Research On Frame Fatigue Reliability Of Mining Dump Truck Based On The Strain Energy Method

With the rapid development of national economy recently,the demands for energy and minerals are increasing.Considered as the main transport vehicle in large open mineral sites,the mining dump trucks are rapidly increasing as well.Because of the lagging research and design in domestic industry,the mines relied on the imported mining dump truck in a very long time.In order to change this situation,the mining dump truck is classified as major technical equipment by State Congress in key areas,which implies that the urgent needs of the mining dump truck with independent intellectual property are undisputed.Therefore,the researches on the mining dump truck by advanced technology are in line with national policy requirements,which could enhance the major equipment manufacturing level,and ensure the normal national energy and mineral mining,and have important economic and engineering application value.The mining dump truck is running on the mine road surface year and year,so that the structural performances of this truck have higher requirements under poor working conditions.Considered as the main bearing component,the frame's strength,stiffness,modal characteristics and fatigue life play a decisive role on the vehicle's safety,reliability and quality.Recently,with the improvement of testing method,updating test devices and gradually mature simulation technique,the researches on the vehicle and engineering equipment by the test,finite element analysis,multi-body dynamics analysis and structural optimization and design become quite common.However,those techniques are rarely utilized in the off-highway mining dump truck,or the accuracy of the existing research results has room to be improved.For the special structure and working conditions of one domestic mining dump truck,this paper combines experimental work with the numerical simulation technology to research the frame's structural performances,which systematically and deeply focuses on the frame fatigue reliability and structural optimization design.This paper mainly focuses on:1.Researches on fatigue life experiment of the frame parental material and welded joint are conducted.The frame of this mining dump truck is made of one imported high-strength low-alloy quenched and tempered steel,whose mechanical properties and fatigue behavior parameters are the important basis for the finite element analysis in the following steps.Considering the scarce material parameters ofthis imported steel,this paper conducts the parental material fatigue life test for the different stress levels under stress control,which obtains the material S-N curve and relative parameters.Similarly,the welded joint is applied the cyclic loading for different strain levels under strain control to get the strain fatigue life curve and the values of the parameters in the Manson-Coffin equation.Those works provide the basic data for the finite element analysis and optimization of the frame and its welded joint.2.The frame's dynamic random loads are obtained on the basis of the road acceleration test.Due to the special structure of huge mining dump truck,it is hard to get the dynamic random load directly by the experimental method.However,the single multi-body dynamics analysis is not easy to ensure the accuracy of the simulated load.Therefore,one method combined the road acceleration test with the multi-body dynamics analysis is presented to calculate the input load assessing the fatigue reliability of this mining dump truck.Based on the testified rigid and flexible coupling dynamics model,the frame's accurate load history curves at different locations are acquired for several working conditions.3.The analysis of the frame static and dynamic performances based on the weld simulation with shell elements is conducted.The frame of this truck is made up of different thickness steels,which connect with each other by the welding.It is worth to mention that the mechanical properties of the welded joints are closely related to the frame structural performances.This paper mainly constructs the shell elements to simulate the weld beads located at the region around the front and rear suspension and obtain the structural stress.The frame's finite element model is testified by the stress test.On the basis of this accurate model,the safety factors under different working conditions,stiffness characteristics,main low order frequency and relative vibration shapes are obtained.4.The fatigue life assessment method for welded joints based on the modified strain energy method is presented.In terms of the crack around local weld beads,the author believes that it is not enough accurate to predict the fatigue life based on the normal fatigue life assessment method when only considering the elastic strain under cyclic loading.Therefore,this paper presents one strain energy density method included the elastic and plastic strain parts to predict the weld bead fatigue life,after the comparison of different approaches.The current strain energy density calculation is based on the perfect closed strain and stress response curve.However,the strain and stress response curve is crossed with each other,when the real weld beads bear thecomplicated load.Therefore,one modified calculation method for the strain energy density is presented to improve the frame weld beads' strain energy density computing.Using this method to predict the fatigue life of the frame's weld,the predicted results show that the simulated low fatigue life regions are similar with the real failure locations under the downhill and turning brake condition.5.The frame fatigue reliability analysis based on the fuzzy theory is conducted.The large mining dump truck is yearly running on the mine road surface,so that it works under large load and heavy burden,harsh environment,frequent transport.Considered as the main bearing component,the reliability of the frame should be ensured necessarily.The frame fatigue reliability analysis relates to the random variables or fuzzy variables.Therefore,in order to accurately analyze this reliability,this paper considers the main direction loads and relative weld material parameters as random input variables.Then,the performance function of the frame fatigue reliability analysis is acquired by the response surface method.According to the Monte Carlo principle,the random input variables and fuzzy design variables are sampled enough times,and the frame fatigue reliability value is calculated for the fuzzy design variables under different membership functions,which offers the important reference for the frame fatigue reliability assessment.6.The frame anti-fatigue lightweight optimization based on the approximate model is conducted.Considering the increased mass of the new frame obtained from the multi-objectives topology optimization,one frame lightweight optimization method is presented when the traditional frame weight redundancy exists.The Kriging approximate model is constructed between the frame's volume,fatigue life and different thickness steels.On the basis of the verified approximate model,the multi-objectives genetic algorithm is used to change the thickness of different steels.The optimized frame structure has longer fatigue life and less weight finally.In summary,this dissertation systematically conducts an intensive study on the frame fatigue reliability analysis and structural optimization,which contributes valuable reference for thinking and approaches to the research on this subject.