• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.8
• /
• pp.1388-1397
• /
• 2003

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.26 no.2
• /
• pp.121-143
• /
• 2010

To investigate the effect of implant types and bone resorption on the fracture characteristics. 4 types of Osstem$^{(R)}$Implant were chosen and classified into external parallel, internal parallel, external taper, internal taper groups. Finite elements analysis was conducted with ANSYS Multi Physics software. Fatigue fracture test was performed by connecting the mold to the dynamic load fatigue testing machine with maximum load of 600N and minimum load of 60N. The entire fatigue test was performed with frequency of 14Hz and fractured specimens were observed with Hitachi S-3000 H scanning electron microscope. The results were as follows: 1. In the fatigue test of 2 mm exposed implants group, Tapered type and external connected type had higher fatigue life. 2. In the fatigue test of 4 mm exposed implants group, Parallel type and external connected types had higher fatigue life. 3. The fracture patterns of all 4 mm exposed implant system appeared transversely near the dead space of the fixture. With a exposing level of 2 mm, all internally connected implant systems were fractured transversely at the platform of fixture facing the abutment. but externally connected ones were fractured at the fillet of abutment body and hexa of fixture or near the dead space of the fixture. 4. Many fatigue striations were observed near the crack initiation and propagation sites. The cleavage with facet or dimple fractures appeared at the final fracture sites. 5. Effective stress of buccal site with compressive stress is higher than that of lingual site with tensile stress, and effective stress acting on the fixture is higher than that of the abutment screw. Also, maximum effective stress acting on the parallel type fixtures is higher. It is careful to use the internal type implant system in posterior area.

• Journal of Korean Society of Steel Construction
• /
• v.23 no.2
• /
• pp.159-167
• /
• 2011

Steel structure construction is currently increasing on account of the many merits of steel structures. Due to numerous environmental factors, many cracks and extensive corrosion occur in steel structures, which cause the deterioration of the performance and life cycle of such structures. Maintenance of steel structures is thus strongly demanded, for safety control. The inspection methods that are currently being used, however, are very limited and can detect only local defects in steel structures. They also take much time to use and incur high maintenance costs. Moreover, such methods cannot be applied to huge steel structures, which men find unapproachable. They also require much time due to the need for periodic checks, and may lead to cost loss. Therefore, the development of a monitoring system that can detect defects in whole structures and can reduce the repair and strengthening costs at an early stage is very much needed. In this study, the generation and propagation of cracks were monitored via the electric-potential-drop method (EPDM).