Nondestructive Evaluation of a Metal Matrix Composite

Abstract

Abstract : Samples of aluminum metal matrix composites (AlMMCs) have been examined with nondestructive evaluation techniques. A literature search identified ultrasonic C-scans as one of the most promising techniques, and this approach was used along with an eddy-current based approach, Meandering Winding Magnetometer (MWM), that also had some potential usefulness for flaw detection. Samples with known flaws were first investigated to ascertain the sensitivity of the equipment. Subsequent tests were performed on samples obtained from the University of Delaware. The findings were that both ultrasonics and MWM could detect gross flaws (cracks, delaminations, lack of matrix infusion, etc.) but that more subtle defects such as fiber waviness could not be detected unequivocally. Since fiber volume content determines to a large extent the strength of that AlMMC, a quantitative relationship between fiber volume content and the sonic velocity was developed. It was also noted that as fiber volume content increased, the ultrasonic signal attenuation increased. High signal attenuation due to high fiber volume content in some of the earlier ultrasonic scans led to a misinterpretation of those scans that was subsequently corrected.