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研究了取样于汽车发动机缸体上的HT250灰铸铁的常温低周疲劳行为。对循环应力-应变和应变-疲劳寿命数据进行了分析,给出了该材料在常温下的疲劳参数。循环应力响应行为表明,HT250灰铸铁在较小应变幅下经历初期循环硬化、循环软化、断裂;而较大应变幅下几乎无硬化阶段,循环软化至断裂,原因在于循环形变过程中位错之间以及位错与石墨、夹杂物之间的相互作用。疲劳断口分析表明:疲劳裂纹萌生于片状石墨尖端,夹杂物及局部软点,且沿石墨扩展;疲劳断裂的方式是准解理脆断和沿晶断裂的复合机制,断口有解理面和二次裂纹,并存在韧性断裂特征;断口附近的气孔、夹杂等铸造缺陷较多,部分石墨片互相连接成网状,导致局部区域强度降低,促进失效。
The low temperature fatigue behavior of HT250 gray cast iron sampled from automobile engine block was studied. The cyclic stress-strain and strain-fatigue life data were analyzed, and the fatigue parameters of the material at room temperature were given. Cyclic stress response behavior shows that the HT250 gray cast iron undergoes initial cyclic hardening, cyclic softening and fracture under a small strain amplitude, and softens to fracture during the hardening phase at large strain amplitude due to the dislocation And dislocations and graphite, inclusions between the interaction. Fatigue fracture analysis shows that fatigue crack initiation occurs at the tips of graphite flakes, inclusions and local soft spots, and extends along the graphite. The way of fatigue fracture is quasi-cleavage of the complex mechanism of brittle fracture and intergranular fracture. The fracture surface has cleavage planes and Secondary cracks, and ductile fracture characteristics; fracture near the pores, inclusions and other casting defects more, part of the graphite sheet connected to each other into a network, resulting in the strength of the local area to reduce and promote failure.