Ultrasonic Crack Detection Research Articles

Enhanced ultrasonic detection of fatigue cracks by laser-induced crack closure

Fatigue cracks are usually initiated by small geometrical irregularities or material inhomogeneities that give rise to sharp local stress concentrations. In the early stages of fatigue, small cracks often remain hidden from conventional ultrasonic detection by stronger scattering from the very same structural imperfection that produced them in the first place. A new experimental method was developed to selectively increase the sensitivity of ultrasonic echographic techniques for such hidden fatigue cracks by exploiting one of their most characteristic features, their susceptibility for closure under compressive stress. Thermo-optical modulation by pulsed infrared laser irradiation was introduced to produce a temporary compressive thermal stress on the surface of the specimen. The resulting dynamic closure of microcracks was detected by a high-frequency ultrasonic surface wave technique. It is demonstrated that this method can be used to effectively distinguish fatigue cracks from other structural imperfections present in the material.

Subdivision of Grading Units Can Increase the Reliability of Performance Testing

This study examined the effect of subdividing grading units on performance test reliability. That is, instead of increasing test length by adding grading units comparable to existing grading units, this experimental approach attempted to increase test length, and hence reliability, by subdividing existing grading units into comparable subunits. The effect of subdividing grading units was assessed empirically using a performance test of the ultrasonic detection of cracks in pipe welds. Five-hour performance tests involving the examination of 10 pipe-weld specimens were completed by each of 52 experienced ultrasonic operators as part of their qualification for performing tasks of this type in nuclear power plants. Subdivision of grading units was found to increase the reliability of the test from 0.28 to 0.92, to decrease the standard error of measurement of the test from 13.81 to 1.35, and to decrease the 90% confidence band around test scores from ± 22.60 to ±2.20. Moreover, the increased reliability was predicted by the Spearman-Brown Prophecy Formula, the method commonly employed for predicting the effect of increased length on test reliability.

High-Resolution Ultrasonic Detection of Subsurface Transverse Cracks in CFRP Laminates. Simulation and Experiments

Article High-Resolution Ultrasonic Detection of Subsurface Transverse Cracks in CFRP Laminates. Simulation and Experiments was published on December 1, 1996 in the journal Science and Engineering of Composite Materials (volume 5, issue 3-4).

48424 Ultrasonic detection of cracks below bolts in aircraft skins

48424 Ultrasonic detection of cracks below bolts in aircraft skins

Ultrasonic detection of cracks in wheel set axles: Szelazek, J. NDT international, vol. 20, no. 3, pp. 177–180 (3 Jun. 1987)

Ultrasonic detection of cracks in wheel set axles: Szelazek, J. NDT international, vol. 20, no. 3, pp. 177–180 (3 Jun. 1987)

Ultrasonic crack detection and sizing wedges

Ultrasonic crack detection and sizing wedges

Ultrasonic detection of cracks in wheel set axles

This paper presents a means of testing railway carriage wheel sets with ultrasonic probes mounted on the cylindrical surface of the axle between the bearing and the wheel disc. The results of tests show that the method provides a consistent coupling efficiency, using liquid coupling, while the probe is rotated on the smooth cylindrical surface of the axle collar.

Ultrasonic detection of cracks in wheel set axles

Ultrasonic detection of cracks in wheel set axles

Determination of minimum flaw size detectable by ultrasonics in titanium alloy plates

Titanium alloys, due to their light weight, high strength, and corrosion resistant properties, are employed in many structural applications. For design purposes it is important to determine the limit of sensitivity of ultrasonic crack detection techniques for these alloys. This paper demonstrates that it is possible to detect electronic discharge mill (EDM) slots as small as 0.025 mm deep in thick plates, using commercial ultrasonic instrumentation. The effect of grain size, frequency and orientation of the flaw upon the limit of detection is also discussed.

Stress and the ultrasonic detection of fatigue cracks in engineering metals

The authors describe investigation on surface fatigue cracks penetrating part of the Nay through flat plates of steel, titanium and aluminium. The cracks were induced by tension-tension loading the plates in a three-point bending configuration at a frequency of 28 Hz and under constant load and R-factor. The metals were D6ac steel heat-treated to 1 447 MN m −2, annealed Ti-61-4V and 2219-T87 Al. The investigators then found the response of the cracks to ultrasonic shear waves by delta-scan. Elox slots of 1.52 × 0.25 × 0.76 mm length, width and depth served throughout the experiments as reference reflectors. The investigators found that stress relieving affected the ultrasonic response as did tension, cyclic compression and time. In fact, the ultrasonic echo in the aluminium and titanium was greater after many cycles of small compression or few cycles of great compression. But steel gave no such result. Tension increased the ultrasonic response to a degree related to the load. The echo lessened with time, however, because of creep.

A method for ultrasonic detection of corrosion cracks in 18-10 type steels

A method for ultrasonic detection of corrosion cracks in 18-10 type steels

Ultrasonic detection and measurement of fatigue cracks in notched specimens: Klima, S.J. and Freche, J.C. Experimental Mechanics, Vol 9, No 5 (May 1969) p193–203 (2291)

Ultrasonic detection and measurement of fatigue cracks in notched specimens: Klima, S.J. and Freche, J.C. Experimental Mechanics, Vol 9, No 5 (May 1969) p193–203 (2291)

Ultrasonic detection and measurement of fatigue cracks in notched specimens

An ultrasonic technique was developed and used to observe the formation and growth of fatigue cracks in notched cylindrical specimens subjected to reversed axial cyclic loading. Fatigue curves of life-to-initial detectable cracks as well as life-to-fracture were obtained for an aluminum-, a titanium- and a cobaltbase alloy, as well as a maraging steel. Depth of initially detectable cracks ranged between approximately 0.0005 and 0.004 in. (0.013 and 0.10 mm). Curves were also obtained relating ultrasonic system output voltage to crack depth up to 0.030 in. (0.76 mm) for three materials. These curves were used to demonstrate the capability of the device for monitoring crack growth.