• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.307-311
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• 2007

In the case of the railway bridges, uplift forces were occurred at the edge of the segments when vehicular loads were applied. These forces made the compressive and tensile forces occur in the fastening system. Therefore, the structural analysis was performed to investigate the safety of fastening system which was modeled as one directional spring element. In this case, the stiffness of the spring element was obtained from experimental study which was conducted by compressive load. For that reason, to perform rational and exact structural analysis, the translational stiffness of the fastening system obtained from the experimental study applied the tensile load and the rotational stiffness should be considered because it was occurred the tensile force as well as the compressive force in fastening system. In this study, an elastic and inelastic experimental study was performed for six specimens. The translational stiffness along the vertical axis of rail and the rotational stiffness along the strong axis of rail were investigated. Also structural behavior of the fastening system was analyzed.

• International Journal of Safety
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• v.1 no.1
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• pp.24-27
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• 2002

Recently the steel parts used in automobiles are required to be used under high stress more than ever before due to the need of keeping the weight down. To achieve this requirement of the high strength steel, it must be necessary to decrease inclusion contents and surface defects as like decarburization, surface roughness etc. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG408l-SUP7, SAE 9254 and DIN 50CrV4) are shaped. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotating bending fatigue test and it results from (1) decreasing the surface roughness (2) unchanging the surface hardness (3) increasing the compressive residual stress. Moreover, results also show fatigue failures originated at the inclusion near the surface, and this inclusion type is turned out to be an alumina of high hardness.

• International Journal of Ocean System Engineering
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• v.1 no.4
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• pp.230-235
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• 2011

Reinforced polyurethane foam (RPUF) is one of the important materials of Mark III type insulation systems used in liquefied natural gas (LNG) cargo containment systems. However, RPUF is the most difficult material to use with regard to its safety assessment, because there is little public and reliable data on its mechanical properties, and even some public data show relatively large differences. In this study, to investigate the structural response of the system under compressive loads such as sloshing action, time-dependent characteristics of RPUF were examined. A series of compressive load tests of the insulation system including RPUF under various temperature conditions was carried out using specimens with rectangular section. As a result, the relationship between deformation of RPUF and time is linear and dependent on the loading rate, so the concept of strain rate could be applied to the analysis of the insulation system. Also, we found that the spring constant tends to converge to a value as the loading rate increases and that the convergence level is dependent on temperature.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.71-79
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• 2001

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel(JISG4081-SUP ,SAE 9254, DIN 50CrV4, ) are made. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) Decreasing the surface roughness (2) Unchanging the surface hardness (3) Increasing the compressive residual stress But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.1
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• pp.185-192
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• 2003

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to Dow the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG4081-SUP7, SAE 9254, DON 50CrV4) are made. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) Decreasing the surface roughness (2) Unchanging the surface hardness (3) Increasing the compressive residual stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of hish hardness.

• Smart Structures and Systems
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• v.20 no.6
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• pp.739-757
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• 2017

The main goal of this study is to investigate the hysteretic behavior of polyurethane rubber springs in compression with and without precompression. The precompression is introduced to provide rigid force in the behavior, and thereby a precompressed rubber spring can be used for a restoring element. For the goal, this study prepares nine rubber springs for three suites which are all cylindrical in shape with a hole at the center. The rubber springs in each suite have different dimensions of diameter and length but have similar shape factors; thus, they are designed to have a similar compressive stiffness. Three rubber springs from the nine are tested with increasing compressive strain up to 30% strain to investigate the behavior of the rubber springs without precompression as well as the effect of the loading strain. The nine springs are compressed up to 30% strain with increasing precompressive strain from 0 to 20% at increments of 5%. The study analyzes the effective stiffness and damping ratio of the rubber springs with and without precompression, and the rigid force of the precompressed rubber springs is discussed. Finally, this study suggests a regression method to determine the minimum required precompression to eliminate residual strain after unloading.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.1
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• pp.1-7
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• 2007

In this study, the influence of compressive residual stress and corrosive condition for corrosion fatigue crack was investigated, after immersing in 3.5%NaCl, $10%HNO_3+3%HF,\;6%FeCl_3$. The immersion period was performed for 90days. The fatigue characterization of a spring steel with processed shot peening were performed by considering the several corrosion environments in the range of stress ratio of 0.05 by means of opening mode displacement. By using the methods mentioned above, the following conclusions have been drawn: The fatigue life shows more improvement in the shot peened material than that in the un peened material. And the fatigue life shows improvement in ambient than in corrosion conditions. Threshold stress intensity factor range of the shot peened materials has higher than of the un peened materials. And the threshold stress intensity factor range was decreased in corrosion environments over ambient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1099-1104
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• 2012

The study investigates the mechanical deformation of a newly developed screwless omega-wire dynamic system for stabilization of the spine. The omega-wire spring stabilization system was tested under tension, compression, and dynamic compressive fatigue loads. In addition, its bending deformation was compared to that of a spiral-wire spring system using FEA. A model whose hanger inter-center distance is 60 mm showed an ultimate tensile stress of 3981.7 N at a displacement of 3.61 mm and an ultimate compressive load of 535.6 N at a displacement of 2.16 mm. Under fatigue loading of 5 Hz with 10 N/1 N, it did not show any failure over 5 million cycles, and the displacement was restricted to 8-9 mm. In the FEA, the omega-wire spring system showed more flexible bending features than did the spiral-wire spring system.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.341-346
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• 2002

In this study, an effect that compressive residual stress formed by shot-peening the surface of spring steel(JISG SUP-9) at each shot velocity(1800, 2200, 2600, 3000rpm) on the fatigue crack growth property and threshold stress intensity factor, ${\Delta}K_{th}$, was examined. Followings are the result (1) Compressive residual stress on surface of specimen was determined at each -601 MPa(1800rpm), -638 MPa(2200rpm), -587 MPa (2600rpm), -550 MPa(3000rpm) by shot velocity of shot peening and threshold stress intensity factor, ${\Delta}K_{th}$, fatigue crack growth rate, da/dN, on fatigue crack growth is obstructed by the compressive residual stress was determined at each $5.619\;MPa\sqrt{m}$(Un-peening), $8.319\;MPa\sqrt{m}$(1800rpm), $8.797\;MPa\sqrt{m}$(2200rpm), $7.835\;MPa\sqrt{m}$(2600rpm), $7.352\;MPa\sqrt{m}$(3000rpm) (2) Existing compressive residual stress by effect of shot velocity of shot-peening on relation of crack length. a, and number of cycle, N, was 2 times progressed in case of 2200rpm than specimen of Un-peening on fatigue life. And fatigue life was 1.6 times progressed incase of 3000rpm by Over peening. (3) Fatigue life of Material on Paris' law, $da/dN=C({\Delta}K)^m$, that effect of material constant, C, and fatigue crack growth exponent, m, was influenced by effect of. C and m.

• Journal of Ocean Engineering and Technology
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• v.17 no.3 s.52
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• pp.39-45
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• 2003

Shot peening is an effective method of improving the fatigue strength of components and structures. The compressive residual stress produced by surface plastic deformation with shot peening is usually regarded as the major factor in increasing fatigue strength. In this study, the influence of shot peening on corrosion was investigated. Spring steel immersed in $3.5\%$ NaCl prior was used to evaluate the effect of shot peening on fatigue properties. The immersion test was performed on the five kinds of specimens with shot peened and unpeened. The distributions of residual stresses of shot peened spring steels were measured in an X-ray diffraction apparatus, using the two-point method. Corrosion potential, polarization curve, residual stress, etc. were investigated, based on the experimental results. From test results, the effect of shot peening on the corrosion was evaluated.