• 대한조선학회논문집
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• 제38권4호
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• pp.75-82
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• 2001

건조 후 수행하는 수압시험 또는 화물의 적재 등과 같은 정하중은 파랑변동하중에 비하여 선체구조물에 상당히 큰 응력을 유발한다. 이러한 정하중이력에 의하여, 선체구조물의 응력집중으로 인해 피로강도가 문제되는 용접이음부에서는, 재료의 탄소성 거동에 의하여 초기용접잔류응력이 상당히 이완될 것으로 예상된다. 따라서, 이러한 용접이음부의 피로강도를 평가할 때에는 이완된 잔류응력의 영향을 고려하는 것이 보다 합리적이다. 본 연구에서는 선체구조물의 여러 가지 용접형태 중 Padding plate가 용접된 형태에 대하여 정하중이력($0.5{\sigma}Y,\;0.85{\sigma}Y$)에 의한 초기 용접잔류응력의 변화를 측정하며, 잔류응력의 변화가 피로강도에 미치는 영향을 검토한다.

• 대한치과보철학회지
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• 제30권4호
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• pp.508-525
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• 1992

The purpose of this study was to evaluate the effect of some resistance form designs on the bond strength of resin-retained prosthesis. Six sub-groups are designed in natural teeth group and resin teeth group . The framework designs in natural teeth group: 1) no groove preparation 2) groove at the center of distal surface 3) groove at the distobuccal line angle 4) 45 degree lateral load with no groove 5) 45 degree lateral load with center groove 6) splint two teeth with no groove. The framework designs in resin teeth group: 1) no groove preparation 2) groove at the center of distal surface 3) groove at the distobuccal line angle 4) metal covered the 1/2 of distal surface 5) metal covered the 1/2 of mesial surface 6) metal extended over the 114 of buccal surface. Specimens were treated electrolytic etching by Oxy-Etch and cemented with Panavia EX. Failure load was measured by Instron. Another 30 specimens were carried out fatigue tests by MTS 810 fatigue testing machine for 5000 cycles at different load level. The following results were obtained from this study. 1. The failure load was significantly increased by resistance forms. 2. The failure load was not increased by increase of total surface area bonded with teeth. The distal surface area played an important role in failure load. 3. In 45 degree lateral load group, the failure load was decreased significantly than that of in vertical load group. 4. Bond failure modes between static test and fatigue test exhibited no differences.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.183-186
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• 2003

Long shafts for power transmission should transmit torsional load with vibrational stability. Hybrid shafts made of unidirectional fiber-reinforced composite and metal have high fundamental bending natural frequency as well as high torque transmission capability. However, thermal residual stresses due to the coefficient difference of thermal expansion of the composite and metal are developed so that the high residual stresses decrease fatigue resistance of the hybrid shafts, especially at low operating temperatures. In this work, axial compressive preload was given to the shaft in order to change the residual stresses. Static and fatigue torsional tests were performed and correlated with stress analyses with respect to the preload and service temperature.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1172-1175
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• 2004

At present, CHS(Compression Hip Screw) is one of the best prosthesis for the intertrochanteric fracture. There is nothing to evaluate the CHS itself with the finite element analysis and mechanical tests. They have same ways of the experimental test of the ASTM standards. The purpose of this study is to evaluate the existing CHS and the new CHS which have transformational design factors with finite element analysis and mechanical tests. The mechanical tests are divided into compression tests and fatigue test for evaluating the failure load, strength and fatigue life. This finite element method is same as the experimental test of the ASTM standards. Under 300N of compression load at the lag screw head. There are less differences between Group (5H, basic type) and Group which has 8 screw holes. However, there are lots of big differences between Group and Group which is reinforced about thickness of the neck range. Moreover, the comparison of Group and Group shows similar tendency of the comparison of Group and Group . The Group is reinforced the neck range from Group. After the experimental tests and the finite element analysis, the most effective design factor of the compression hip screws is the reinforcement of the thickness, even though, there are lots of design factors. Moreover, to unite the lag screw with the plate and to analyze by static analysis, the result of this method can be used with experimental test or instead of it.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.389-392
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• 1999

Fatigue is a process of progressive permanent internal structural change in a material subjected to repeitive stresses. These change may be damaging and result in progressive growth of cracks and complete fracture if the stress repetitins are sufficiently large. For structural members subjected to cyclic loads, the continuous and irrecoverable damage processes are taking place. These processes are referred as the cumulative damage processes due to fatigue loading. Moreover, increased use of high strength concrete makes the fatigue problem more important because the cross-section and dead weight are reduced by using high strength concrete. The purpose of this study is to investigate the shear fatigue behavior of reinforced concrete beams according to shear reinforcement ratio and concrete compressive strength under repeated loadings. For this purpose, comprehensive static and fatigue tests of reinforced concrete beams were conducted. The major test variables for the fatigue teats are the concrete strength and the amount of shear reinforcements. The increase of deflections and steel strains according to load repetition has been plotted and analyzed to explore the damage accumulation phenomena of reinforced concrete beams. An analytical model for shear fatigue behavior has been introduced to analyze the damage accumulation under fatigue loads. The failure mode and fatigue lives have been also studied in the present study. The comparisons between analytical results and experimental data show good correlation.

