• Journal of Korean Neurosurgical Society
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• v.58 no.5
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• pp.412-418
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• 2015

Objective : To investigate the effects of posterior implant rigidity on spinal kinematics at adjacent levels by utilizing a cadaveric spine model with simulated physiological loading. Methods : Five human lumbar spinal specimens (L3 to S1) were obtained and checked for abnormalities. The fresh specimens were stripped of muscle tissue, with care taken to preserve the spinal ligaments and facet joints. Pedicle screws were implanted in the L4 and L5 vertebrae of each specimen. Specimens were tested under 0 N and 400 N axial loading. Five different posterior rods of various elastic moduli (intact, rubber, low-density polyethylene, aluminum, and titanium) were tested. Segmental range of motion (ROM), center of rotation (COR) and intervertebral disc pressure were investigated. Results : As the rigidity of the posterior rods increased, both the segmental ROM and disc pressure at L4-5 decreased, while those values increased at adjacent levels. Implant stiffness saturation was evident, as the ROM and disc pressure were only marginally increased beyond an implant stiffness of aluminum. Since the disc pressures of adjacent levels were increased by the axial loading, it was shown that the rigidity of the implants influenced the load sharing between the implant and the spinal column. The segmental CORs at the adjacent disc levels translated anteriorly and inferiorly as rigidity of the device increased. Conclusion : These biomechanical findings indicate that the rigidity of the dynamic stabilization implant and physiological loading play significant roles on spinal kinematics at adjacent disc levels, and will aid in further device development.

• Computers and Concrete
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• v.20 no.1
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• pp.39-47
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• 2017

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.345-356
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• 2013

Numerical simulation on rock cutting by a TBM disc cutter was carried out using SPH (Smoothed Particle Hydrodynamics) code. AUTODYN3D, a commercial software program based on finite element method, was used in this study. The three-dimensional geometry of a disc cutter and a rock specimen were modeled by Lagrange and SPH code respectively. The numerical simulation was carried out for Hwangdeung granite for 10 different cutting conditions. The results of the numerical simulation, i.e. the relation between cutter force and failure behavior, had a good agreement with those from LCM test. The cutter forces measured in the numerical simulation had 10% deviation from the LCM test results. Moreover, the optimum cutter spacing was almost identical with the experimental results. These results indicate that SPH code can be successfully used had applicability for simulation on rock cutting by a TBM disc cutter. However, further study on Lagrange-SPH coupled modelling would be necessary to reduce the computation time.

• Mycobiology
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• v.35 no.2
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• pp.45-46
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• 2007

Lecanora muralis was found on the rock along coastal line during the field trip in Jeju island in 2006. Thallus crustose, placodioid, closely adnate, forming orbicular patches; upper surface grayish green, glossy; central lobes areolate, marginal parts plane, edges thin pruinose; lower surface ecorticate; apothecia sessile, lecanorine type, exciple dense and intact when young, and disc plane, but when mature, exciple laciniate, disc protrudent, yellowish brown to orange, $0.5{\sim}1.5$ mm in diameter; ascospores ellipsoid, simple, colorless, $12.5{\sim}15.0{\times}5.0{\sim}7.5\;{\mu}m$. Usnic acid and zeorin contained in thallus. This is the first record of this species in South Korea.

• Fibers and Polymers
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• v.7 no.4
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• pp.414-419
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• 2006

The paper presents information concerning metrological and technical characteristics of KTU-Griff-Tester device, the optimization of its parameters and the cases of its application. It was defined that the behaviour of textile material during its extraction through a rounded hole depends upon its structure. Variations of geometrical shape of woven and knitted specimens can be described by mathematical expressions of shortened epicycloids and Cassini ovals. It is shown that waving process of disc shaped specimen can be predicted on the basis of the law of sine curve. The examples of textiles treatment with different types of commercial softeners are presented, herewith showing the suitability (sensitiveness) of the new device to detect the changes of textile hand. Meantime it is shown that the level of materials anisotropy can be decided on the basis of transformations of specimen's geometrical shape.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.511-516
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• 2001

Recently small punch creep testing (or miniature disc bend creep test) has received much attention through European collaborative research projects. This method was considered as a substitute for the conventional creep rupture testing by which the residual creep life is measured from the specimen taken out from serviced components of high temperature plants. It would be beneficial if the material creep properties such as power law creep constants as well as the creep rupture life can be measured from the small punch creep test. In this paper a method of assessing creep constants from the small punch creep testing is proposed. Finite element analyses were performed to investigate evolution of stress and strain rate at the weakest locations of the small punch creep specimen. Elastic-plastic-secondary creep analyses were carried out. The estimation equations for creep constants by the small punch creep testing are proposed based on the finite analysis results. Small punch creep tests were also performed with 9Cr steel and the accuracy of the proposed equation was verified by the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1493-1500
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• 2001

