摘要
应用超声疲劳试验技术,对两种高强度钢(42CrMo4,100Cr6)在20kHz频率下的超高周疲劳性能进行测试分析。实验结果表明:两种钢的S-N曲线在106周发生了明显的变化,出现了水平渐近线。尽管23个42CrMo4钢试样用于1010周的疲劳试验,但在8.76×107循环周次以上,没有疲劳破坏发生,42CrMo4钢存在疲劳极限,而100Cr6钢的S-N曲线呈现台阶型。高精度热成像仪检测不同载荷条件下疲劳试样温度的变化结果显示:温度的变化与试验材料和加载水平有关。试样温度的快速升高发生在超声疲劳试验的初期,温度的变化反映了材料内部的热耗散过程。裂纹萌生后,微裂纹处不可逆的局部塑性变形导致裂纹萌生区温度急剧升高,疲劳试样内部温度场的变化反映材料的疲劳损伤过程。SEM观察表明:在长寿命区,疲劳裂纹常萌生于试样内部或次表层组织缺陷处。
Fatigue properties in the very high cycle regime of two kinds of high strength steels （42CrMo4 and 100Cr6） have been investigated with the ultrasonic fatigue testing technique at load ratio R = -- 1 and cycling frequency 20 kHz. Both steels show a distinct change of slope in the S N curves at approximately 106 cycles, it shows horizontal asymptote. No specimen failed above 8.76 × 107 cycles although 23 specimens were stressed to over 10^10 cycles for 42CrMo4. For 100Cr6, however, many specimens failed above 10^7 cycles, it shows a step-wise curve. An advanced infrared camera was also used to record specimen temperatures, results show temperature evolution of fatigue specimen depends on the material type and loading level, the temperature increased sharply just at the beginning of the test, which is correspondent to the thermal dissipation in the specimen. After fatigue crack initiated, irreversible local plastic deformation in the crack initiation zone can result in local temperature increase evidently. The temperature field of ultrasonic fatigue specimen is correspondent to the fatigue damage process. On the basis of micro structural characterization and fracture surface analysis by scanning electron microscopy, it shows that fatigue damage was governed by the formation of cracks, and interior or subsurface crack initiation was dominant in very high cycle range.
出处
《材料工程》
EI
CAS
CSCD
北大核心
2009年第3期49-53,共5页
Journal of Materials Engineering
基金
国家自然科学基金(50775182)
陕西自然科学基金(2006E133)资助
