Design Method And Experimental Study On The Roll-over Protective Structures For Engineering Vehicles

Engineering vehicles generally include loader, grader, dozer, backhoeloader, scraper, dumper, roller, etc. Roll-over accidents often happen because oflarge deadweight of engineering vehicles, bad stability of full-scale vehicle andcomplicated working conditions. The drivers' life is often threaded by such kind ofincidents. Presently, roll-over protective structure, also abbreviated ROPS, is themost effective method to protect drivers' life in the engineering vehicle roll-over.ROPS is a system of metallic structural members whose primary purpose is toreduce the possibility of a seat-belted operator being crushed in the event of amachine overturning. Structural members of ROPS include any subframe, bracket,mount, socket, bolt, pin, suspension or flexible shock absorber used to secure thesystem to the machine frame. Until now, it is also encountering many difficultieson the design method, calculation theory and testing method of ROPS. As along asrequirement of engineering vehicle working safety increases, the research ofdesign theories and experimental methods is needed in the Engineering vehiclesindustry.It is deeply researched the design methods and experimental technique ofthe roll-over protection structures of engineering vehicles in this thesis. Theresearch combines the "863" project: "Robotic Engineering Machine" and"Development of ZL80G wheel loader" from the item of "Prospering Old IndustryBase of DongBei" supported by the National Development and ReformCommittee". At the same time, this study is supported by many engineering vehicleenterprises. Firstly, this thesis presents the research significance, content andmethods. It is introduced study history on ROPS home and aboard, and the issuesneeded to research. Secondly, It is presented the computer simulation of the plasticlarge deformation of ROPS. A lot of ruinous experiments are performed accordingto the newest international standard, and the ruinous modes and the invalidationcausation are analyzed. Computer simulation methods of ROPS are studied and thebasic principle is presented. It is difficult to satisfy energy requirement for ROPSof large-scale engineering vehicle, so energy absorption control design methods isput forward. Lastly, the ROPS global optimization methods based on the Krigingmodel and the genetic algorithms are put forward.The main research works can be described as follows:(1) Chapter 1 presents the research background, significance, and practicalworthiness of the ROPS of engineering vehicles. Then the history and trend of theexperimental and theoretical research on the ROPS of engineering vehicle wereshown. The issues needed to research are pointed out. The methods used in thisthesis and main works are introduced.(2) the plastic large deformation nonlinear simulation method were deducedaccording to the successively medium mechanics theories, the Updated LagarangeEquation and the plastic large deformation finite element method, and incrementalvirtual power balance equation. Considering computational precision andefficiency, the simulation methods basing on the beam, shell and solid elementtheory were put forward. Definition method of limit carrying capacity wasintroduced. The research results above offer convenient measures to the ROPSdesign basing on the limit loading ability.(3) The research methods of ROPS include the field roll-over experiment, thelaboratory loading experiment. Because of lack of relative design theory, testingmethod as well as experiment funds, it is not practical to make a lot of fieldexperiments. Therefore it is discussed ROPS experiment requirement, methods andthe acceptance criteria of the newest edition standard. A lot of ROPS destructiveexperiment was performed. it is also analyzed the deformation and invalidationmechanism of lateral, vertical and longitudinal loading. Above research in thisthesis will be helpful to design, manufacture and test ROPS. At the same time, it isprovided guidance to the theoretical calculation and computer simulation.(4) The full –scale vehicle ROPS model is found and simulated numerically.That simulation results agree with test well indicates the simulation methodpresented in the paper can predict the performance of ROPS in the design stage.The regulation of lateral deformation, carrying capacity and energy absorption wasanalyzed. On the base of the lateral loading, computer simulations and laboratoryexperiments on the vertical and longitudinal loading were performed. This chapteralso did improvement on shock absorber, discussed the variety rule of ROPScarrying capability influenced by shock absorber characteristics,material property,loading position, the stiffness of bracket and frame. Lastly,it is pointed out basicdesign principle of ROPS, comparing test with simulation results.(5) The ROPS of engineering vehicles design includes the strength, stiffnessand energy design, and difficulty lies in energy design. Hence design method basedon energy absorption control was put forward. Full-scale vehicle model of CLG872wheel loader was found and then the computer simulation of ROPS lateral energyabsorption capacity was performed. Conducted experiments of ROPS prototypeverified the full-scale vehicle simulation. The results show that making plastic jointholes on the post of ROPS and controlling of the plastic joint's appearance positionand time can effectively make the energy absorption control design. Meanwhilethe brittleness breakage can be avoided by taking advantage of the ductility of theplastic joint.(6) In order to solve the problem of mismatching the lateral energy absorptioncapacity and the lateral carrying capacity, optimization model is founded with theobject function of dispersion of lateral force meeting the energy absorptionstandard requirement and lateral carrying capacity demanded in the standard. Andperformance requirement of ROPS is set as constraints in the optimization.Because of the uniqueness of ROPS energy design, it is difficult to express theexplicit expression between objection function and design variables. Therefore it isintroduced the basic theory of RSM, ANN and Kriging model, and thecharacteristics of three models are compared in this thesis. Approximate model ofobjection function and design variables is founded based on Kriging model, andthe structure of ROPS is optimized globally applying the genetic algorithm. Andthen, taking two posts ROPS as example, the global optimization design was made,and better optimization results was achieved.Lastly,the main research of this paper is summarized, the innovation is given,and the further research direction is pointed out.It is deeply studied the in computer simulation, destructive experiment, designmethod and global optimization of ROPS in this paper, and results can be used tohelp ROPS design. It is meaningful to enhance safety function of engineeringvehicle as well as to master the key technique about ROPS for enterprise. Theresearch in the thesis can also help our engineering vehicle enterprise master thedesign method of roll-oer protective structure, quicken our engineering vehicle tooccupy the international market, and protect the driver efficiently.