• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.745-754
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• 2007

This paper presents a unified modeling technique for tension stiffening effect in structural concrete members. The model is mathematically derived from the bond stress-slip relationships which account for splitting crack. The relationships in CEB-FIP Model Code 1990 and Eurocode 2 are employed together with the assumptions of a linear slip distribution along the interface and the uniform condition of concrete tensile contribution for the mid section of cracked member at the stabilized cracking stage. With these assumptions, a model of tension stiffening effect is proposed by accounting for the force equilibrium and strain compatibility condition associated to the steel strain and concrete contribution by bond stress. The model is applied to the test results available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured behavior.

• Journal of Dental Rehabilitation and Applied Science
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• v.31 no.4
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• pp.316-328
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• 2015

Purpose: The objects of this study was to evaluate the accuracy of the dental stone casts made from alginate impressions according to storage condition and stone pouring time. Materials and Methods: Each of upper and lower impressions of dental model was taken. The dental stone models were made immediately, 10, 30, 60, 180, 360 minutes after the impressions were taken at each storage condition. 3D models were constructed by scanning the stone model using 3D laser scanner. With Reference points, positioned on digital models, linear measurements of the dimensional change were compared by 3D metrology software, 3D average models were made and superimposition to identify the specific site of dimensional change and to measure surface deviation (mm). Results: Dental stone models which were made immediately after taking the impression showed the smallest linear dimensional change. As the stone pouring time was prolonged, the linear dimensional change was increased. More than 180 minutes after impression taking, linear dimensional change and surface distortion increased in the posterior molar region, regardless of the storage condition. Conclusion: For the optimum accuracy of the dental stone casts, alginate impression should be poured as soon as possible. If there were a need for storing, a humidor with 100% relative humidity must be used and be stored less than 180 minutes to fabricate the accurate dental model.

• Journal of Chest Surgery
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• v.31 no.5
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• pp.456-465
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• 1998

Cardiopulmonary bypass(CPB) in children is associated with the accumulation of body water after cardiac operation, as a consequence of an inflammatory capillary leak. Following work by Elliott in 1991, modified ultrafiltration(MUF) was introduced after bypass as a means of hemoconcentrating patients and a potential way of removing water from the tissues. We have carried out a prospective randomized study of 20 children undergoing open heart surgery, comparing MUF with nonfiltered controls. MUF was carried out for a mean of 18.9 minutes after completion of CPB to a hematocrit of 37.1%(mean). The mean water volulme removed by the ultrafiltration was 38.4 ml/kg and the mean blood volume retransfused from the oxygenator during the ultrafiltration was 32.1 ml/kg. Fluid balance, hemodynamics, hematocrit, osmolarity and dosage of drug treatment were recorded for 4∼12 hours postoperatively. The results were analyzed using Student t-test and ANOVA, comparing controls(n=10) to MUF(n=10). Blood loss(ml/kg/24hr) was 14.5(mean) in MUF versus 13.7 in controls; blood transfused(ml/kg/24hr) 6.6 in MUF versus 15.2 in controls; plasma transfused(ml/kg/24hr) 65.7 in MUF versus 59.6 in controls. There was rise in arterial blood pressure and hematocrit during MUF. Percent rise of systolic blood pressure was 28.8% in MUF versus 18.7% in controls(p=0.366); percent rise of diastolic blood pressure was 28.8% in MUF versus 8.5% in controls(p=0.135); and percent rise of mean blood pressure was 36.2% in MUF versus 8.2% in controls (p=0.086). Percent rise of hematocrit was 40.0% in MUF versus 23.5% in controls(p=0.002). There was no significant difference in the inotropic requirement and the postoperative serum osmolarity between two groups. The number of days on the ventilator, the duration of stay in the intensive care unit, and the postoperative hospital stay were not significantly different between the two groups.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.353-362
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• 2016

An accurate hysteresis model of an elastomer is important for quantifying viscoelastic energy loss. We suggest a highly nonlinear hyper-viscoelastic constitutive model of elastomers. The model captures a nonlinear viscoelastic characteristic by combining Yeoh's hyperelastic model and Hoofatt's hysteresis model used Neo-Hookean hyperelastic model. Analytical and numerical models were generated from uniaxial cyclic tests of an elastomer under a sinusoidal load with a mean strain of 150%, amplitudes of 20~80%, and frequencies of 0.02~0.2Hz. The viscoelastic model can highly capture the viscoelastic energy loss up to a strain of 230%.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.53-65
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• 2011

This is the third of several companion papers dealing with the derivation of material constants for ductile failure criteria under hydrostatic stress. It was observed that the ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tended to increase and decrease, respectively, because of the stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that the curves from the two approaches very closely coincide. Failure strains are obtained from the equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress drops suddenly. After introducing the new concept of average stress triaxiality and accumulated average strain energy, the material constants of the Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. The experimental results obtained for EH-36 steel were in relatively good agreement with the 100% critical energy, whereas the literature states that aluminum fits with a 15% critical energy. Therefore, it is expected that a unified failure criterion for critical energy, which is available for most kinds of ductile materials, can be provided according to the used materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1461-1469
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• 2011

