In situ measurement of fatigue crack opening stresses by nonlinear vibro-acoustic modulation testing

Abstract

The difficulty of accurately measuring crack closure regions has hindered measurements of opening or closure stresses, and ultrasonic methods have shown great potentialities in evaluating closure area. Many recent researches have confirmed the advantages of nonclassical nonlinear acoustic approaches in detecting short cracks and even micro-or mesocracks. However, there are few reports on using nonclassical nonlinear acoustic approaches to measure crack closure. The aim of this article is to verify the applicability of vibro-acoustic modulation approach in estimating opening stresses of fatigue cracks. A procedure of approximating the opening stress by the applied tensile load of the inflection point of the modulation intensity curve is proposed. To study the performance of this measuring method experimentally, in situ vibro-acoustic modulation tests were carried out on a central cracked 5052-H32 aluminum alloy fatigue sample. The experimental estimations match well with other researches. Analysis of the experimental results suggests that the vibroacoustic modulation technology is not only capable of measuring the fatigue cracks opening stresses, but also capable of analyzing the crack closure behavior, even for physically short cracks.

Integrated acoustic‐vibration frequency‐modulation technology to detect the contact nonlinear features of mechanical structure

“…The vibro‐acoustic modulation (VAM) technology shows unique advantages in the detection of nonlinear characteristics of structures. VAM approach has been extensively considered for nondestructive assessment of different applications 23 . Although numerous attempts have been applied, there is still confusion to understand the phenomenon of nonlinearity resulting from the crack‐wave contact.…”

“…VAM approach has been extensively considered for nondestructive assessment of different applications. 23 Although numerous attempts have been applied, there is still confusion to understand the phenomenon of nonlinearity resulting from the crack-wave contact. Several concepts such as the nonlinear stiffness spring (NSS) mechanism, 24,25 the dissipative mechanism of elastic hysteresis, 26,27 and the contact acoustic nonlinearity (CAN) mechanism 28,29 have been recommended in the literature to clarify the nonlinearity detection.…”