• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.1
• /
• pp.55-61
• /
• 2010

An impact bending test method was used to evaluate the reliability for the solder joint of lead-free solder ball. In order to standardize the test method, the four point impact bending test was applied under the conditions of various frequencies and amounts of +/-amplitude respectively. Effects on the results were analysed. The optimum condition for impact bending test achieved in this study was the frequency of 10 Hz, and the amplitude of (+12/-1)~(+15/-1). 3 kinds of surface finishes Cu-OSP (Organic Solderability Preservative), ENIG (Electroless Nickel Immersion Gold), and ENEPIG (Electroless Nickel, Electroless Palladium, Immersion Gold) were used. Fracture surface showed that cracks were initiated and fractured along the intermetallic layer in the case of surface finishes of Cu-OSP and ENIG, while in the case of ENEPIG the cracks were initiated and propagated in the solder region.

• 연구논문집
• /
• s.29
• /
• pp.131-139
• /
• 1999

The effect of ball milling conditions in the milling of aluminium foil scraps was studied. Initial foil thickness, ball size. content of oleic acid. weight ratio of mineral spirits/foil. charged amount of foil were varied in wet ball milling process. It is impossible to make flake powders by milling of foil scraps with thickness $120 \mum$. As foil thickness decreases from $60\mum$ to $6.5\mum$, Mean size of powder milled for 30 h decreases from 107 µm to 17 µm. Bigger ball is slightly beneficial for milling of foils to the flake powders due to the larger impact energy produced by them. It is impossible to mill the foil without oleic acid to fabricate the flake powder. As content of oleic acid increases from 1.5 % to 5 %, mean size of flake powder milled for 30 h is drastically decreased. For the mineral spirits content below 50 %, foil scrap was not milled because sliding motion of balls by lubricant effect between balls and wall of container. As weight ratio of mineral spirits and foil increase over 100 %, foils were milled powders with mean powder size 15 - 20 때 irrespective of mineral spirits content due to reduced lubricant effect. As charged amount of foil decreases, mean powder size decreases due to increased collision frequency between ball and foil.

• Structural Engineering and Mechanics
• /
• v.53 no.2
• /
• pp.325-336
• /
• 2015

This paper presents a study based on the damage due to the fatigue life of thrust ball bearings using vibratory analysis. The main contribution of this work lies in establishing a relation between modal damping and the rolling contact fatigue damage of the thrust ball bearing. Time domain signals and frequency spectra are extracted from both static and dynamic experiments. The first part of this research consists in measuring the damping of damaged thrust ball bearings using impact hammer characterization tests. In a second part, indented components representing spalled bearings are studied to determine the evolution of damping values in real-time vibration spectra using the random decrement method. Dynamic results, in good agreement with static tests, show that damping varies depending on the component's damage state. Therefore, the method detailed in this work will offer a possible technique to estimate the thrust ball bearing fatigue damage variation in presence of spalling.

• Journal of the Korean Applied Science and Technology
• /
• v.36 no.2
• /
• pp.448-455
• /
• 2019

This study aims to discover whether there are other factors, such as the ball position and address that will increase the percentage of holed putts from different angles of surface. In this study, we selected five male tour professional golfers that has been of 15 years or longer on the Korea Golf Association. As a research tool, after installing a video camera at an artificial site that's similar with the real green, and with the player's own putter, motion analysis was carried out using a Titleist V1x, which is commonly used by golfers. We use SPSS programs, significance level a=.05. According to the ball movement during the ball movement during the ball position putt by section, it is confirmed that the ball speed and angular velocity increase as the ball position changes from left to right. If the uphill putt, ball movement was found to be increased same change flat putt and There is no significance deviation. In this study, we investigate how the clubface and ball move during impact by varying the position of the address ball according to the slope during the ascent putt, which should increase the success rate among the various slopes. This study was conducted to present scientific data.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.5
• /
• pp.156-163
• /
• 2003

