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Objective. The study investigated the effect of weather and day of the week on the daily circulation numbers in two public libraries in Japan. Method. Datasets on library circulation were collected from one library in an urban area, and another in a rural area. The data were then divided according to rainy day and other days, holiday and workday, and day of the week, and the presence or absence of significant differences in daily circulation was analyzed. Automatic linear modeling was performed to analyze the effect of weather, day of the week, and holiday on daily circulation. Results. The results revealed that day of the week have a considerable impact on daily circulation for both libraries. However, weather exerted a significant impact in the urban area only. Automatic linear modeling explained the daily circulation based on day of the week and holiday with an accuracy of 71.5% for the rural library, and explained the circulation numbers based on day of the week, holiday, and precipitation amount with an accuracy of 81% for the urban library. Published version This work was supported by JSPS grant KAKENHI JP 19H04428 and 16K16161.

Ageing steel bridges suffer fatigue cracks thereby necessitating immediate inspection, structural integrity evaluation or repair in the life cycle of steel bridges. We propose nondestructive evaluation techniques employing infrared thermography enabling us to remotely inspect the fatigue cracks in steel bridges and evaluate the structural integrity on the basis of thermoelastic stress measurement. This study presents a structural integrity assessment of steel bridges using remote measurement of the stress field around the fatigue cracks. We focus upon experimental results confirming reduction in the severity of the stress distribution around the fatigue cracks after the repair or reinforcement of members in steel bridges.

For large-scale steel structures such as orthotropic steel decks in highway bridges, nondestructive inspection of deteriorations and fatigue damages are indispensable for securing their safety and for estimating their remaining strength. As conventional NDT techniques for steel bridges, visual testing, magnetic-particle testing and ultrasonic testing have been commonly employed. However, these techniques are time- and labor- consuming inspections, because special equipment is required for inspection, such as scaffolding or a truck mount aerial work platform. The present authors developed a new thermography NDT technique for crack detection, which is based on temperature gap appeared on the surface of structural members due to thermal insulation effect of the crack. The practicability of the developed technique to through crack was demonstrated by the field experiments for highway steel bridges in service. In this paper, the applicability of the inspection technique based on temperature gap measurement to back-surface crack detection is investigated by the laboratory testing. The testing was conducted for several specimens. A fatigue crack was introduced in a back surface of each specimen by 4 point bending fatigue test. This investigation has revealed that back surface fatigue crack can be detected by the proposed technique.

In order to investigate the effects of new surface modification method “Laser quenching after coating” on the rolling contact fatigue strength of ceramic coated steel, CrAlN coated specimens were processed by this method under various laser power conditions, and the thrust type rolling contact fatigue tests were carried out for these specimens. The delamination initiation life of CrAlN coated specimen increased with the laser power, however the excessive laser power decreased the delamination initiation life. The adhesive strength of CrAlN coated specimen showed similar variation for the increase of the laser power. The film hardness was almost constant for the increase of the laser power, however the excessive laser power also decreased the film hardness. From these results, it was considered that the increase of the delamination initiation life of CrAlN coated specimen was caused by the increase of the adhesive strength, and the decrease of the delamination initiation life at high laser power was affected by the decrease of the adhesive strength and/or the film hardness.

Fatigue crack propagation in aging steel bridges has become a serious problem. Nondestructive evaluation of fatigue damage propagation is necessary to ensure safety and to estimate the remaining life of the bridges. Conventionally employed nondestructive testing (NDT) techniques such as visual testing, magnetic particle testing and ultrasonic testing are time- and labor- consuming techniques, further these NDT techniques cannot be used to directly evaluate the remaining strength of the bridges. Thermoelastic stress analysis (TSA) using infrared thermography has been widely used as an effective full-field experimental stress measurement technique. In this study, TSA was applied for on-site measurement of stress distributions around fatigue cracks, and the future crack propagation behavior was estimated by the fracture mechanics approach. Experimental studies were conducted for laboratory specimens which modeled a part of welded structure in steel bridges. The stress intensity factors were calculated from stress distributions measured by TSA technique. Relationship between stress intensity factor ranges and crack propagation rates was obtained. It is found that the obtained relationship shows a good correspondence with the Paris law. Further TSA technique was applied to evaluate the effectiveness of repair or reinforcement for defective portions. Severity reduction in stress distribution around the fatigue crack after treatment was confirmed for actual steel bridge members by TSA. Crack propagation rate was estimated from the stress intensity factor calculated from on-site stress measurement data. As the result, 55% reduction in crack propagation rate was ascertained indicating the positive effect of the crack repair.

In order to investigate the effects of a new surface modification method, ‘the substrate quenching after coating’ on the rolling contact fatigue strength, TiN coated steel specimens and CrAlN coated steel specimens were processed by this method and the thrust type rolling contact fatigue tests were carried out for these specimens. In the process of the substrate quenching after coating, two types of quenching methods, furnace quenching and laser quenching, were used.For the furnace quenched specimens, the delamination initiation life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidisation of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the delamination initiation life of the laser quenched specimens was longer than that of the furnace quenched specimens. After the initiation, the delamination of the furnace quenched specimen grew much faster than that of laser quenched specimen. These...

