Fatigue Life Assessment For Crawler Crane Lattice Boom Based On Hot Spot Stress Method

Tubular K-joints are widely used in lattice boom of crawler cranes. As the crane lifts frequently, the weld zone of K-joints which structured by chords and braces absorb tension and compression loads. That is to say the safety of crawler cranes is determined by the fatigue strength of K-joints. Therefore, it is quite important to focus on K-joints while considering of the anti-fatigue design of crawler cranes.Based on hot spot stress method, this paper takes the K-joint at the bottom section of boom as study focus. And then the assessment of boom’s fatigue life under the typical load type is made. As a result, a new fatigue life assessment algorithm is established. The major research and achievements are as follows:(1) To find out the dangerous parts of the boom, numerical analysis of25t crane boom is done with FEM. And the result is verified by stress tests.(2) FE modeling method of Tubular K-joints is described in detail, especially about details of weld. And the impact of different element types and mesh sizes of the hot spot stress is also taken into account. As a result, a simplified method of modeling weld is studied for parametric modeling with using APDL.(3) Forty-five FE models subjected to axial loads are analyzed, and all the geometry parameters and loads type are adjusted to fit crawler cranes well. Then, considering of the influence of secondary bending moments in lattice girders, the distribution of stress concentration factors along the weld toe are obtained with using hot spot stress method. Subsequently, some recommendations are given for anti-fatigue design of crawler cranes.(4) For predicting the stress distribution along the weld toe in tubular K-joints, the parametric equation is derived with the dependent variable i.e. SCF and independent variables including τ, β,γ and (p according to FE results. Additionally, the precision of the equation is also proved to be acceptable.(5) Visualization of the algorithm is carried out with using MATLAB. As a result, it becomes more convenient to make fatigue life assessment for different booms under typical loads type. And this provides a reference for practice.