Flow characteristics and hot workability of a typical low-alloy high-strength steel during multi-pass deformation

Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.

Application of 3D Electrical Resistivity Tomography for Diagnosing Leakage in Earth Rock-Fill Dam

The leakage occurs during operation of the dam in Liuhuanggou reservoir. It’s a threat to the safety of the people’s lives and property in downstream. In order to eliminate the hidden danger of reservoir, ensure the safety of the dam, play better the function of flood control and water storage of the reservoir etc., we apply the 3D electrical resistivity tomography detecting technology and volume rendering image processing technology, make the measurement in field, process the data and combine the field survey to find out the leakage channels inside the dam. The results show that the 3D resistivity images appear the low resistivity zone corresponding with the leakage channels. There are two main leakage channels that come from different location inside the dam. It is feasible to diagnose the leakage in earth rock-fill dam by applying 3D electrical resistivity tomography.

Analysis of the Probability Model of Wind Load on the Offshore Wind Turbine

According to the actual measurement data, probability models of horizontal wind load were obtained based on wind velocity statistic and power spectral density function of fluctuating wind velocity through stochastic sampling and using spectrum analysis method. Through the comparison of two models, probability models of horizontal wind load based on probability models of fluctuating wind velocity were obtained by revising the mean and variance of fluctuating wind velocity. Results show that the variance takes lower value when the power spectral density function of fluctuating wind velocity is used to obtain the probability model of horizontal wind load. The quadratic term of fluctuating wind velocity takes a small contribution value in total wind load with almost no contribution to the model of horizontal wind load. It is convenient for practical engineering to obtain the models of horizontal wind load by using probability models of fluctuating wind velocity.

Application Study on Rigidity Correlation Method for Density Inversion of Rockfill

Based on the theoretical model of rigidity correlation method, the study on application was carried out with Chinese Liyuan face rockfill dam as example. The linear relation equations between the rockfill rigidity and density measured by pit method were established, and the regression performance and accuracy of rigidity correlation method were analyzed by calculating the inversion values of density. The results show that the regression equations of rigidity correlation method are high significant so as to work out the rockfill density precisely;rigidity correlation method is used for density inversion of rockfill with minor error and namely high accuracy, which is proper with satisfactory results.

Comparison between the Isotope Tracking Method and Resistivity Tomography of Earth Rock-Fill Dam Seepage Detection

This paper compares the different inversion results of three different earth rock-fill dam models with the actual leakage passages by performing isotope tracing tests and resistivity tomographic tests. The accuracy of the experimental results is evaluated, and the characteristics of these two methods are analyzed. As a result, some significant references are offered for earth rock-fill dam’s hidden defects detection. The experimental results show that the leakage and the direction of the seepage can be judged by isotope tracing tests, meanwhile, the degree of the leakage can be confirmed through the determination of the horizontal seepage velocity and the vertical seepage velocity, but it is difficult to properly determine the position of leakage passages and the range of leakage. Relatively speaking, the positions of the leakage passages can be accurately and directly displayed through resistivity tomographic tests. The experiment results show that the resistivity tomographic method is much better than isotope tracing method with regard to earth rock-fill dam’s hidden defects detection, and the resistivity tomographic method expresses much more convenience and much higher precision than isotope tracing method.

Genome architecture and selective signals compensatorily shape plastic response to a new environment

Transcriptional plasticity interacts with natural selection in complexways and is crucial for the survival of species under rapid climate change.How 3D genome architecture affects transcriptional plasticity and its interaction with genetic adaptation are unclear.We transplanted estuarine oysters to a new environment and found that genes located in active chromatin regions exhibited greater transcriptional plasticity,and changes in these regions were negatively correlatedwith selective signals.

300M高强钢大型构件全流程锻造变形机理及工艺研究进展

高强钢大型构件是国防工业和国民经济中高端装备的关键承力构件,其质量直接关系着高端装备的使用性能及服役安全.高强钢大型构件往往结构尺寸大、形状复杂,锻造成形过程中变形道次多,使得在变形过程中材料的软化机制多且复杂、温度分布差异大、流动行为难控,进而使得其形性协调难控制.因此,有必要开展高强钢大型构件锻造中的变形机理及工艺研究.本文综述了本团队联合中国第二重型机械集团德阳万航模锻有限责任公司(下文简称“二重万航”),围绕高强钢大型构件全流程锻造变形机理及工艺所做的研究工作.在机理方面,讨论了高强钢大型构件全流程锻造微观演化机制及宏微观建模与模拟.在工艺方面,讨论了材料热加工性能评估方法、毛坯-预锻件联合优化设计方法及局部控温控流工艺.在应用方面,介绍了二重万航基于上述理论指导及技术支持,实现不同机型起落架外筒及活塞杆成功研制实例,突破了大型构件整体模锻技术所面临的难题.最后对大型构件锻造机理及工艺进行了总结和展望.

植物次生细胞壁生物合成的转录调控网络

植物次生细胞壁包含纤维素、半纤维素和木质素,赋予细胞壁机械强度及疏水性,这种特性对植物直立生长、水分和营养物质运输以及抵御生物和非生物胁迫十分重要。该文总结了调控次生细胞壁生物合成的转录因子及其调控机制,包括NAC转录因子调控次生壁合成的一级开关作用,AtMYB46/AtMYB83及其下游调控因子的二级开关作用,以及其它转录因子对次生壁生物合成的调控作用,并对未来研究内容和方法进行了展望,以期为深入系统理解次生细胞壁生物合成的转录调控网络提供参考。

Collaborative Control of Novel Uninterrupted Propulsion System for All-Climate Electric Vehicles

Over the past decade,the electric vehicle industry of China has developed rapidly,reaching one of the highest technological levels in the world.Nevertheless,most electric buses currently serve urban areas,being unsuitable for all-climate operations.In response to the objective of massively adopting electric vehicles for transportation during all the events of the 2022 Beijing Winter Olympics,a dual-motor coaxial propulsion system for all-climate electric vehicles is proposed.The system aims to meet operating requirements such as high speed and adaptability to mountainous roads under severely cold environments.The system provides three operating modes,whose characteristics are analyzed under different conditions.In addition,dual-motor collaborative control strategy with collaborative gearshift and collaborative power distribution is proposed to eliminate power interruption during gearshift process and achieve intelligent power distribution,thus improving the gearshift quality and reducing energy consumption.Finally,gear position calibration for all-climate operation and proper gearshift is introduced.Experimental results demonstrate the advantages of the proposed dual-motor coaxial propulsion system regard-ing gearshift compared with the conventional single-motor automatic transmission.

Heating Lithium-Ion Batteries at Low Temperatures for Onboard Applications:Recent Progress,Challenges and Prospects

Lithium-ion batteries(LIBs)are commonly used in electric vehicles(EVs)due to their good performance,long lifecycle,and environmentally friendly merits.Heating LIBs at low temperatures before operation is vitally important to protect the battery from serious capacity degradation and safety hazards.This paper reviews recent progress on heating methods that can be used onboard.The existing methods are divided into two categories,namely external heating methods and internal heating methods,mechanisms,advantages and limitations of each method are systematically reviewed.Then,the rates of temperature rise,energy consumptions,and maximum temperature gradient of different methods are quantitatively summa-rized to compare the heating performances of each method.In addition,features related to the onboard application of each method are qualitatively compared,which is essential for the rapid cold start of EVs in frigid weather.Finally,prospects of external and internal heating methods are given.This paper aims to provide researchers and engineers with guidelines about how to select a method based on their requirements and application environments.