• Explosives and Blasting
• /
• v.39 no.1
• /
• pp.10-21
• /
• 2021

Brittle materials such as rocks and concretes exhibit large strain-rate dependency under dynamic loading conditions. This means that the mechanical properties of such materials can significantly be varied according to load velocity. Thus, the strain-rate dependency is recognized as one of the most important considerations in solving problems of blast engineering or rock dynamics. Unfortunately, however, studies for characterizing the dynamic properties of domestic rocks and other brittle materials are still insufficient in the country. In this study, dynamic tensile tests were conducted using the Hopkinson pressure bar apparatus to characterize the dynamic properties of Geochang granite and high-strength concrete specimens. The dynamic Brazilian disc test, which is suggested by ISRM, and the spalling method were applied. In general, the latter is believed to have some advantages in experiments under high-strain rate deformation. It was found from the tests that there were no significant difference between the dynamic tensile strengths obtained from the two different test methods for the two materials given. However, this was not the expected result before the tests. Actually, authors expected that there be some differences between them. Hence, it is thought that further investigations are needed to clarify this results.

• Journal of the Microelectronics and Packaging Society
• /
• v.29 no.3
• /
• pp.25-29
• /
• 2022

Recently, the importance of electronic packaging technology has been attracting attention, and heterogeneous integration technology in which chips are stacked out-of-plane direction is being applied to the electronic packaging field. The 2.5D integration circuit is a technology for stacking chips using an interposer including TSV, and is widely used already. Therefore, it is necessary to make the interposer mechanically reliable in the packaging process that undergoes various thermal processes and mechanical loadings. Considering the structural characteristics of the interposer on which several thin films are deposited, thermal stress due to the difference in thermal expansion coefficients of materials can have a great effect on reliability. In this study, the mechanical reliability of the metal pad for wire bonding on the silicon interposer against thermal stress was evaluated. After heating the interposer to the solder reflow temperature, the delamination of the metal pad that occurred during cooling was observed and the mechanism was investigated. In addition, it was confirmed that the high cooling rate and the defect caused by handling promote delamination of the metal pads.

• Journal of the Korea Concrete Institute
• /
• v.14 no.5
• /
• pp.677-688
• /
• 2002

A analytical model is developed which can simulate a complete inelastic biaxial moment-curvature relations of a reinforced concrete column. The model can simulate sudden drop in moment capacity after peak moment and due to spalling of cover concrete. Parametric studies are performed examine the effects of constituent material properties as well as topological arrangement of reinforcements on moment-curvature relations and P-M interaction curve. It has been analytically observed that ductility of a reinforced concrete column is influenced mostly by magnitude of the axial load and spacings or the volume of lateral reinforcements. Compared to ACI P-M interaction curve, overall increase about 10％ in square root of sum of squares of axial force and moment, and about 20％ in peak load are observed for the columns reinforced according to ACI seismic design code.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.2
• /
• pp.139-143
• /
• 2011

The problem of delamination of composite tubes by impact has been acknowledged in aerospace and automobile industry. Non-destructive testing(NDT) methods in composite material structure are important to evaluate reliability of composite structure. There are many kinds of NDT methods which can detect the inside defect of the composite material such as Infrared Thermography(IRT). Infrared thermal imaging of object is different from that of a defect, in heated composite tubes with an internal defect, and then location and size of a defect can be measured by the analysis of thermal imaging pattern. In this study, Lock-in Infrared thermography detect internal defects of Impacted composite tubes by the inspection of infrared lay radiated from the surface of composite tubes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.1
• /
• pp.72-78
• /
• 2008

In this study, advanced (fluid-structure interaction (FSI)) analysis system has been developed in order to predict turbine cascade performance with blade deformation effect due to aerodynamic loads. Intereference effects due to the relative movement of the rotor cascade with respect to the stator cascade are also considered. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation k-ω SST turbulence models are solved to accurately predict fluid dynamic loads considering flow separation effects. A fully implicit time marching scheme based on the (coupled Newmark time-integration method) with high artificial damping is efficiently used to compute the complex fluid-structure interaction problem. Predicted aerodynamic performance considering structural deformation effect of the blade shows somewhat different results compared to the case of rigid blade model. Cascade performance evaluations for different elastic axis positions are importantly presented and its aeroelastic effects are investigated.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.3
• /
• pp.139-149
• /
• 2016

