Time Series Forecasting Fusion Network Model Based on Prophet and Improved LSTM

Time series forecasting and analysis are widely used in many fields and application scenarios.Time series historical data reflects the change pattern and trend,which can serve the application and decision in each application scenario to a certain extent.In this paper,we select the time series prediction problem in the atmospheric environment scenario to start the application research.In terms of data support,we obtain the data of nearly 3500 vehicles in some cities in China fromRunwoda Research Institute,focusing on the major pollutant emission data of non-road mobile machinery and high emission vehicles in Beijing and Bozhou,Anhui Province to build the dataset and conduct the time series prediction analysis experiments on them.This paper proposes a P-gLSTNet model,and uses Autoregressive Integrated Moving Average model(ARIMA),long and short-term memory(LSTM),and Prophet to predict and compare the emissions in the future period.The experiments are validated on four public data sets and one self-collected data set,and the mean absolute error(MAE),root mean square error(RMSE),and mean absolute percentage error(MAPE)are selected as the evaluationmetrics.The experimental results show that the proposed P-gLSTNet fusion model predicts less error,outperforms the backbone method,and is more suitable for the prediction of time-series data in this scenario.

Variant selection, coarsening behavior of α phase and associated tensile properties in an α+β titanium alloy

Effect of cooling rates,i.e.,air cooling and furnace cooling,after solution in α+β phase-field on variant selection,coarsening behavior of α phase and microstructure evolution were investigated in α+β TC21 alloy.The textures of primary α(α_(p))and lamellar α(α_(L))in β phase transformation microstructure(β_(t))were analysed separately,and the orientation relationship among α_(p),α_(L) and the parent β phase were studied.In addition,the influence of the microstructure characteristics on the tensile properties was investigated.The results showed that all parent β grains,despite their different orientations,produced 12 ideal α_(L) variants with the same texture components and interweave to form a basketweave β_(t) structure under the air-cooling condition.The α_(p) without Burgers orientation relationship(BOR)with β phase exhibited obviously texture component without overlapping theαL texture component.The volume fraction of α_(p) in the furnace-cooled sample(about 50%)was higher than that of the air-cooled sample(about 12%),while the size of it slightly increased with decreasing the cooling rate.In each β grain,the thick α_(L) in the same orientation formed anαcolony.A typical 3 variant colonies which were related to each other were observed.Consequently,the α_(L) spatial orientation distribution showed more heterogeneity.Moreover,the BOR between α_(p) and β and the same orientation of some α_(L) and the surrounding α_(p) grains resulting in the overlapping of α_(p) texture component and α_(L) texture component.At last,the relationship between microstructure and tensile properties was analysed.

Toughening effects of Mo and Nb addition on impact toughness and crack resistance of titanium alloys

Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb alloys were prepared to investigate the toughening effects ofβstabilizers Mo and Nb on impact toughness and crack resistance of titanium alloys.Instrumented Charpy impact tests showed that the total impact absorbed energy of Ti-6Al-2Mo and Ti-6Al-3Nb(∼64 J)were two times higher than that of Ti-6Al(∼30 J),indicating the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.Analysis of load-displacement curves revealed the similar crack initiation energy of Ti-6Al,Ti-6Al-2Mo and Ti-6Al-3Nb(15.4 J,16.1 J and 15.0 J,respectively).However,the higher crack propagation energy of Ti-6Al-2Mo and Ti-6Al-3Nb(46.7 J and 48.3 J,respectively)were about three times higher than that of Ti-6Al(14.4 J),indicating the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Post-mortem analysis of impact samples demonstrated that the increased dislocation density and deformation twinning were mainly responsible for the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb.Due to the invisibility of dislocation activation and deformation twinning during the Charpy impact process,a mathematical model has been proposed to evaluate the effects of Al,Mo and Nb elements on dislocation mobility based on the Yu Rui-huang electron theory.Addition of Mo and Nb elements significantly improved the dislocation mobility in Ti-6Al-2Mo and Ti-6Al-3Nb compared to that in Ti-6Al alloy.Therefore,more dislocations were activated in Ti-6Al-2Mo and Ti-6Al-3Nb which supplied the larger plastic deformation under impact loading.A dislocation-based model also has been proposed to interpret the nucleation and propagation of deformation twinning under the impact loading.Dislocation pileup atα/βinterfaces provided potential sites for nucleation of deformation twinning in Ti-6Al-2Mo and Ti-6Al-3Nb.Furthermore,deformation twinning facilitated the dislocation motion inαgrains with hard orientations.The increased dislocation mobility and deformation twinning were responsible for the stronger crack resistance as well as the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys.

