ABSTRACT Acoustic nonlinearity measurements via contact and noncontact generations of surface acoustic waves (SAWs) were performed in order to characterize the thermal aging of aluminum alloy. The experiments were conducted on aluminum alloy samples (Al6061-T6) that were heat-treated at 220°C for different times (0 min, 20 min, 40 min, 1 h, 2 h, 10 h, 100 h, 1,000 h) and thus had the different levels of thermal aging. The acoustic nonlinearity of the specimens in two types of SAWs was observed according to the thermal aging. The fractional changes in the acoustic nonlinearity exhibited similar trends in both contact and noncontact SAWs, showing that the acoustic nonlinearity measurement via SAWs is independent of the SAW-excitation method. Furthermore, the fractional changes agreed well with the variation in the yield strength, which was a minimum when the acoustic nonlinearity reached its first peak. Then, the acoustic nonlinearity drastically dropped while the yield strength increased to its highest value. Thus, the variation in the acoustic nonlinearity can be perceived as an indicator of the aging level. These results demonstrate the potential feasibility of acoustic nonlinearity measurements via SAWs for the nondestructive evaluation of material degradations.

中文翻译：

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通过表面声波的声学非线性测量评估铝合金的热老化

摘要 通过接触式和非接触式表面声波 (SAW) 生成进行声学非线性测量，以表征铝合金的热老化。实验在铝合金样品 (Al6061-T6) 上进行，在 220°C 下热处理不同时间（0 分钟、20 分钟、40 分钟、1 小时、2 小时、10 小时、100 小时、1,000 小时）因而具有不同程度的热老化。根据热老化，观察了两种类型的声表面波样品的声学非线性。声学非线性的分数变化在接触式和非接触式 SAW 中表现出相似的趋势，表明通过 SAW 进行的声学非线性测量与 SAW 激发方法无关。此外，分数变化与屈服强度的变化非常吻合，这是声学非线性达到其第一个峰值时的最小值。然后，声学非线性急剧下降，而屈服强度增加到最高值。因此，声学非线性的变化可以被视为老化水平的指标。这些结果证明了通过 SAW 进行声学非线性测量对材料退化进行无损评估的潜在可行性。