cycle ratio of HCF to LCF, causing a reduction in CCF life is ascribed to elevated HLCF and creep damages. The calculated damage proportion results from the proposed model are consistent with the observations of the fracture characteristics using a scanning electron microscope (SEM), indicating the necessity of considering creep damage in CCF life prediction at high temperatures. [ABSTRACT FROM AUTHOR]