• Transactions of Materials Processing
• /
• v.29 no.1
• /
• pp.20-26
• /
• 2020

In the design of the metal forming processes, various types of ductile fracture criteria are used to predict crack initiation and to fabricate metallic products without any defects. However, the quantitative measurement method for determination of crack initiation is insufficient. It is very difficult to detect crack initiation in ductile metals with excellent deformability because no significant load drop is observed due to crack generation. In this study, the applicability of acoustic emission sensors, which are commonly used in facility diagnostics, to measure crack initiation during the metal forming process was analyzed. Cylindrical notch specimens were designed using the finite element method to induce a premature crack on the surface of pre heat-treated steel (ESW90) material. In addition, specimens with various notch angles and heights were prepared and compression tests were carried out. During the compression tests, acoustic emission signal on the dies and images of the surface of the notch specimen were recorded using an optical camera in real time. The experimental results revealed that the acoustic emission sensor can be used to detect crack initiation in ductile metals due to severe plastic deformation.

• Structural Engineering and Mechanics
• /
• v.22 no.3
• /
• pp.311-330
• /
• 2006

Standard compression tests of steel fiber reinforced concrete (SFRC) cylinders are conducted to formulate compressive stress versus compressive strain relationship of SFRC. Axial pullout tests of SFRC specimens are also conducted to explore its tensile stress strain relationship. Cover concrete spalling and reinforcement buckling models developed originally for normal reinforced concrete are modified to extend their application to SFRC. Thus obtained monotonic material models of concrete and reinforcing bars in SFRC members are combined with unloading/reloading loops used in the cyclic models of concrete and reinforcing bars in normal reinforced concrete. The resulting path-dependent cyclic material models are then incorporated in a finite-element based fiber analysis program. The applicability of these models at member level is verified by simulating cyclic lateral loading tests of SFRC columns under constant axial compression. The analysis using the proposed SFRC models yield results that are much closer to the experimental results than the analytical results obtained using the normal reinforced concrete models are.

• Geomechanics and Engineering
• /
• v.8 no.1
• /
• pp.17-31
• /
• 2015

An experimental program was performed to study the effects of cement stabilization on the geotechnical characteristics of sandy soils. Stabilizing agent included lime Portland cement, and was added in percentages of 2.5, 5 and 7.5% by dry weight of the soils. An analysis of the mechanical behavior of the soil is performed from the interpretation of results from unconfined compression tests and direct shear tests. Cylindrical and cube samples were prepared at optimum moisture content and maximum dry unit weight for unconfined compression and direct shear tests, respectively. Samples were cured for 7, 14 and 28 days after which they were tested. Based on the experimental investigations, the utilization of cemented specimens increased strength parameters, reduced displacement at failure, and changed soil behavior to a noticeable brittle behavior.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2001.10a
• /
• pp.351-354
• /
• 2001

Undrained cyclic triaxial compression tests were performed on Saemangeum dredged sand to evaluate factors affecting liquefaction strength and liquefaction behaviour characteristics. The results of these tests show that cyclic liquefaction can occur not only very loose sand(Relative density is 30%) but also dense sand(Relative density is 70%). To evaluate effect of the over consolidation ratio on the liquefaction strength, a series of undrained cyclic triaxial compression test was peformed, and the result of this test showed that the liquefaction of this test showed that the liquefaction strength of Saemangeum dredged sand approximately increased to square root of over consolidation ratio in the range of O.C.R value of 1.0 to 4.0. In the anisotropically consolidated sample tests, the liquefaction strength is increased by increasing the effective consolidation ratio.

• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.11
• /
• pp.34-41
• /
• 2001

This study is to investigate the energy absorption characteristics of CFRP(Carbon-Fiber Reinforced Plastics) tubes on static and dynamic tests. Axial static compression tests have been carried out using the static testing machine(Shin-gang buckling testing machine) and dynamic compression tests have been utilized using an vertical crushing testing machine. When such tubes are subjected to crushing loads, the response is complex and depends on the interaction between the different mechanisms that could control the crushing process. The collapse characteristics and energy absorption have been examined for various tubes. Energy absorption of the tubes are increased as changes in the lay-up which may increase the modulus of tubes. The results have been varied significantly as a function of ply orientation and interlaminar number.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.9 no.6
• /
• pp.195-200
• /
• 2001

Composites have wide applications in aerospace vehicles and automobiles because of the inherent flexibility in their design for improved material properties. Composite tribes in particular, are potential candidates for their use as energy absorbing elements in crashworthiness applications due to their high specific energy absorbing capacity and the stroke efficiency. Their failure mechanism however is highly complicated and rather difficult to analyze. This includes fracture in fibres, in the matrix and in the fibre-matrix interface in tension, compression and shear. The purpose of this study is to investigate the energy absorption characteristics of CFRP(Carbon Fiber Reinforced Plastics) tubes on static and impact tests. Static compression tests have been carried out using the static testing machine and impact tests have been carried out using the vertical crushing testing machine. Interlaminar number affect the energy absorption capability of CFRP tubes. Also, theoretical and experimental have the same value.

