Modified relative arrival time technique for sizing inclined cracks Mohammad R. Hoseini a,⇑ , Xiaodong Wang b , Ming J. Zuo b a WorleyParsons Canada, Edmonton Operations, Canada b Department of Mechanical Engineering, University of Alberta, Canada article info Article history: Received 3 June 2013 Received in revised form 16 December 2013 Accepted 23 December 2013 Available online 7 January 2014 Keywords: Ultrasonic Time of flight Crack length estimation B-scan abstract In this paper, a modified relative time technique is proposed for estimating the length and the orientation of inclined cracks using ultrasonic B-scan signals. The proposed technique utilizes the relative position of the tip diffraction echo to the corner reflection echo in an ultrasonic B-scan image to estimate the crack length and the crack inclination angle. Both finite element simulated signals and experimental signals, which are obtained from a spec- imen with a 3 mm crack with different inclination angles, are used to evaluate the estima- tion error of the proposed technique. The results show that the proposed technique overcomes the shortcoming of the conventional relative arrival time technique in sizing inclined cracks. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Ultrasonic non-destructive testing and evaluation has been extensively practiced for detection of defects in engineering structures [1]. Many factors contribute to the popularity of the ultrasonic testing (UT) among the non- destructive testing practitioners. UT does not require implementing safety measures as needed for radiography. It is applicable to a wide range of engineering materials, such as steel and concrete. UT is able to detect both surface flaws, e.g. cracks, and internal flaws, e.g. voids or inclusions of foreign material. In addition to detecting flaws, UT can be used for sizing flaws. In fact, the accuracy of ultrasonic testing in sizing crack-like flaws is unique among non- destructive testing and evaluation techniques [2,3]. Existing ultrasonic non-destructive testing and evalua- tion techniques use time of arrival (TOA), amplitude of the echo or spectral features of the received signal for defect detection and sizing. However, among these tech- niques, TOA-based techniques, such as relative arrival time technique [4,5], are now more extensively used because of their excellent probability of detection and accurate measurement of defects [6–9]. Relative arrival time technique (RATT), proposed by Gruber [10], is frequently used in crack sizing [11,2]. It has advantages in detection and sizing of small surface cracks [12]. RATT sizes a crack based on the separation of the times of arrival of the corner reflection echo, hereinaf- ter referred to as R-wave, and the tip diffraction echo, here- inafter referred to as D-wave. The concept of RATT is illustrated in Fig. 1. As shown in Fig. 1, conventional RATT assumes that cracks are perpendicular to the specimen surface. However, this assumption does not hold in gen- eral, causing error in crack length estimation. Ciorau [13] investigated the inherent error in using RATT for sizing in- clined cracks. However, they did not provide a method to account for this error. Harumi et al. [14] proposed using multi-tip waves resulting from mode conversion and multiple reflections for sizing inclined cracks. However, these tip echoes have low intensities and often interfere with each other. There- fore, detection and interpretation of these echoes are bur- densome in using this technique. Recently, Satyanarayan et al. [4] simulated the ultra- sonic phased-array B-scan image for different crack 0263-2241/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.12.031 ⇑ Corresponding author. Tel.: +1 7806552767. E-mail address: mohammad.hoseini@worleyparsons.com (M.R. Hoseini). Measurement 50 (2014) 86–92 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement