This work aims at studying the effect of porosity in particulate reinforced metal-matrix composites on the statistical amplitude distribution of backscattered laser-induced ultrasonic pulses in these composites. A special laser-ultrasonic transducer used in experiments combines laser excitation and piezoelectric detection of broadband ultrasonic pulses in composite specimens with only one plane surface available for laser irradiation. We studied stir cast hypereutectic aluminium-silicon alloy A336 matrix composites reinforced with the SiC micro particles (volume fractions of 0.033-0.135) and in-situ reactive cast aluminum matrix composites reinforced with the Al3Ti intermetallic particles (volume fractions of 0.04-0.115). The amplitude distribution width of the backscattered ultrasonic pulse was determined by approximating the experimental data by the Gaussian probability distribution applicable for statistics of large number of independent random variables. The results show that the amplitude distribution width increases with the growth in the specimen porosity independent of sizes and fractions of the reinforcing particles. The empirical relationship between the local porosity and distribution width of the backscattered ultrasonic signal amplitudes was obtained for porosities up to 4.5%. This relationship can be used for nondestructive testing of the local porosity in engineering products fabricated from the studied composite materials. The proposed laser-ultrasonic technique is especially promising for structural health monitoring of particulate reinforced metal-matrix composites during their service.

中文翻译：

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孔隙率对颗粒增强金属基复合材料中背散射超声脉冲统计振幅分布的影响

本工作旨在研究颗粒增强金属基复合材料中的孔隙率对这些复合材料中背散射激光诱导超声脉冲的统计振幅分布的影响。一种用于实验的特殊激光超声换能器将复合样品中宽带超声脉冲的激光激发和压电检测相结合，只有一个平面可用于激光照射。我们研究了用 SiC 微粒增强的搅拌铸造过共晶铝硅合金 A336 基复合材料（体积分数为 0.033-0.135）和用 Al3Ti 金属间化合物颗粒增强的原位反应浇铸铝基复合材料（体积分数为 0.04-0.115）。背散射超声脉冲的振幅分布宽度是通过适用于大量独立随机变量统计的高斯概率分布逼近实验数据来确定的。结果表明，振幅分布宽度随着试样孔隙率的增加而增加，而与增强颗粒的尺寸和分数无关。对于高达 4.5% 的孔隙率，获得了局部孔隙率和反向散射超声信号幅度分布宽度之间的经验关系。这种关系可用于对由所研究的复合材料制成的工程产品的局部孔隙率进行无损检测。