查看更多>>摘要：Recognizing target intent is crucial for making decisions on the battlefield.However,the imperfect and ambiguous character of battlefield situations challenges the validity and causation analysis of classical intent recognition techniques.Facing with the challenge,a target intention cau-sal analysis paradigm is proposed by combining with an Intervention Retrieval(IR)model and a Hybrid Intention Recognition(HIR)model.The target data acquired by the sensors are modelled as Basic Probability Assignments(BPAs)based on evidence theory to create uncertain datasets.Then,the HIR model is utilized to recognize intent for a tested sample from uncertain datasets.Finally,the intervention operator under the evidence structure is utilized to perform attribute inter-vention on the tested sample.Data retrieval is performed in the sample database based on the IR model to generate the intention distribution of the pseudo-intervention samples to analyze the cau-sal effects of individual sample attributes.The simulation results demonstrate that our framework successfully identifies the target intention under the evidence structure and goes further to analyze the causal impact of sample attributes on the target intention.
查看更多>>摘要：The traditional clustering algorithm is difficult to deal with the identification and division of uncertain objects distributed in the overlapping region,and aimed at solving this problem,the Evidential Clustering based on General Mixture Decomposition Algorithm(GMDA-EC)is pro-posed.First,the belief classification of target cluster is carried out,and the sample category of tar-get distribution overlapping region is extended.Then,on the basis of General Mixture Decomposition Algorithm(GMDA)clustering,the fusion model of evidence credibility and evi-dence relative entropy is constructed to generate the basic probability assignment of the target and achieve the belief division of the target.Finally,the performance of the algorithm is verified by the synthetic dataset and the measured dataset.The experimental results show that the algorithm can reflect the uncertainty of target clustering results more comprehensively than the traditional probabilistic partition clustering algorithm.
查看更多>>摘要：The Ti17(α+β)-Ti17(β)dual alloy-dual property blisk produced using Linear Friction Welding(LFW)is considered as high-performance component in advanced aeroengine.However,up to now,microstructure evolution and relationship between microstructure and micro mechanical properties of LFWed Ti17(α+β)/Ti17(β)dissimilar joint have not been thoroughly revealed.In this work,complex analyses of the phase transformation mechanisms of the joint are conducted,and phase transformations in individual zones are correlated to their microhardness and nanohard-ness.Results reveal that α dissolution occurs under high temperatures encountered during LFW,which reduces microhardness of the joint to that of Ti17(α+β)and Ti17(β).In Thermo-Mechanically Affected Zone of Ti17(α+β)(TMAZ-(α+β))side joint,a large number of nanocrystalline α phases form with different orientations.This microstructure strengthens signifi-cantly by fine grains which balances partial softening effect of α dissolution,and increases nanohardness of α phase and microhardness of TMAZ-(α+β).Superlattice metastable β phase precipitates from metastable β in Weld Zone(WZ)during quick cooling following welding,because of short-range diffusion migration of solute atoms,especially β stabilizing elements Mo and Cr.The precipitation of the superlattice metastable β phase results in precipitation strengthening,which in turn increases nanohardness of metastable β and microhardness in WZ.
查看更多>>摘要：Previous Particle Boundary(PPB),as the detrimental structure in Powder Metallurgy(PM)components,should be eliminated by subsequent hot process to improve the mechanical properties.The objective is to investigate the Dynamic Recrystallization(DRX)nucleation mech-anisms and grain growth behavior of the 3rd-generation PM superalloy with PPB structure.Microstructure observation reveals that PPB decorated with(Ti,Ta,Nb)C carbides belongs to the discontinuous chain-like structure.The elimination of PPB networks can be achieved effectively via hot deformation due to the occurrence of DRX.Four different DRX nucleation mechanisms were proposed and discussed in detail according to the special microstructure characteristics of the PM superalloy.Firstly,local lattice rotations can be detected in the vicinity of(Ti,Ta,Nb)C carbides during hot deformation and thus PPB structure serves as the preferential nucleation sites for DRX grains via Particle-Stimulated Nucleation(PSN).Then,Discontinuous-DRX(DDRX)characterized by grain boundary bulging dominates the microstructure refinement and Continuous-DRX(CDRX)operated by subgrain rotation can be regarded as an important assis-tant mechanism.At last,the initial ∑3 boundaries would lose their twin characteristics owing to the crystal rotation and then transform into the general High Angle Grain Boundaries(HAGBs).The distorted twins provide additional DRX nucleation sites,viz.,twin-assisted nucleation.Partic-ular attention was focused on the grain growth behavior of the PM superalloy in subsequent anneal-ing process.The recrystallization temperature was determined to be about 1110 ℃ and 1140 ℃ can be considered as the critical temperature for grain growth.The findings would provide theoretical support for microstructure refinement of the 3rd-generation PM superalloy,which is of pivotal sig-nificance for improving the mechanical properties of aviation components.