In order to investigate the possibility of punching process of brittle material by ball impact, the effects of sealing materials about impact damage of soda-lime glass by small spheres were evaluated experimentally. The using of sealing materials in the development of perfect cone crack was more effective than no using of sealing materials. At the sealing materials condition, in the case of 5mm-thick specimen, Copper and PMMA sealing were more effective in producing a perfect cone formation than the other sealing materials. And in the case of 8mm-thick specimen, Aluminum sealing was most effective in producing a perfect cone formation. The impact velocity range over which perfect cones were formed was influenced by both the thickness of specimen and sealing materials. By a proper selection of sealing materials, the application fur industrial technology for hole (or nozzle) punching process of brittle materials is expected.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.7
• /
• pp.2196-2204
• /
• 1996

The damage mechanism by the impact of steel ball on the soda-lime glass having a different surface roughness was investigated. An initiation and a propagation behavior of cracks formed by each impact velocity were quantitatively studied. A 4-point bending test was carried out to evaluate the remaining bending strength of a scratched soda-lime glass which impacted by the steel ball. As the surface roughness was increased, the shape of cracks became more irregular rather than those of the smooth specimens. The phenomenon of turning up in the wing of cone cracks occurred even at the lower velocity than the critical velocity caused the crushing. The threshold velocity of cracks initiation generally became lower than those of smooth specimen. An initiation and a propagation behavior of radial cracks had no relation with the direction of scratch on the surface. The remaning benidng strength of the scratched specimen according to impact velocity had no big difference compared with those of the smooth specimen.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.10a
• /
• pp.274-279
• /
• 2004

Currently, carbon-fiber reinforced plastics(CFRP) are widely used in both space and civil aircraft due to their superior stiffness and strength to weight ratios compared to conventional metallic materials. This paper is to study the effects of curvature and stacking sequence on the penetration characteristics of composite laminated shell. And were performed to investigate the penetration characteristics of composite laminated shells by the oblique impact. They are stacked to [0$_3$/90$_3$]s, [90$_3$/0$_3$]s and [0$_2$/90$_3$/0]s, [90$_2$/0$_3$/90]s their interlaminar number two and fore. They are manufactured to varied curvature radius (R=100, 150, 200mm and $\infty$). When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determining the time for it to pass two ballistics-screen sensor located a known distance apart. In general, the critical penetration energy interface decrease and slope angle on the impact surface increased. [0$_3$/90$_3$]s and [0$_2$/90$_3$]s specimens higher than [90$_3$/0$_3$]s and [90$_2$/0$_3$/90]s specimens.

• Advances in concrete construction
• /
• v.8 no.4
• /
• pp.305-309
• /
• 2019

Pervious concrete pavements are the need of the day to avoid urban flooding and to facilitate ground water recharge. However, the strength of pervious or porous concrete is considerably less compared to conventional concrete. In this experimental investigation, an effort is made to improve the strength of pervious concrete by adopting fibres and a small amount of fine aggregate. A porous concrete with cement to aggregate ratio of 1:5 and a water-powder ratio of 0.4 is adopted. 30% of the cement is replaced by cementitious material ground granulated blast furnace slag (GGBS) for better strength and workability. Recron fibres at a dosage of 0.5, 1.0 and 1.5% by weight of cement were included to improve the impact strength. Since concrete pavements are subjected to impact loads, the impact strength was also calculated by "Drop ball method" in addition to compressive strength. The effect of fine aggregate and recron fibres on workability, porosity, compressive and impact strength was studied. The investigations have shown that 20% inclusion of fine aggregate and 1.5% recron fibres by weight of cement give better strength with an acceptable range of porosity.

• Composites Research
• /
• v.13 no.4
• /
• pp.75-82
• /
• 2000

A small diameter steel-ball impact experiment was performed to study the impact resistance of the surface of glass plates bonded with glass fabric/epoxy lamina. Five kinds of materials were used in this study: soda-lime glass plates, glass/epoxy lamina(one layer)-bonded and unbonded glass plates, glass/epoxy lamina(three layers)-bonded and unbonded glass plates. The range of impact velocity was 40 120m/s. The maximum stress and absorbed fracture energy were measured on the back surface of glass plates. With increasing impact velocity, various types of surface cracks such as ring, cone, radial and lateral cracks took place in the interior near the impacted site of glass plates. The cracks drastically decreased with glass/epoxy lamina coating. The surface fracture behavior could be evaluated using the maximum stress and the absorbed fracture energy.

• Fire Protection Technology
• /
• s.45
• /
• pp.28-36
• /
• 2008