【摘要】 本文用线弹性断裂力学原理和方法研究稀土镁球墨铸铁的疲劳断裂问题.试验研究球墨铸铁为铁素体、珠光体以及珠光体加部分牛眼状铁素体等三种不同强度、塑性、韧性配合的基体组织.通过不同加载制度,不同缺口尖锐度试样的疲劳裂纹萌生期N₀、疲劳裂纹扩展速率da/dN、门槛值△K_th以及条件疲劳总寿命N_f的测定,得出主要看法为:球铁具有较高的△K_th值,随珠光体量增加△K_?下降,至80%珠光体后趋向稳定;疲劳裂纹孕育期的大小,在尖锐缺口时主要取决于塑性,较平缓缺口时主要取决于强度.疲劳裂纹扩展速率da/dN随塑性的增加而降低,低周疲劳,尖锐缺口试样,增加塑性有助于疲劳寿命的提高;高周疲劳,钝缺口试样,增加强度有助于疲劳寿命的提高.还通过电境断口分析,就球铁疲劳裂纹萌生、扩展的特征及其微观机制进行了简明的描述和解释.更多还原

【Abstract】 The fatigue fracture of nodular cast iron is investigated by using the prin（?）iple and the method of the linear elastic fracture mechanics, Nodular cast irons whose znatrices are composed of ferrite, pearlite and 80% pearlite combined with bull’s eye ferrite are investigated. Due to the difference in the matrix composition these three cast iron varies all exhibit different properties in strength, plasticityn ad toughness.The number of stress cycles N₀ for initiation of fatigue crack, the rate of fatigue crack propagation da/dN, the threshold stress intensity factor range △Kth and the total number of stress cycles N’_f for fatigue fracture were investigated with different loading regimes and different sharpness of the notch in the specimen. It has been found that △Kth in nodular cast iron is rather high; △Kth decreases as the percentage of pearlite increases, untill about 80% pearilite when it remains almost unchanged with further increases of percentage of pearlite; the variation of N₀ depends mainly on the strength of materials in caes of blunt notched specimens and on the plasticity of meterials in case of sharp notched specimens; da/dN decreases as plasticity increases; While N_f’ increases as strength increases in blunt specimen under high cycle fatigue while N’_f increases in sharp notched specimen under low cyclic fatigue.The characteristics and micro fracture mechanism of fatigue crack initiation and propagation in nodular cast iron have been described and explained in the light of metallographic and electron fractographic observstions.更多还原