查看更多>>摘要：The 8 mm-thick 2195 Al-Li alloy joints were achieved by Friction Stir Welding(FSW).The microstructural evolution,temperature-dependent mechanical properties,and fracture proper-ties were studied.The Ti,δ'/β'and θ'precipitates were observed in the Base Metal(BM)and the Heat Affected Zone(HAZ).Most of the precipitates,except for re-precipitated δ'/β'phases,were dissolved in the Nugget Zone(NZ).The tensile specimens that failed at cryogenic temperatures(-196 ℃)had the maximum Ultimate Tensile Strength(UTS),and the fracture surface showed the inter-granular fracture characteristics.Compared to those at room temperature(25 ℃),the decreasing tensile properties at high temperature(180 ℃)were related to microstructure and strain hardening effects.The NZ presented the optimal fracture toughness,and the Crack Tip Opening Displacement(CTOD)was mutually dominated by microhardness and grain size.Analysis on Fati-gue Crack Growth(FCG)rates indicates that the Thermal-Mechanically Affected Zone(TMAZ)exhibited the most superior fatigue resistance performance at stress intensity range below 17 MPa.m1/2 due to compressive residual stress and the crack closure effect.The fatigue fracture surfaces reveal that the crack propagation zone was characterized by the striations and secondary cracks.Also,inter-granular fracture behavior was responsible for the fastest FCG rates in the NZ.
查看更多>>摘要：Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC com-posites,ablation experiments under different Laser Energy Density(LAED)and LAG experiments are conducted.Evolution rules and mechanism of physical phase,ablation morphology and crack characteristics caused by laser irradiation are investigated.The forces of LAG and Conventional Grinding(CG)are compared.The results show that ablation surface changes from slight oxidation to obvious material removal with LAED increasing,and ablation depth increases gradually.The ablation products change from submicron SiO2 particles to nanoscale particles and floccule.High LAED promotes SiC decomposition and sublimation,which leads to the increase of C element.The SiC phase forms corrugated shape in recast layer and columnar shape in Heat Affected Zone(HAZ)at 56 J/mm2.The cold and heat cycle leads to formation of fishbone crack.For ablation specimen under 30 J/mm2,the grinding force can be reduced by a maximum of 39％and brittle damage region is reduced.The material removal and microcrack generated will significantly reduce the hardness and improve machinability,which can promote grinding efficiency.
查看更多>>摘要：Submerged abrasive waterjet peening(SAWJP)is an effective anti-fatigue manufacturing technology that is widely used to strengthen aeroengine components.This study investigated the correlation of SAWJP process parameters on surface integrity and fatigue life of titanium alloy TA 19.SAWJP with different water pressures and standoff distances(SoDs)was conducted on the TA19 specimens.The surface integrity of the specimens before and after SAWJP with different process parameters was experimentally studied,including microstructure,surface roughness,micro-hardness,and compressive residual stress(CRS).Finally,fatigue tests of the specimens before and after SAWJP treatment with different process parameters were carried out at room temperature.The results highlighted that the fatigue life of the TA19 specimen can be increased by 5.46,5.98,and 6.28 times under relatively optimal process parameters,which is mainly due to the improved surface integrity of the specimen after SAWJP treatment.However,the fatigue life of specimens treated with improper process parameters is decreased by 0.55 to 0.69 times owing to the terrible surface roughness caused by the material erosion.This work verifies that SAWJP can effectively improve the surface integrity and fatigue life of workpieces,and reveals the relationship between process parameters,surface integrity,and fatigue life,which provides support for the promotion of SAWJP in the manufacturing fields.
