Fatigue Life Evaluation of Excavator Working Device Based on Equivalent Structural Stress Method

doi:10.12141/j.issn.1000-565X.210689

Abstract

Abstract:

The working device of the excavator is a large welded structure, which is prone to damage at the weld due to various complex loads during the operation, and its fatigue strength is directly related to the service life and performance of the whole machine. In order to evaluate the fatigue life of its welds more effectively, an evaluation method of weld fatigue life of excavator working device was proposed based on the equivalent stress method in this paper. That is, based on the node force and node moment on the welding line, the structural stress that is not sensitive to the grid is calculated. The fatigue life is evaluated by the fatigue cumulative damage criterion and the main S-N curve of welded joints, which can unify with different joint types, plate thicknesses, and loading modes. By building the finite element models with detail information of the welding seam for the boom and bucket, the fatigue damage assessment was carried out for six key welds on the boom and the bucket by the equivalent structural stress method. The fatigue assessment accuracy of the boom and the bucket is comparatively studied with the fatigue experiment results in this study, the results indicate that the deviations obtained through the nominal stress method are 9.2% and 14.2%, and they reach to 24.4% and 23.4% by employing the hot spot stress method and decrease to 6.6% and 9.5% in the approach with equivalent structural stress analysis. Therefore, compared with the nominal stress method and the hot spot stress method, the evaluation results of the equivalent structural stress method are the closest to the fatigue test results. The evaluation results of the nominal stress method tend to be bold, while the evaluation results of the hot spot stress method tend to be conservative, which means that the equivalent structural stress method is very effective and reliable for the fatigue life assessment of excavator working device. The proposed method can provide ideas for the fatigue life assessment of other welded structures.

Key words: excavator, working device, equivalent structural stress method, welding structure, fatigue life evaluation

CLC Number:

TU621

CAO Leilei, WANG Liutao, WANG Yan, et al. Fatigue Life Evaluation of Excavator Working Device Based on Equivalent Structural Stress Method[J]. Journal of South China University of Technology(Natural Science Edition), 2022, 50(8): 62-70.

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级数	载荷上限/kN	载荷下限/kN	循环次数
1	46.83	-78.31	157 121
2	69.47	-99.83	32 631
3	92.08	-121.39	9 983
4	110.89	-139.39	3 138
5	126.09	-153.63	2 610

级数	载荷上限/kN	载荷下限/kN	循环次数
1	77.2	-21.8	157 683
2	94.6	-31.2	37 155
3	112.1	-56.7	13 025
4	126.6	-71.2	4 608
5	138.2	-82.9	4 628

焊线编号	焊线具体位置	板厚/mm
L1	动臂上翼板与斗杆油缸支座连接焊缝在上翼板表面上的焊线	16
L2	动臂侧板与上翼板连接焊缝在侧板表面上的焊线	14
L3	动臂侧板与下底板连接焊缝在侧板表面上的焊线	14
L4	动臂铰孔轴套与侧板连接焊缝在侧板表面上的焊线	14
L5	斗杆上翼板与铲斗油缸支座连接焊缝在上翼板表面上的焊线	14
L6	斗杆铰孔轴套与侧板连接焊缝在侧板表面上的焊线	17

载荷级数	试验循环次数	疲劳循环次数	疲劳损伤比
1	157 683	3 419 892	0.046 107 59
2	37 155	1 762 450	0.021 081 45
3	13 025	700 700	0.018 588 55
4	4 608	425 460	0.010 830 63
5	4 628	300 801	0.015 385 59

构件	焊线编号	破坏位置	寿命/h
动臂	L1	动臂上翼板与油缸支座连接焊缝前端焊趾中部	9 781
	L2	动臂侧板与上翼板连接焊缝焊趾中部	97 422
	L3	动臂侧板与下底板连接焊缝焊趾中部	176 208
	L4	动臂铰孔轴套与侧板连接焊缝上端焊趾中部	31 665
斗杆	L5	斗杆上翼板与油缸支座连接焊缝前端焊趾中部	8 929
斗杆	L6	斗杆铰孔轴套与侧板连接焊缝前端焊趾中部	24 270