The Fatigue Design Of The Auxiliary Frame Of The Agitator Truck Based On Equivalent Static Loads And The Response Surface Method

Fatigue damage is the main form of early failure of the mechanical parts. Withthe modern machinery developing at high-speed and in large-scale, many componentsare operated in very harsh working environment, such as high temperature, highpressure, heavy load and corrosion. Also it is difficult to find fatigue damage onaccount of its imperceptibility and abruptness, so fatigue failure accidents, doinggreat harm to life and property, occur one after another.In recent years, with the large-scale of infrastructure construction, the AgitatorTruck plays an important role in the project construction，so major manufacturers andcompanies pay much attention to the fatigue problem. For the problem that AuxiliaryFrame is prone to fracture in practical use and fatigue life is far longer than that of thedesign requirements, this thesis then unifies the engineering actual problem toconduct the thorough research on fatigue design of the Auxiliary Frame of theAgitator Truck using the equivalent static load method, dynamic topologyoptimization, response surface method and6σ robust optimal design.The main research work is as follows:(1) A simplified simulation model of the Agitator Truck is established. In thismodel, tires and leaf spring are replaced with the spring of certain stiffness anddamping, while the engine, cab, Agitator Truck tanks and other structures which haveno direct contact with the Auxiliary Frame are attached to the Agitator Trucksimulation model in the form of non-structural quality. Using the simplified model tooptimize the design of the Auxiliary Frame can improve calculating efficiency andshorten the design cycle while ensuring calculating accuracy.(2) Finite element analysis and fatigue life prediction on the Agitator Truck areexecuted. Pavement spectrum when the Agitator Truck is going on poor road isgenerated using the Matlab software, according to the regulations of road roughnessin national standard. Then the pavement spectrum is loaded into simulation model ofthe Agitator Truck for transient response analysis and the stress distribution ofAuxiliary Frame is obtained. Static analysis is executed by the action of gravity aloneand stress distribution of the Auxiliary Frame is got when the Agitator Truck turns off.We can see extremely uneven stress distribution in the Auxiliary Frame, resulting inshort local life of the Auxiliary Frame. Taking the shortest position of the fatigue life as a key point in the Auxiliary Frame, the fatigue life at this point is calculatedthrough Miner’s rule, which provides guidance and basis for further optimization ofthe Auxiliary Frame.(3) For the problem that fatigue life distribution is extremely uneven in theAuxiliary Frame as a result of unreasonable design for structure, dynamic topologyoptimization is introduced to fatigue design in early design of the Auxiliary Frame.Topology optimization design is executed taking beams distribution area as designspace, upper bound of volume fraction of beams distribution area as optimizationconstraint, stress of longitudinal beam as the optimization objective. This methodconverts the problem of optimal topology of structure into that of seeking for theoptimal distribution of material in a given design area, thus making the structurestress distribution relatively uniform and improving the fatigue life. Through dynamictopology optimization of the mixer vice frame, the fatigue life is relatively evenlydistributed and the fatigue life of the key points is improved from8.0E5to6.5E6,laying a foundation for further optimization design.(4) For the problems that the sensitivity analysis is difficult, dynamic constraintis hard to handle and the development for optimized dynamic software is morecomplex in dynamic topology optimization, combining equivalent static load methodand dynamic topology optimization method, the time factor of dynamic load isremoved and dynamic topology optimization is converted to the static topologyoptimization of multiple loading cases. The topological optimization of the AuxiliaryFrame is executed using the static topology optimization method that is mature intheory or practice, thus, dynamic topology optimization is simplified and theefficiency of the optimization design is also improved.(5) Aiming at the problem of long time in the fatigue life design, responsesurface method is applied to the fatigue life design, which means fatigue lifesimulation model of complex structures with a large degree of freedom will besubstituted by response surface model．The optimization model of fatigue life isestablished by combing finite element analysis,experiment design，response surfacemethod and optimization algorithm．The results of the optimization of the AuxiliaryFrame of the Agitator Truck show that the response surface method can effectivelyimprove efficiency in solving optimization problem and be fit for the fatigue designproblem of complex structure.(6) For the problem that the fatigue life of structure disperses widely,6σ robustoptimization design method is introduced in the fatigue design.6σ Robust optimization design of the fatigue life based on the response surface method isproposed combining the response surface method, robust design and optimum design.Through the application of this method, the mean and variance of fatigue life aredecreased on the basis of fatigue life to meet the reliability, taking into account thediscrete nature of the fatigue life. At the same time, the purpose of avoiding a largesurplus of fatigue life, reducing material consumption and increasing the AgitatorTruck’ economy is achieved. The difference between the logarithmic mean value ofthe fatigue life and the logarithm design life, the logarithm variance of the fatigue lifeand the mass of the Auxiliary Frame are both reduced to different degrees.This thesis, taking some type of a homemade Agitator Truck as an example,focused on the problem that the structure is prone to fatigue failure and excess fatiguelife, conducted fatigue design of the Auxiliary Frame of the Agitator Truck. In thisthesis, establishment of simplified Agitator Truck model, fatigue life prediction of thekey points of the Auxiliary Frame, dynamic topology optimization of the AuxiliaryFrame and6σ robust design are studied. The research methods and findings providevaluable engineering guidance for the fatigue design of mechanical parts.