• Transactions of Materials Processing
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• v.19 no.6
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• pp.337-343
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• 2010

Current need of weight reduction in automotive part increases the application for high strength steel (HSS). The various types of high strength steels have been used to produce chassis part, control arms and trailing arms for weight reduction and increasing of fatigue durability such as dual phase steel (DP) and ferrite bainite steel (FB). But, DP and FB steels have proven to show inferiority in durability as well as press formability. Edge cracking occurred often in flange forming and hole expansion processes is the major failure encountered. This paper discussed the behavior of edge stretchability of high strength steel of DP and FB steels. Experimental works have been conducted to study the effect of punch clearance and burr direction on hole expansion ratio (HER). Also finite element simulation (FEM) has been preformed to clarify the mechanism of flange crack and support the experimental results on HER of DP and FB steels. It was simulated the whole process of blanking process following by hole expansion process and ductile fracture criterion named the modified Cockcroft-Latham model which was used to capture the fracture initiation. From the hole expansion tests and FEM simulation studies it was concluded that ferrite bainite steel showed better stretch-flangeability than dual phase steel. It was attributed to the lower work hardening rate of ferrite bainite steel than dual phase steel at the sheared edge.

• Structural Engineering and Mechanics
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• v.76 no.3
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• pp.279-291
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• 2020

The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (W_pi) normalized by the product of the story shear force (Q_yi) and drift (δ_yi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, W_pi/ΣW_pj, can be evaluated from the deviation of Q_yi with respect to an "optimum value" that would make the ratio W_pi/(Q_yiδ_yi) -i.e. the damage- equal in all stories. This paper investigates how the soil type and ductility demand affect the optimum lateral strength distribution. New optimum lateral strength distributions are put forth and compared with others proposed in the literature.

• Journal of the Korea Convergence Society
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• v.13 no.4
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• pp.287-292
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• 2022

In this paper, the stochastic distribution of the springback amount is investigated for the stamping process of a U-channel shaped-product with ultra-high strength steel. Using the reliability-based design optimization technique (RBDO), stochastic distribution of process parameters is considered in the analysis including material properties and process variation. Quantification of the springback scatters is carried out with the statistical analysis method according to the material strength. It is found that the scattering amount of springback decreases while the amount of springback increases as the tensile strength of the blank material increases, which is investigated by analyzing the strain and stress distribution of the punch and die shoulder. It is noted that the proposed scheme is capable of predicting and responding to the unavoidable scattering of springback in the sheet metal forming process.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.1
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• pp.95-104
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• 2020

PURPOSE: A prospective study was conducted to investigate the correlation between the inspiration ability, bone mineral density, lumbar muscle strength, and muscular endurance for the national softball athletes in the national training center. METHODS: The general characteristics of study subjects, inspiration ability, bone mineral density, muscle strength, and muscular endurance data were analyzed using descriptive statistics. In addition, the Pearson product moment correlation was performed to investigate the correlation between the inspiratory capacity, bone mineral density, muscle strength, and muscular endurance. RESULTS: The inspiration, flow rates, and volume were not correlated with the bone mass and bone mineral density. Inspiration and the flow rates and volume were not correlated with the bone mass and bone mineral density. On the other hand, inspiration was correlated with the Extensor muscles (r=.464, p=.006) at an angular velocity of 60°/s and the flexors (r=.463, p=.006) and extensor muscles (r=.615, p<.001) at an angular velocity of 180°/s. The flow rate was also correlated with the extensor muscles (r=.444, p=.009) at an angular velocity of 60°/s and with flexor muscles (r=.432, p=.011) and extensor muscles (r=.589, p<.001) at an angular velocity of 180°/s. Finally, the volume was correlated at the extensor muscles at an angular velocity of 180°/s (r=.534, p=.001). CONCLUSION: The correlation between the inspiratory capacity, bone mineral density, muscle strength, and muscular endurance of softball athletes did not correlate with the bone mass and bone density. On the other hand, the lumbar muscle strength increased with increasing inspiratory capacity.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.650-657
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• 2021

