Study On The Anti-fatigue Optimization With Discrete Variables Of Hd-mdt Frame Based On Estimated Interval

With the recovery of global mining and the fully advanced of “One Belt,One Road” strategy,the demand for Heavy Duty-Mining Dump Trucks in large domestic mines and countries along the Belt and Road will usher in a new growth.In the face of such a broad potential market,it is necessary to make breakthroughs in the increasingly centralized and stable HD-MDT industry competition pattern.The key is to solve product problems to increase product reliability and improve product performance under the premise of maintaining the Life Cycle Cost.It requires that the theory and practice should be fully integrated in the optimization of the MDT while the in-depth study on the actual engineering problems in the development stage will be carried out to improve the product market competitiveness effectively.The MDT runs on mine roads with poor conditions all the year round.The load changes drastically during its driving and loading.The frame is the most important bearing component and runs through the life cycle of the MDT that is a typical structure welded with steel plates of different thicknesses and different directions.The welds of the frame are large in size and densely arranged.The fatigue life of the welds often determines the fatigue life of the frame.Therefore,it is important to improve the fatigue reliability of the frame by optimizing the frame structure to improve the fatigue life of the weld and avoid the failure of early weld cracking.However,during the welding process of the frame,the weld is partially melted and then naturally cooled,so this difficult-to-accurate molding process is an uncertain factor in the fatigue performance of the weld and affects the fatigue life of the weld.In the traditional frame structure optimization process,the optimization is restricted because the size optimization does not involve the frame topology,and the results of the continuum topology optimization are difficult to be converted into the actual structure,which limits the application of the optimization results.These objective problems lead to a large gap between the scientific research and the engineering practice of the frame antifatigue optimization.To this end,this paper aims at realizing the anti-fatigue structure optimization with discrete variables of the frame considering the the actual working condition of a MDT combined with experimental and numerical simulation techniques to conduct an in-depth and comprehensive study on the interval uncertainty problem of fatigue life and discrete structure optimization method.The main research contents of this paper are as follows:1.Establishment of key weld model of frame.Taking the dangerous welds of frame as the research object is the key to refine the research object and strengthen the research pertinence.In this paper,the finite element model of the frame is verified by a static test.The dangerous positions of the welds are analyzed referring to the frame structure of the dump truck.The corresponding local joint structure is extracted to verify the relationship between the local joint and the overall frame.Then,based on Verity method,the weld model is established in the joint structure to compare the structural stress distribution of each key weld under different typical working conditions.2.Study on fatigue life of frame welds.The accurate load spectrum information and fatigue life analysis under deterministic conditions are the basis of fatigue reliability research under uncertain conditions.In this paper,the rigid-flexible coupled dynamic model of the mining dump truck is established and verified by road test.Then,the loading and unloading conditions of the truck are introduced and the dynamic model is simulated under full working conditions.The load time history of each hinge joint of the dump truck frame is obtained and converted into the load spectrum of every weld node.Combined with the fatigue test data of frame weld material,the fatigue parameters of master S-N curve under certain conditions are obtained,and the fatigue life of the dump truck under full working condition is analyzed.3.Study on the estimation method of fatigue parameter intervals.Obtaining the interval bounds of the fatigue parameters through a small amount of data is the core of applying the interval uncertainty method to the actual engineering problem.On the basis of presenting the uncertainty of fatigue parameters with interval numbers,an interval estimation method is proposed for obtaining the interval bounds to avoid the simple way of direct designation of the interval number or setting a percentage of the median value as the interval radius.Firstly,the rough interval bounds are constructed by reconstructing a small amount of test data and using the least squares method.Secondly,the deviation evaluation index based on the extended root mean square error(e RMSE)is established to evaluate the quality of data reconstruction.The crossover of the extreme values in the bounds of rough interval is modified to realize the interval estimation of fatigue parameters interval bounds.4.Study on the fatigue reliability evaluation under interval uncertainty.Studying the fatigue reliability evaluation index under interval uncertainty is a bridge between the fatigue reliability problem and the interval uncertainty method.The limitations of traditional interval evaluation method in fatigue problem is comprehensively analyzed.Considering the numerical asymmetry and importance asymmetry of the interval bounds,the interval fatigue reliability evaluation method is proposed.By establishing the weak ternary interval of fatigue life,the mentality index is introduced to describe the mentality tendency in the design process,and the evaluation function is constructed to calculate the interval equivalent fatigue life for the evaluation of the interval fatigue reliability.Then,the intervals of the master S-N curve parameters are obtained through the fatigue test data of the frame weld material and interval estimation method.The interval fatigue reliability of every key weld of the frame is analyzed and its optimization potential is evaluated.5.Anti-Fatigue optimization of MDT frame with discrete variables.Discrete structure optimization for the local joint with dangerous welds is a concrete practice that combines scientific research results with engineering practice in the optimization of the plate structure.In order to ensure the achievability of the optimization results,the stiffeners arrangement of each local joint with key welds is used as the optimization object.By the establishment of the ground structure model,the stiffener layout variable is transformed into the {0,1} discrete variable to demonstrate the birth or death of each stiffener.Then,the joint mass constraints are converted into the constraints of number of stiffeners and recoded.Combined with the multi-island genetic algorithm(MIGA)for gradient-free information,the discrete structure optimization of the local joints is realized with the objective of the minimum equivalent fatigue life of the weak ternary interval.The achievability of the optimized results is ensured under the small modification of the frame while the minimum fatigue life of dangerous welds is significantly improved and the anti-fatigue optimization of the MDT frame is realized finally.In summary,the fatigue reliability of HD-MDT frame under interval uncertainty is deeply studies in this dissertation,and the anti-fatigue optimization with discrete variables of frame joint is conducted based on the evaluation index of interval fatigue reliability.It provides a new idea and method for analysis of fatigue performance and optimization of such kind of plate structure.