DEFINITION OF FATIGUE CRACKS THROUGH NONDESTRUCTIVE TESTING

THE ABILITY OF FOUR NONDESTRUCTIVE TESTING (NDT) TECHNIQUES TO LOCATE, IDENTIFY, AND MEASURE FATIGUE CRACKS WAS DETERMINED EXPERIMENTALLY. THE NONDESTRUCTIVE TESTING TECHNIQUES USED WERE: X-RAY, MAGNETIC-PARTICLE INSPECTION, PENETRANT INSPECTION, ULTRASONIC INSPECTION, AND EDDY CURRENT INSPECTION. THE MATERIALS USED WERE 7075-T6511 ALUMINUM AND 4330 VANADIUM MODIFIED STEEL HEAT TREATED TO 220 TO 240 KSI ULTIMATE TENSILE STRENGTH. SURFACE FATIGUE CRACKS WERE INITIATED IN 1/4 IN. THICK, 3 IN. OUTSIDE DIAMETER TEST CYLINDERS. STANDARD NDT INSPECTION PROCEDURES WERE USED TO DETECT AND MEASURE THE LOCATION AND GEOMETRY OF THE CRACK. THE SPECIMENS WERE FAILED IN TENSION TO DETERMINE THE ACTUAL GEOMETRY OF THE CRACK FROM MEASUREMENTS ON THE FRACTURE SURFACE. THE SENSITIVITY OF EACH NDT METHOD IN DETECTING THESE CRACKS WAS DETERMINED FOR EACH CRACK SIZE RANGE CHOSEN. THE SIZE OF THE CRACK AS DETERMINED USING EACH NDT METHOD WAS COMPARED TO THE ACTUAL SIZE OF THE CRACK. THE ACCURACY OF EACH NDT METHOD TO LOCATE THE END POINTS OF THE CRACK ALSO WAS DETERMINED. THE RESULTS SHOW THAT THE RELIABILITY OF THE PRESENT NDT METHODS FOR DETECTING SMALL CRACKS NEEDS TO BE IMPROVED. NO CRACKS SMALLER THAN 0.10 IN. CAN BE DETECTED CONSISTENTLY WITH ANY OF THE NDT METHODS EXAMINED. ALL NDT METHODS HAVE RESULTED IN VERY HIGH ACCURACIES IN LOCATING THE LONGER CRACKS, AND LOW ASSURANCE INDEXES ARE PRIMARILY DUE TO TWO FACTORS: (1) THE INABILITY OF THE NDT METHOD TO MEASURE THE CRACK LENGTHS ACCURATELY AND (2) THE SENSITIVITY OF THE NDT METHODS IN DETECTING CRACKS LESS THAN 0.20 IN. IN LENGTH. THE X-RAY METHODS USED WERE UNABLE TO DETECT SMALL TIGHT SURFACE FATIGUE CRACKS IN BOTH THE ALUMINUM AND STEEL SPECIMENS UNLESS THE CRACK LENGTH WAS OVER 0.45 IN. LONG. THE SENSITIVITY OF THE SHEAR WAVE ULTRASONIC TECHNIQUE USED WAS SUPERIOR TO ALL OTHER METHODS EXAMINED. /AUTHOR/

• Supplemental Notes:
  • Vol 4, No 3, PP 666-700, 16 FIG, 5 TAB, 8 REF
• Authors:
  • PACKMAN, P F
  • Pearson, H S
  • Owens, J S
  • Young, G
• Publication Date: 1969-9

Media Info

• Serial:
  • Journal of Materials
  • Publisher: American Society for Testing and Materials (ASTM)

Subject/Index Terms

• TRT Terms: Alloy steel; Aluminum; Cracking; Eddy currents; Fatigue (Physiological condition); Magnetic detectors; Measurement; Nondestructive tests; Penetrants; Specimens; Surfaces; Ultrasonic tests; X ray analysis
• Uncontrolled Terms: Surface cracks
• Old TRIS Terms: Magnetic measurements
• Subject Areas: Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00216905
• Record Type: Publication
• Files: TRIS
• Created Date: Dec 29 1994 12:00AM