Crack progress characteristic of steel in air and corrosive environment

(3)两级波动载荷下的裂纹扩展特性(1)与恒定载荷试验相比，波动载荷下过大载荷下的裂纹张开和闭合应力减小。(2)即高水平载荷下的裂纹张开和闭合应力由低水平载荷下的相应应力决定。(3)在波动载荷作用下，与恒定载荷相比，晶粒场出现了大量的扩展裂纹。扫描电子显微镜观察证实了这一点。2)钢在盐水环境下的微裂纹行为(1)载荷水平的不同显著影响了咸水环境下的裂纹扩展行为。(2)当载荷较小时，腐蚀环境下也不存在微裂纹区。(3)咸水环境下裂纹萌生时间受应力状态控制，裂纹扩展驱动力占全载荷的85%。另一方面，在大气环境下，这一比例约为75%。研究结果如下：(1)单侧和两侧的裂纹扩展特性(1)当应力比R为R&gt；O区时，裂纹扩展的驱动力随R的增大而加快。(2)对于应力比&lt；O区，裂纹张开和闭合应力对应于载荷的中性应力。(3)拉伸侧的所有幅值都是裂纹扩展的驱动力。(4)裂纹张开和闭合应力/总幅应力与应力比R呈直线关系。

3)Crack progress characteristic of two stage fluctuating load (1) The crack opening and closing stress at an excessive load at the fluctuating load decreases compared with that of the constant load examination. (2) That is, the crack opening and closing stress at a high-level load is ruled by the correspond stress at a low-level load. (3) At the fluctuating load, there are a lot of progressing cracks of the crystal grain field compared with the constant load. This could be confirmed from the SEM observation.2)Micro-rack behavior of steel under salt water environment (1) The different of the load level remarkably influenced the crack progress behavior under the salt-water environment. (2) The micro-crack area does not exist under the corrosive environment when the load is small either. (3) The crack generation time is controlled by the stress condition under the salt-water environment , the crack progress driving force accounts for 85% of the full load. On the other hand, it was about 75% under an atmospheric environment. That is, the crack growth rate becomes early under the salt-water environment.The research results are as follows:1) Crack progress characteristic of single and both sides' amplitude (1) When stress ratio R is R>O region, the crack growth rate quickens because the crack progress driving force increases as R increases. (2) For stress ratio<O region,the crack opening and closing stress is corresponding to a neutral stress of the load. (3) All amplitudes in the tension side work as crack progress driving force. (4) There is a straight-line relation between the value of the crack opening and closing stress/the total amplitude stress and the stress ratio R.