Using three-dimensional (3-D) FE analyses, this paper provides a method for analyzing the effects on stresses and strains produced by angular and concentric misalignment of a test specimen for a torsion test. To quantitativele compare of the FE results, the average bending strain for the angular, concentric, and combined misalignment was proposed. To verify the effects of axial misalignment of the test specimens, we used both circular and tubular specimens. From the FE results, we proposed general predictions for the effects caused by the various types of axial misalignment and its direction. In addition, we confirmed the effect of initial yielding moment based on the initial yielding condition for axial misalignment of specimens in torsion tests.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.2
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• pp.11-19
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• 2009

Thermo-mechanical behaviors of wire-bond plastic ball grid array (WB-PBGA) package assemblies are characterized by high-sensitivity moire interferometry. Using the real-time moire setup, fringe patterns are recorded and analyzed for several temperatures. Experiments are conducted for three types of WB-PBGA package that have full grid pattern and perimeter pattern with/without central connections. Bending deformations of the assemblies and average strains of the solder balls are investigated, with an emphasis on the effect of solder interconnection grid patterns, Thermal strain distributions and the location of the critical solder ball in package assemblies are quite different with the form of solder ball grid pattern. For the WB-PBGA-PC, The largest of effective strain occurred in the inner solder ball of perimeter closest to the chip solder balls. The critical solder ball is located at the edge of the chip for the WB-PBGA-FG, at the most outer solder ball of central connections for the WB-PBGA-P/C, and at the inner solder ball closest to the chip for the WB-PBGA-P.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.15-22
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• 2003

In the conventional load transfer analysis for a steel pipe drilled shaft, it was assumed that the concrete's strain is the same as the measured steel's strain and the elastic modulus of the steel and the concrete calculated by the formular as prescribed by specification is used in the calculation of pile axial load. But, the pile axial load calculation by conventional method differed to some extent from the actual pile load. So, the behavior of a steel pipe drilled shaft could not be analyzed exactly. Thus, the necessity to measure the strain for each pile component was proposed. In this study, a new approach for load transfer measurement of large diameter drilled shafts was suggested ; the strain of each pile component(i. e., steel and concrete) was measured by DRS(Deformable Rod Sensor), the elastic modulus was determined by the uniaxial compression test for concrete specimens made at test site and a value of elastic modulus was evaluated as average tangential modulus corresponding to the stress level of the (0.2-0.6)$f_{ck}$. Field application was confirmed by the results of load transfer measurement tests for 3 drilled shafts. The errors for calculated pile head load were -11 ∼16% and 3.4% separately.

• The korean journal of orthodontics
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• v.29 no.6 s.77
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• pp.673-688
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• 1999

This study was conducted in order to analyze the mechanical characteristics of multiloop edgewise archwire (MEAW). The purposes were 1) to compare load deflection rate (LDR) of MEAW with that of various other arch wires in the individual interbracket span, 2) to compare the wire stiffness in the interbracket span with that in the multi-L-loop region (the span from distal border of the bracket of the lateral incisor to the mesial border of the buccal tube of the second molar), and 3) to verify the experimental results with theoretically derived formula. The single L-loops of five different horizontal lengths and multi-L-loops for the upper and lower arches were made out of .$016\times.022$ permachrome stainless steel wire. Straight segment of plain stainless steel, TMA and NiTi wire of the same dimension were prepared. The LDR was measured using Instron model 4466 with the load cell of 50N capacity at cross head speed of 1.0mm/min, and maximum deflection of 1.0mm. Five specimens were tested under each experimental condition. The wire stiffness number for each interbracket region and multi-L-loop region was calculated from the LDR and the interbracket spans. By dividing the theoretical model of multi-L-loop into 35 linear segments, the energy stored in each segment was obtained. Then the LDR and wire stiffness of single L-loop and multi-L-loop were calculated and compared. The findings were as follows : 1) The average LDR of MEAW in the individual interbracket region was 1/1.53 of that of the NiTi,1/2.47 of TMA and 1/5.16 of the plain stainless steel wire. 2) The wire stiffness of MEAW in the multi-L-loop region was 1.53 times larger than that in the interbracket region, and the LDR was almost twice as large as that of NiTi in that region. 3) According to the theoretically derived equation, the wire stiffness of the single L-loop was lower than that of multi-L-loop. The results of this study suggest that MEAW has the unique mechanical Property which could allow individual tooth movement and transmit elastic force effectively through the entire arch wire.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.1
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• pp.75-83
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• 2000

This paper deals with the application of two dimensional filtering technique for strain calculation using old and new geodetic data, and discusses the characteristics of general strain pattern in terms of seismic activity and tectonics. The mean rate of maximum shear strain is $0.12{\mu}/yr$. The mean direction of principal axes distribution of the compression is about $N80^{\circ}E$.