• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.15-22
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• 1998

The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.533-537
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• 1995

The stress in Permalloy thin films fabricated by rf magnetron sputtering on the Si (100) substrates has been investigated with various deposition parameters such as the film thickness, argon pressure, and rf power. The internal stress changes from compressive to tensile with higher input power and argon pressure. The cause of stress variations with these deposition parameters is discussed in terms of thermal and/or intrinsic stress changes. Low coercive force is obtained from Permalloy thin films at a condition of low compressive stress.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.133-141
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• 2006

The Low cycle fatigue behavior of 11.7Cr-1.1Mo heat-resisting steel has been investigated under strain-controlled conditions with mean stresses at room temperature and $300^{\circ}C$. For the tensile mean stress test, the initial high tensile mean stress generally relaxed to zero at room temperature, however, at $300^{\circ}C$ initial tensile mean stress relaxed to compressive mean stress. Low cycle fatigue lives under mean stress conditions are usually correlated using modifications to the strain-life approach. Based on the fatigue test results from different stain ratio of -1, 0, 0.5, and 0.75 at room temperature and $300^{\circ}C$, the fatigue damage of the steel was represented by using cyclic strain energy density. Total strain energy density considering mean stress indicated well better than not considering mean stress at $300^{\circ}C$. Predicted fatigue life using Smith-Watson-Topper's parameter correlated fairly well with the experimental life at $300^{\circ}C$.

• Advances in concrete construction
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• v.14 no.5
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• pp.355-368
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• 2022

This paper investigates the impact of length and volume fractions (VFs) of banana fibres (BFs) on the mechanical and physical properties of concrete. The mechanical properties were compressive strength, splitting tensile, flexural strength, and bond stress, while the physical properties were unit weight and absorption. The slump test was used to determine workability. The concrete's behaviour with BFs was studied using scanning electron microscopy. Experimental work of concrete mixtures with BFs of various lengths (12 mm, 25 mm, and 35 mm) and VFs (0%, 0.5%, 1.0%, and 1.5%) were carried out. The samples did not indicate any agglomeration of fibres or heterogeneity during mixing. The addition of BFs to concrete with VFs of up to 1.50% for all fibre lengths have a significant impact on mechanical properties, also the longer fibres performed better than shorter ones at all volume fractions of BFs. The mix10, which contain BFs with VFs 1.5% and length 35 mm, demonstrated the highest mechanical properties. The compressive strength, splitting tensile, flexural strength, and bond stress of the mix10 were 37.71 MPa, 4.27 Mpa, 6.12 MPa, and 6.75 MPa, an increase of 7.37%, 20.96%, 24.13%, and 11.2% over the reference concrete, which was 35.12 MPa, 3.53 MPa, 4.93 MPa, and 6.07 MP, respectively. The absorption is increased for all lengths by increasing the VFs up to 1.5%. Longer fibres have lower absorption, while shorter fibres have higher absorption. The mix8 had the highest absorption of 4.52%, compared to 3.12% for the control mix. Furthermore, the microstructure of concrete was improved through improved bonding between the fibres and the matrix, which resulted in improved mechanical properties of the composite.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.403-407
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• 2010

Gecko adhesion system consists of beam-shaped seta and spatula which has the role of adhesive pad. In this paper, adhesion mechanism of gecko adhesion system is performed by using adhesive beam contact model. this model has a feature of non-uniform stress profile on the contact surface and adhesion/detachment mechanism is determined by the tensile stress of the contact region. a spatula tip pad has the role of reduction of maximum tensile stress and adhesive force is increased due to this effect. As for a reverse loading case, maximum compressive stress drops by the spatula effect and this cause unsymmetric loading conditions between adhesion and detachment forces. In this study, finite element method is used for the analysis of adhesive beam contact model and the results for spatula effect are presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.405-413
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• 1997

In the present paper, it is attempted to reconfirm the "Intelligent" material properties using both the sintered TiNi/Al(1100) matrix composite made by powder metallurgy method and the squeeze-casted TiNi/Al6061 specimens. A metal matrix composite is, its fault has been considered to deteriorate a strength of composite by heating residual stress of the matrix. Therefore, it is necessary to remove a tensile residual stress, to produce the strength of a composite better. On the contrary, if compressive residual stress happens in matrix of composite in place of tensile residual stress, it will make the strength of composite better. So that, this paper introduce the development of a high strength of composite, by using compressive residual stress well, on the study. By using these specimens, shape memory strengthening effects in tensile strength and fatigue crack propagation above inverse transformation temperature of TiNi fiber were investigated. We occurs the prestrain and volume fraction for to discuss the effects of a composite strength. Moreover, by SEM observation, the effect of the residual stress at the interface between Al matrix and TiNi fiber and some brittle precipitation layers such as inter metallic compounds on fracture mechanisms was discussed metallurgically.urgically.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.1
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• pp.101-124
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• 1996