查看更多>>摘要：Heterogeneous pressure-carrying medium was employed to establish a differentiated pressure field on sheet metal in flexible die forming process in this work,which aimed at matching the non-symmetric shape of target component and improving metal inflow to avoid local tensile instability.Specifically,metal inflow corresponding to the differentiated pressure field was analyti-cally evaluated.Forming of a typical non-symmetric shell component was experimentally and numerically studied based on the proposed method.Compared with forming processes based on the uniform pressure,difference of metal inflow in two sides of the non-symmetric component increased from 2.16 mm to 3.36 mm and metal inflow in critical region increased by 11.9％when differentiated pressure field(taking heterogeneous elastomer #4-3 for example)was employed.The resultant maximum thinning ratio decreased by 4.2％and the uniformity of shell thickness increased by 16.9％.With the decrease of Shore hardness of elastomer in the formed region,stress path in the ready-to-form region transferred towards the bi-axial tension stress state,i.e.,stress ratio(α)increased.And,stress triaxiality(η)in characteristic regions were regulated appropriately,which decreased the risk of tensile instability.It was attributed to the decreased normal pressure and fric-tional resistance at sheet/elastomer interface in the formed region.
查看更多>>摘要：For rough machining of a complex narrow cavity,e.g.,a complex blisk channel on an aero-engine,the typically used cutting tools are the slender cylindrical cutter and conical cutter.Nevertheless,as neither of the two is particularly suited for rough machining,wherein the main pur-pose is to remove a large volume as quickly as possible,the machining efficiency is low,especially when the part materials are of hard-to-cut types(e.g.,Titanium-alloy)for which it often takes days to rough machine a blisk.Fortunately,disc machining provides a new and efficient roughing solu-tion,since a disc cutter with a large radius enables a much larger cutting speed and thus a larger material removal rate.However,due to the large radius of the disc cutter,its potential collision with narrow and twisted channels becomes a serious concern.In this paper,we propose a novel two-phase approach for efficiently machining a complex narrow cavity workpiece using a disc-shaped cutter,i.e.,3+2-axis disc-slotting of the channel by multiple layers(rough machining)+five-axis disc-milling of the freeform channel side surfaces(semi-finish machining).Both simulation and physical cutting experiments are conducted to assess the effectiveness and advantages of the pro-posed method.The experimental results show that,with respect to a same cusp-height threshold on the channel side surfaces,the total machining time of the tested part by the proposed method is about only 36％of that by the conventional approach of plunging-milling(for roughing)plus milling by a slender cylindrical cutter(for semi-finishing).
查看更多>>摘要：The wheel brake system of an aircraft is the key to ensure its safe landing and rejected takeoff.A wheel's slip state is determined by the brake torque and ground adhesion torque,both of which have a large degree of uncertainty.It is this nature that brings upon the challenge of obtaining high deceleration rate for aircraft brake control.To overcome the disturbances caused by the above uncertainties,a braking control law is designed,which consists of two parts:runway surface recognition and wheel's slip state tracking.In runway surface recognition,the identification rules balancing safety and braking efficiency are defined,and the actual identification process is realized through recursive least square method with forgetting factors.In slip state tracking,the LuGre model with parameter adaptation and a brake torque compensation method based on RBF neural network are proposed,and their convergence are proven.The effectiveness of our con-trol law is verified through simulation and ground experiment.Especially in the experiments on the ground inertial test bench,compared to the improved pressure-biased-modulation(PBM)anti-skid algorithm,fewer wheel slips occur,and the average deceleration rate is increased by 5.78％,which makes it a control strategy with potential for engineering applications.
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