New insights in the development ofαphase during continuously heating in aβ-quenched Ti-5321 alloy

Near β titanium alloys are attractive materials for aeronautical applications due to their high specific strength,excellent damage tolerance performance and good hardenability.Their mechanical properties are strongly governed by the microstructural characteristics,especially the morphology,volume fraction,orientation and distribution of theαphase.

Processing of metastable beta titanium alloy:Comprehensive study on deformation behaviour and exceptional microstructure variation mechanisms

Thermomechanical processing(TMP)is especially crucial for metastableβtitanium alloys,which has received significant attention in the community for a long time.In this contribution,the processing-responding behaviour including microstructure evolution process,texture variation mechanism,and un-derlying deformation process of powder metallurgy Ti-5553 alloy in a wide processing parameter range was comprehensively investigated.Thermal physical simulation was performed on the alloy at temper-atures ranging from 800℃ to 1100℃,and strain rates between 0.001 s^(−1) and 10 s^(−1),to varied defor-mation degrees of 20%-80%height reduction.It was found that the processing parameters(i.e.temper-ature,strain rate,and deformation degree)are influential on the deformation process and resultant mi-crostructure.Varied microstructural evolution processes forβphase including flow localization,dynamic recovery,dynamic recrystallization,and grain coarsening are activated in different processing domains,while different evolution mechanisms forαphase including dynamic precipitation,phase separation,dy-namic coarsening,and mechanical shearing also play their roles under different processing conditions.In particular,four exceptional evolution mechanisms ofαprecipitation which have not been previously reported in titanium alloys were discovered and clearly demonstrated,more specifically,they are multi-interior twinning,internal compositing,layered coarsening and selective diffusion-actuated separation.After the establishment of comprehensive microstructural evolution mechanism maps,the guidance for precise processing and the knowledge reserve extension for deformation process of metastableβtita-nium alloys can be effectively achieved.

Deformation mechanisms in aβ-quenched Ti-5321 alloy:In-situ investigation related to slip activity,orientation evolution and stress induced martensite

The deformation behavior ofβ-quenched nearβTi-5321(Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe)alloy was systematically studied using in-situ tensile test monitored by the scanning electron microscopy(SEM).Besides,the electron backscatter diffraction(EBSD)was performed to thoroughly discuss the deformation mechanisms.The results indicated that slip activities,crystal rotation and stress induced martensite transformation were the major deformation mechanisms in theβ-quenched Ti-5321 alloy during in-situ tensile testing.The slip activities were investigated by using the EBSD-trace analysis,which demonstrated that{110}<111>,{112}<111>and{123}<111>slip systems were activated and the{110}<111>slip system dominated.Besides,βgrains rotated about 7.8°to accommodate the increased macrostrain.Notably,the stress induced martensiteα″which was related to the double yielding behavior during tensile process exhibited multiple characteristics.The differentα″variants divided theβmatrix into smallerβblocks with a typical zigzag morphology,in which oneα″variant passed through another one by deflecting its initial growth direction.Moreover,the deformation twinning in martensiteα″and slip bands cutting through martensiteα″effectively accommodated the local strain.These systematically analysis can provide insightful information about the deformation mechanisms in nearβtitanium alloys.

The relationship between slip behavior and dislocation arrangement for large-size Mo-3Nb single crystal at room temperature

The slip behavior and mechanism of large-size Mo-3Nb single crystal have been investigated and disclosed comprehensively at room temperature by quasi-static compression with various strains.With the increase of deformation,the slip traces change from shallow non-uniform slip lines to dense and uniform slip bands.Different slip traces in the same deformation condition were observed,suggesting that the slip traces in the single crystal are controlled by different types and arrangement mechanisms of mobile dislocation.To clarify the relationship between slip behavior and dislocation arrangement,TEM and AFM analyses were performed.Significant discrepancy between the mobility of screw segments and edge segments caused by double cross-slip multiplication mechanism is the reason why different slip features were witnessed.During the whole slip deformation process,screw dislocations play a dominant role and they are inclined to form wall-substructures by interaction and entanglement.With the development of dislocation accumulation,the entangled dislocation walls evolve into dislocation cells with higher stability.