Crack progress characteristic of steel in air and corrosive environment

3)两阶段波动荷载下裂纹进展特征(1)与恒载试验相比，波动荷载下过大荷载下的裂纹开闭应力减小。(2)即高荷载下的裂缝开闭应力受低荷载下的相应应力支配。(3)与恒定载荷相比，在波动载荷作用下，晶粒场出现了大量的递进裂纹。这可以从扫描电镜观察中得到证实。(1)不同荷载水平对咸水环境下钢的裂纹发展行为有显著影响。(2)载荷较小时，腐蚀环境下也不存在微裂纹区。(3)咸水环境下裂缝产生时间受应力条件控制，裂缝进展驱动力占满载时的85%。另一方面，大约75%是在大气环境下。即在盐水环境下，裂纹扩展速率变早。研究结果如下：1)单、双幅裂纹扩展特征(1)当应力比R为R>区域时，裂纹扩展速度加快，因为随着R的增大，裂纹扩展驱动力增大。(2)对于应力比< 0的区域，裂缝的开闭应力对应于荷载的一个中性应力。(3)受拉侧的所有振幅都作为裂纹进展的驱动力。(4)裂缝开闭应力/总幅值与应力比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.