Recently small punch creep testing (or miniature disc bend creep test) has received much attention through European collaborative research projects. This method was considered as a substitute for the conventional creep rupture testing by which the residual creep life is measured from the specimen taken out from serviced components of high temperature plants. It would be beneficial if the material creep properties such as power law creep constants as well as the creep rupture life can be measured from the small punch creep test. In this paper a method of assessing creep constants from the small punch creep testing is proposed. Finite element analyses were performed to investigate evolution of stress and strain rate at the weakest locations of the small punch creep specimen. Elastic-plastic-secondary creep analyses were carried out. The estimation equations for creep constants by the small punch creep testing are proposed based on the finite analysis results. Small punch creep tests were also performed with 9Cr steel and the accuracy of the proposed equation was verified by the experimental results.

• Journal of the Korean institute of surface engineering
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• v.38 no.5
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• pp.202-206
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• 2005

Nitriding treatments were conducted on tool steel (SKD 61) at a temperature of $500^{\circ}C$ for 5 hr using high vacuum direct current (DC) plasma, with ammonia and argon as source gases. The structural and compositional changes produced in the nitrided layers by applying different ratios of Ar to $NH_{3}\;(n_{Ar}/n_{NH3}) were investigated using glancing x-ray diffraction (GXRD), optical microscopy, atomic force microscopy (AFM), micro-Vickers hardness testing, and pin-on-disc type tribometer. Nitriding case depths of around of $50{\mu}m$ were produced, varying slightly with different ratios of $n_{Ar}/n_{NH3}. It was found that the specimen surface hardness was 1150 Hv with $n_{Ar}/n_{NH3}=1, increasing to a maximum value of 1500 Hv with $n_{Ar}/n_{NH3}=5. With a further increase in ratio to $n_{Ar}/n_{NH3}=10, the surface hardness of the specimen reduced slightly to a value of 1370 Hv. These phenomena were caused by changes of the crystallographic structure of the nitride layers, i.e the $\gamma'-Fe_{4}N$ phase only was observed in the sample treated with $n_{Ar}/n_{NH3}$=1, and the intensity of the $\gamma'-Fe_{4}N$ phase were reduced but new phase of $\varepsilon'-Fe_{3}N$, which was known as a high hardness, with increasing $n_{Ar}/n_{NH3}. Also, the relative weight loss of counterface of the pin-on-disc with unnitrided steel was 0.2. And that of nitrided steel at a gas mixture ($n_{Ar}/n_{NH3}) of 1, 5, 7, and 10 was 0.4, 0.7, 0.6, and 0.5 mg, respectively. This means that the wear resistance of the nitrided samples could be increased by a factor of 2 at least than that of unnitrided steel.

• Tunnel and Underground Space
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• v.32 no.4
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• pp.243-253
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• 2022

In this study, the cutting efficiency of TBE (Tunnel Boring Extender) was evaluated by using rotary cutting tester. In the rotary cutting test, a specimen which has a drilled hollow hole at the center was made of rock-like material. The specimen was cut by UDC (undercutting disc cutter) with spiral cutting path to simulate the cutting process of TBE. The cutting forces and specific energy were evaluated under different cutting conditions. The results indicated that the cutter forces of UDC linearly increased with the vertical and radial penetration depths. Among the three directional cutter forces, the normal force is larger than other force components. While the specific energy decreased with the two penetration depths, in particular, it was presumed that the specific energy was minimized at a certain value of the ratio of radial to vertical penetration depth.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.2
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• pp.114-119
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• 2011

The aim of this study was to investigate effect of specimen preparation method on the microtensile bond strength of veneering ceramic to zirconia core. Materials and methods: Cylindrical Lava zirconia block (3M ESPE, Seefeld, Germany) was cut into discs using a diamond disc. After sintering, the core specimens were placed in an adjustable mold and veneered with Lava ceram (3M ESPE, Seefeld, Germany). The disc shaped specimen of group 1 was cut into microbars ($1{\times}1{\times}7\;mm^3$) using a low speed diamond disc under water cooling (n = 15). The specimen of group 2 was cut into microbars ($1.2{\times}1.2{\times}7\;mm^3$) in the same way. Whereafter the microbars were trimmed ($1{\times}1{\times}7\;mm^3$) using a thick diamond disc under water cooling (n = 15). The microtensile bond strength was tested in a microtensile tester (Instron 8848, $Instron^{(R)}$ Co., Norwood, USA). Fractured microtensile specimens were analyzed under a stereomicroscope (MZ6, Leica Microsystems GmbH, Wetzlar, Germany) at magnification ${\times}30$. Results: The microtensile bond strength of group 1 ($28.8{\pm}7.0\;MPa$) was significantly higher than group 2 ($11.0{\pm}33\;MPa$) (P=.00). Conclusion: It appears advisable to avoid the trimming action, especially high strength ceramic specimens.