• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1327-1334
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• 1988

In this study rotating bending fatigue tests have been carried out with the deep non-through radial holed notch specimens of low carbon steels(SM 22C). It is investigated that the behaviors of surface and interior fatigue crack propagation and the variations of the shape of the cracked surface on the magnitude of bending stresses. The Obtained results are summarized as follows. (1) The relations between [Crack length] and [Cycle ratio] are expressed by following eq. in the 0.1~0.6 range of N/ $N_{f}$ long[ crack length] = A + B [N/ $N_{f}$ ] In case of surface crack length, values of A and B are uniformed independent upon the magnitude of bending stress, but those are variable according to the magnitude of bending stress for interior crack length. (2) The following eq. is derived on the surface crack propagation rate, bending stress and surface crack length. (dl/dN)=(3.94*10$^{-12}$ ).sigma.$^{4.54}$l (3) Under small stress, interior crack propagation rate increase with the interior crack growth but it decrease for large stress. (4) The shape of cracked surface depends upon the magnitude of bending stress. Under small stress fatigue crack propagates as an semi-ellipse with semi-major axis of surface crack length with semi-major axis of interior crack length for large stress.s.

• Journal of the Korean Wood Science and Technology
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• v.51 no.4
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• pp.239-252
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• 2023

In this study, bending and compression strength tests were performed to investigate effect of composition of layer layout of Larix cross-laminated timber (CLT) on mechanical properties. The Larix CLT consists of five laminae, and specimens were classified into four types according to grade and composition of layer. The layer's layout were composited as follows 1) cross-laminating layers in major and minor direction (Type A), and 2) cross-laminating external layer in major direction and internal layer applied grade of layer in minor direction (Type B). E12 and E16 were used as grades of lamina for major direction layer of Type A and external layer of Type B according to KS F 3020. In results of the bending test of CLT using same grade layer according to layer composition, the modulus of elasticity (MOE) of Type B was higher than Type A. In case of prediction of bending MOE of Larix CLT, the experimental MOE was higher than 1.00 to 1.09 times for Shear analogy method and 1.14 to 1.25 times for Gamma method. Therefore, it is recommended to predict the bending MOE for Larix CLT by shear analogy method. Compression strength of CLT in accordance with layer composition was measured to be 2% and 9% higher for Type A using E12 and E16 layers than Type B, respectively. In failure mode of Type A, progress direction of failure generated under compression load was confirmed to transfer from major layer to minor layer by rolling shear or bonding line failure due to the middle lamina in major direction.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.370-375
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• 2004

Fatigue tests were carried out to find the fatigue characteristics in the super-long life range by using a cantilever type rotational bending fatigue test machine. Three kinds of specimen in bearing steels with the quenched and tempered in air (A and B, B: shot peened after heal treatment) and under vacuum conditions(C:non-shot peened)were tested in this study. S-N curves obtained from fatigue tests of C specimen tend to come dawn again in the super-long life range due to fish-eye type cracking, while most of A and B specimens fractured by surface defects such as scratches and slip lines. This duplex S-N behavior for the high strength steels have to be reviewed by the change of fracture modes.

• Structural Engineering and Mechanics
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• v.32 no.5
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• pp.609-620
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• 2009

In this paper the results of a series of experimental tests upon three-point bending specimens made of polystyrene and containing re-entrant corners are firstly described. Tests involved different notch angles, different notch depths and finally different sizes of the samples. All the specimens broke at the defect, as expected because of the material brittleness and, hence, the generalized stress intensity factor was expected to be the governing failure parameter. Recorded failure loads are then compared with the predictions provided by a fracture criterion recently introduced in the framework of Finite Fracture Mechanics: fracture is assumed to propagate by finite steps, whose length is determined by the contemporaneous fulfilment of energy balance and stress requirements. This fracture criterion allows us to achieve the expression of the generalized fracture toughness as a function of the tensile strength, the fracture toughness and the notch opening angle. Comparison between theoretical predictions and experimental data turns out to be more than satisfactory.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.734-737
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• 2004