• Journal of the Korea Safety Management & Science
• /
• v.3 no.1
• /
• pp.127-137
• /
• 2001

Because of the inherent flexibility in their design for improved material properties, composites have wide applications in aerospace vehicles and automobiles. The purpose of this study is to investigate the energy absorption characteristics of CFRf (Carbon Fiber Reinforced Plastics) tubes on static and impact tests. Static compression tests have been carried out using the static testing machine(Shin-gang buckling testing machine) and impact compression tests have been carried out using the vertical crushing testing machine. When such tubes were subjected to crushing loads, the response is complex and depends on the interaction between the different mechanisms that control the crushing process. The collapse characteristics and energy absorption were examined. Trigger and interlaminar number affect the energy absorption capability of CFRP tubes.

• Journal of the Society of Naval Architects of Korea
• /
• v.57 no.4
• /
• pp.182-190
• /
• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.33 no.5
• /
• pp.470-478
• /
• 2007

The purpose of this study was to investigate the clinical, biomechanical, and histologic changes in new distraction osteogenesis(DO) technique combined with a compression stimulation in accordance to different compression-distraction force ratio. 23 adult male rabbits underwent open-osteotomy at the mandibular body area and a external distraction device was applied. In the control group of 8 rabbits, only a 8 mm of distraction was performed by conventional DO technique. In an experimental group of 15 rabbits, a distraction followed by a compression force was performed according to the ratio of compression-distraction suggested by authors. The rate of experimental group I was set up as a 2 mm compression versus 10 mm distraction and the rate of experimental group II was set up as a 3 mm compression versus 11 mm distraction. All the rabbits were sacrificed for a gross finding, biomechanical, histomorphometric and histologic findings at the time of 55 days from the operation day. The results were as follows: 1. On the gross findings, because all rabbits had a sufficient healing time, every distracted new bone had good bone quality and we could not find any difference among all three groups. 2. In the histologic findings, rapid bone maturation(wide lamellar bone formation in the cancellous and cortical bone areas) was observed in two experimental groups compared to the control group. 3. On the bone density tests, the experimental group II showed higher bone density than the other experimental group and control group(control group-$0,2906g/cm^2$, experimental group I-$0.2961g/cm^2$, experimental group II-$0.3328g/cm^2$). 4. On the biomechanical tests, the experimental group II had significantly higher bone microhardness than the other experimental group and control group(control group-252.7 MPa, experimental group I-263.5 MPa, experimental group II-426.0 MPa). 5. On the microhardness tests, when we compared the hardness ratio of distracted bone versus normal bone, we could find experimental group II had significantly higher hardness ratio than the other experimental group and control group(control group-0.47, experimental group I-0.575, experimental group II-0.80). From this study, we could deduce that the modified distraction osteogenesis method with a compression stimulation might improve the quality of bone regeneration and shorten the consolidation period in comparison with conventional distraction osteogenesis techniques.

• Journal of Navigation and Port Research
• /
• v.33 no.2
• /
• pp.119-125
• /
• 2009

The effect of plastic board drains (PBDs)on ground improvement was checked out considering three crucial factors: ground settlement, undrained shear strength, and residual water head. First, the settlement analysis including initial settlement induced by reclamation of sand mat was conducted by back calculation analysis with measured data. Its result showed toot the PBDs used for this site worked well on improving soft ground. Secondly, the undrained shear strength was investigated by laboratory and in-situ tests including unconsolidated-undrained triaxial compression (UU) tests, unconfined compression tests, in-situ vane tests, and cone penetration tests. From the test results, they showed that the undrained shear strength of the improved ground by PBDs was significantly increased as well as the strength increasing ratio especially $10{\sim}15m$ below the ground surface on site. Thirdly, the residual water head measurement from the in situ dissipation test was found the same as the static water head, which indicated primary consolidation was completed and the effect of soil improvement with PBDs can be confirmed.