ABSTRACT
Regulating the microstructure of powder metallurgy (P/M) nickel-based superalloys to achieve superior mechanical properties through heat treatment is a prevalent method in turbine disk design. However, in the case of dual-performance turbine disks, the complexity and non-uniformity of the heat treatment process present substantial challenges. The prediction of yield strength is typically derived from the analysis of microstructures under various heat treatment regimes. This method is time-consuming, expensive, and the accuracy often depends on the precision of microstructural characterization. This study successfully employed a coupled method of Artificial Neural Network (ANN) and finite element analysis (FEA) to reveal the relationship between the heat treatment process and yield strength. The coupled method accurately predicted the location specified and temperature-dependent yield strength based on the heat treatment parameters such as holding temperatures and cooling rates. The root mean square error (RMSE) and mean absolute percentage deviation (MAPD) for the training set are 50.37 and 3.77, respectively, while, for the testing set, they are 50.13 and 3.71, respectively. Furthermore, an integrated model of FEA and ANN is established using a Abaqus user subroutine. The integrated model can predict the yield strength based on temperature calculation results and automatically update material properties of the FEA model during the loading process simulation. This allows for an accurate calculation of the stress-strain state of the turbine disk during actual working conditions, aiding in locating areas of stress concentration, plastic deformation, and other critical regions, and provides a novel reliable reference for the rapid design of the turbine disk.
ABSTRACT
A new grain growth model was developed by introducing the ultimate grain size to the traditional model. The grain growth behavior and its ultimate size under the Zenner pinning force are also discussed. This model was applied to the nickel-based superalloy and integrated into an FEM code. The grain evolution of a forged third-generation powder superalloy heat treated at different temperatures and holding times was studied. A gradient heat treatment setup was designed and implemented for a full-size turbine disc based on the model prediction to meet the accurate dual-microstructure requirements of an advanced aero-engine turbine disc design. The predicted temperature was validated by thermal couple measurements. The relative error between the prediction and the measurements is less than 2%. The metallographic examination of the whole turbine disk through sectioning showed that the grain size was ASTM 7-8 at the rim area and ASTM 11-12 at the bore region, which agrees well with the prediction. The predicted values of the three measurement areas are ASTM 12.1, ASTM 9.1, and ASTM 7.1, respectively, with a maximum error of 5% compared to the measured values. The proposed model was validated and successfully applied to help manufacture a dual-microstructure aero-engine turbine disc.
ABSTRACT
This study was designed to evaluate the ameliorating effects of curculigoside from Curculigo orchioides Gaertn on learning and memory in aged rats. In the present study, the ameliorating effects of curculigoside were determined through animal behaviour studies (including step-down test and Y-maze test), and the possible mechanisms were explored by evaluation of the activity of acetylcholinesterase (AchE) and determination of the expression of BACE1. Oral adminstration of the curculigoside (20, 40 mg/kg/day) for 14 days can significantly improve the latency and number of errors in aged rats based on the behaviour study results. In addition, the activity of AchE can be decreased by treatment of the curculigoside (10, 20, 40 mg/kg/day). Moreover, the expression of BACE1 can be down-regulated in the hippocampus of aged rats treated with curculigoside. The results of our present work have indicated that curculigoside can improve cognitive function in aged animals, possibly by decreasing the activity of AchE in the cerebra and inhibiting the expression of BACE1 in the hippocampus. In conclusion, our results suggested that curculigoside can be possible developed as a new drug for the treatment of Alzheimer's disease in the future.
