• International Journal of Naval Architecture and Ocean Engineering
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• 제8권4호
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• pp.360-374
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• 2016

The present paper studies the ultimate torsional strength of stiffened box girders with large deck opening due to the influence of cracks. Three types of hull girders with different spans are provided for comparison. Potential parameters which may have effects on the torsional strength including the mesh refinement, initial deflection, material strain hardening, geometric properties of crack and stiffener are discussed. Two new concepts that play an significant role in the ultimate strength research of damaged box girders are introduced, one of which is the effective residual section (ERS), the other is the initial damage of the failure zone (IDFZ) for intact structures. New simple formulas for predicting the residual ultimate torsional strength of cracked stiffened box girders are derived on the basis of the two new concepts.

• 한국표면공학회지
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• 제37권5호
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• pp.273-278
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• 2004

The requirements of getting spring steel with higher fatigue strength have been increased to achieve the weight reduction of a vehicle. As the possible increment in fatigue strength by using the conventional shot peening treatment is found to be limited, it is necessary to modify the shot peening treatment. In this study, to investigate the effects of warm shot peening on increasing fatigue strength, tests are conducted on spring steel SAE9524. By the results of rotating bending fatigue tests, the fatigue strength increases up to 23.8% in warm shot peening specimens at $200^{\circ}C$ compared with conventional shot peening. The major reason why the warm shot peening is effective to the improvement of fatigue strength is the increment of the compressive residual stress, which can be effectively formed by shot peening under the condition of warm temperature than room temperature.

• 산업기술연구
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• 제21권B호
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• pp.213-222
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• 2001

In the study, the fatigue strength improvement and mechanism have been estimated by the Spot-Heating treatment on welded bead toes. For this, web-gusset specimens were made without residual stresses and the others with residual stresses imposed by Spot-Heating. The 4-point bending tests were performed in order to estimate the effect of spot-heating on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue test, fatigue strength of As-Welded specimen for non load-carrying fillet welded joints subjected to pure bending has satisfied the grade of fatigue prescribed in specifications of korea, AASHTO and JSSC. As compare with As-Welded specimen and Spot-Heating specimen have increased about 20% for the fatigue strength at $7.7{\times}10^6$ cycles. The Spot-Heating by reformation of the residual stress on welded bead toes has greatly affected the fatigue crack propagation life, but has slightly affected the fatigue crack initiation life.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.256-261
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• 2007

The purpose of this study is to investigate the effect of shot peening on the fatigue strength and fatigue life of two kinds of aluminum alloys. The fatigue strength behavior of aluminum alloys were estimated by the stress ratio and shot velocities. The fatigue life and strength increased with increasing the test shot velocity. However, at the shot velocity range between 50m/s and 70m/s, the compressive residual stress phenomena were observed in test conditions of different shot velocity. The optimal shot velocity is acquired by considering the peak values of the compressive residual stress, dislocations, brittle striation, slip, and fisheye on the fracture surface of test specimen. It was observed from the SEM observation on the deformed specimen that the brittle striation, fisheye were showed in the intergranular fracture structure boundaries at the this velocities. Therefore, fatigue strength and fatigue life would be considered that shot velocity has close relationship with the compressive residual stress.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.941-944
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• 2008

본 연구는 화재피해를 입은 고강도 철근 콘크리트 구조부재의 폭렬발생시 구조성능을 파악하기 위한 연구로 압축강도 55MPa의 휨 부재와 압축부재를 화재피해를 입은 시간을 주요변수로 30분, 60분 및 90분간 화재 실험을 실시하였다. 휨 부재의 경우 피복두께에 따라 폭렬의 정도와 구조성능의 감소에서 차이를 보였으며, 피복 두께가 두꺼운 경우에 폭렬 면적 및 잔존강도의 감소폭이 크게 나타났다. 압축부재의 경우 폭렬로 인해 손실된 면적의 양은 화재피해를 입은 시간에 영향을 크게 받지 않았으나, 잔존강도의 경우 콘크리트가 고온에 오래 노출될수록 큰 감소폭을 보였고, 부재강성의 감소폭은 더욱 크게 나타났다. 따라서 고강도 콘크리트구조물에 화재가 발생하였을 경우 폭렬의 양상과 화재피해를 입은 시간에 따라 구조물의 잔존강도를 예측 할 수 있으며, 이를 이용하여 구조물의 재사용 여부의 판단 및 보수 보강에 필요한 자료를 제시할 수 있다.

