【作者】 汪保良；

【导师】 汤红卫；

【作者基本信息】 山东大学 ， 固体力学， 2008， 硕士

【摘要】 金属构件因疲劳破坏是造成构件失效的最普遍、最常见的形式之一。尤其在工程中应用十分普遍的低碳钢,由于服役环境复杂,极易发生锈蚀现象,更易发生破坏,其个别结构的破坏往往造成灾难性的巨大损失。因此研究锈蚀对低碳钢疲劳寿命及裂纹扩展速率的影响具有巨大的现实意义。本文主要是通过在中、外大量文献对疲劳裂纹及扩展研究的基础上,采用电化学快速锈蚀模拟低碳钢在自然环境下的锈蚀,制作疲劳光滑试样和紧凑拉伸(C(T))试样,研究其在不同锈蚀率下疲劳寿命及裂纹扩展(da/dN)行为,具体研究内容和结果如下:1、本文开发的电化学快速锈蚀试验装置可以在较短的时间内成功模拟低碳钢在自然条件下的锈蚀;本文采用对锈蚀后试件表面进行“镀铬色自动喷漆”的处理在试验过程中可以使裂纹更加清晰的观察记录;结果证明了这一方法的有效性。2、在疲劳寿命试验中,5%锈蚀率试件的萌生寿命大大低于未锈蚀试件的萌生寿命,萌生寿命和疲劳寿命大约降低了55%,疲劳极限大大降低;由图5-5知锈蚀对低周疲劳寿命的影响大于对高周疲劳寿命的影响。3、本文提出的da/dN=Ca~k裂纹扩展速率公式可以较好地描述低碳钢基材在不同锈蚀率下的疲劳裂纹扩展规律。4、锈蚀率对疲劳裂纹扩展速率影响不大,主要是因为裂纹扩展过程中在裂纹尖端会形成塑性区,而塑性区的粗晶纤维组织可促进氧化物的产生并诱发裂纹闭合现象的发生,再加上锈蚀促进裂尖塑性变形,必然导致裂尖后部的塑性延伸量增大,从而使裂纹闭合程度得到提高。同时,锈蚀必然导致裂纹面粗糙,而裂纹面粗糙可以提高材料的疲劳断裂阻力。锈蚀率对疲劳裂纹扩展速率影响不大是以上因素共同作用的结果。5、由疲劳寿命试验和裂纹扩展试验可以看出:裂纹萌生寿命占到了疲劳寿命的主要部分,可以达到90%,而裂纹扩展寿命只占很小一部分;锈蚀主要影响的是裂纹萌生寿命,而对裂纹产生后的裂纹扩展速率影响并不明显。更多还原

【Abstract】 That metal component are failed because of the fatigue failure is one of the most popular and common form. The low-carbon steels are used widely in the engineering. They are corroded and damaged easily because of the complex service environment. And the local failure often leads to a huge loss of catastrophic damage. So it will have the great practical significance that the influence of the corrosion on the fatigue life and crack growth rate of the low-carbon steels.Based on the research on fatigue cracks and crack propagation in the vast literature, a rapid electrochemical corrosion is used to simulate the corrosion the low carbon steels in the natural environment, and to make the fatigue and smooth specimens and compact tension specimens. And their rate of corrosion in different fatigue life and the behavior of crack growth are researched. The specific studies and results are as followings:The rapid development of the electrochemical corrosion testing device developed in this paper can simulate corrosion of the low-carbon steels under natural conditions in a short time. The treatment technology of "chrome-automatic painting" on the surface of the corroded specimens will make crack more clear to be observed and recorded in the test. The results prove that these methods are effective.The crack growth formula (da)/(dN)=Ca~k proposed can describe the fatigue crack growth law of the low carbon substrate under various corrosion rates.Corrosion rate has little effect on the fatigue crack growth. The plastic zone appears at the crack tip during the crack growing. Coarse grain fibrous tissue in plastic zone promotes the production of Oxide and appears the phenomenon of the fatigue crack closure, and plastic deformation appears because of corrosion. All of above result in the increase of the plastic extension amount at the crack tip and the extent of crack closure. Meantime, the resistance of fatigue fracture is improved by the roughness of the crack surface which caused by the corrosion. The little effect of the corrosion rates on the fatigue crack growth rate is the result of above factors.Experimental research on fatigue life and crack growth shows that crack initiation life is the main part of Fatigue Life,can each to 90%,while crack propagation life is a very little part. Corrosion has great influence on crack initiation life and no obvious effect on crack Growth Rate更多还原