【作者】 芦平；

【导师】 王东坡；

【作者基本信息】 天津大学 ， 材料加工工程， 2007， 硕士

【摘要】 随着工业技术的发展,许多工业零部件受高速交变载荷的作用,在服役期内构件疲劳工作寿命已达109周次,甚至更高。使用常规疲劳试验技术只已经不能满足工业技术发展的要求。因此,关于材料在107周次以上疲劳寿命引起了广泛关注。用现有的常规疲劳试验方法完成107~1010超高周范围内疲劳试验要耗费大量的时间和费用。因此,本文利用一种加速疲劳实验装置即超声疲劳实验装置对以16Mn为材料的超声疲劳试件进行了研究。由于一直以来超声疲劳设备的研制是困扰人们研究材料超高周疲劳的一个重要问题,因此本文首先对本次试验所使用的,本课题组自行研制的HJ-Ⅱ型超声冲击机作了简要介绍,并对其数字化核心技术DSP硬件控制电路设计作了详细的说明。同时由于超声疲劳试验对试件的尺寸和样式有严格的要求,因此本人又对试件的样式进行了设计,并按照严格的公式推导出试件的尺寸。最后对以16Mn为材料的试件进行了超声疲劳试验,并得出与传统的在107存在疲劳极限的不同的S-N曲线,即连续下降的S-N曲线。因此得出用107循环周次下的条件疲劳极限去设计服役寿命在109循环周次以上的结构件是很危险的,这一重要结论。同时通过显微电镜对断口的宏观行貌进行观察,发现裂纹一般在试件表面或次表面起裂,区别于当今国际上关于材料超高周疲劳裂纹萌生机制的主流观点。即在对材料施加超高周循环载荷的情况下,材料的裂纹在内部或次表面夹杂处萌生。更多还原

【Abstract】 With the development of industrial technology, a lot of industry components were affected by high speed cycle of loading. The working life of the component already needs to endure 109 cycles even higher in the military service. Using the routine fatigue test technology is unable to adjust to the request of development of industrial. Thus the fatigue property of metallic materials in the UHCF range tends to be an important subject in the mechanical design to ensure the long term safety of the mechanical structures.Since performing experiments of the ultra-high-cycle regime in the range of 107-1010 cycles using a conventional fatigue testing method is very time consuming and expensive, in this paper, a kind of acceleration fatigue test technique, called the ultrasonic fatigue testing, was developed and studied. The design of ultrasonic fatigue equipment is an important question which makes people puzzled a long time. So, I fist introduce the experiment equipment called HJ-II ultrasonic peening machine which was developed by our team, and make a detail about the core technique-the designing of the hardware circuit of DSP.A the same time , ultrasonic fatigue specimen must be designed very precisely ,so I did the job and designed the shape and dimension by accurately deducing. At last I used the specimen which is made of 16Mn to do the ultrasonic fatigue test. As a result of the test I got an S-N curve which is different from the traditional one. It is a curve which is declined continuously. So I made an important conclusion which is that it is too dangerous to design a structure which only can endure 107 cycles, but were used in the situation where the loading were 109 cycles.In addition, I inspect the macro shape of the fracture section by electronic microscope, and found that the crack always originate inside. It is just as the same as the main idea about the law of which the crack originate. It is that the crack of material will originate inside or in the semi-surface in which there is a lot of defect when the material is exerted super high cycle loading.更多还原