• 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.

• Transactions of Materials Processing
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• v.16 no.7
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• pp.509-515
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• 2007

As the springback of sheet metal during unloading may cause deviation from a desired shape, accurate prediction of springback is essential for the design of sheet stamping operations. When considering the case of a sheet metal being bent to radius $\rho$ that is such that the maximum stress induced exceed the elastic limit of the material, plastic strain in the outer surface will occur and the material will take a permanent set: but since, on removing the bending moment, the recovery of the material is not uniform across the thickness, springback will occur and the radius $\rho$ will not be maintained. Furthermore, when a tensile load being applied to each end of specimen, the tensile stress due to bending is increased and the compressive stress is decreased or cancelled and eventually the whole specimen may be in varying degree of tension. On the removal of the applied load the specimen loses its elastic strain by contracting around the contour of the block, the radius $\rho$ will be determined by the residual differential strain. Therefore in this study the springback is analytically estimated by the residual differential strains between upper and lower surfaces of greatest radius after elastic recovery, and a springback model based on the bending moment is also analytically derived for comparison purpose.

• Journal of the Korean Society of Safety
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• v.25 no.3
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• pp.34-39
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• 2010

Unidirectional Carbon Fiber Reinforced Plastics (CFRP) are advanced materials which combine the characteristics of the light weight, high stiffness and strength. For those reasons, the use of the unidirectional CFRP has increased in jet fighters, aerospace structures. However, unidirectional CFRP composites have a lot of problems, especially delamination, compared with traditional materials such as steels and aluminums, and so forth. Therefore, the interlaminar fracture toughness for a laminate CFRP composite is very important. In this study, The mode II interlaminar fracture toughness was measured by using center notched flexure(CNF) test specimen. The CNF specimens using unidirectional carbon prepreg were fabricated by a hot-press with the gage pressure and temperature controller. And three kinds of a/L ratio was applied to these specimens. Here, we discuss the relations of the crack growth and the mode II interlaminar fracture under the four point bending CNF test. From the results, we shows that mode II interlaminar was occurred when the more $a_0$/L ratio, the less load. And $G_{IIC}$ also were obtained as 5.33, 2.9 and $0.58kJ/m^2$ according to $a_0$/L ratio=0.2, 0.3 and 0.4.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.59-62
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• 1997

Recently, quasimolecular dynamics has been successfully used to simulate the deformation characteristic of actual size material. In quasimolecular dynamics, which is an attempt to bridge the gab between atomistic and continuum simulations, molecules are aggregated into large units, called quasimolecules, to simulate the large scale material behavior. In this paper, a numerical simulation using quasimolecular dynamics has been performed to investigate the laminar composite material fracture and crack propagation behaviors in bending process of laminar composite material which is made of fictitious materials. The simulation of the bending of laminar composite material has clarified the effects of strength of material at outer surface upon the fracture behviors of the specimen.

• Journal of the Korean Wood Science and Technology
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• v.41 no.5
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• pp.392-398
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• 2013

This study investigated the effect of test zone selection for evaluating bending strength of visually graded lumber. This will contribute to the understanding of two different methods under different standards. In method I, the major defect was randomly placed in the test specimen. In method II, the major defect was randomly placed in the maximum moment zone (MMZ). The results showed that the method II is more accurate for reflecting the effect of defects governing the grade of lumber. Unless the maximum strength-reducing defect (MSRD) is placed in MMZ, the evaluated value would be higher than that of MSRD. For evaluating the modulus of rupture (MOR) of visually graded lumber in test set-up of Method I, the Eq. (5) needs to be considered.

• Journal of Korean Association for Spatial Structures
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• v.19 no.3
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• pp.77-83
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• 2019

AU(A plus U-shaped) composite beam was developed for reducing the story height in the residential buildings, and saving the cosrtuction cost of floor structures. Structural performance and economic feasibility of the composite beam have been sufficiently approved through the structural experiments and the analytical studies. Fire safety for the practical application of the composite beam has also been verified through the fire resistance tests and the heat transfer analyses. In this study 2-points bending tests were performed on the four specimens already tested for fire resistance to evaluate the residual bending strength of AU composite beam after fire accident. The same bending test was performed on the one fresh specimen having the same section and span of the specimens for practically comparative study.

• Journal of the Korean Society of Safety
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• v.9 no.3
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• pp.28-33
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• 1994

It is very important to have exact informations on the properties and characteristics of the sintering material as a new material of machine elements. To study the sintering spur gear and the sintering specimen to be consisted of Fe-Cu-C, the constant stress amplitude fatigue test is performed by using an electrohydrolic survo-controlled pulsating tester. Consequently, the S-N curves are obtained and the fatigue strength is compared with flaw depth. Accordingly, this study presents the fatigue strength of sintering spur gears, the critical notch depth of sintering materials and the effects of flaw depth on the bending fatigue strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1078-1084
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• 2011

In design of sport footwear, bending stiffness of its toe part is an important factor though it can be hardly measured. This paper introduces a device for measuring the bending stiffness. The device is simply designed with aluminum frames, one AC motor, two load-cells, one encoder and control hardwares. The mechanism measuring the bending moment of a shoe is described. Then, it was used to observe how the midsole material and design of a sports shoe affect on its bending stiffness. For the experiments, various specimens prepared, where each midsole of the specimens is different in terms of material, thickness and hardness. With those specimens, experiments were performed by using the device and then the bending stiffness was computed by applying the least square curve fitting after the bending moment data were measured. The specimen with Poly-urethane(PU) midsole has the higher bending stiffness than the one with Phylon(PH) midsole, and the midsole thickness affects more on the bending stiffness than the midsole hardness. Based on those results, it can be concluded that the measurement device can provide consistent bending stiffness data to sports footwear and the bending stiffness of a footwear measured by the developed device can be used as a major parameter in the footwear design.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1715-1720
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• 2010

In this study, we analyzed the crack-healing characteristics of specimens; different crack lengths and coating methods of $Si_3N_4$ ceramic structures with long cracks were analyzed. Cracks with lengths of about $100-500\;{\mu}m$ were obtained using a Vickers indenter for a load of 24.5-98 N. In the case of a crack obtained by applying a load of 24.5 N, the crack-healed specimen with $SiO_2$ nanocolloid coating exhibited the highest bending strength, which was higher than that of a smooth specimen by 140%, but the bending strength of a crack-healed specimen that had a $SiO_2$ nanocolloid coating and originally had multiple cracks was lower than that of a smooth specimen. However, when compared to the cracked specimens, the bending strength of most specimens with multiple cracks increased slightly. On the basis of these results, the crack-healing characteristics of $Si_3N_4$ ceramic structures with multiple indentations were studied for different coating methods. The most effective coating method for long-crack specimens was hydrostatic pressure coating.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.229-235
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• 1993

Thermal history and thermal stress of alumina specimen, which occured from thermal shock process, were calculated by finite difference method. Stress intensity factor and crack growth in cyclic thermal fatigue were calculated from single thermal shock temperature history and thermal stress. Cyclic thermal life were estimated by bending strength after cyclic thermal shock under critical thermal shock temperature. Calculated stress intensity factor was compared with real experimental thermal fatigue life of specimen. Fatigue life until critical stress intensity factor and real experimental result were comparable.