Fatigue life prediction of 2524‐T3 and 7075‐T62 thin‐sheet aluminium alloy with an initial impact dent under block spectrum loading

This paper presents a fatigue life prediction model of post‐impacted sheets considering the effects of dent size and stress ratio. Low‐velocity impact tests at four different impact energies were performed on specimens cut from sheets of 2524‐T3 and 7075‐T62 aluminium alloy. Following the impact tests, static tensile and uni‐axial constant amplitude and block spectrum fatigue experiments were conducted. Numerical models were generated to determine the initial residual stress patterns, residual stress relaxation, and stress concentration factors around the impact dent. The S‐N curves and corresponding stress concentration factors and relaxed residual stresses of three of the post‐impacted specimens were used to determine the model parameters. Good agreement was achieved between the predictions and experimental results, and it has been demonstrated that the fatigue life prediction model can effectively simulate the effects of residual stress, stress concentration, and stress ratio on fatigue damage for post‐impacted thin sheet aluminium alloy materials

Surface regulation of Cu-based catalysts to adjust the selectivity and promotion strategy of electrochemical reduction of CO2 to C2 products

Electrochemical CO2 reduction reaction (CO2RR) holds great promise as a method for converting CO2 into valuable fuels and chemical raw materials using renewable energy. Cu, a key element in CO2RR, has garnered significant attention for its ability to transform CO2 into high-value fuels. In recent years, there has been a widespread focus on understanding various factors influencing the catalytic performance of copper, including crystal orientation, morphology, and size. Additionally, the presence of additive elements has been found to impact the reaction process through different mechanisms, influenced by concentration and binding forms. The catalytic design process is complicated by the intricate interplay of these factors, making it challenging to isolate individual effects. In this review, we examine the recent advancements in catalyst design, focusing on the influence of the surface structure of metallic Cu on the selectivity of CO2RR. Additionally, we provide a summary of how additives contribute to enhancing catalyst performance. Novel concepts are put forth for the design of Cu-based catalysts, with the aim of overcoming the current selectivity challenges. To begin, we elucidate the impact of surface structure design on CO2RR selectivity, with a specific emphasis on ethylene and ethanol production. Subsequently, we highlight the remarkable contributions of bimetallic catalysts to the selectivity of CO2RR. Finally, we propose the incorporation of cooperative and confinement effects as a strategy to modulate the selectivity of CO2RR. We look ahead to the future prospects of CO2RR, anticipating further breakthroughs in this field.</p

Harmonics propagation and interaction evaluation in small-scale wind farms and hydroelectric generating systems

The harmonics exacerbated by the integration of distributed energy such as wind power has been extensively studied. However, the interaction and propagation mechanism between harmonic sources in the hydro-wind complementary generation system are still not clear. To tackle this challenge, the presented study establishes the hydro-wind complementary generation system model and explores the harmonics propagation and interaction in all components. Then three operation mode of complementary system (scenario 1: stand-alone Hydroelectric Generating System, scenario 2: stand-alone Wind Farm (WF) and scenario 3: complementary generation system) are selected. The results demonstrate that the integration of HGS diminishes the harmonic at DFIG side but at the grid side. In complementary generation system, the THDu rises but the corresponding THDi declines due to the regulation of power grid. Furthermore, the odd harmonics interactions analysis reveal that the doubly-fed induction generator's (DFIG) side and the stator's side are the two high-risk sources in the complementary generation process. The presented results provide a basis for power quality evaluation of hydro-wind complementary generation system

Optimization and decision making of guide vane closing law for pumped storage hydropower system to improve adaptability under complex conditions

The pumped storage hydropower system (PSHS) is considered a high-quality peaking and frequency regulation energy source due to its operational flexibility and fast response. However, its frequent regulation leads to complex operating conditions with potential harm to the stability of the system. This paper focuses on analyzing and improving the adaptability of guide vane closing law under complex conditions. This is obtained by proposing a refined numerical model of PSHS considering non-linear factors and analyzing the effects of the guide vane closing law and initial operating conditions on the load rejection. The results revealed that a suitable two-stage guide vane closing law effectively reduces the risk of load rejection. In addition, when the initial load of two units is different, it is beneficial to improve the load rejection characteristics when the unit with the smaller load rejects the load first. Finally, three groups of parameters for the optimal guide vane closing law (the Pareto solution sets) are obtained by multi-objective sparrow search algorithm (MOSSA) under the rated, maximum water head, and maximum rotational speed conditions. The obtained Pareto solution and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) are used for scoring the solutions and obtain an optimal suitable for complex operating conditions. The water head and rotational speed are reduced by an average of 7.76 % and 3.74 % for the different operating conditions compared to the model validation results, respectively. These results provide a theoretical basis for the selection of the optimal guide vane closing laws and improve the safety during load rejection under complex practical operating conditions

Liquid flow spinning mass-manufactured paraffin cored yarn for thermal management and ultra-high protection

Thermal management and ultra-high protection textiles are critical for polar scientists, astronauts and firefighters. Phase change materials (PCMs) effectively retard huge thermal changes, and thermal damage by absorbing or releasing heat during phase transition. However, due to the materials and engineering challenges inherent in PCMs based textiles, commercial PCMs usually suffer with high rigidity, no-breath-ability, easy leakage and abrasion, limiting their potential applications. Herein, we proposed a mass-producible liquid flow spinning (LFS) method, in which molten paraffin is poured into continuous hollow silicon tubes and then wrapped by staple fibers to form paraffin-coated yarns (PCYs) on a friction spinning frame. The obtained PCYs showed enhanced mechanical properties (break strength of 7.80 N, wear resistance of 2000 cycles) due to the novel core-sheath yarn structure. Besides, thanks to the high melting enthalpy (60.967 J/g) of PCYs, the yarns showed the excellent temperature regulating effect. A double-sided joint PCYs fabric (PCYF) is fabricated to study the PCYs performance further, results show that the PCYF can withstand 10,000 cycles of abrasion without breakage and PCMs leakage. Furthermore, owing to the much gaps provided by the stretch fibers and interweaving points, the fabric exhibits good breathability. In particular, compared with commercial PCMs based textiles, our PCYF is superior in thermal protection performance (9 °C lower). The fireproof performance is also excellent as our PCYF can withstand flame temperatures higher than 1142 °C. The PCYs production method provided here could pave the way for human thermal protection textiles