• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.307-313
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• 2009

In this study, in order to research the repair-strengthening methods, when fatigue crack occurs in the coped stringers of a steel railway bridge, we manufacture the full size of crossbeam-stringer and floor system model. Also the experimental test is performed on the coped stringers applying the repair-strengthening methods using the stop hole, combination plate, connection plate, bracket, and so on. The results indicate that, the most effective method is to set up connection plate and bracket in the top flange and bottom flange of the stringers, while we can consider the method of punching stop holes in the end of the crack as a subsidiary method. It is necessary to set up the combination plate when the length of crack is quite long.

• Journal of the Korean Institute of Gas
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• v.17 no.1
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• pp.19-25
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• 2013

The joining methods of steel structures of gas facilities, bridges, ships etc. by welding are composed mostly of T-type or cruciform fillet welding and full penetration or partial penetration according to the uses and the shape of the structures. In this study, it was examined the characteristics of fatigue crack according to penetration depth in relation to material thickness in the cruciform fillet welded joints. From the results, it was investigated the safe design stresses within the range of infinite life. When the LOP length is long the range of infinite life is small with root failure and when the LOP length is short the range of infinite life is large with teo failure. For the specimen of material thickness, 20mm welded by 3 pass compared with 10mm, 15mm welded by 2 pass, the fatigue strength and the range of infinite life was more improved by increasing of notch toughness from formation of micro-ferrite acicular structure.

• Composites Research
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• v.16 no.3
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• pp.9-17
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• 2003

In order to simulate the crack connection between cords and the interply crack growth in the belt-layer of real tire, 2 ply rubber/cord laminate specimens with exposed edges were tested in 4~11mm displacement control. Measurement of the crack connection is evaluated when crack reaches the half of the length between 45$^{\circ}$ aligned cords, and the amount of the crack growth is measured by the steel probe method. 2 dimensional analytic modeling was performed to simulate the crack connection between cords at the exposed edges. Also, the theoretical life of the specimens was calculated from the crack connection life between cords(critical value) and from the critical value to the final failure by the use of Tearing energy(T); the strain energy release per unit area of one fracture surface of a crack. Then, theoretical life was compared with those of experiments. The life prediction up to the critical value has about 20% error compared to experimental life, and up to the final failure about 65% error. Therefore, total theoretical life has about 45% error compared to the experimental life, which is conceivable in the case of rubber.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.1-8
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• 2015

In this paper, computational evaluation method for fatigue crack growth rate(FCGR) based on material viscoplastic-damage model is proposed. Viscoplastic-damage model expressing material constitutive behavior of 7% nickel steel is introduced and is implemented into commercial finite element analysis(FEA) code, ABAQUS, as a user defined material subroutine(UMAT) for application in the FEA environments. Verification of developed UMAT and material parameters of material model are carried out by uniaxial tensile test simulations of 7% nickel steel. Moreover, jump-in-cycles procedure and rearrangement of critical damage are employed and also implemented to the ABAQUS UMAT for fatigue damage analysis. Typical FCGR test results such as relationship between crack length and number of cycles and relationship between da/dN and ${\Delta}K$ could be obtained from FCGR test simulation using developed UMAT and these results are compared with experimental results in order to verify of proposed computational method.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.5
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• pp.512-521
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• 1997

This paper deals with an evaluation of the residual stress due to shot peening induced in a car¬burized gear tooth and its application to the fatigue crack propagation problem. The residual stress is estimated based on the assumption that the main cause of residual stress is the volume difference between the case and core due to martensitic transformation in cooling, and the influ¬ence of both the reduction of retained austenite and the strain in the surface layer induced by shot peening are considered. The reliability of the method is examined by comparison with stresses measured by the X-ray diffraction method. The stresses intensity factors are computed by the influence function method and the reduction of the factor due to the residual stress is demonstrat¬ed and discussed based on the fracture mechanics.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.146-152
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• 1996

Polypropylene fiber reinforced mortar and concrete as civil material or architectural material have been used in America and British etc, and have been researched. Polypropylene fibers have many advantages in many points ; in economical costs, chemical stability and durability. It has been reported that polypropylene fiber can control restrained tensile stresses and cracks and increase toughness, resistance to impact, corrosion, fatigue and durability. This study has been performed to obtain the properties of polypropylene fiber reinforced concrete such as compressive strength, flexural strength, toughness, slump, drying shrinkage crack and drying shrinkage characteristics. The test variables are fiber contents, fiber length, fiber types, and so on. From the results of this study, we can expect the effects of the admixtures of polypropylene fiber about strength and drying shrinkage properties in concrete and mortar.