In our previous studies, a new surface modification method by combination of ceramic coating and heat treatment, named “substrate quenching after coating” was developed. The thrust type rolling contact fatigue tests were carried out for TiN coated steels and CrAlN coated steels processed by substrate quenching after coating, and the effects of the type of ceramic coating (TiN or CrAlN) and the quenching methods (by furnace quenching or by laser quenching) on the flaking initiation life were investigated. For the specimens quenched by furnace, the flaking life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidization of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the flaking life of the specimens quenched by laser was longer than that of the specimens quenched by furnace. This reason could be explained by the difference of the process time of the furnace quenching and the laser quenching. It is considered that laser quenching after coating could be an effective way to improve the flaking initiation life under rolling contact fatigue.

A new surface modification method “laser quenching after coating” using a high power diode laser equipped with a 2dimensional galvano-scanner unit was developed to process a larger area of ceramic coated steel uniformly and efficiently. The laser irradiation tests for 3 kinds of ceramic-coated steels: CrAlN, TiAlN and CrN, were carried out with the scanning laser, and the appropriate irradiation conditions to achieve the uniformly quenched substrate without any surface damage were clarified for these ceramic-coated steels. The area of the substrate surface wider than the laser spot size could be easily quenched by the scanning laser. The adhesive strength, the film hardness of the laser-irradiated regions and the deformation caused by laser irradiation were evaluated. Laser quenching with the scanning laser can effectively improve the adhesive strength and substrate hardness without any detrimental effect on the film hardness of the ceramic-coated specimens. In the deformation of the laserirradiated specimens, two features were recognized; one is the bending, and the other is the expansion of laser-irradiated part. It was found that the deformation of ceramic-coated steel by laser irradiation under the same heat input condition does not depend on the kind of ceramic thin film but on the steel type of the substrate. It was concluded that “laser quenching after coating” with scanning laser could easily improve the adhesive strength and substrate hardness without any detrimental effect on the film hardness of large surface areas in the tested all types of ceramic-coated specimens. Copyright © 2014 VBRI press.

In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. In the present research, in order to quench a larger area of ceramic coated steel uniformly and efficiently, a high power diode laser equipped with a galvano-scanner was used in the laser heat treatment process. The scanning laser irradiation conditions to achieve uniformly quenched substrates without any surface damage were investigated for three kinds of ceramic coated steels: CrAlN, TiAlN and CrN. The film hardness and adhesive strength of the laser irradiated regions were evaluated. It is shown that scanning laser quenching after coating effectively improved the mechanical properties for larger area of ceramic coated steels.

In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible t...

In order to identify the mechanisms of changes in the magnetic flux density distribution around fatigue cracks that occur during crack propagation, JIS SCM440 specimens were fatigue tested, and the relation between crack morphology and magnetic flux density distribution was investigated. Two features were observed: a high intensity area around the crack tip, and a low intensity area around the crack root. The low intensity area grew larger for wide open cracks and disappeared when the crack was closed by external force. It was hence found that the magnetic flux density distribution is strongly affected by the crack opening.

An efficient inspection method for detecting fatigue cracks on orthotropic steel decks was developed. The bead-penetrating crack between a deck plate and trough rib can be detected remotely with high degree of accuracy by this method. This method is called “temperature gap method”, since the fatigue crack is identified by detecting the temperature gap at the crack with an infrared thermography. The inspection with this method is done in a systematic manner with priority of the bridges set from the data of cumulative traffic volume of large vehicles. The infrared camera system and the crack detection system were also developed for the efficient inspection. This paper is to report on the inspection for orthotropic steel decks with the infrared thermography.

Introduction It is difficult to make a definite diagnosis of a cracked tooth solely based on an inspection within the root canal, especially in case of microcracks. At present, there seems to be no established method to detect dentinal microcracks in roots; therefore, the current detection techniques need to be improved. Vibrothermography (VibroIR) helps to detect microcracks by the friction heat generated from ultrasonic vibration. The purpose of this study was to establish a novel method using VibroIR to detect dentinal microcracks. Methods The root canals of 20 roots with cracks and control roots were prepared after removing the tooth crowns. A tapered indenter was inserted into the root canal and pressed until a microcrack was created under an optical microscope. Using VibroIR, the detection trials for dentinal microcracks were performed with an ultrasonic vibration power ranging from 0.43 to 1.48 W at an angle of 0°, 30°, 45°, 60°, and 90° between the ultrasonic vibration point and the microcrack line. After the detection test, the microcrack width was measured with an optical microscope. Results Frictional heat was detected in the microcracks with thermography at 0.89 to 1.48 W and at an ultrasonic vibration point angle less than 60° from the crack line for 10 seconds. Microcracks with a width of 4 to 35.5 μm were detected with this method. Conclusions VibroIR may be an effective method for the diagnosis of root dentinal microcracks.