Alkali activators that stimulate mineral compounds are expensive materials, but in order to replace industrial products of high alkali in gredien ts, both product an d econ omic feasibility must be satisfied. In this study, alkali in dustrial waste(LW) from the LCD man ufacturin g process were used for the purpose of alkali active reaction of GGBFS for high stren gth concrete over 50MPa. Concrete mixed with LW had reduced workability, but it had the characteristic of increasing compressive strength. Analysis using ACI 209 Compressive Strength Model Equation was made to compare the changes in strength coefficients according to LW mixing. The durability test of concrete, such as Chloride Penetration Resistance and carbonation resistance, also showed excellent performance. In the Adiabatic temperature rise test results, the concrete mixed with LW had the effect of accelerating the initial hydration heat. However, the final Adiabatic temperature rise was not significantly affected by the mixing of LW.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.259-268
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• 2000

In the friction-type joints the external applied load is transmitted by frictional force acting on the contact area of the plates fastened by the high strength bolts. This frictional force is proportional to the product of the bolt clamping force and slip coefficient of the faying surface. But the bolt clamping force is dependent on many factors when the turn-of-nut method is used. The preserved thread length and length-to-diameter ratios are one of the major factors governing the bolt clamping force. This paper presents the correct method of high strength bolt tightening through the experiment on the mechanical properties on sets of high strength bolts in accordance with preserved thread length and length-to-diameter ratios.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.87-96
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• 2004

As a special concrete, which is a mixture of soil, cement and water, has strength like regular concrete for pavement, soil cement has been used in various field such as pavement and soft soil improvement. The objective of this study was to investigate the characteristic of unconfined compressive strength and time dependent behavior of soil cement that is made from decomposed granite soil or coluvial and inorganic solidification liquid. The results showed that the unconfined compressive strength appears to increase as the amount of cement and curing time increase In addition, the strength seems to decrease with increase of the potion of fine particles(No 200 sieve). The result of XRD indicated that there is Vermiculite, the product of reaction, in the soil cement. The dynamic properties of material, such as shear complex compliance, shear complex modulus, and phase angle could be calculated from the hysteresis loop obtained from the Haversine Creep Tests. Finally, creep behavior was able to be predicted from these dynamic properties.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.443-449
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• 2022

When fiber reinforced concrete is manufactured, it is useful to utilize lathe scrap as an aiternative material of steel fiber, because it is not only economical as an by-product of steel manufactures, but also has a very similar composition to that of steel fiber. The purpose of this experimental research is to evaluate the compressive strength and tensile behavior and then propose a material model of lathe scrap reinforced mortar. For this purpose, the lathe scrap reinforced mortars were ma de a ccording to their tota l volume fra ction of 1.5 % for wa ter-binder ra tio of 30 % a nd 40 %, respectively, a nd then the mechanical properties such as compressive strength, direct tensile strength, and stress-strain curve of those were evaluated. Also, based on the experimental results of lathe scrap reinforced mortar the material model for tensile behavior was suggested. It was revealed that the experimental results and the proposed material model corresponded relatively well.

• Journal of Korea Foresty Energy
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• v.20 no.1
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• pp.73-80
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• 2001

This study was carried out to investigate the strength and technical feasibility of arch type laminated lumber from the domestic small lumbers(Pinus densiflora S. et Z. and Larix kampferi Catt.). Arch type lumbers manufactured with different compositions of laminae. It was designed to improve the strength and stiffness. Strength S. rt Z. U;timate load Carr. laminated lumbers were higher than that of the Pinus densiflora S. et Z. Ultimate load of 7-ply laminated lumbers were 2 times higher than the 5-ply laminated lumbers. The strength of finger jointed lumbers were found to be about 15.8% less than that of the no joint lumber. One solution for this problem is to use veneer as face lamina. The veneer laminated lumbers was considerably greater than that of the non-veneer laminated lumbers. It was suggested that this small lumber may be a candidate for high valued product member to provide the proper combination of laminae.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3396-3402
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• 2014

The importance of shape design for strength is highly regarded when applied to thin plate products in Ceramic Injection Molding (CIM), such as cases for electronic goods. This study analyzed the characteristics of the mechanical strength of CIM product by measuring the flexural strength and elastic modulus through a 3-point bending test according to the thickness of a thin plate test piece prepared by CIM. The specimen with a thickness of 0.48mm required a 82.9~94.5N fracture load, whereas a 1.0mm thick test piece required 233.6~345.8N. The increase in thickness by 0.5mm resulted in a 3-fold increase in the fracture load, whereas the elastic modulus decreased by 20%. The thicker the specimen, the lower relative density and surface hardness of the specimen. This is because the thicker the specimen, the lower the powder fraction of the ceramic mixture, and the material properties partially change after sintering.