• 상하수도학회지
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• 제20권6호
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• pp.867-874
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• 2006

The goal of this study is to assess cast iron pipes (CIPs) and present a residual tensile strength prediction model using pit characteristics and fracture toughness. The results is the followings. First, average pit depths of collected CIPs were in the range from 0.63 to 6.49 mm, loss of tensile strength compared with net metallic tensile strength were from -7.06 to 67.91 percent. Second, fracture toughness for NS-CR-1, NS-CR-2, and NS(2)-CR-1 were in the range from 62.85 to $89.39kgf/mm^2{\sqrt{mm}}$, and average of those samples was $73.69kgf/mm^2{\sqrt{mm}}$ on CIPs. Third, the models developed in this study by using pit characteristics and fracture toughness showed a little good correlation for measured residual tensile strength, and the results will be expected to help for water utilities to manage CIPs in the aspect of rehabilitation and assessment of structural safety on CIPs.

• Computers and Concrete
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• 제23권4호
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• pp.281-294
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• 2019

The post-fire behavior of structural elements and the cooling process has always been one of the main concerns of the structural engineers. The structures can be cooled at different rates, where they affect the structure's behavior. In the present study, a numerical model has been developed using the Abaqus program to investigate the effect of cooling rate on the post-fire behavior of the CFST column. To verify the model, results of an experimental study performed on CFST columns within a full heating and cooling cycle have been used. In this model, coMParison of the residual strength has been employed in order to examine the behavior of CFST column under different cooling rates. Furthermore, a parametric study was carried out on the strength of steel and concrete, the height of the specimens, the axial load ratio and the cross-sectional shape of the specimen through the proposed model. It was observed that the cooling rate affects the behavior of the column after the fire, and thus the higher the specimen's temperature is, the more effect it has on the behavior. It was also noticed that water cooling had slightly more residual strength than natural cooling. Furthermore, it was recognized from the parametric study, that by increasing the strength of steel and concrete and the load ratio, as well as modifying the cross-sectional shape from circular to square, residual strength of column at the cooling phase was less than that of the heating phase. In addition, with reducing column height, no change was witnessed in the column behavior after the cooling phase.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.145-146
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• 2023

In this study, the effect of hybrid fiber reinforcement on the residual strength and impact resistance of high-strength cementitious composites exposed to high temperatures was investigated. A cementitious composites was manufactured in which 0.15 vol% of polypropylene fiber (PP) and 1.0 vol% of smooth steel fiber (SSF) were double-mixed, and a residual strength test was conducted while thermal stress was applied by heating test, and then a high-velocity impact test was performed. In the case of general cementitious composites, the rear surface is damaged due to explosion and low tensile strength during high temperature or impact, while hybrid fiber reinforced cementitious composites can repeatedly absorb and distribute stress until multiple fibers are damaged to suppress the propagation of impact and resistance to explosion. Therefore, this study analyzed the residual strength of cementitious composites exposed to high temperatures depending on whether hybrid fibers were mixed or not, and collected research data on fracture behavior through high-speed impact tests to evaluate impact resistance and mechanical properties.

• 대한기계학회논문집A
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• 제21권3호
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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.

• 대한기계학회논문집
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• 제17권11호
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• pp.2752-2761
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• 1993

The purpose of this study is to confirm the decreasing problems of residual bending strength, and the fracture machanism experimentally when CFRP composite laminates are subjected to Foreign Object Damage. Composite laminates used for this experiment are CFRP orthotropy laminated plates, which have two-interfaces [O/sub 6//sup o//90/sub 6//sup o/]sub sym/ and four-interfaces [O/sub 3//sup o//90/sub 6//sup o//O/sub 3//sup o]/sub sym/. When the specimen is subjected to transverse impact by a steel ball, the delamination area generated by impact damage is observed by using SAM(Scanning Acoustic Microscope). also, Thefracture surfaces obtained by three-point bending test were observed by using SEM (Scanning Electron Microscope). Then, fracture mechanism was investigated based on the observed delamination area and fracture surface. The results were summarized as follows; (1) It is found that for the specimen with more interface, the critical delamination energy is increased while delamination-development energy is decreased. (2) Residual bending strength of specimen A is greater than that of Specimen B within the impact range of impact energy 1. 65J (impacted-side compression) and 1. 45J (impacted-side tension). On the other hand, when the impact energy is beyond the above ranges, residual bending strength of specimen A is smaller than that of specimen B. (3) In specimen A and B, residual strength of CFRP plates subjected to impact damage is lower in the impacted-side compression than in the impacted-side tension. (4) In the case of impacted-side compression, fracture is propagated from the transverse crack generat-ed near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-B delamination in the case of impacted-side tension.