• Structural Engineering and Mechanics
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• v.42 no.3
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• pp.409-424
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• 2012

Since relatively low elasticity modulus of the FRP materials results in lower natural frequencies, it is necessary to study the free vibration of FRP transmission poles. In this paper, the free vibration of tapered FRP transmission poles with thin-walled circular cross-section is investigated by a tapered beam element. To model the flexible joints of the modular poles, a rotational spring model is used. Modal analysis is performed for typical FRP poles with/without joint and they are also modeled by ANSYS commercial finite element software. There is a good correlation between the results of the tapered beam finite element model and those obtained from ANSYS as well as the existing experimental results. The effects of different geometries, material lay-ups, concentrated masses at the pole tip, and joint flexibilities are evaluated. Moreover, it is concluded that using tougher fibres at the inner and outer layers of the cross-section, results in higher natural frequencies, significantly.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.25-31
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• 2015

Due to environmental regulations (RoHS, WEEE and ELV) of the European Union, electronics and automotive electronics have to eliminate toxic substance from electronic devices and system. Specifically, reliability issue of lead-free solder joint have an increasing demand for the car electronics caused by ELV banning. The authors prepared engine control unit and cabin electronics soldered with Sn-3.0Ag-0.5Cu (SAC305). To compare with the degradation characteristics of solder joint strength, thermal cycling test (TC), power-thermal cycling test (PTC) and series tests were conducted. Series tests were conducted for TC and PTC combined stress test using the same sample in sequence and continuously. TC test was performed at $-40{\sim}125^{\circ}C$ and soak time 10 min for 1000 cycles. PTC test was applied by pulse power and full function conditions during 100 cycles. Combined stress test was tested in accordance with automotive company standard. Solder joint degradation was observed by optical microscopy and environment scanning electron microscopy (ESEM). In addition, to compare with deterioration of bond strength of quad flat package (QFP) and chip components, we have measured lead pull and shear strength. Based on the series test results, consequently, we have validated of series test method for lifetime and reliability of Pb-free solder joint in automotive electronics.

• Journal of Welding and Joining
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• v.6 no.3
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• pp.21-26
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• 1988

The behavior of angular distortion in butt joint wleding of thin plate structure is investigated with an experimental model and partially with a computational model. The experimental model studying the effects of specimene size and degree of restraint on the angular distorion offers a good method for analyzing the behavior of the distrotion. In addition, the distrotion during welding was demonstrated by both experimental measurement and numericla prediciton. The facts evealed in this study are as follows : 1) distrotion angles were changed with variations of specimene wldth. 2) With the restraint, angular distrotion was reduced to 20% to that of free joint. 3) After the restraint being removed, the effect of restraint was also remained. 4) Same heat input per unit thickness caused same amount of distortion. 5) The mode of angular distortion was expected to be changed with expected to be changed with time, i.e. convex movement during heating and concave one during cooling.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2334-2343
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• 2000

This paper proposes an efficient beam-shell modeling technique for the free vibration analysis of a T-joint thin-walled beam structure. Except a small portion of a T-joint which is modeled by shell elements, the structure is modeled by thin-walled beam elements that can describe warping and distortion. In order to match the shell and thin-walled beam elements at the interface of the dissimilar elements, a technique based on a pseudo inverse matrix is formulated. This paper also examines the role of the thin-walled element taking into account the distortion and warping deformation degrees of freedom in predicting accurately the dynamic characteristics of a T-joint thin-walled structure.

• Korean Journal of Child Studies
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• v.25 no.4
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• pp.33-48
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• 2004

The purpose of this study was to examine if mothers and their children used different interaction strategies depending on the interacting contexts. Sixty-five mothers and their children were observed while they interacted with each other in two contexts, that is, a free play context and a joint problem solving context. The result of this study showed that first, the mothers' strategies and their children's strategies were closely related. When the mothers used positive strategies, their children also responded with positive strategies. In contrast, when the mothers used negative strategies, their children also tended to use negative strategies. Second, the contexts which the mothers and their children interacted affected the strategies that the mothers and their children used. The mothers and the children were more likely to use positive strategies in the context of free play than in the context of the joint problem solving. This result points out the importance of free play as the context of producing a positive atmosphere where the mothers and their children interacted positively and had a good time. Suggestions for further study and implications for parents were provided.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.19-24
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• 2015