The synthetic fibers such as polypropylene(PP) and polyvilyl-alcohol(PVA) fiber are poised as a low cost alternative for reinforcement in structural applications. It has been reported that synthetic fiber in cement composites can control restrained tensile stresses and cracks and increase toughness, resistance to impact, corrosion, fatigue and durability. High performance fiber reinforced cementitious composite(HPFRCCs) shows ultra high ductile behavior in the hardened state, because of the fiber bridging properties. Therefore, a variety of experiments have being performed to access the performance of HPFRCCs recently. The research emphasis is on the flexural behavior of HPFRCCs made in synthetic fibers, and how this affects the composite property, and ultimately its strain-hardening performance. Three-point bending tests on HPFECCs are carried out. As the result of the bending tests, HPFRCCs showed high flexural strength and ductility. HPFRCCs made in PVA or Hybrid fiber were, also, superior to PP of singleness. On the other hand, effect of sand volume fraction on HPFRCCs made in PP was insignificant.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.1
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• pp.38-47
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• 2018

For safe operation of nuclear power plants, a loose-part monitoring system (LPMS) is used to detect and locate loose-parts within the reactor coolant system, and to estimate their mass and damage potential. There are several methods to estimate mass, such as the center frequency method based on the Hertz's impact theory, a frequency ratio method and so on, but it is known that these methods cannot provide accurate information on impact response for identifying the impact source. Thanks to increasing computing power, finite element analysis (FEA) method recently become an available option to calculate reliably impact response behavior. In this paper, a finite element analysis model to simulate the propagation behavior of the bending wave, generated by a metal ball impact, is validated by performing a series of impact tests and the corresponding finite element analyses for flat plate and shell structures. Also, a FEA-based metal sphere signal map is developed, and then blind tests are performed to verify the map. This study provides an accurate simulation method for predicting the metal impact behavior and for building a metal sphere signal map, which can be used to estimate the mass of loose-parts on site in nuclear power plants.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.76-82
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• 2005

Cable fairings of guided missiles are generally used for protection of electric cables under aerodynamic heating and mechanical loading. The stress distributions between a cable fairing and missile main body along a cable fairing are necessary for its design. In this paper, a method for bonding stress and strength analysis of a cable fairing has been investigated and its computer program developed. Tensile and three-point bending tests of generally used bonding materials were also conducted to supply basic material properties for design of cable fairings.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1195-1205
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• 2008

Composite piles have been used in ground conditions where conventional piles are unsuitable or uneconomical. They may consist of a combination of timber and concrete pile in Europe. One method of doing this was to drive a steel tube to just below water level, and a concrete pile was lowered down it and driven to the required level where corrosion was susceptible in U.K. Recently, a fiber reinforced polymer (FRP) composite pile was developed to use in many marine locations for piers and waterfront buildings in the USA(Hoy, 1995; Phair, 1997). A steel composite (SC) pile reinforced concrete spun pile with steel tube was also proposed and used for the foundation acting a high lateral earthquake load. Composite piles have been developed and researched to increase lateral resistance or to prevent corrosion in marine structures. In paper, the composite pile consisting of the steel upper portion and the concrete lower portion is proposed and are carried out several tests to confirm the capacity of the pile such as lateral load test, dynamic load tests and bending test. It is noted that the composite pile would be a economical pile being capable of increasing lateral resistance.

• Advanced Composite Materials
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• v.16 no.1
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• pp.45-61
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• 2007

This paper describes a damage accumulation mechanism in cross-ply CFRP laminates $[0_2/90_2]_{2S}$ subjected to out-of-plane loading. Drop-weight impact and static indentation tests were carried out, and induced damage was observed by ultrasonic C-scan and an optical microscope. Both tests gave essentially the same results for damage modes, sizes, and load-deformation history. First, a crack occurred in the bottom $0^{\circ}$ layer accompanying some delamination along the crack caused by bending stress. Then, transverse cracks occurred in the middle $90^{\circ}$ layer with decreasing contact force between the specimen and the indenter. Measured local strains near the impact point showed that the stress state changed from a bending dominant state to an in-plane tensile dominant state. A cohesive interface element was used to simulate the propagation of multiple delaminations and transverse cracks under static indentation. Two types of analytical models are considered, one with multiple delaminations and the other with both multiple delaminations and transverse cracks. The damage obtained for the model with only multiple delaminations was quite different from that obtained from the experiment. However, the results obtained from the model with both delaminations and transverse cracks well explain the characteristics of the damage obtained in the experiment. The existence of the transverse cracks is essential to form the characteristic impact damage.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.106-113
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• 2004

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP-N$\sub$f/ curve. However, since the fatigue data on the ΔP-N$\sub$f/ curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shea. type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP-N$\sub$f/ curves Previously obtained from the fatigue tests for each type were rearranged into the Δ$\sigma$-N$\sub$f/ relations with the maximum stresses at the nugget edge of the spot weld.