• Structural Monitoring and Maintenance
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• v.4 no.2
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• pp.133-151
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• 2017

The paper describes the results of an experimental and numerical investigation into the structural and damage response of sandwich composites to low-velocity impact. Sandwich panels consisting of laminated composite skins with three different layups bonded to a PVC foam core were subjected to impact at various energy levels corresponding to barely visible impact damage (BVID) in the impacted skins. Damage assessment analyses were performed on the impacted panels to characterise the extent and the nature of the major failure mechanisms occurring in the skins. The data collected during the experimental analyses were finally used to assess the predictive capabilities of an FE tool recently developed by the authors for detailed simulation of impact damage in composite sandwich panels. Good agreement was observed between experimental results and model predictions in terms of structural response to impact, global extent of damage and typical features of individual damage mechanisms.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.243-245
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• 2004

Failure mechanisms of weldments under fatigue loads are interpreted that multiple collinear surface cracks initiating along weld toe propagate under the mutual interaction and coalescence of adjacent two cracks. To estimate fatigue crack propagation life for these weldments, the stress intensity factors of the multiple surface cracks have to be calculated which are influenced strongly by the geometrical complexity of weld toes and attachments. The Ak-factors derived by a parametric study can be introduced for the effective calculation of the stress intensity factors taking into account the geometrical complexity. The fatigue life was estimated by using the Ak-factors and the method considering the propagation mechanisms of the multiple surface cracks. The estimated values showed a good agreement with the measured fatigue life experimentally.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.3
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• pp.122-131
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• 2003

In this study, some characteristics of conductive and non-conductive adhesive inter-connections are derived, based on data from literature and own projects. Assembly of flip chip on flex is taken as a carrier. Potential failure mechanisms of adhesive interconnections reported in literature are reviewed. Some methods that can be used to evaluate the quality of adhesive interconnections and to evaluate their aging behavior are given. Possible finite element simulation approaches are introduced and the required critical materials properties are summarized. Response to temperature and moisture, resistance to reflow soldering and resistance to rapid change in temperature and humidity are elaborated. The effect of post cure during accelerated testing is discussed. This study shows that only a combined approach using finite element simulations, and use of appropriate experimental evaluation methods can result in revealing, understanding and quantifying the complex degradation mechanisms of adhesive interconnections during aging.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.1
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• pp.83-88
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• 2015

At the early stages of engineering design, a number of design concepts may be suggested. With a great degree of freedom, making a good choice may be a challenge at this stage. In this study, a simplified evaluation criterion for design concepts is presented based on cost, simplicity and safety. Cost is estimated by the amount of materials and the required level of tolerance. Simplicity is represented by the number of parts, assembly steps, and fasteners. Safety is assessed by the level of potential failure. The proposed criterion is applied to an example design of driving mechanisms for cervical vertebrae massage machine.

• Journal of Welding and Joining
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• v.22 no.4
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• pp.73-81
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• 2004

Failure mechanisms of welded joints under fatigue loads are interpreted that multiple collinear surface cracks initiating randomly along the weld toes propagate under the mutual interaction and coalescence of adjacent two cracks. To estimate fatigue crack propagation life for three types of the representative welded joints, i.e. non-load carrying cruciform, cover plate and longitudinal stiffener joint, the stress intensity factors at the front of the surface cracks have to be calculated, which are influenced strongly by the geometry of attachments, weld toes and the crack shapes. For the effective calculation of the stress intensity factors the Mk-factor was introduced which can be derived by a parametric study performed by FEM considering influence of the geometrical effects. The fatigue life of the cruciform joint was estimated by using the Mk-factors and the method considering the propagation mechanisms of the multiple surface cracks. Analysis results for the fatigue life had a good agreement with that of experiment.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.4
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• pp.81-86
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• 2009

In this paper, we propose a new algorithm to store streams seamlessly using fixed servers when DMB receivers cannot receive signals properly due to weak signals. This algorithm includes mechanisms for synchronization and playout by retransmitting streams stored in the server. The results showed that signals were normally generated for 95.5% of the delivery failure cases caused by radical changes or turbulence of signals and that the new mechanisms allow AVs played seamlessly even though there were slight stops.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.105-108
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• 2004

In general, the nonlinear behavior of composite structures composing of steel and concrete is analyzed on the basis of the assumption of the perfect bond actions in steel-concrete interface in which the interface slip or separation is not allowed. The assumption is based on the fact that the full interface bond behavior is provided with the mechanical connectors of studs. However, since the number and spacing of the studs are determined by the stress resultants calculated in the interface area, the interface analysis is required to evaluate the stress resultants. This paper describes the nonlinear steel-concrete interface behavior considering the two interface failure mechanisms of slip and separation. Elastoplastic constitutive relation is developed. thru the formulation framework using the two energy dissipation mechanisms. As the result, the steel plate push-out tests sandwitched between concrete blocks are analyzed and compared with the test results with which the good agreements are observed.

• Development and Reproduction
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• v.21 no.4
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• pp.351-359
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• 2017

Implantation is a highly organized process that involves an interaction between a receptive uterus and a competent blastocyst. In humans, natural fecundity suggests that the chance of conception per cycle is relatively low (~30%) and two-third of lost pregnancies occur because of implantation failure. Defective implantation leads to adverse pregnancy outcomes including infertility, spontaneous miscarriage, intrauterine fetal growth restriction and preeclampsia. With use of advanced scientific technologies, gene expression analysis and genetically-engineered animal models have revealed critical cellular networks and molecular pathways. But, because of ethical restrictions and the lack of a mechanistic experiment, comprehensive steps in human implantation have still not been completely understood. This review primarily focuses on the recent advances in mechanisms of implantation. Because infertility is an emerging issue these days, gaining an understanding the molecular and hormonal signaling pathway will improve the outcome of natural pregnancy and assisted reproductive technology.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.378-384
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• 2000

This paper presents the results of the repeated sliding tests to determine the wear-life of TiN coated AISI 52100 bearing balls deposited by PVD method and to show the wear mechanisms of those. The sliding tests were carried out using a ball-on-disk tribometer under ambient conditions. The coefficient of friction, wear volume and the cycles to failures of TiN coated bearing balls were measured with different normal loads and roughness of lower specimens. On the wear-life diagram, the normal loads and the cycles to failure showed the good linear relation on log-log coordinate. With a decreasing normal load, the diagram showed that the wear-limits, at which the coated bearing balls survived more than 4000cycles were under 0.1N of the normal load.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.427-431
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• 2005

In this study, 6' GaAs wafer bonding system is designed and optimized to bond 6 inches device wafer and material wafer. Bonding process is performed in vacuum environment and resin is used to bond two wafers. Vacuum module and double heating mechanisms are adopted to minimize wafer warpage and void. Structure and heat transfer analysis, et al of the core modules review the designed mechanisms are very effective in performance improvement. As a result, high productivity (tack time cut-down) and stabilized process can be obtained by reducing breakage failure of wafer.