• Tribology and Lubricants
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• v.30 no.4
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• pp.199-204
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• 2014

Various heat-treated and surface coating methods are used to mitigate abrasion in sliding machine parts. The most cost effective of these methods involves hard coatings such as diamond-like carbon (DLC). DLC has various advantages, including a high level of hardness, low coefficient of friction, and low wear rate. In practice, a supporting layer is generally inserted between the DLC layer and the steel substrate to improve the load carrying capacity. In this study, an indentation and sliding contact problem involving a small, hard, spherical particle and a DLC-coated steel surface is modeled and analyzed using a nonlinear finite element code, MARC, to investigate the influence of the supporting layer thickness on the coating characteristics and the related coating failure mechanisms. The results show that the amount of plastic deformation and the maximum principal stress decrease with an increase in the supporting layer thickness. However, the probability of the high tensile stress within the coating layer causing a crack is greatly increased. Therefore, in the case of DLC coating with a supporting layer, fatigue wear can be another important cause of coating layer failure, together with the generally well-known abrasive wear.

• Design & Manufacturing
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• v.14 no.1
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• pp.36-41
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• 2020

Recently, due to the development of MEMS technology, researches for the production of effective micro structures and shapes have been actively conducted. However, the process technology based on chemical etching has a number of problems such as environmental pollution and time problems due to multi-process. Various processes to cope with this process are being studied, and one of the mechanical etching processes is the powder blasting process. This process is a method of spraying fine particles, which has the advantage of being an effective process in manufacturing hard brittle materials. However, it is also a process that adversely affects the material surface roughness and material properties due to the impact of the injection of fine particles. In this study, after fabricating micro-channels in fused silica glass with excellent optical properties among the hard brittle materials, we used the nano indentation system to analyze the micro parts using nano-particles as well as machinability and surface roughness analysis of the processed surface. The analysis was performed for the effective processing of powder blasting.

• Animal cells and systems
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• v.16 no.2
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• pp.121-126
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• 2012

In this study, a neural network (NN) modeling approach has been used to predict the mechanical and geometrical behaviors of mouse embryo cells. Two NN models have been implemented. In the first NN model dimple depth (w), dimple radius (a) and radius of the semi-circular curved surface of the cell (R) were used as inputs of the model while indentation force (f) was considered as output. In the second NN model, indentation force (f), dimple radius (a) and radius of the semi-circular curved surface of the cell (R) were considered as inputs of the model and dimple depth was predicted as the output of the model. In addition, sensitivity analysis has been carried out to investigate the influence of the significance of input parameters on the mechanical behavior of mouse embryos. Experimental data deduced by Fl$\ddot{u}$ckiger (2004) were collected to obtain training and test data for the NN. The results of these investigations show that the correlation values of the test and training data sets are between 0.9988 and 1.0000, and are in good agreement with the experimental observations.

• Composites Research
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• v.14 no.5
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• pp.46-53
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• 2001

In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subjected to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, acoustic emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. The damage process of SOP FML was divided by three parts, i.e., crack initiation, crack propagation, and penetration. The AE characteristics during crack initiation show that the micro crack is initiated at lower ply of the plate, then propagate along the thickness of the plate with creating tiber debonding. The crack grow along the fiber direction with occurring 60∼80dB AE signal. During the penetration, the fiber breakage was observed. As fiber orientation increases, talc fiber breakage occurs more frequently. The AE signal behaviors support these results. Cumulative AE counts could well predict crack initiation and crack propagation and AE amplitude were useful for the prediction of damage failure mode.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.1
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• pp.53-59
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• 2014

Because a molten steel carrier is used in high-temperature and corrosive environments, erosion and corrosion decrease the thickness of the structure and expand the vent hole for emitting gas generated from refractory bricks. This increases the stress throughout the structure and introduces a significant stress concentration around the vent hole. In addition, the high-temperature environment degrades mechanical properties such as the yield and tensile strengths. These problems seriously affect the safety of the structure. In this study, the safety of a 10-year-old structure was evaluated by analyzing the stress distribution and measuring the mechanical properties of the structure. The mechanical properties were directly measured on the structure surface using the instrument indentation technique.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1453-1463
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• 2013

In this study, we investigated the effect of the indenter geometry on the crack characteristics by indentation cracking test and FEA. We conducted various cohesive finite element simulations based on the findings of Lee et al. (2012), who examined the effect of cohesive model parameters on crack size and formulated conditions for crack initiation and propagation. First, we verified the FE model through comparisons with experimental results that were obtained from Berkovich and Vickers indentations. We observed whether nonsymmetrical cracks formed beneath the surface during Berkovich indentation via FEA. Finally, we examined the relation between the crack size and the number of cracks. Based on this relation and the effect of the indenter angle on the crack size, we can predict from the crack size obtained with an indenter of one shape (such as Berkovich or Vickers) the crack size for an indenter of different shape.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.419-428
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• 2023

Seawater has been used to cool devices in nuclear power plants. However, the pipes used to transport seawater are vulnerable to corrosion; hence, the inner side of pipelines is coated with an epoxy layer as prevention. Upon coating damage, the pipe becomes exposed, and corrosion progresses. The major cause is widely known as cavitation corrosion, causing the degradation of mechanical properties. In this study, corroded specimens were prepared using cavitation and immersion methods to clarify the degradation trend of mechanical properties with corrosion. Three different types of epoxy coatings were used, and accelerated cavitation procedures were composed of amplitudes of 15 ㎛, 50 ㎛, and 85 ㎛ for 2 h, 4 h, and 6 h. The immersion periods were 3 and 6 weeks. We conducted instrumented indentation tests on all degradation samples to measure mechanical properties. The results showed that higher cavitation amplitudes and longer cavitation or immersion times led to more degradation in the samples, which, in turn, decreased the yield strength. Of the three samples, the C coating had the highest resistance to cavitation and immersion degradation.

• Tribology and Lubricants
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• v.35 no.2
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• pp.106-113
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• 2019

We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to $1586cm^{-1}$, indicating that the $sp^3$ content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.96-100
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• 2000

It is difficult to predict material behavior of forming process because the plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. In view of the direct relationship between instable material flow and quality defects of the products we should find out their phenomena, In this study we introduced the plastic spin and the kinematic hardening considering the kinematic hardening constitutive equation for rate-dependent material. Also analysis of upset forging is carried out using the rigid plastic FEM with Al7075

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.269-271
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• 2006