• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.449-454
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• 2009

This paper presents an experimental study on the failure characteristics of SnAgCu lead-free solder balls. To estimate the effect of Ag, three types of SnAgCu balls are first prepared by varying the weight percent of Ag(1.0, 3.0, 4.0 wt%) and then analyzed by reliability tests such as thermal shock, high speed ball shear, and drop tests. Thermal shock test reveals that the higher the weight percent of Ag is, the longer the fatigue lift becomes. To the contrary, high speed ball-shear test and drop test show that the shear strength and the fracture toughness of solder balls are inversely proportional to the weight percent of Ag, respectively, Reasons for these observations will be further investigated In the future work.

• Korean Journal of Applied Biomechanics
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• v.31 no.1
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• pp.64-71
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• 2021

Objective: This study investigated the different in isokinetic peak strength of the knee joint, and kinetics and kinematics in drop landing pattern of lower limb between the patellofemoral pain syndrome (PFPS) patients and normal. Method: 30 adult females were divided into the PFPS (age: 23.13±2.77 yrs; height: 160.97±3.79 cm, weight: 51.19±4.86 kg) and normal group (age: 22.80±2.54 yrs, height: 164.40±5.77 cm, weight: 56.14±8.16 kg), with 15 subjects in each group. To examine the knee isokinetic peak strength, kinematics and kinetics in peak vertical ground reaction force during drop landing. Results: The knee peak torque (Nm) and relative strength (%) were significantly weaker PFPS group than normal group. In addition, PFPS group had significantly greater hip flexion angle (°) than normal group. Moreover, normal group had significantly greater moment of hip abduction, hip internal rotation, and left ankle eversion than PFPS group, and PFPS group had significantly greater moment of knee internal rotation. Finally, there was significant differences between the groups at anteroposterior center of pressure. Conclusion: The PFPS patients had weakened knee strength, and which can result in an unstable landing pattern and cause of more stress in the knee joints despite to effort of reduce vertical ground reaction force.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.14-15
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• 2021

Even though the Al. form system, which was developed to replace the Euro-form, has been used as the slab lower formwork for almost all concrete structures based on the light weight and high conversion rate, the low-noise Drop method has been developed and used in order to overcome the limitations of the Al. Form system such as noise pollution and safety accidents caused by free fall during the demolding. However, as the low-noise drop method is still insufficient, Safety Full Drop Al. Form method is expected to be in the spotlight in the construction market based on its excellent advantages compared to the developed methods. In addition, we plan to conduct research to further contribute to securing the quality of the overall structure through continuous improvement and supplementation by introducing an automation system to the very construction method.

• Korean Journal of Applied Biomechanics
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• v.16 no.2
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• pp.25-35
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• 2006

The purpose of this study was to investigate the shock attenuation mechanisms while varying the loads in a backpack during drop landing. Ten subjects (age: $22.8{\pm}3.6$, height: $173.5{\pm}4.3$, weight: $70.4{\pm}5.2$) performed drop landing under five varying loads (0, 5kg. 10kg. 20kg. 30kg). By employing two cameras (Sony VX2100) the following kinematic variables (phase time, joint rotational angle and velocity of ankle, knee and hip) were calculated by applying 2D motion analysis. Additional data, i.e. max vertical ground force (VGRF) and acceleration, was acquired by using two AMTI Force plates and a Noraxon Inline Accelerometer Sensor. Through analysing the power spectrum density (PSD), drop landing patterns were classified into four groups and each group was discovered to have a different shock attenuation mechanism. The first pattern that appeared at landing was that the right leg absorbed most of the shock attenuation. The second pattern to appear was that subject quickly transferred the load from the right leg to the left leg as quickly as possible. Thus, this illustrated that two shock attenuation mechanisms occurred during drop landing under varying load conditions.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.78-82
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• 2001

Impact behaviors of Aluminum Honeycombs Sandwich Panel(AHSP) by drop weight test were investigated. Two types of specimens with 1/2" and 1/4" cell size were tested by two impactors which are weight of $5.25\textrm{kg}_{\textrm{f}}$ and $11.9\textrm{kg}_{\textrm{f}}$. Parametric studies were achieved including the impactor weight and impact sites which consist face, long-edge, short-edge, and point of the specimen. Face one of impact sites was the strongest and short-edge one of impact sites was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is equal to impact energy. After 3 point bending test, fracture modes of AHSP were analyzed with AE counts. Lower facesheet was fractured in the long-edge direction and then separated between facesheet and core. In the short-edge direction after core wrinkled, lower facesheet tear occurred. Impact behavior by FE analysis were increased localized damage in fast velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity was caused on the localized damaged area.aged area.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.2
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• pp.35-41
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• 2011

Recently, board level solder joint reliability performance of IC packages during drop impact becomes a great concern to semiconductor and electronic product manufacturers. The handheld electronic products are prone to being dropped during their useful service life because of their size and weight. The IC packages are susceptible to solder joint failures, induced by a combination of printed circuit board (PCB) bending and mechanical shock during impact. The board level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this paper, applying the JEDEC (JESD22-B111) standard present a finite element modeling of the FBGA. The simulation results revealed that maximum stress was located at the outermost solder ball in the PCB or IC package side, which consisted well with the location of crack initiation observed in the failure analysis after drop reliability tests.

