LAMB WAVE INSPECTION OF ALUMINUM SHEET

An effective and practical Lamb wave inspection system has been developed by Reynolds Metals Research to inspect aluminum sheet in gages from 0.25 mm (0.010 in.) to 3.20 mm (0.125 in.). Utilizing this system, an ultrasonic number is derived which relates the Lamb wave indication in the sheet to the final product quality. This ultrasonic number can readily be computed for each Lamb wave indication. Surface defects, small internal discontinuities and inclusions are detected by performing an inspection at frequencies from 12 to 15 MHz. 100%, of the volume of a sheet sample (e.g., 0.50 m (20 in.) wide by 1.2 m (48 in.) long by 0.43 mm (0.017 in.) thick) can be inspected in one traverse of the sheet width. When this is completed, the sheet material, if on a continuous coil is indexed to the next inspection position. An application of this technique to aluminum can stock will be described. Twenty-nine coils of can stock were sampled in our laboratory. 770 Lamb wave indications (presumed to be discontinuities) were selected for study. An ultrasonic number for each was computed. A can blank was obtained from the sheet in such a way that when the can was formed, the Lamb wave-detected discontinuity would occur in a known critical area of the final product. The 770 Lamb wave indications yielded ultrasonic numbers ranging from 1.6 to 38.5. Our study shows that, depending on the confidence level needed, a specific ultrasonic number can be used for determining a "go-no go" test when inspecting sheet material. For example, we have found that for ultrasonic numbers greater than or equal to 10,71% of the can blanks produced critical defects in the final product. As we increase or decrease this number, generally the percent critical defects increases or decreases, respectively. Equipment and procedures currently are being developed for plant installation. /Author/

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  • Supplemental Notes:
    • Society for Nondestructive Testing, 21-24 October 1974, Detroit
  • Corporate Authors:

    American Society for Nondestructive Testing

    914 Chicago Avenue
    Evanston, IL  USA  60202
  • Authors:
    • Mansfield, T L
  • Publication Date: 1975-4

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 96-100
  • Serial:
    • Materials Evaluation
    • Volume: 33
    • Issue Number: 4
    • Publisher: American Society for Nondestructive Testing
    • ISSN: 0025-5327

Subject/Index Terms

Filing Info

  • Accession Number: 00096212
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 2 1975 12:00AM