• Advances in Computational Design
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• v.4 no.3
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• pp.295-305
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• 2019

The sealing cement of total hip arthroplasty is the most widely used binder in orthopedic surgery for anchoring implants to their recipient bones. Nevertheless, this latter remains a fragile material with weak mechanical properties. Inside this material cracks initiate from cavities. These cracks propagate under the effect of fatigue and lead to the failure of this binder and consequently the loosening of the prosthesis. In this context, this work consists to predict the position of cracks initiation and their propagations path using the Extended Finite Element Method (XFEM). The results show that cracks can only be initiated from a sharp edges of an ellipsoidal cavity which the ratio of the minor axis over the major axis is equal to 0.1. A maximum crack length of 19 ?m found for a cavity situated in the proximal zone position under a static loading. All cracks propagate in same(almost) way regardless of the cavity(site of initiation) position and its inclination in the proximal zone.

• Structural Engineering and Mechanics
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• v.20 no.5
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• pp.589-608
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• 2005

There is a growing need for the development and implementation of new methods for the rapid and cost-effective rehabilitation of deteriorating steel structural components to offset the drawbacks related to welding and/or bolting in the field. Carbon fiber reinforced polymer (CFRP) composites provide a potential alternative as externally bonded patches for strengthening and repair of metallic structural members for building and bridge systems. This paper describes results of an investigation of tensile and fatigue response of steel/CFRP joints simulating scenarios of strengthening and crack-patching. It is shown that appropriately designed schemes, even when fabricated with levels of inaccuracy as could be expected in the field, can provide significant strain relief and load transfer capability. A simplified elasto-plastic closed form solution for stress analysis is presented, and validated experimentally. It is shown that the bond development length remains constant in the linear range, whereas it increases as the adhesive is deformed plastically. Fatigue resistance is shown to be at least comparable with the requirements for welded cover plates without attendant decreases in stiffness and strength.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.333-340
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• 2004

The use of the othotropic steel deck is steadily increased due to the advance of the technology in the steel bridges which recently have been longer. But the othotropic steel deck bridge is the structure that is very fragile to the fatigue, especially, the fatigue crack at the cross of the longitudinal rib and transversal rib is one of the biggest problems that othotropic steel deck bridges have. The causes of these fatigue cracks come from the secondary stress on out-plane behavior of transversal rib. In this study, we conducted the experiment to find the optimal details to improve fatigue strength on intersection between longitudinal rib and transversal rib in the othotropic steel deck bridge through numerical analysis using the experiment of the fatigue in the 3-dimensional real structure and program LUSAS. As a result of study, it is showed that the details of the korean standard section attached with a curved bulkhead plate is the most profitable. And, it is indicated that the stress which is generated when the reform improved section by parametic study can be reduced by about 50% at most or more. Along with the reduced stress and the longer interval between transversal ribs(G=400), the decreased steel amount by 4% and the shortened welding length by 34% make it possible to produce the othotropic steel deck bridge which is strong against fatigue.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.234-241
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• 1999

Rails have residual stresses produced during manufacturing processes. The residual stresses play all important role on brittle fracture, fatigue strength and derailment by producing cracks in the web of rail. The web saw-cut test is a technique developed to measure the bulk longitudinal residual stress level. It is a simple mettled to estimate a stress intensity factor, $_{4}$ for a web crack by using the radii of curvature of the upper and lower portions of a cut rail. But according to this method, $_{4}$ varies along the rail length because the curvatures along tile rail length vary In this paper, tile residual stress was estimated by Finite Element Method and tile web saw-cut method. In addition tile variation of the residual stress with time was investigated.