Fatigue Failure Mode And Life Evaluation Of Welded Joints In Hydraulic Excavators

As the main equipment widely used in industrial engineering,how to ensure the fatigue service life and safety reliability of the main structure of hydraulic excavator such as boom and bucket rod has important theoretical and engineering application value.However,it is still difficult for the existing fatigue evaluation methods to accurately and conveniently evaluate the fatigue crack initiation position of complex welded joint structure,the failure crack propagation angle(propagation path)at the root of fillet weld and its fatigue life.In view of this,the fatigue failure modes and life prediction methods of typical welded joints in hydraulic excavators were studied in this paper.Firstly,the hot spot stress,notch stress,structural stress and strain energy density methods were used to simulate and analyze the V-groove butt joint with backing plate in excavator boom and bucket rod.The fatigue dangerous position and the corresponding failure mode were predicted,and the influence law of the lack of geometric roughness on the transfer of failure position was considered.It was found that the hot spot stress and structural stress method were suitable for determining the failure position of welded joints controlled by structural stress.The equivalent notched stress method was unable to predict the fatigue failure location of welded components with angular deformation and other geometric irregularity due to the excessive consideration of the impact of notched stress concentration on the fatigue performance of joints.The strain energy density method can accurately predict the fatigue failure location and failure mode of welded joints.Then,aiming at the T-shaped side plate fillet weld joint with incomplete penetration defects starting from the root,an equivalent stress intensity factor method(KEQ method)based on stress analysis was proposed to calculate stress intensity factor effectively and accurately,and obtains the fatigue crack propagation angle of fillet weld root failure.Based on the equivalent stress intensity factor method,the maximum circumferential stress method and the effective structural stress method,the crack propagation angles of the joint were 25.6°,25.9° and 32.2° respectively.Compared with the root crack propagation angle of 24.0° in the confirmatory fatigue test,the corresponding errors were 6.7%,7.9% and 34.0% respectively.It was proved that the accuracy of solving fatigue crack propagation angle based on KEQ method was the highest,it was more suitable to predict the root crack propagation angle of T-joint fillet weld under bending moment load.Finally,according to the theory of fracture mechanics and KEQ method,the fatigue life of T-joint fillet weld root crack was accurately predicted,and the effects of different incomplete penetration depth,failure angle and load mode on its fatigue life were explored.The results showed that the incomplete penetration depth,as the initial defect,had the greatest influence on the fatigue life,with a difference of about 25.5times.The effect of failure angle on fatigue life was relatively small,and the difference was 6.0 times.Under the same stress level,tensile loading had the greatest influence.The predicted fatigue life of the root crack of fillet weld of T-shaped joint under bending moment and stretch-bending combined load is 19.2 times and 3.2 times of that under tensile load,respectively.