Ti-6Al-4V合金における内部疲労き裂の発生および初期進展に及ぼす応力比の影響
Ti-6Al-4V合金における内部疲労き裂の発生および初期進展に及ぼす応力比の影響
复制标题
应力比对Ti-6Al-4V合金内部疲劳裂纹萌生和初始扩展的影响
DOI：
10.1299/kikaia.70.1116
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
徹 野口
中科院分区：
文献类型：
--
作者：
博幸 小熊;孝 中村;秀治 横山;徹 野口
对（α+β）Ti-6Al-4V合金在不同应力比（R=σmin/σmax）下进行了单轴疲劳试验，直至高周疲劳区。采用扫描电镜断口分析方法，研究了应力比对超高周疲劳性能的影响。正应力比下的S-N曲线显示出复杂的褶皱形状，在长寿命区出现陡倾角，在长寿命区出现通道源断裂。另一方面，负应力比下的S-N曲线具有一个普遍特征，即疲劳寿命随应力的降低而单调增加。SEM观察表明，内部裂纹是由多个内部裂纹源紧密连接而成。这种类型的内部裂纹在正应力比下的低应力下尤其明显。正应力比有利于裂纹的萌生和裂纹的连锁。这种趋势可能与正应力比下S-N曲线的陡峭倾斜有关。一个明显的差异，观察到的表面和走廊起源的骨折之间的断裂表面。少量微米级的颗粒状物质仅存在于隧道源裂隙的断口上。负应力比加速了颗粒区的形成。压缩载荷可能在这种现象中起重要作用。
Uniaxial fatigue tests of (α+β) Ti-6Al-4V alloy were carried out at various stress ratios (R=σmin/σmax) up to very high cycle region. The effect of stress ratio on very high cycle fatigue behavior was investigated based on SEM fractography. The S-N curves under positive stress ratios showed a complex folding shape with a steep incline in a long life region where interior-originating fractures occurred. On the other hand, the S-N curves under negative stress ratios had a general feature ; a monotonic increase of the fatigue lives with decreasing stress. SEM observations revealed that an interior crack was formed by linking of small cracks propagated from many interior origins located closely. This type of interior crack was particularly observed in low stress under positive stress ratios. The positive stress ratios facilitated the initiations of cracks and subsequent linkage of the cracks. This tendency may relate with the steep inclination of S-N curves under positive stress ratios. A clear difference was observed on the fracture surfaces between surface-and interior-originating fractures. A few micro-meter size granular substances existed only on the fracture surfaces of interior-originating fractures. The formation of the granular region was accelerated by negative stress ratios. Compressive loads may play an important role in the phenomenon.