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An ultrasonic method for dynamic monitoring of fatigue crack initiation and growth
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Image of FIG. 1.
FIG. 1.

Specimen geometry including transducer locations and ultrasonic beam paths (thickness and hole diameter ).

Image of FIG. 2.
FIG. 2.

Typical segment from the fatigue loading spectrum where the 100% value corresponds to .

Image of FIG. 3.
FIG. 3.

Photograph of a two-hole fatigue coupon with attached angle beam transducers.

Image of FIG. 4.
FIG. 4.

Typical angle beam through transmission signal showing the single and double V path arrivals.

Image of FIG. 5.
FIG. 5.

Effects of tensile loading on the received through transmission angle beam signals. (a) Before the onset of cracking, the ultrasonic signal is shifted in time as load is applied but the amplitude is unaffected. (b) After crack initiation, increasing load causes the ultrasonic signal to both shift in time and decrease in amplitude.

Image of FIG. 6.
FIG. 6.

Change in time of flight of the ultrasonic signal versus load referenced to the zero-load time at the start of each fatigue block. (a) Single V arrival. (b) Double V arrival.

Image of FIG. 7.
FIG. 7.

Loads calculated from the change in ultrasonic time of flight as determined from 50 consecutive dynamic measurements.

Image of FIG. 8.
FIG. 8.

Calculated change in time of flight versus load for both single and double V arrivals due to geometrical effects only.

Image of FIG. 9.
FIG. 9.

Coordinate system definition for acoustoelasticity analysis of angle beam ultrasonic wave propagation.

Image of FIG. 10.
FIG. 10.

Theoretical change in time of flight compared to measurements for data recorded after six fatigue blocks. (a) Calculations using the same transducer-hole distance for both single V and double V paths. (b) Transducer-hole distances adjusted to compensate for differences in single V and double V paths.

Image of FIG. 11.
FIG. 11.

Energy versus load at various fatigue blocks where energy is normalized to the zero load value for each block.

Image of FIG. 12.
FIG. 12.

Comparison of energy versus fatigue cycles as determined from both static and dynamic measurements. (a) No load. (b) Load of .

Image of FIG. 13.
FIG. 13.

Comparison of normalized energy ratio versus fatigue cycles as determined from both static and dynamic measurements for two specimens. (a) S3-0001 (7075-T7351). (b) S4-0030 (7075-T651).

Image of FIG. 14.
FIG. 14.

Cross-sectional images of two holes after coupons were fractured. (a) S3-0001 (7075-T7351). (b) S4-0030 (7075-T651).


Generic image for table

Lamé second-order elastic constants ( and ) and Murnaghan third-order elastic constants (, and ) for 7075-T651 aluminum.22


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An ultrasonic method for dynamic monitoring of fatigue crack initiation and growth