• Structural Engineering and Mechanics
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• 제77권4호
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• pp.559-569
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• 2021

This study was conducted to investigate the residual bearing capacity of steel-concrete composite beams under high-cycle fatigue loading through experiments and theoretical analysis. Six test beams with stud connectors were designed and fabricated for static, complete fatigue, and partial fatigue tests. The failure modes and the degradation of several mechanical performance indicators of the composite beams under high-cycle fatigue loading were analyzed. A calculation method for the residual bearing capacity of the composite beams after certain quantities of cyclic loading cycles was established by introducing nonlinear fatigue damage models for concrete, steel beam, and shear connectors beginning with the material residual strength attenuation process. The results show that the failure mode of the composite beams under the given fatigue load appears to be primarily affected by the number of cycles. As the number of fatigue loadings increases, the failure mode transforms from mid-span concrete crushing to stud cutting. The bearing capacity of a 3.0-m span composite beam after two million fatigue cycles is degraded by 30.7% due to premature failure of the stud. The calculated values of the residual bearing capacity method of the composite beam established in this paper agree well with the test values, which indicates that the model is feasibly applicable.

• Steel and Composite Structures
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• 제34권4호
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• pp.499-509
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• 2020

The purpose of this paper is to investigate the degradation law of stiffness of steel-concrete composite beams after certain fatigue loads. First, six test beams with stud connectors were designed and fabricated for static and fatigue tests. The resultant failure modes under different fatigue loading cycles were compared. And an analysis was performed for the variations in the load-deflection curves, residual deflections and relative slips of the composite beams during fatigue loading. Then, the correlations among the stiffness degradation of each test beam, the residual deflection and relative slip growth during the fatigue test were investigated, in order to clarify the primary reasons for the stiffness degradation of the composite beams. Finally, based on the stiffness degradation function under fatigue loading, a calculation model for the residual stiffness of composite beams in response to fatigue loading cycles was established by parameter fitting. The results show that the stiffness of composite beams undergoes irreversible degradation under fatigue loading. And stiffness degradation is associated with the macrobehavior of material fatigue damage and shear connection degradation. In addition, the stiffness degradation of the composite beams exhibit S-shaped monotonic decreasing trends with fatigue cycles. The general agreement between the calculation model and experiment shows good applicability of the proposed model for specific beam size and fatigue load parameters. Moreover, the research results provide a method for establishing a stiffness degradation model for composite beams after fatigue loading.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.333-336
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• 2008

FRP는 내부식성의 특성을 가지며 가볍고 인장강도가 커서 최근에 강재긴장재 대신 콘크리트 구조물에 활용되고 있다. 그러나 파단 시까지 선형 탄성거동을 하는 FRP는 콘크리트 보에 적용시 취성적인 파괴 경향을 보여준다. 이에 연성확보를 위해 제안된 공법이 부분 비부착 공법이다. 부분비부착공법은 긴장재 일부를 비부착시켜 연성을 확보하고 나머지 부분을 부착시켜 안전하게 정착구 역할을 대신하는 공법으로 본 연구에서 획기적으로 제안한 공법이다. 제안된 공법은 선행 연구 및 실험에 의해 연성거동을 보여 주었다. 하지만 실구조물 적용 시 안전도를 확실히 하기 위해 장기간 사용 하중에 대한 피로 성능을 검증 해야만 한다. 따라서 본 연구에서는 부분 비부착된 보를 제작하여 정적실험 결과와 피로실험 후 정적 실험결과를 비교하여 피로에 대한 정적 능력을 검증하였다. 실험 결과, CFRP로 부분비부착된 프리스트레스 콘크리트 보는 피로하중에 대해 양호한 피로성능을 보여주었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.72-72
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• 2018

A dynamic fatigue characteristic of dental implant system has been evaluated with applying single axial compressive shear loading based on the ISO 14801 standard. For the advanced dynamic fatigue test, multi-directional force and motion needed to be accompanied for more information of mechanical properties as based on mastication in oral environment. In this study, we have prepared loading and motion protocol for the multi-directional fatigue test of dental implant system with single (Apical/Occlusal; AO), and additional mastication motion (Lingual/Facial; LF, Mesial/Distal; MD). As following the prepared protocol (with modification of ISO 14801), fatigue test was conducted to verify the worst case results for the development of highly stabilized dental implant system. Mechanical testing was performed using an universal testing machine (MTS Bionix 858, MN, USA) for static compression and single directional loading fatigue, while the multi-directional loading was performed with joint simulator (ADL-Force 5, MA, USA) under load control. Basically, all mechanical test was performed according to the ISO 14801:2016 standard. Static compression test was performed to identify the maximum fracture force with loading speed of 1.0 mm/min. A dynamic fatigue test was performed with 40 % value of maximum fracture force and 5 Hz loading frequency. A single directional fatigue test was performed with only apical/occlusal (AO) force application, while multi directional fatigue tests were applied $2^{\circ}$ of facial/lingual (FL) or mesial/distal (MD) movement. Fatigue failure cycles were entirely different between applying single-directional loading and multi-directional loading. As a comparison of these loading factor, the failure cycle was around 5 times lower than single-directional loading while applied multi-directional loading. Also, the displacement change with accumulated multi-directional fatigue cycles was higher than that of single directional cycles.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.706-711
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• 1998

Structural tests of the PSC Beam bridge using high strength concrete, concrete compressive strength 700kg/$\textrm{cm}^2$, are conducted for the application including durability and serviceability of the bridge. Current design safety factors with respect to the jacking force and the service design load DB-24 are applied to the design of the bridge. Concrete compressive strength 700kg/$\textrm{cm}^2$, girder depth 2.3m, girder space 3.2m, span length 20m, and slab thickness 27cm are selected for the bridge test. The Bulb-Tee section of the girders is applied instead of I section because it is well known more stable to the longer span(40m). Static load test(4 beams) with composite and non-composite section, and fatigue load test(1 beams) with composite section are conducted. Crack moment, ultimate load, deflections with load steps, and strains of the beam section for those bridges are investigated. The structural test results of the bridges showed a good performance for a safety and a serviceability.