• Physical Therapy Korea
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• v.30 no.1
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• pp.68-77
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• 2023

Background: The weakness of the gluteus medius (GM) is associated with various musculoskeletal disorders. The increasing GM activity without synergistic dominance should be considered when prescribing pelvic drop exercise (PD). Isometric hip extension or flexion of the non-weight bearing leg using thera-band at the ankle during PD may influence hip abductor activities. Objects: To determine how isometric hip extension or flexion of the non-weight bearing leg using thera-band at the ankle during PD influences the activities of three subdivisions of GM (anterior, GMa; middle, GMm; posterior, GMp), tensor fasciae latae (TFL), contralateral quadratus lumborum (QL), and GMp/TFL, GMm/QL activity ratios in patients with GM weakness. Methods: Twenty-three patients with GM weakness were recruited. Three types of PD were performed: PD, PD with an isometric hip extension of the non-weight bearing leg (PDE), and PD with an isometric hip flexion of the non-weight bearing leg (PDF). Surface electromyography (SEMG) was used to measure hip abductor activities. One-way repeated-measures analysis of variance was used to assess the statistical significance of muscle activities and muscle activity ratios. Results: GMa, GMm, and GMp activities were significantly greater during PDF than during PD and PDE (p < 0.001, p = 0.001; p = 0.001, p = 0.005; p = 0.004, p = 0.004; respectively). TFL activity was significantly greater during PDE than during PD and PDF (p < 0.001, p < 0.001, respectively). QL activity was significantly greater during PDF than during PD (p = 0.003). GMp/TFL activity ratio was significantly lower during PDE than during PD and PDF (p = 0.001, p = 0.001, respectively). There were no significant differences in the GMm/QL activity ratio. Conclusion: PDF may be an effective exercise to increase the activities of all three GM subdivisions while minimizing the TFL activity in patients with GM weakness.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.1
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• pp.1-9
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• 2020

PURPOSE: Many patients with stroke have difficulties in walking with foot-drop. Various types of ankle-foot orthoses (AFOs) have been developed, but their weight needs to be reduced with the assistance of the ankle dorsiflexor. Therefore, an elastic AFO (E-AFO) was devised that not only improves the stability and flexibility of the ankle but also assists with ankle dorsiflexion while walking. This study examined the effects of an E-AFO, on the walking patterns of foot-drop patients with stroke. METHODS: Fourteen patients walked with and without an E-AFO, and the gait parameters were assessed using the GAITRite system. The spatiotemporal data on the gait patterns of stroke patients with foot-drop were compared using paired t-tests; the level of statistical significance was set to α<.05. RESULTS: No significant differences were observed in the velocity (p=.066) and affecte+d step length (p=.980), but the affected and less-affected stance (p=.022, p=.002) and swing time (p=.012, p=.005) were significantly different. The E-AFO produced a significant difference in the less-affected step length (p=.032). CONCLUSION: The E-AFO has a significant effect on the walking patterns of individuals with foot-drop and stroke. The E-AFO could be a useful assistive device for gait training in stroke patients.

• Korean Journal of Applied Biomechanics
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• v.21 no.2
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• pp.197-205
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• 2011

Various jumping and landing motions are shown during sports event. But most previous studies have not considered landing height and distance simultaneously. The purpose of this study was to identify the effects of landing height and distance on knee injury mechanism. Fourteen male(age: $28.86{\pm}1.99$ yrs, height: $177.00{\pm}4.69$ cm, weight: $76.50{\pm}6.41$ kg) participated in this study. The subjects attempted drop landing task onto the ground from 30 cm to 45 cm heights and to 20 cm to 40 cm distances. The results were as follows. First, higher drop landing height and longer distance showed greater degree of maximal knee flexion and valgus. Second, higher drop landing height and longer distance showed greater maximal knee extension moment and varus moment. Third, higher drop landing height and longer distance showed larger maximal knee absorption power. Lastly, higher drop landing height showed increased Peak GRF. Landing height was more related to the cause of injury, which was indicated by increased maximal knee extension moment, peak GRF and maximal knee absorption power. Landing distance was also associated with increased knee valgus moment and absorption power during landing. These results suggest that landing height and distance may be the cause of injury.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2805-2816
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• 1994

This paper describes dynamic finite element analyses performed to study the dynamic behaviors of a shipping container under the impact onto rigid target due to the accidental fall from the hight of 9 m. Using two and three dimensional techniques, the shipping container which gave the maximum damage, ten different drop orientations are considered ; at intervals of $5^{\circ}$ from $45^{\circ}$ to $90^{\circ}$ According to the present results, the orientation of the shipping container which gave the maximum damage is $85^{\circ}$ from horizontal for oblique drop in the primary impact. In the optimal design of the shipping container, the impact limiter material must be considered importantly because it's proper selection affects the weight and the manufacturing cost of the shipping container. The analysis of the shipping container in this paper demonstrated that the shipping container is structurally sound relative to the regulatory drop test requirements.