840D车轮辐板孔边裂纹扩展机理分析

Analysis on the Growth Mechanism of Cracks Emanating from Holes in 840D Wheel Spoke

利用有限元法对840D货车车轮在长坡道制动工况下产生的温度场、热应力场进行分析,进而得到裂纹在扩展过程中应力强度因子的变化规律。分析表明:裂纹在穿透辐板厚度之前,裂纹的扩展以内侧周向扩展为主,并且稳定扩展;裂纹在穿透辐板厚度时,由于沿辐板厚度方向的裂纹尖端Ⅱ型应力强度因子存在突变,可能导致裂纹产生不稳定扩展突变;裂纹在穿透辐板厚度之后,由于内侧裂纹的Ⅱ型裂纹应力强度因子持续增加,外侧裂纹的Ⅱ型裂纹应力强度因子大于Ⅰ型裂纹应力强度因子,但都小于内侧裂纹的Ⅰ型裂纹应力强度因子,因而裂纹仍以辐板周向扩展为主,但裂纹扩展的方向稳定性变差,裂纹可能向轮辋扩展。

The temperature field and thermal stress field of 840D freigth train induced by braking on the long ramp are analyzed by using finite element .method （FEM）. The stress intensity factors （SIFs） of cracks with different length are calculated respectively, and a rule of SIFs variety in the process of crack growth is found. Analysis indicates that before the spoke is penetrated, the crack growth is dominated by inner circumferential and expands in a stable velocity. On the thickness orientation as the spoke is being penetrated, mutation in the unstable crack growth can be generated because of the mutation in SIFs of the Ⅱ mode crack （KⅡ） at the crack tip. After the spoke is penetrated, however, both the value of KⅡ at inner crack with a sustaining increase and the greater value of KⅡ compared with SIFs of the I mode crack （KⅠ） at outer flank are smaller than that of KⅠ at inner crack, thus growth is still dominated by circumferential growth, but the crack growth is instability and the crack growth may expand to rim.