【作者】 植柏宇；

【导师】 鲁连涛；

【作者基本信息】 西南交通大学 ， 精密仪器及机械， 2010， 硕士

【摘要】 超声波振动加载实验是实现超高周疲劳实验研究的一种加速实验方法。然而对于钢铁材料,超声振动一方面可能带来“频率效应”,即,由于材料的位错运动速度远远小于超声波加载速度,材料的塑性变形响应滞后于加载速度,实际承受应力小于加载应力,导致实验获得的材料疲劳强度上升和寿命的延长；另一方面,超声振动使材料的内摩擦加剧,可能引起“温度效应”,即,疲劳实验过程中试样升温,造成试样的热损伤,导致疲劳寿命下降。高速铁路机车车辆的转向架构架及其零部件,航空航天机械、汽车、发动机、发电机及海洋结构、桥梁等在服役期内要承受109次以上的交变载荷,要保证这些设备和结构的长期安全使用,必须研究结构材料的超高周疲劳性能。因此,研究超声加载频率对结构材料超高周疲劳性能的影响,从而确定加速疲劳实验的妥当性十分必要。本论文对比研究了80Hz轴向疲劳加载和20kHz超声轴向疲劳加载的加载频率对GCr15轴承钢超高周疲劳性能的影响。对于超声疲劳实验,分别采用了压缩空气和水冷却试样,并采用连续和间歇加载方式,以比较超声振动引起的试样升温对疲劳性能的影响。断口观察表明,80Hz轴向加载试样,在全应力幅范围既发生表面破坏又发生由夹杂物引起的内部破坏；压缩空气冷却的连续加载超声试样,在全应力幅范围以夹杂物引起的内部破坏为主,当萌生裂纹的夹杂物距试样表面较深时,夹杂物周围伴有高温烧痕；水冷却的连续加载超声试样,在高应力幅区,发生不受水腐蚀影响的内部破坏；压缩空气冷却的间歇加载超声试样,在全应力幅范围均为夹杂物引起的内部破坏。实验结果及分析表明,超声加载频率提高了试样的寿命,超声振动引起的高温降低了试样的寿命。更多还原

【Abstract】 Ultrasonic fatigue testing system delivers accelerated testing of materials fatigue in giga-cycle region. However, for Iron and Steel Materials, on the one hand, ultrasonic vibration may lead to "frequency effect", that is, the stress that materials practical endure is less than theoretical loading stress, in that dislocation velocity of materials is far less than ultrasonic loading speed, resulting to increase fatigue life of materials.On the other hand, the Aggravation of inner friction induced by the ultrasonic vibration, probably induces "temperature effect", namely, temperature rising in the experimental process that leads to thermal damage of materials, resulting in decrease fatigue life of materials.Many mechanism and engineering structure, such as bogie frame, automobile, engine, generator, marine structure and bridge etc., bears alternating load over 109 cycles in service period. It is essential to research giga-cycle fatigue properties of these structures and equipments to guarantee safe running in the long term. Therefore, it is necessary to determine the appropriateness of ultrasonic fatigue test for researching the effect of frequency on giga-cycle fatigue properties for structural materials.In order to investigate the effect of frequency on giga-cycle fatigue properties for GCr15 steel, ultrasonic fatigue (test frequency:20kHz, continuous loading and interval loading) and cyclic axial loading (test frequency:80Hz) tests with stress ratio R=-1 were carried out for GCr15 steel using hourglass-shaped specimens.During fatigue test, the specimens used for ultrasonic fatigue were cooled with dry air and water, respectively, to examine the effect of temperature raising inside specimens.The fractography observation results show that the fatigue fracture occurred at surface flaws, a surface inclusion or an internal inclusion in the whole stress amplitude level under 80Hz cyclic axial loading, whereas it mainly occurred at an internal inclusion in the whole stress amplitude level under ultrasonic continuous loading with dry air cooling. Under the condition of dry air cooling, when an inclusion induced fatigue facture locates at the deeply interior of specimen, a burned area surrounding the inclusion was observed by optical microscope. Under ultrasonic continuous loading with water cooling, it mainly occurred at an internal inclusion in the high stress amplitude level. Under ultrasonic interval loading with air cooling, it all occurred at an internal inclusion in the whole stress amplitude level.Experimental results show that the ultrasonic loading frequency increased the fatigue life of GCr15 steel, and the high temperature originated in ultrasonic vibration decreased the fatigue life of GCr15 steel.更多还原