液压挖掘机斗杆台架疲劳试验载荷等效方法

为了克服斗杆各铰点力分别编制成载荷谱进行疲劳试验加载时各力之间关联特性无法再现的问题，即为了获得能够反映实际工况，且能用于编制台架疲劳试验程序谱的基础载荷数据，提出一种复杂载荷等效方法。首先分别采用三维销轴力传感器、压力传感器、位移传感器和应变片，实测挖掘机工作过程中斗杆与铲斗的铰点力、油缸力、摇杆力、工作姿态及斗杆疲劳关键点应力时间历程；其次根据各铰点力的规律和斗杆的运动特征，确定在斗杆局部坐标系下进行台架疲劳试验的加载方案；再根据斗杆截面应力状态，提出以斗杆最大弯矩截面上应力最大点的应力一致为载荷等效基准，将斗杆上的各铰点力等效为斗杆局部坐标系下的1个单向载荷，最后将该等效载荷加载下斗杆结构上3个疲劳关键点的应力-时间历程与对应测点实测应力-时间历程进行对比。结果表明：2条应力曲线相关程度在1^#测点处达到97.21%，在2^#测点处为91.54%，在3^#测点处，相关程度略低，但也达到88.6%；各疲劳关键点处由等效载荷引起的损伤均与实测应力产生的损伤十分接近，从而验证了载荷等效方法的有效性；按该等效方法求得的等效载荷是编制斗杆疲劳计算载荷谱和台架疲劳试验程序谱的基础数据。

Load Equivalent Method for Fatigue Bench Test of Hydraulic Excavator Stick

A load equivalent method is proposed to overcome the problem of the correlation characteristics between forces not being reproduced when each hinge force is compiled separately into the load spectrum and applied to the fatigue bench test. In other words, the load equivalent method is proposed to obtain the basic data that reflect the actual working situations of the stick and can be used to compile the programmed load spectrum for a bench fatigue test. Three-dimensional pin-shaft force sensors, pressure sensors, displacement sensors, and strain gauges, were used to measure the time history of the stick's hinge force connected to the bucket, cylinder force, rocker force, working posture, and stress of the critical fatigue measuring points on the stick. The loading scheme of the fatigue bench test in the local coordinate system of the stick was determined according to the change of each hinge force and the stick's movement characteristics. On the basis of the stick cross section's stress state, it is proposed that maintaining the consistency of stress at the maximum stress point of the stick's maximum bending moment cross-section should be used as the load equivalent benchmark. Then, each hinge force on the stick would be equivalent to a unidirectional force. The calculated stress history caused by the equivalent load at each critical fatigue measuring point on the stick was compared with the measured stress history of the corresponding measuring point. The results revealed that the correlation degree of the two stress curves reached 97.21% at point 1 and 91.54% at point 2, while it was slightly lower at point 3, where it reached 88.6%. At the same time, at each critical fatigue measuring point, the calculated fatigue damage caused by the equivalent load was very close to the measured fatigue damage caused by the measured stress, which verified the load equivalent method. Moreover, the load obtained by the equivalent method comprised the basic data for compiling the load spectrum for fatigue life prediction and the programmed load spectrum for the fatigue bench test.