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在渗碳试样疲劳断口上,通常能看到一个小而光滑的穿晶起始裂纹,周围是大面积的沿晶区域,裂纹可以位于表面或表面以下。迄令,尚不知第一条小裂纹是如何萌生和如何长大的,以及沿晶部分是否真是疲劳裂纹。为阐明这一点,在承受弯曲疲劳的渗碳梁型试样上进行了裂纹萌生与扩展的研究。用醋酸纤维素复型记录表面裂纹形状,再用显微镜仔细观察其复型。由一系列复型的观察结果就能估算出裂纹长大速率。根据从复型和断口得到的资料讨论了裂纹的萌生机制。本文还提供了由最终断裂的实际裂纹形状计算的断裂韧性数据。
On the fatigue fracture of the carburized specimen, a small, smooth, transgranular initiation crack can often be seen surrounded by a large area of intergranular fracture that can be located below or below the surface. As of yet, it is unknown how the first small crack initiates and how it grows, and whether the intergranular part is really a fatigue crack. To illustrate this point, crack initiation and propagation were investigated on carburized beam specimens subjected to bending fatigue. The shape of the surface crack was recorded with a cellulose acetate replica, and then the replica was carefully observed with a microscope. The rate of crack growth can be estimated from a series of complex observations. The initiation mechanism of cracks was discussed based on the data obtained from the compounding and fracture. This article also provides fracture toughness data calculated from the actual crack shape of the final fracture.