缺口根部小裂纹疲劳扩展特性及闭合效应实验研究

THE MEASUREMENTS OF THE PROPAGATION AND CLOSURE OF FATIGUE SMALL CRACKS AT NOTCHES

对LY12CZ铝合金缺口根部疲劳小裂纹闭合特性及扩展行为进行了实验研究。采用光学金相显微镜测量了小裂纹的起裂及扩展。通过测量裂尖后两岸显微硬度压痕随裂纹张开闭合的距离变化,建立了缺口根部角裂纹裂尖附近的裂纹张开位移和载荷的关系,以此确定裂纹的张开应力。根据测得的σ_(op)/σ_(max)及按Newman模型计算的σ_(op)/σ_(max),进行闭合效应修正后算得的小裂纹疲劳扩展速率与实验结果基本符合。在小裂纹的情况下,所得结果与Newman方法所得结果相比,更为接近实际情况。

Closure and propagation properties of fatigue small cracks in double-edge-notched LY12CZ Al-alloy plate specimens were measured. The initiation and growth of small cracks are observed bv using optical microscope. The varying distance between the microhardness indentations at the blanks of the cracks as a function of applied loads could be monitored to determine the crack opening displacements near the crack tip, which were used to obtain the crack opening load. Δk was replaced by ΔKeff = Kmax-Kop in Paris formula to account for the closure effects of small cracks using the experimental values and the Newman's prediction values σop/σmax. The da/dN values thus predicted were in good agreement with the tested values.