Joint properties of electric control unit (ECU) module using Sn-Cu-(X)Al(Si) lead-free solder alloy were investigated for automotive electronics module. In this study, Sn-0.5Cu-0.01Al(Si) and Sn-0.5Cu-0.03Al(Si) (wt.%) lead-free alloys were fabricated as bar type by doped various weight percentages (0.01 and 0.03 wt.%) of Al(Si) alloy to Sn-0.5Cu. After fabrications of lead-free alloys, the ball-type solder alloys with a diameter of 450 um were made by rolling and punching. The melting temperatures of 0.01Al(Si) and 0.03Al(Si) were 230.2 and $230.8^{\circ}C$, respectively. To evaluation of properties of solder joint, test printed circuit board (PCB) finished with organic solderability perseveration (OSP) on Cu pad. The ball-type solders were attached to test PCB with flux and reflowed for formation of solder joint. The maximum temperature of reflow was $260^{\circ}C$ for 50s above melting temperature. And then, we measured spreadability and shear strength of two Al(Si) solder materials compared to Sn-0.7Cu solder material used in industry. And also, microstructures in solder and intermetallic compounds (IMCs) were observed. Moreover, thickness and grain size of $Cu_6Sn_5$ IMC were measured and then compared with Sn-0.7Cu. With increasing the amounts of Al(Si), the $Cu_6Sn_5$ thickness was decreased. These results show the addition of Al(Si) could suppress IMC growth and improve the reliability of solder joint.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.74-80
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• 2014

Due to environmental regulations (RoHS, WEEE and ELV) of the European Union, electronics and automotive electronics have to eliminate toxic substance from their devices and system. Especially, reliability issue of lead-free solder joint is increasing in car electronics due to ELV (End-of-Life Vehicle) banning from 2016. We have prepared engine control unit (ECU) modules soldered with Sn-40Pb and Sn-3.0Ag-0.5Cu (SAC305) solders, respectively. Degradation characteristics of solder joint strength were compared with various conditions of automobile environment such as cabin and engine room. Thermal cycle test (TC, $-40^{\circ}C$ ~ ($85^{\circ}C$ and $125^{\circ}C$), 1500 cycles) were conducted with automotive company standard. To compare shear strength degradation rate with eutectic and Pb-free solder alloy, we measured shear strength of chip components and its size from cabin and engine ECU modules. Based on the TC test results, finally, we have known the difference of degradation level with solder alloys and use environmental conditions. Solder joints degradation rate of engine room ECU is superior to cabin ECU due to large CTE (coefficient of thermal expansion) mismatch in field condition. Degradation rate of engine room ECU is 50~60% larger than cabin room electronics.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.7-13
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• 2012

A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Charpy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from $1.8{\times}10^3s^{-1}$ and $8.5{\times}10^3s^{-1}$. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn-3.0Ag-0.5Cu and copper substrate were between 21.7 MPa and 8.6 MPa in the high strain range.

• Journal of Welding and Joining
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• v.19 no.4
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• pp.406-412
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• 2001

This study is focussed on the numerical prediction of the thermal fatigue life of a ${\mu}BGA$(Micro Ball Grid Array) solder joint. Numerical method is used to perform three-dimensional finite element analysis for Sn-37mass%Pb. Sn-3.5mass%Ag solder alloys during the given thermal cycling. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. In this study, a practical correlation for the prediction of the thermal fatigue life is suggested by using the dimensionless variable $\gamma$. As a result. it could be found that Sn-3.5mass%Ag has longer fatigue life than Sn-37mass%Pb in low cycle fatigue. In addition. the result with ${\gamm}ashow$a good agreement with the FEA results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.519-522
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• 1997

In this study, the collision free path planning method of the articulated manipulator using sequential search is proposed. This method is to find the joint path of the manipulator with many degrees of freedom from the distal joint to the proximal one. To do this, the initial work space of the gantry manipulator, which is a remote maintenance equipment of the radioactive environment, is defined from the condition that the distal joint configuration is determined by the posture of maintenance. Then, 2-dimensional configuration space with the obstacle area is represented and the collision free path of manipulator is searched in the configuration space. And, this method is verified using the graphic simulation in virtual workcell for the spent fuel disassembling processes. The result of this study can be effectively used in implementing the maintenance processes for the hot cell equipment and enhance the reliability of the spent fuel management.