Experimental studies on fatigue crack growth rate at elastic-plastic state of aeronautical aluminum alloy
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摘要: 研究含长裂纹薄壁结构弹塑性状态下的裂纹扩展规律对于保证机体结构安全具有重要意义.设计了民机用铝合金大宽板裂纹扩展速率测试用试验件和夹具,进行了2024-T3和7075-T6两种铝合金大宽板弹塑性状态下裂纹扩展速率测试.讨论了应力强度因子变程(ΔK)和裂纹中心线处的张开位移变程(Δδ)作为弹塑性状态下裂纹扩展速率表征参量的适用性.研究结果表明:中、高级应力水平作用下,含长裂纹铝合金大宽板裂纹进入快速扩展阶段,裂纹扩展ΔK~da/dN曲线发生明显转折,不能用Paris公式拟合.在裂纹扩展后期,Δδ~da/dN曲线在双对数坐标下呈线性关系,可用Δδ~da/dN关系曲线来表征弹塑性状态下铝合金的裂纹扩展速率.Abstract: Studying the crack propagation behavior of the thin-walled structure with long cracks is very significant for ensuring the safety of the airframe. The specimen and fixture of aluminum alloy wide plate was designed for fatigue crack propagation rate (da/dN) testing. The fatigue crack growth rate was tested for 2024-T3 and 7075-T6 aluminum alloy at elastic-plastic state. The relationship between the range of stress intensity factor (ΔK) or crack central line displacement (Δδ) and da/dn was discussed to describe the crack propagation behavior of aluminum alloy. The experimental results show that under medium-high loading, the long crack of wide plate grows quickly; the da/dN~ΔK curve turns obviously at this stage; the crack growth behavior cannot be expressed as Paris law. At the final stage, there is a linear relationship between Δδ and da/dn in the logarithm coordinate. The crack propagation behavior of aluminum alloy at elastic-plastic could be described by Δδ~da/dN curve.
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