Ultrasonic Measurement of the Crack Depth and the Crack Opening Stress Intensity Factor Under a No Load Condition
Tóm tắt
This paper describes a new methodology for evaluating the crack depth and the crack opening stress intensity factor of small closed cracks using an ultrasonic technique. Surface connected back-wall cracks of depth ranging from 0.4 to 4.0 mm in steel specimens are considered. The crack corner echo amplitude of an ultrasonic shear wave, SW, beam of 50° incidence in material is used. First, the ultrasonic echo response of an open crack is determined as a function of crack depth. Next, based on changing the crack closure stress, an empirical relation between the crack closure stress and the crack-echo response is formulated. The crack depth and the crack closure stress of an unknown closed crack based on these relations are determined by inverse analysis of the ultrasonic response of the crack. From the evaluated crack depth and crack closure stress, the crack opening stress intensity factor is determined. The accuracy and reliability of this new nondestructive evaluation (NDE) method is verified by comparing the evaluated crack depth with the actual one. The latter is measured on the fractured surface obtained after carrying out ultrasonic testing. The ultrasonic method developed is proved to be a powerful tool for quantitative and nondestructive evaluation of the crack depth as well as the crack closure stress.
Tài liệu tham khảo
W. Elber, "The significance of fatigue crack closure" ASTM STP 486, pp. 230–242 (1971).
M. Saka and H. Abé, "Sizing closed cracks by ultrasonics and analysis" in Topics in Engineering, Computational and Exper-imental Fracture Mechanics, Developments in Japan, edited by H. Nisitani, Vol. 16, pp. 165–185, 1994, Computational Mechan-ics Publications, Southampton, UK.
M. Kikukawa, M. Jono, K. Tanaka, and M. Takatani, "Mea-surement of fatigue crack propagation and crack closure at low stress intensity level by unloading elastic compliance method." J. Soc. Mater. Sci. Jpn. 25(276), pp. 899–903 (in Japanese) (1976).
N. A. Fleck, "Compliance methods for measurement of crack length," in Fatigue Crack Measurement: Techniques and Appli-cations, edited by K. J. Marsh, R. A. Smith, and R. O. Ritchie, pp. 69–73, 1991, Engineering Materials Advisory Services, Warley.
O. Buck, C. L. Ho, and H. L. Marcus, "Plasticity effects in crack propagation." Eng. Fract. Mech. 5(1), pp. 23–34 (1973).
H. Kobayashi, T. Ogawa, H. Nakamura, and H. Nakazawa, "Measurement of crack closure and evaluation of near-threshold characteristics in fatigue crack growth for A508-3 steel." Trans. JSME, Ser. A 50(451), pp. 309–319 (in Japanese) (1984).
D. Bouami and D. D. Vadder, "Detection and measurement of crack closure and opening by an ultrasonic method." Eng. Frac. Mech. 23(5), pp. 913–920 (1986).
M. Saka and T. Uchikawa, "Simplified NDE of a closed ver-tical crack using ultrasonics." NDT & E Int. 28(5), pp. 289–296 (1995).
S. R. Ahmed and M. Saka, "A sensitive ultrasonic approach to NDE of tightly closed small crakcs." Trans. ASME, J. Pressure Vessel Technol. 120(4), pp. 384–392 (1998).
S. R. Ahmed and M. Saka, "Quantitative nondestructive testing of small, tight cracks using ultrasonic angle beam technique," Mater. Eval. 58(4), pp. 564–574 (2000).
S. R. Ahmed and M. Saka, "A new ultrasonic angle beam tech-nique for sensitive evaluation of closed cracks." NDT & E Int. 33(4), pp. 261–271 (2000).
M. A. S. Akanda and M. Saka, "Ultrasonic shear wave tech-nique for sensitive detection and sizing of small closed cracks," JSME Int. J., Ser. A 45(2), pp. 252–261 (2002).
M. A. S. Akanda and M. Saka, "Relationship between closure stress of small fatigue crack and ultrasonic response" J. Nonde-str. Eval., 23(2), pp. 37–47 (2004).
—Annual Book of ASTMStandards, Metals Test Methods and An-alytical Procedures, Vol. 03.01, Sect. 3, July 1997, ASTM Des-ignation: E 399-90, 1997 (Reapproved).
J. Krautkramer and H. Krautkramer, Ultrasonic Testing of Materials, 4th ed., 1990, Springer Verlag, Berlin.
G. N. Vanderplaats, Numerical Optimization Techniques for Engineering Design, 1984, McGraw-Hill, New York.
H. F. Bueckner, "Field Singularities and Related Integral Rep-resentations," in Mechanics of Fracture, edited by G. C. Sih, 1973, Noordhoff International Leyden, Vol.1,MA.