Abstract
A new remote nondestructive inspection technique, based on thermoelastic temperature measurement by infrared thermography, is developed for detection and evaluation of fatigue cracks propagating from welded joints in steel bridges. Fatigue cracks are detected from localized high thermoelastic temperature change at crack tips due to stress singularity under variable loading from traffics on the bridge. Self- reference lock-in data processing technique is developed for the improvement of signal/noise ratio in the crack detection process. The technique makes it possible to perform correlation processing without an external reference signal. It is very difficult to detect through-deck type fatigue cracks in steel decks by the conventional NDT technique, since they are not open to the inspection. In this paper, self-reference lock-in thermography is applied for detection of through-deck type fatigue cracks. Experiments are carried out to steel deck sample, which simulates an actual steel bridge, during crack propagation test. It is found that significant stress concentration zone can be observed near the crack front, which enabled us to detect through-deck type fatigue cracks and to estimate its size.
Highlights
IntroductionDevelopment of remote and noncontacting effective nondestructive testing techniques for back surface crack is required
It was found that significant stress concentration zone appeared near the semi-elliptical crack front, which enabled us to detect through-deck type fatigue cracks and to estimate its half crack length in longer direction of trough rib
5.1 Experimental procedure Detection of through-deck type fatigue cracks in a steel deck sample under the traveling wheel load was conducted by the self-reference lock-in thermography
Summary
Development of remote and noncontacting effective nondestructive testing techniques for back surface crack is required. Infrared thermography is an effective tool for remote and full-field measurement of temperature distribution on the objective surface. The present authors developed a self-reference lock-in thermography [3], which does not require any external reference signals and can be employed even under random loading. Nondestructive inspections of fatigue cracks in steel bridges were conducted by the proposed selfreference lock-in thermography in the previous paper [4]. Detection of through-deck type fatigue cracks in a steel deck specimen is conducted by the self-reference lock-in thermography. Experiments are carried out for steel deck sample, which simulates an actual steel bridge, during crack propagation test under point load and traveling wheel load
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