Detection and Location of Transverse Matrix Cracks in Cross-Ply Gr/Ep
Detection and Location of Transverse Matrix Cracks in Cross-Ply Gr/Ep(1995)
摘要
An advanced acoustic emission (AE) approach was utilized in a study of transverse matrix cracking in AS4/3502. Broad band sensors, digital acquisition and storage of data, and plate wave propagation based analysis of signals were used. Cross ply specimen of six different thicknesses ([0n, 90n, 0n], n = 1 to 6) with dimensions of 25.4 x 279.4 mm., were tested under quasi-static tensile loading. AE signals from cracks were differentiated from other signals by their plate wave characteristics. Microscopic analysis of polished specimen edges confirmed the presence and location of the cracks detected by AE. This allowed a one to one correspondence to be established between crack generated AE signals and actual cracks. The average absolute value of the difference between the crack location as measured under the microscope and the location determined from AE signals was 3.2 mm. for a nominal sensor gage length of 152 mm. Back scatter ultrasonic and penetrant enhanced X-ray techniques were also used to verify the presence and location of the cracks. These measurements demonstrated that all cracks extended the full width of the specimen. Four AE sensors were used, a pair at each end of the sensor gage length. The sensors of each pair were positioned side by side, each at the lateral edge of the specimen. This arrangement permitted evaluation of whether the crack initiation site was at a specimen edge or in its interior. For almost all crack signals analyzed (27 of 28), the location of the initiation site, within the uncertainty of the measurement, was at one of the specimen edges. This strongly suggests that the cracks initiated at the specimen edges. This is in agreement with mechanical models which predict that cracks initiate at defect sites resulting from the machining or cutting process along the edges. Further tests on wider specimen will be used to confirm this behavior.
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关键词
crack initiation site,crack location,polished specimen edge,AE sensor,Transverse Matrix Cracks,Cross-Ply Gr,AE signal,specimen edge,actual crack,wider specimen,ply specimen,crack signal
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