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超高强度钻杆在冬季低温环境下容易发生脆性断裂事故,为了从断裂力学角度揭示其冷脆现象的本质,采用ZBC2302-D型示波冲击试验机,获得了不同温度下超高强度钢在冲击断裂过程中的力-位移曲线,并对比分析了冲击功、起裂功和裂纹扩展功之间的变化关系。采用国家标准GB 4161—2007中的计算公式,计算了冲击试样的裂纹扩展量Δa和阻抗应力强度因子K_R;同时,引入K_R阻力曲线,得到超高强度钻杆在不同温度下的剩余强度图。结果表明,当冲击试样开始出现裂纹时,随温度降低,钻杆的初始起裂应力有所增加,出现硬化现象。当钻杆出现一定长度的裂纹时,随温度降低,阻抗应力强度因子越来越小,而且降低速度越来越快,剩余强度也表现出相同的变化趋势。随温度降低,材料抵抗裂纹扩展的能力逐渐下降,表明钻杆在低温下更容易断裂。
In order to reveal the nature of cold brittleness from the point of fracture mechanics, the ultra-high strength drill pipe is prone to brittle fracture under low temperature environment in winter. ZBC2302-D oscillometric impact tester is used to obtain ultra-high strength steel under different temperatures The force-displacement curve in the process of impact fracture, and the relationship between the impact energy, the crack initiation work and the work of crack propagation is comparatively analyzed. Using the calculation formula in national standard GB 4161-2007, the crack propagation amount Δa and the impedance stress intensity factor K_R of the impact specimen were calculated. At the same time, the K_R resistance curve was introduced to obtain the residual strength of the ultra-high strength drill rod at different temperatures . The results show that when the impact specimen begins to crack, the initial cracking stress of the drill pipe increases with the decrease of temperature, and the hardening phenomenon appears. When the length of the drill pipe cracks appear, with the temperature decreases, the impedance of the stress intensity factor is getting smaller and smaller, and reduce the faster and faster, the residual strength also showed the same trend. As the temperature decreases, the ability of the material to resist crack propagation gradually decreases, indicating that the drill rod is more prone to fracture at lower temperatures.