• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.1 s.244
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• pp.8-17
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• 2006

When subjected to severe shear deformation by ECAP, microstructure of Al2024 becomes extremely refined. To measure the strength of that, small punch(SP) testing method was adopted as a substitute for the conventional uniaxial tensile testing because the size of material processed by ECAP were limited to ${\psi}12\;mm$ in transverse direction. SP tests were performed with specimens in longitudinal and transverse directions of Al2024 ECAP metal. For comparing the strength values with those assessed by SP tests, uniaxial tensile tests were also conducted with specimens in longitudinal direction. Failure surfaces of the tested SP specimens showed that failure mode was shear deformation and Al 2024 ECAP metal has an anisotropy in strength. Thus, conventional equations proposed for assessing the strength characteristics were improper to assess those of Al2024 ECAP metal. In this paper a way of assessing the strength of Al 2024 ECAP metal was proposed and was proven to be effective.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.9-14
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• 2014

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and $CO_2$ and needs less energy consumption. In this study, static and fatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was found to be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatigue tests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region, but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied load amplitude $P_{amp}$ and lifetime of cycle N for the tensile-shear, $P_{amp}=3395.5{\times}N^{-0.078}$. Using the stress-strain curve of the Al-5052 from tensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relation between von-Mises equivalent stress amplitude and number of cycles was found to be ${\sigma}_{eq}=514.7{\times}N^{-0.033}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.752-760
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• 2000

Mechanical press joining has been used in sheet metal joining processes because of its simple process and possibility of joining dissimilar metals, such as steel and aluminum. The strength of mechanical press joining varies with joining conditions. The optimum joining conditions considering tensile-shear and peel-tension strength have to be established to assure the reliability in the joining strength. Therefore, optimization of joining conditions has been investigated for improving joining strength of sheet metal. It is possible to obtain optimum strength from improvement on the joining strength of peel-tension mechanical press joint under multiaxial stress states.

• Journal of the Korean Society of Industry Convergence
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• v.11 no.1
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• pp.35-40
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• 2008

Various characters of the concrete are greatly improved as the effect of the steel fiber. As the improvement effect of the steel fiber, the increment in flexural strength, shear strength, toughness, and impact strength are remarkable, and tenacious concrete is obtained. This paper presents model which can predict mechanical behavior of the structure according to aspect ratio and volume fraction of steel fiber. Experiments on compressive strength, elastic modulus and tensile strength were performed with self-made cylindrical specimens of variable aspect ratios. This paper presents an analytical study on the behavior of a beam specimen with steel fiber reinforced concrete(SFRC). The effect of the SFRC on the crack pattern, failure mode and the flexural behavior of the structure were investigated. The analysis model based on the nonlinear layered finite element method was successfully able to find the necessary amount of steel fibers, tensile steels and beam section which can best approximate flexural strength and ductility of a given conventionally reinforced concrete beam.

• Geomechanics and Engineering
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• v.29 no.6
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• pp.627-643
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• 2022

Water-rock interactions have a significant influence on the mechanical behavior of rocks. In this study, uniaxial compression and tension tests on different water-treated sandstone samples were conducted. Acoustic emission (AE) monitoring and micro-pore structure detection were carried out. Water-rock interactions and their effects on rock mechanical behavior were discussed. The results indicate that water content significantly weakens rock mechanical strength. The sensitivity of the mechanical parameters to water treatment, from high to low, are Poisson ratio (𝜇), uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), elastic modulus (E), and peak strain (𝜀). After water treatment, AE activities and the shear crack percentage are reduced, the angles between macro fractures and loading direction are minimized, the dynamic phenomenon during loading is weakened, and the failure mode changes from a mixed tensile-shear type to a tensile one. Due to the softening, lubrication, and water wedge effects in water-rock interactions, water content increases pore size, promotes crack development, and weakens micro-pore structures. Further damage of rocks in fractured and caved zones due to the water-rock interactions leads to an extra load on the adjoining coal and rock masses, which will increase the risk of dynamic disasters.

• Structural Engineering and Mechanics
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• v.38 no.4
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• pp.385-403
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• 2011

Continuous deep girders which transmit the gravity load from the upper wall to the lower columns have frequently long end shear spans between the boundary of the upper wall and the face of the lower column. This paper presents the results of tests and analyses performed on three 1:2.5 scale specimens with long end shear spans, (the ratios of shear-span/total depth: 1.8 < a/h < 2.5): one designed by the conventional approach using the beam theory and two by the strut-and-tie approach. The conclusions are as follows: (1) the yielding strength of the continuous RC deep girders is controlled by the tensile yielding of the bottom longitudinal reinforcements, being much larger than the nominal strength predicted by using the section analysis of the girder section only or using the strut-and-tie model based on elastic-analysis stress distribution. (2) The ultimate strengths are 22% to 26% larger than the yielding strength. This additional strength derives from the strain hardening of yielded reinforcements and the shear resistance due to continuity with the adjacent span. (3) The pattern of shear force flow and failure mode in shear zone varies depending on the amount of vertical shear reinforcement. And (4) it is necessary to take into account the existence of the upper wall in the analysis and design of the deep continuous transfer girders that support the upper wall with a long end shear span.

