Strain-Gauge Method of Detecting Subcritical Fatigue Cracks in Low-Carbon Steel Welds

Abstract

A. O. Lukashevich, V. A. Leonets', UDC 621.791.052 and L. M. Chaus Detection of subcritical fatigue cracks in low-carbon steel welds with the strain-gauge nullindicator method based on the amplitude difference and phase difference procedures was investigated. It was established that a marked growth of the difference in strain amplitudes pointed to the origin of a main crack 1 mm long near the weld. An initial increase in strain amplitude differences reveals fatigue damage much earlier in comparison with the visual crack detection. The phase difference procedure cuts down the time of fatigue damage detection in low-carbon steel welds tens of times from the visual method.

Front face strain compliance for quantification of short crack growth in fatigue testing

“…Back face strain compliance and clip gauges are widely used as relatively simple and sensitive techniques that can monitor fatigue crack growth. [18][19][20] However, these methods lack the sensitivity required to detect shorter crack length (a=W40:1). 21,22 In a study of the fatigue propagation of short cracks at the weld toe of automatic fillet welds, Verreman et al 23,24 implemented a method for measuring the crack length and closure level.…”

“…Back face strain compliance and clip gauges are widely used as relatively simple and sensitive techniques that can monitor fatigue crack growth. 18–20 However, these methods lack the sensitivity required to detect shorter crack length ( a / W ≤ 0 . 1 ). 21,22…”

“…Potential drop techniques necessitate close spacing between probes to achieve the required sensitivity, and they may not provide accurate results if tested in a corrosive environment. Back face strain compliance and clip gauges are widely used as relatively simple and sensitive techniques that can monitor fatigue crack growth [18,19,20]. However, these methods lack the sensitivity required to detect shorter crack length (a/W ≤ 0.1) [21,22].…”

“…Takeuchi (2012) [25] also suggested methods for applying strain gauges for estimating the mechanical response of the tested material and for crack monitoring based on the current methods for predicting the fatigue life of welded joints. Variations in measured strain amplitude and a phase difference process between two strain gauges attached across the region of interest were used by Lukashevich et al (2015) [19] as an indication of crack growth near welds of low-carbon steel butt welded joints. Chaudhuri (2019) [26] investigated the effect of the local weld toe geometry on fatigue crack initiation life by positioning a series of strain gauges across the weld toe.…”

Crack Detection of Reinforced Concrete Structures Based on BOFDA and FBG Sensors

“…e two cracks often form cracks inside and outside the structure. For the monitoring of cracks in reinforced concrete structures, traditional methods include identification from visual images [13][14][15], resistance strain gauges [16], the ultrasonic rebound method [17,18], and the X-ray CT method [19,20]; however, due to the influence of external environmental factors, the cracking of a reinforced concrete structure is often random. e above methods require manual assistance and suffer from hysteresis and thus cannot realise long-term, real-time, extensive monitoring.…”