| With the development of national economy and industrial technology,the demand for mine energy rises increasingly.In recent years,the domestic market has been monopolized by imported equipment,which is unable to achieve technological breakthroughs.Therefore,in order to promote the independent development of electric wheel dump truck,the state council has successively issued the revitalization plan for equipment manufacturing industry and the outline of the national medium and long-term plan for scientific and technological development(2006-2020),listing electric wheel dumper as one of the 16 key areas of technical equipment so as to promote product innovation and technological development.This will not only meet domestic demand further,but also improve the country's external economy efficiently.Especially,the running environment of the electric wheel dump truck is extremely poor,and even the daily operation is as long as more than ten hours.Moreover,the load is extremely heavy and the mine road has so many bends that the electric wheel dump truck turns frequently.This means it is easy to cause fatigue damage of the steering system.As the most important load bearing part of the steering system of electric wheel dumper,A-type frame is very important to ensure its fatigue reliability.It is made of a large number of medium and thick steel plates welded together,and the weld material parameters have certain dispersion due to some factors made by human in the manufacturing process.At the same time,there are some differences between the shape and size in the factual A-type frame and "ideal" structure of A-type frame under the traditional empirical design.In addition,the steering load on the hinged position of A-type frame is random and variable due to the uneven road surface in the actual vehicle operation.Therefore,the randomness of its material parameters,structure size and load in the hinged position makes its stress distribution random,which will have significant impact on the fatigue reliability of the A-type frame.What's more,based on the traditional"stress-strength" interference theory,the stress higher than the fatigue limit is always considered when evaluating the fatigue reliability of mechanical structural parts,while the stress lower than the fatigue limit is ignored,which is obviously inaccurate in evaluating the fatigue reliability of mechanical structural parts.More importantly,the traditional optimization technology always takes the improvement of fatigue performance of structural components as a single optimization goal,without considering the lightweight problem of structural components.Therefore,how to realize the multi-objective optimization of structural components to find the balance between fatigue reliability and weight has become an urgent problem to be solved.However,at present,we seldom hear about combined material test,numerical simulation test,fuzzy theory and multi-objective optimization method in China.Thus,this thesis employs material test,finite element numerical analysis,fuzzy theory,blind number theory and interval analysis method to study the A-type frame in electric wheel dumper.The main contents are as follows:1.Mechanical properties and cyclic mechanical properties of welding joints of A-type frame were obtained by finished monotone tensile test and weld strain fatigue life test of its welding joints.A-type frame finite element model is established using UG and HYPERMESH software.and then through the vehicle coupled multi-body dynamics model,this paper get its key hinge position load time history,and by using the real vehicle road test key test point on the stress analysis,the accuracy of the A-type frame finite element model is verified comparing the actual test and numerical experiments in the test point stress state,which laies foundation for A-type frame finite element analysis.Then,random variables and fuzzy variables were determined influencing A-type frame stress distribution,and these variables were sampled with the help of Latin hypercube method.Elastic-plastic finite element analysis was carried out by using abaqus software simulation to obtain the response values of random variables under cycle loading.Next,based on the response surface method,fatigue reliability function was built.Finally,the fatigue reliability of it was evaluated under the braking condition of full load downhill turning on the basis of fuzzy theory.However,the results showed that the fatigue reliability of A-type frame could not meet the service requirements.2.Through the stress grading statistics of the stress time history in the position of the minimum fatigue life of A-type frame,the stress statistics data are obtained.Based on the traditional fuzzy membership function,the fuzzy fatigue life of A-type frame was predicted and compared with the actual life.Secondly,new fuzzy membership function was construct by using the statistical data sand stress,and corresponding failure probability analytical expression was derived based on the new fuzzy membership function.Then,giving full consideration to the process of design,processing and use of uncertainty factors of A-type frame,fuzzy fatigue reliability optimization function was built so that fuzzy fatigue reliability could be assessed.Finally,the optimal design was carried out based on multi-island genetic algorithm with the maximum equivalent stress of it as single optimization objective.The optimization results showed that the fuzzy fatigue reliability of model met the engineering requirements.3.The welding seam fatigue strength of A-type frame was taken as the interval value,and the interval fatigue strength value was determined based on the blind number theory.According to the loading time history of the key hinge position of it,its fatigue stress and reliability were analyzed.Second,regarding maximum equivalent stress and A-type frame weight as the optimization goals,its structure of the steel plate size as design variables,and the weld material elastic modulus,density as well as traction joint position load as uncertainty variables,fatigue strength and the interval weight limit as constraint conditions,design variable and random variable were sampled using Latin hypercube method so as to finite element analysis under cycle loading response value and then established the approximate mathematical model between optimization goal and design variables based on interval analysis method in order to carry out the A-type multi-objective optimization.The results showed that the optimized A-type frame improved the fuzzy fatigue reliability and the weight slightly increased. |
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