Roof cladding of buildings are required for the measures about the 'screw pull-out' which causes the casualties and the property damage by typhoons. In this study, the pull-out resistance was increased by increasing the penetration depth of the screw installing a ironware called 'insert nut' on the roof cladding frame. Tensile tests were conducted to compare the pull-out strengths of a general screw-joint and a nut insert joint. Roof cladding that is actually being used in the field was produced using the 'solid work' and then the roof claddings using a general screw-joint and a nut insert joint were compared by a static test and dynamic test.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.21 no.3
• /
• pp.251-260
• /
• 2001

Damage Profess of CFRP laminates under monotonic tensile test was characterized by the correlation between Acoustic Emission(AE) and Ultrasonic Test(UT). The amplitude distribution of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pullout and fiber fracture as load is increased. In addtion, the characteristics of ultrasonic amplitude attenuation are useful lot analysis of the different type of fracture mechanism. Different orientation of carbon fiber reinforced plastic specimens were used to investigate the AE amplitude range and ultrasonic amplitude attenuation. Finally, loading-unloading tests were carried out to check Felicity effect. During the tests, ultrasonic amplitude attenuation was investigated at the same time and compared with AE parameters. The result showed that two parameters of both AE and UT could be effectively used for analysis of fracture mechanism in CFRP laminates.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.38 no.2
• /
• pp.311-317
• /
• 2018

The new asphalt surface reinforcement method (ASRM) is one of the preventive maintenance methods in asphalt concrete pavements. The adhesion performance of new ASRM satisfied the standard of non-slip pavement and bridge waterproofing materials. As a results of durability tests (as wheel load, rolling bottle and UV resistance test), the new ASRM showed sufficient resistance to traffic and environmental loads. The waterproof and chemical resistance tests of new ASRM were conducted to evaluate whether the pavement could be protected from water and chemicals and the performances of new ASRM were satisfactory. Furthermore, the new ASRM demonstrated some rejuvenation effects due to its toughness increases in recycled asphalt concrete mixture by 5% compared to the conventional hot mix asphalt mixture using reclaimed asphalt pavement. In conclusion, the new ASRM was evaluated to protect the asphalt concrete pavement and increase the lifetime.

• International Journal of Highway Engineering
• /
• v.7 no.3 s.25
• /
• pp.71-78
• /
• 2005

This study focuses on finding out engineering characteristics of asphalt concrete mixtures using mineral fillers with recycled waste lime, which is a by-product in the Soda Ash(Na2CO3) production course. The materials tested in this study were made with 25%, 50%, 75% and 100% of mixing ratio based on the conventional mineral filler ratio to analyze the recycle possibility of the waste lime. The asphalt concrete mixtures with recycled waste lime and hydrated lime, and conventional asphalt concrete mixtures were evaluated through their fundamental engineering properties such as Marshall stability, indirect tensile strength, resilient modulus, permanent deformation characteristics, moisture susceptibility and fatigue resistance. The results indicate that the application of recycled waste lime as mineral filler improves the permanent deformation characteristics, stiffness and fatigue endurance of asphalt concrete mixtures at the wide range of temperatures. It is also found that the mixtures with recycled waste lime show higher resistance against stripping than conventional asphalt concrete mixtures. It is concluded from various test results that the waste lime can be used as mineral fillers and especially can greatly improve resistance to permanent deformation of asphalt concrete mixtures at high temperatures.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.8 no.3
• /
• pp.149-158
• /
• 2004

In this study, deep beam specimens are designed to have the effective shear span to depth ratio 1.0 and web opening within effective shear region. The purpose of this study is to investigate experimentally the shear strengthening effect between before failure and after failure upon using fiber sheets for RC deep beam with opening in web. The results can be summarized as follows; 1)When deep beams with web opening were failed in shear, their initial diagonal crack load and crack width were not influenced by their types of the arranged steel bars. 2)Deep beam with the horizontal reinforced bar was effective in the ultimate load of deep beam with web opening in shear failure 3)There were the approximate values between the experimental values and the analysis of finite element method. 4)The ultimate failure strengths of the repaired and strengthened specimens were increased about 34.4%~83.8% in comparison with specimens not to be strengthened.