• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.911-916
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• 2002

It is important to consider the effect of depth when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of reinforced concrete beam was experimentally investigated. For this purpose, a series of beam specimens subjected to 2-point bending load were tested. More specifically, three different depth (d=15, 30, and 60 cm) of reinforced concrete beams were tested to investigate the size effect. The shear-span to depth ratio (a/d=3) and thickness (20 cm) of the specimens were kept constant where the size effect in out-of-plan direction is not considered. The test results are fitted using least square method (LSM) to obtain parameters for modified size effect law (MSEL). The analysis results indicate that the flexural compression strength and ultimate strain decreases as the specimen size increases. Finally, more general parameters for MSEL are suggested.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.228-234
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• 2002

The CO$_2$ laser beam irradiation strengthening of 35kgf/mm$_2$ grade steel sheet is investigated to reduce the weight of bumper beam. The increase of tensile strength is dominated by the number of fully penetrated melting lines. The optimal laser irradiation pattern is obtained by 3-point bending test of hat-type specimens. Laser should be irradiated not only on the center specimen densely in the width direction, but also on the edge densely in the longitudinal direction. Local laser strengthening may be effective for the weight reduction of automobile bumper beam.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.114-119
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• 2008

The modern automotive industry develops innovative vehicle designs to meet increasing stability of car and performance demands of their customers. The improvement of frame rigidity by the structural foam is thought to be an effective means to improve the performance because of high applicability and minimum weight. The object of this paper is to examine the use of structural foam in a hat section as an optimum reinforcing means, to compare the reinforcing performance of structural foam versus a plastic reinforcement. The result of this paper indicated that reinforcing efficiencies are achieved by structural foam and plastic reinforcement shape.

• Journal of Biomedical Engineering Research
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• v.10 no.3
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• pp.261-268
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• 1989

The characteristics of aging of near-equiatomic Ni-Ti alloy has been studied by the three point bend test and the measurement of Differential Scanning Calorimetry(DSC). The DSC is used to measure precise transformation temperatures and the amount of thermal energy required for the corresponding phase transformation. The effort of hardness on aging treatment in saline solution of $37^{\circ}C$ was higher for the annealed than solution treated specimens. As the testing temperature inc- rease from under $M_f$ to above $A_f$ temperature, the elastic stiffness increased. Almost full recovery can be achieved after bending below Belo outer fiber strain. Total bend recovery decreased gradually as aging time and bend angle is increased.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.185-190
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• 2000

The effect of specimen thickness and notch's depth and the validity of J-integral analysis were studied on the fracture behavior of concrete. Through the 3-point bending test, the stress-deformation curves were experimentally measured. Concrete fracture toughness is calculated from stress-displacement curves. Concrete fracture toughness decreases when notch's depth is longer. So, Gf is less sensitive than JIc and Gf is more useful factor as concrete fracture toughness parameter. The values of J-integral and fracture energy increase when the breadth of concrete specimen get longer from 75mm to 150mm. Therefore, the breadth effect of specimen has to be considered in determining the concrete fracture toughness.

• Journal of the Korean Society for Precision Engineering
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• v.8 no.4
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• pp.118-125
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• 1991

Acoustic microscopy has attracted much interest recently as potential nondestructive evaluation technique for detecting and sizing defects of surface and sub-surface. Also acoustic emission testing method has been developed for detecting microcracks which is more than 30${\mu}m$ in length quantitatively on ceramics. In the present paper, acoustic emission during the four point bending test in hot-pressed sintered $Si_3N_4$ specimen which was stressed by thermal shock, has been measured by high sensitive sensing system. The surface and sub-surface cracks were detected by scanning acoustic micrscope of 800 MHz and conventional ultrasonic testing in C-scope image. The purpose was to investigate the location and size of cracks by SAM and AE technique, whose experimental data demonstrate good for detecting microcracks.

• Computers and Concrete
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• v.1 no.4
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• pp.371-388
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• 2004

Our objective is to model static multi-cracking processes in concrete. The explicit dynamic relaxation (DR) method, which gives the solutions of non-linear static problems on the basis of the steady-state conditions of a critically damped explicit transient solution, is chosen to deal with the high geometric and material non-linearities stemming from such a complex fracture problem. One of the common difficulties of the DR method is its slow convergence rate when non-monotonic spectral response is involved. A modified concept that is distinct from the standard DR method is introduced to tackle this problem. The methodology is validated against the stable three point bending test on notched concrete beams of different sizes. The simulations accurately predict the experimental load-displacement curves. The size effect is caught naturally as a result of the calculation. Micro-cracking and non-uniform crack propagation across the fracture surface also come out directly from the 3D simulations.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.103-108
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• 2000

Since the ceramic/metal joint material is made at a high temperature, the residual stress development when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of $Si_3N_4/STS304$ joints quantitatively and to compare the strength of Joints. The difference of residual stress is measured when repeated thermal cycle is loaded under the conditions of the practical use of the ceramic/metal joint. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a residual it is known that the stress of joint decreases as the number of thermal cycle increases.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.3
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• pp.160-168
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• 1994

This was studied about mechanical characteristic of AC4A/SiCw 10-30% reinforced composites. Tensile strength of pressed base metal(base metal) with SiCw preform was higher than without pressed base metal(AC4A). If SiCw whisker volume fraction was increased, tensile strength at room temperature was increased. And tensile strength of SiCw 30% was about $35kg/mm^2$. Tensile strength of SiCw 30 % $400^{\circ}C$ at same time aging was the most excellence, about $40kg/mm^2$. The fracture energy value of composite material at three point bending test was higher than AC4A. Dislocation at matrix of composite material was evenly distributed. But dislocation around whisker of composite material was more existed than matrix. The reasom was thought of pile-up around whisker.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.04a
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• pp.127-133
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• 1991

Acoustic microscopy has attracted much intrest recently as potential mondestructive evalution technique for detecting and sizing defects of surface and sub-surface. Also acoustic emission testing method has been developed for detecting microcracks which is more than 30 umm in length quintitatively on ceramics material. In the present paper, acoustic emission during the four point bending test in hot-pressed sintered Si$\_$3/N$\_$4/ specimen which was stressed bythermal shock has been measured by high sensitive sensing system. The surface and sub-surface cracks were detected by scanning acoustic microscope of 800 MHz and conventional ultrasonic testing in C-scope image. The purpose was to investigate the location and size of cracks by SAM and AE technique, whose experimental datas demontrates good agreement for detecting microcracks.