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研究了预超载提高K_(Is) cc的规律及其影影因素。采用σ_(0.2)为170kgf/mm~2的30CrMnSiNi2A钢预裂纹试样,在空气和3.5％NaCl水溶液中予超载(15～94％K_(Ic),而后完全或部分卸载,再进行悬臂梁K_(Is) cc试验。结果表明,K_(Is) cc值随预超载载荷的增加而直线增加。预超载低到某一门槛值时,K_(Is) cc达到恒定,与正常加载的K_(Is) cc相等。在空气中预超载提高K_(Is) cc的效果比在3.5％NaCl溶液中大。预超载后完全卸载比部分卸载效果好。预超载改变了正常加载时裂纹尖端的应力分布,是提高K_(Is) cc的主要原因。氧充足是在空气中比在3.5NaCl％溶液中预超载效果大的原因。完全与部分卸载效果不同,归之于它们改变应力分布不同。
The law and shadow factors of K_ (Is) cc pre-overloading were studied. A pre-cracked specimen of 30CrMnSiNi2A steel with σ 0.2 (0.2) of 170 kgf / mm 2 was overloaded (15-94% K Ic) in air and 3.5% NaCl aqueous solution and then completely or partially unloaded. (Is) cc test.The results show that the value of K_ (Is) cc increases linearly with the increase of pre-overload load.The K_ (Is) cc reaches a constant value when the pre-overload drops below a certain threshold, ) cc.The pre-overloading in air increases K_ (Is) cc better than that in 3.5% NaCl solution.The complete unloading after pre-overloading is better than the partial unloading.The pre-overloading changes the stress distribution at the crack tip under normal loading, Is the main reason for increasing K_ (Is) cc. Oxygen sufficiency is the reason that pre-overloading is more effective in air than in 3.5NaCl% solution, completely different from partial unloading, which is due to the different stress distribution changes.