• Computers and Concrete
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• v.22 no.1
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• pp.93-100
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• 2018

It is seldom possible that geotechnical materials like rocks and concretes found without joints, cracks, or discontinuities. Thereby, the impact of micro-cracks on the mechanical properties of them is to be considered. In the present study, the effect of micro-crack on the failure mechanism of rock specimens under uniaxial compression was investigated experimentally. For this purpose, thermal stress was used to induce micro-cracks in the specimens. Several cylindrical and disk shape specimens were drilled from granite collected from Zanjan granite mine, Iran. Some of the prepared specimens were kept in room temperature and the others were heated by a laboratory furnace to different temperature levels (200, 400, 600, 800 and 1000 degree Celsius). During the experimental tests, Acoustic Emission (AE) sensors were used to monitor specimen failure at the different loading sequences. Also, Scanning Electron Microscope (SEM) was used to distinguish the induced micro-crack by heating in the specimens. The fractographic analysis revealed that the thin sections heated to $800^{\circ}C$ and $1000^{\circ}C$ contain some induced micro-fractures, but in the thin sections heated to $200^{\circ}C$, $400^{\circ}C$ and $600^{\circ}C$ have not been observed any micro-fracture. In the next, a comprehensive experimental investigation was made to evaluate mechanical properties of heated and unheated specimens. Results of experimental tests showed that induced micro-cracks significantly influence on the failure mode of specimens. The specimens kept at room temperature failed in the splitting mode, while the failure mode of specimens heated to $800^{\circ}C$ are shearing and the specimens heated to $1000^{\circ}C$ failed in the spalling mode. On the basis of AE monitoring, it is found that with increasing of the micro-crack density, the ratio of the number of shear cracks to the number of tensile cracks increases, under loading sequences.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.53-64
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• 2017

Ultra-high performance fiber-reinforced concrete (UHPFRC) is characterized by a post-cracking residual tensile strength with a large tensile strain as well as a high compressive strength. To determine a material tensile strength of UHPFRC, three-point loading test on notched prism and direct tensile test on doubly notched plate were compared and then the design tensile strength is decided. Shear tests on nine I-shaped beams with varied types of fiber volume ratio, shear span ratio and size effect were conducted to investigate shear behavior in web. From the test results, the stress redistribution ability represented as diagonal cracked zone was quantified by inclination of principal stress in web. The test results shows that the specimens were capable of resistance to shear loading without stirrup in a range of large deformation and the strength increase with post-cracking behavior is stable. However at the ultimate state all test specimens failed as a crack localization in the damaged zone and the shear strength of specimens is affected by shear span ratio and effective depth. Strength predictions show that the existing recommendations should be modified considering shear span ratio and effective depth as design parameters.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.62-68
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• 1997

In the first part of the paper, the crack growth process in rolling contact fatigue has been investigated on ring type plate specimens, in which crack growth is two dimensional and cracks are observed on the side surface of the specimens. The results have shown that cracks are initated from the contact surface in tensile mode in the direction approximately normal to the contact surface and after some short length of growth, shear mode growth occurs from the tip of the crack and it grows until the separation of the surface layer, namely flakung type failure, occurs. In the second part, mode U fatigue crack growth tests have been made by using an apparatus designed based on the concept that the subsurface fatigue crack growth in rolling contact fatigue is the mode U fatigue crack growth under the stress state where the tensile mode growth is suppressed by compression stress. The rest results have shown that the mode U fatigue crack growth occurs if the superposed compression stress is enough to suppress the tensile mode growth.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.160-163
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• 1999

The mechanical properties and failure behaviour of carbon/phenolic composites were inverstigated by tension and compression. Carbon/phenolic composites were fabricated by infiltration of matrix into 8 harness satin woven fabric of PAN-based carbon fibers. The tensile and compressive tests were performed at 25℃ under air atmosphere and, at 400℃ and 700℃ under N₂ atmosphere. The tensile strengths of carbon/phenolic composites in with-laminar/0° warp direction were about 10 times higher than those in with-laminar/45° warp direction, which was analyzed due to a change of fracture mode from fiber pull-out by shear to tensile fracture of fibers. The fracture of carbon/phenolic composites in with-laminar/45° direction was analyzed due to delamination by buckling. Tensile and compressive strength of carbon/phenolic composites decreased to about 50% at 400℃, and to about 10% at 700℃ compared to that at room temperature. The main reason for the decrease of tensile or compressive strength with increasing temperature was analyzed due to a reduction of bond strength between fibers and matrix resulting from thermal degradation of phenolic resin.