In this study, we designed the finite element models of mandible with varying their connecting types between the prosthesis on implant fixture and 2nd premolar, which were free-standing case(Mf), precision attachment case(Mp), semiprecision attachment case(Ms) and telescopic case(Mt). The basic model of the designed finite element models, which contained a canine and the 1st & 2nd premolar, was implanted in the edentulous site of the 1st & 2nd molar by two implant fixtures. We applied the load in all models by two ways. A vertical load of 200N was applied at each central fossa of 2nd premolar and 1st implant. A tilting load of 20N with inclination of $45^{\circ}$ to lingual side was applied to buccal cusp tips of each 2nd premolar and 1st implant. And then we analyzed three-dimensional finite element models, making a comparative study of principal stress and displacement in four cases respectively. Three-dimensional finite element analysis was performed for the stress distribution and the displacement using commercial software(IDEAS program) for SUN-SPARC workstation. The results were as follows : 1 Under vertical load or tilting load, maximum displacement appeared at the 2nd premolar. Semiprecision case showed the largest maximum displacement, and maximum displacement reduced in the order of precision attachment, free-standing and telescopic case. 2. Under vertical load. the pattern of displacement of the 1st implant appeared mesio-inclined because of the 2nd implant splinted together. But displacement pattern of the 2nd premolar varied according to their connection type with prosthesis. The 2nd premolar showed a little mesio-inclined vertical displacement in case of free-standing and disto-inclined vertical displacement due to attachment in case of precision and semiprecision attachment. In telescopic case, the largest mesio-inclined vertical displacement has been shown, so, the 1st premolar leaned mesial side. 3. Under tilting load, The pattern of displacement was similar in all four cases which appeared displaced to lingual side. But, the maximum displacement of 2nd premolar appeared larger than that of the first implant. Therefore, there was large discrepancy in displacement between natural tooth and implant during tilting load. 4. Under vertical load, the maximum compressive stress appeared at the 1st implant's neck. Semiprecision attachment case showed the largest maximum compressive stress, and the maximum compressive stress reduced in the order of precision attachment, telescopic and free-standing case. 5 Under vertical load, the maximum tensile stress appeared at the 2nd implant's distal neck. Semiprecision attachment case showed the largest maximum tensile stress, and the maximum tensile stress reduced in the order of precision attachment, telescopic and free-standing case. 6. Under vertical load or tilting load, principal stress appeared little between natural tooth & implant in free-standing case, but large principal stress was distributed at upper crown and distal contact site of the 2nd premolar in telescopic case. Principal stress appeared large at keyway & around keyway of distal contact site of the 2nd premolar in precision and semiprecision attachment case, appearing more broad and homogeneous in precision attachment case than in semiprecision attachment case.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.2
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• pp.145-156
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• 2021

Ultrasonic Nanocrystal Surface Modification (UNSM) is a peening technology that generates elastic-plastic deformation on the material surface to which a static load of a air compressor and a dynamic load of ultrasonic vibration energy are applied by striking the material surface with a strike pin. In the UNSM-treated material, the structure of the surface layer is modified into a nano-crystal structure and compressive residual stress occurs. When UNSM is applied to welds in a reactor coolant system where PWSCC can occur, it has the effect of relieving tensile residual stress in the weld and thus suppressing crack initiation and propagation. In order to quantitatively evaluate the compressive residual stress generated by UNSM, many finite element studies have been conducted. In existing studies, single-path UNSM or UNSM in a limited area has been simulated due to excessive computing time and analysis convergence problems. However, it is difficult to accurately calculate the compressive residual stress generated by the actual UNSM under these limited conditions. Therefore, in this study, a minimum finite element peening analysis area that can reliably calculate the compressive residual stress is proposed. To confirm the validity of the proposed analysis area, the compressive residual stress obtained from the experiment are compared with finite element analysis results.

• Advances in concrete construction
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• v.11 no.3
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• pp.193-206
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• 2021

Extensive research has been conducted on the basic mechanical property and structural applications of engineered cementitious composites (ECC). Despite the high tensile ductility and high toughness of ECC, transverse steel reinforcement is still necessary to confine ECC for high performance. However, limited research has examined performance of ECC confined with practical amount of transverse reinforcement. This paper presents the results of axial compression tests on 14 square ECC columns and 4 conventional concrete columns (used as control specimens) with transverse reinforcement. The test variables were spacing, configuration (square ties or square and diamond shape ties), and yield strength of stirrups. The test showed that ECC columns confined with steel stirrup had good compressive ductility, and the stirrup spacing had the greatest effect on the compressive performance. The self-confinement effect of ECC results in a more uniform but slower expansion of the whole column compared with CC ones. The test results are then compared against the predictions from a number of existing models for conventional confined concrete. It is indicated that these models fail to predict the axial strains at peak axial stress and the trend of the stress-strain curve of steel stirrups-confined ECC with sufficient accuracy. Several new equations are then proposed for the compressive properties of steel-confined ECC based on test results and potential approaches for future studies are proposed.

• Journal of the Korean Ceramic Society
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• v.43 no.7 s.290
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• pp.415-420
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• 2006

The residual stresses in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloy samples using a Finite Element Method (FEM). It was found that the stress distribution of the interface boundary was dependent upon mainly the geometrical shape or its aspect ratio and the thickness of TGO layer, which was formed by growth and swelling behavior of oxide layer. Maximum compressive residual stress in the TBC/TGO interface is higher than that of the TGO/bond coat interface, and the tensile stress had nothing to do with change of an aspect ratio. The compressive residual stresses in the TBC/TGO and TGO/bond coat interface region increased gradually with the TGO growth.