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本文研究了一种球墨铸铁(QT60-2)的疲劳断面。指出,除△K=62.9公斤/毫米~(3/2)外,在其他所有△K值范围内, 宏观裂纹扩展速率(dl/dN)与疲劳纹间距(S)之间,不存在对应关系。断口金相观察初步证明,石墨球的解理或脱开及主裂纹前端由于石墨球(它相当于显微空洞)的存在而加剧的三向应力,使基体除疲劳断裂外,在局部微小区域内,还出现了解理或微坑型断裂。这是导致它即使在相当低的宏观扩展速率范围内,dl/dN就大于S的重要原因。作者们还初步求得宏观扩展速率(dl/dN)与疲劳纹间距(S)的关系式如下: dl/dN=3.18×10~(-5)(△K)~(2.50)S
This article studies the fatigue section of a nodular cast iron (QT60-2). It is pointed out that there is no correspondence between the macroscopic crack growth rate (dl / dN) and fatigue pattern spacing (S) in all other △ K values except for ΔK = 62.9 kg / mm3 . Fracture metallurgical observation initially proved that graphite ball cleavage or disengagement and the front of the main crack due to graphite ball (which is equivalent to the existence of micro-cavities) exacerbated by the existence of three-stress, the matrix in addition to fatigue fracture, in the local micro-area Within, also appeared cleavage or dimple-type fracture. This is an important reason that dl / dN is greater than S even though it is within a relatively low macroscopic rate of expansion. The authors also found that the relationship between the macroscopic expansion rate (dl / dN) and fatigue pattern spacing (S) is as follows: dl / dN = 3.18 × 10 -5 - △ K ~ 2.50 S