2124-T851厚板S向超低周疲劳行为及断裂特征

Extremely Low Cycle Fatigue Behavior and Fracture Characteristics of 2124-T851 Thick Plate in Short Transverse Direction

摘要:

为评价极端循环载荷下的服役性能，采用轴向名义应变控制法研究了2124-T851铝合金厚板短横向超低周疲劳(ELCF)行为。研究表明：该合金在ELCF过程中表现出持续稳定的循环软化特性，软化速率与名义应变幅Δεn/2呈幂函数关系；由Δεn/2表征的Manson-Coffin公式能准确地预测该合金的ELCF寿命。断口分析表明：短横向加载的静态断裂和ELCF断裂方向均趋于长横向，且随Δεn/2减小，断裂模式由切断型逐渐转变为正断型；ELCF微观形貌总体为韧窝断口+挤压平面，且仅在Δεn/2降至0.4%时出现疲劳条带。

Abstract:

In order to assess service properties of 2124-T851 aluminum alloy thick plate in short transverse orientation (S direction) under ultra-high loading, the extremely low cycle fatigue (ELCF) behavior was investigated by controlling nominal axial strain in fatigue experiments of hourglass-type specimens. The results indicate that the 2124-T851 thick plate in S direction exhibits stable cyclic softening in cyclic stress-strain hysteresis loop, and the softening rate can be expressed as a typical?power function of the nominal strain amplitude (Δεn/2). Manson-Coffin formula expressed in Δεn/2 has a good prediction of the ELCF life as compared with the experimental results. The fracture morphology shows that the crack propagation direction tends to follow longitudinal-transverse direction (T direction) in both the monotonic tensile samples and the ELCF fracture samples. With the decrease of Δεn/2, the fracture mode gradually changes from shear mode into normal mode. ELCF microscopic morphology generally?exhibits hybrid fracture?characteristics?of?dimples and extrusion flat caused by two crack surface peened each other. The fatigue striations were found only when Δεn/2 decreased to 0.4%.