【摘要】 对圆柱形和板状2种6065A铝合金试件进行20kHz,106~1010周次的对称拉压超声疲劳试验,并用扫描电镜显微分析技术分析疲劳断口。结果表明:这2种形状的6065A铝合金试件的S—N曲线与传统无限寿命型疲劳曲线不同,而是呈现阶梯下降型特征,疲劳寿命大于107周次的试件仍会发生疲劳断裂;试件的疲劳裂纹以剪切方式沿与试件轴向成约45°方向扩展;圆柱形试件S—N曲线的阶梯下降型特征对应着疲劳裂纹的双萌生机制,在疲劳寿命较低的低周、高周阶段,试件表面局部应力或应变集中区成为疲劳裂纹源;在寿命较高的超高周阶段,试件次表面或内部存在的缺陷成为疲劳裂纹萌生有利的位置;板状试件的疲劳性能明显低于圆柱形试件,其疲劳裂纹呈现多源形核特征,且以表面裂纹萌生为主。更多还原

【Abstract】 Fatigue tests in the very high cycle(106~1010)fatigue regime of 6065Aaluminum alloy with cylinder and plate specimens were conducted by employing symmetric tension and compression loading with a frequency of 20kHz,and the fatigue fractures were observed by scanning electron microscopy(SEM). The results show that the S—Ncurve of 6065Aalloy specimens displays the characteristics of stepwise decrease and is different from that of the infinite life characteristics in traditional fatigue.The fatigue fracture will still occur when the fatigue life is more than 107 cycles.The fatigue crack expands in shear manner along with 45°specimen axial direction.The stepwise decrease characteristics of cylinder specimen S—N curve correspond to the double-initiation mechanism of fatigue crack.In the low or high cycle regimes of lower fatigue life,the fatigue crack initiates in the local stress or strain concentration on specimen surface. In the very high cycle regime of higher fatigue life,the fatigue crack initiates from the subsurface or internal defect of specimen.The fatigue properties of the plate specimens are markedly lower than those of cylindrical specimens.The fatigue crack displays the characteristics of multi-source nucleation,and surface crack initiation is dominant.更多还原