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to quench a larger area of ceramic coated steel uniformly and efficiently, a high power diode laser equipped with a galvano-scanner unit was used in the laser heat treatment process. The scanning laser irradiation conditions to achieve uniformly quenched substrates without any surface damage were investigated for 3 kinds of ceramic-coated steels: CrAlN, TiAlN and CrN. The film hardness and adhesive strength of the laser irradiated regions were evaluated. It is shown that scanning laser quenching after coating effectively improved the mechanical properties for larger area of ceramic-coated steels.

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to demonstrate further development of this method, the fracture strength of laser-irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat-induced changes in the substrate hardness, a cemented carbide WC-Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. Laser quenching has been shown to effectively reduce the fracture strength loss of the ceramic thin films in coated steels.

A new remote nondestructive inspection technique that is based on thermoelastic temperature measurement by infrared thermography was developed for the evaluation of fatigue cracks propagated from welded joints in steel bridges. Fatigue cracks were detected from localized high thermoelastic temperature changes observed at crack tips induced by stress singularity under variable loading resulting from traffic on the bridge. A self-reference lock-in data processing technique was developed for improving the signal/noise ratio of the thermal images recorded in the crack detection process. In this study, remote and nondestructive detection of fatigue cracks in an actual steel bridge in service was performed by the self-reference lock-in thermography method. The accuracy of this method was improved with a motion compensation technique.

A new remote nondestructive evaluation technique based on thermoelastic temperature measurement by infrared thermography was developed for the evaluation of fatigue cracks propagating from welded joints in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature changes at crack tips due to stress singularities generated by wheel loading from traffic on a bridge. A self-reference lock-in data-processing technique was developed to improve the signal-to-noise ratio of the thermal images obtained in the crack detection process. Thermoelastic stress analyses in the vicinity of crack tips were carried out after the crack detection process by self-reference lock-in thermography. The stress distribution under wheel loading by traffic was measured by infrared thermography. Stress intensity factors were directly evaluated from the measured stress distribution. It was found that these fracture mechanics parameters can be evaluated with reasonable accuracy by the proposed technique, enabl...

A new remote nondestructive evaluation technique, based on thermoelastic temperature measurement by the infrared thermography, was developed for evaluation of fatigue cracks propagated from welded joints in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature change at crack tips due to stress singularity under wheel loading from traffics on the bridge. Self-reference lock-in data processing technique was developed for the improvement of signal-to-noise ratio of the thermal images obtained in the crack detection process. In this paper, experimental results of fatigue crack detection by the self-reference lock-in thermography are reviewed.

In recent years, fatigue crack propagations in aged steel bridge which may lead to catastrophic structural failures have become a serious problem. For large-scale steel structures such as orthotropic steel decks in highway bridges, nondestructive inspection of deteriorations and fatigue damages are indispensable for securing their safety and for estimating their remaining strength. As conventional NDT techniques for steel bridges, visual testing, magnetic particle testing and ultrasonic testing have been commonly employed. However, these techniques are time- and labor- consuming techniques, because special equipment is required for inspection, such as scaffolding or a truck mount aerial work platform. In this paper, a new thermography NDT technique, which is based on temperature gap appeared on the surface of structural members due to thermal insulation effect of the crack, is developed for detection of fatigue cracks. The practicability of the developed technique is demonstrated by the field experiments for highway steel bridges in service. Detectable crack size and factors such as measurement time, season or spatial resolution which influence crack detectability are investigated.

Thermoelastic stress analysis (TSA) using by infrared thermography has been widely used as an effective full-field stress measurement technique. The present authors applied TSA technique to nondestructive evaluation of fatigue cracks in steel bridges, in which fatigue cracks were detected based on singular stress fields observed around crack tips and structural integrity was evaluated based on stress intensity factor calculated from observed near tip stress field. In this paper, a new approach for evaluating stress intensity factor based on TSA technique is proposed. The coefficients including stress intensity factor in the near tip stress field function expressed in higher order terms are determined by the least square fitting using experimentally obtained data by TSA. It was found that values of stress intensity factors K I and K II were obtained in good accuracy.

A new remote nondestructive inspection technique based on thermoelastic temperature measurement by infrared thermography was developed for the detection of fatigue cracks in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature changes at crack tips due to stress singularities generated by wheel loading from traffic on a bridge. Self-reference lock-in data-processing technique and motion compensating technique were developed to improve the thermal images obtained in the crack detection process. Advantages and limitations of the proposed nondestructive evaluation technique were discussed based on results of field experiments for highway bridges. Thermoelastic stress analyses in the vicinity of crack tips were also carried out after the crack detection process by self-reference lock-in thermography. The stress distribution under wheel loading by traffic was measured by infrared thermography. Stress intensity factors were evaluated from measured stress distribution. It was found that these fracture mechanics parameters can be evaluated with reasonable accuracy by the proposed technique, enabling the assessment of structural integrity based on the evaluated fracture mechanics parameters.

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. Selfreference 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.