Experimental Research on Fatigue Damage of Reinforced Concrete Rectangular Beam

Fangping Liu,Jianting Zhou 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.9

In order to acquire the law of the fatigue damage development of reinforced concrete rectangular beams, the ultimate load carrying capacity of a tested beam was measured through the static loading test. The carrying capacity of the beam was then taken as the basis of loading amplitudes for the fatigue tests and the constant amplitude fatigue loading tests under different load levels were carried out for another three beams. The experimental results show that the crack in the beam is composed of the oblique crack in the bending shear section and the vertical crack in the pure bending section. The fatigue cracks are symmetrically distributed along the length direction, and the two sides are basically the same. The fatigue fracture of the test beam occurs in one main cracks located in the middle section of the span. According to the crack width, height and the number of cracks, the whole fatigue test process can be roughly divided into three stages, that is, the rapid development stage, the stable stage and the failure stage. The development of the deflection of the beam and the strain increment of the steel bar and the concrete increased significantly at the beginning of the fatigue cycle; with the increase of cycle number of fatigue load, the growth rate slowed down and entered a relatively stable stage of development; as fatigue destruction gets nearer, the speed became great again. The stiffness of the beam has a relatively large decrease at the beginning of the fatigue loading. In the middle of a longer period of time, it is basically in a linear decline phase. Before the failure, the stiffness decreases greatly. Overall, the stiffness degradation of the beam shows a more obvious monotonic decreasing “S” curve. In a word, many aspects reflect that the fatigue damage of reinforced concrete rectangular beam has obvious three stages damage law. In the early and later stages of fatigue test, the damage is developing rapidly; and in the intermediate stage of fatigue test, the damage development is relatively stable.

Fatigue Strength of Fillet Welded Joint subjected to Plate Bending

Biehn Baik,Kentaro Yamada,Toshiyuki Ishikawa 한국강구조학회 2008 International Journal of Steel Structures Vol.8 No.3

Fatigue tests have been carried out on three types of non load-carrying fillet welded joint subjected plate bending, such as single-side fillet welded joint, T-shaped fillet welded joint and cruciform fillet welded joint. Fatigue failure of each welded joint has been demonstrated. The test results show that fatigue crack forms flat semi-ellipse during crack propagation and propagates to about 80% of plate thickness before failure. The fatigue strength and life recorded under bending test have been examined and compared with the previous results obtained by tension test. The fatigue strength of the fillet welded joint under bending is higher than that of the welded joint under tension. Fatigue tests have been carried out on three types of non load-carrying fillet welded joint subjected plate bending, such as single-side fillet welded joint, T-shaped fillet welded joint and cruciform fillet welded joint. Fatigue failure of each welded joint has been demonstrated. The test results show that fatigue crack forms flat semi-ellipse during crack propagation and propagates to about 80% of plate thickness before failure. The fatigue strength and life recorded under bending test have been examined and compared with the previous results obtained by tension test. The fatigue strength of the fillet welded joint under bending is higher than that of the welded joint under tension.

Fatigue Strength Improvement and Fatigue Crack Closure by Portable Pneumatic Needle-Peening Treatment on Welded Joints

Koji Kinoshita,Yuki Banno,Yuki Ono,Shohey Yamada,Mitsuru Handa 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.3

This study experimentally investigates eff ect of fatigue strength improvement of the Portable Pneumatic Needle-Peening treatment (PPP treatment) as a needle peening on out-of-plane gusset welded joints by using plate bending fatigue tests. This study also examined eff ect of the travel speed and the number of treatment passes of the PPP treatment with regards to its fatigue strength improvement. After the fatigue tests, the observation of the fracture surface with Scanning Electron Microscope was carried out in order to clarify the crack initiation. From those test results, it may be concluded that the eff ect of fatigue strength improvement might be governed by treatment passes with suffi cient travel speed. In addition, this study carried out additional fatigue tests that focus on fatigue crack closer by using the PPP treatment. As a result of additional fatigue tests for fatigue crack closure, it might be said that the eff ect of fatigue crack closure is eff ective when the distance between fatigue cracks and treatment area is less than 2.0 mm.

A Study of the Correlation between Sinusoidal Sweep and Random Vibration Durability Tests through Specimen Tests

홍창섭,양홍준,강윤식,오재윤,오택열 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.12

In this paper, we study the correlation between a sinusoidal sweep durability test and a random vibration durability test through specimen tests. We compute random vibration durability test conditions having the same fatigue damage spectrum as a sinusoidal sweep durability test using the numerical analysis method. We use two kinds of specimens of different shape to perform durability tests. This paper proposes a normalization process that uses the average of the fatigue damage time caused only by a sinusoidal sweep durability test, and the average of the fatigue damage time caused only by a random vibration durability test. The normalization process makes it possible to remove the difference of fatigue life due to the difference of specimen shape. Thus, we determine one trend equation that can predict the test results of two kinds of specimen with high reliability. Through the trend equation, we can find the correlation between the fatigue life due to sinusoidal sweep vibration, and the fatigue life due to random vibration, which depends only on the specimen material and the excitation method.

강상판 용접연결부의 피로거동에 관한 연구

한종욱,박영석 명지대학교 대학원 1999 대학원논문집 Vol.3 No.-

Fatigue cracks are developed by weld defects, shapes, stress and a number of cycles to failure in the orthotropic steel plate deck bridges. This fatigue cracks are going to develop structural failure. The purpose of this study is to define the fatigue strength level at the welded connections of the orthotropic steel plate deck bridges by constant amplitude fatigue tests. Two kinds of specimens for fatigue test were suggested ; one has scallop in the trough to crossbeam connections the other doesn't. Fatigue tests were performed by applying the repeated bending moment at the trough to crossbeam connections. Static load test is performed and the stress range of the welded connection was checked. Also, ??e results of the test was compared with the finite element analysis results using structural ?? analysis program 'ANSYS 5.3'. Constant amplitude fatigue test is being performed by MTS(50ton) ?? The results show that the S-N curve for fatigue tests at the through to crossbeam connections in the orthotropic steel plate decks are very close to detail category D of AASHTO design specification.

Empirical test of an explanatory theory of postpartum fatigue in Korea

Song, Ju‐,Eun,Chang, Soon‐,Bok,Park, So‐,Mi,Kim, Sue,Nam, Chung‐,Mo Blackwell Publishing Ltd 2010 Journal of advanced nursing Vol.66 No.12

<P> <SMALL>song j.‐e., chang s.‐b., park s.‐m., kim s. & nam c.m. (2010)</SMALL> Empirical test of an explanatory theory of postpartum fatigue in Korea. <I>Journal of Advanced Nursing</I> <B>66</B>(12), 2627–2639.</P><P><B>Abstract</B></P><P><B>Aim. </B> This paper is a report of a study designed to test an explanatory theory of postpartum fatigue.</P><P><B>Background. </B> Postpartum fatigue is influenced by various factors and affects a mother’s performance. A full understanding of postpartum fatigue is very important for developing effective nursing strategies to reduce postpartum fatigue and enhance mothers’ performance.</P><P><B>Methods. </B> Healthy postpartum women were recruited from five medical centers and one midwifery office in urban area in Korea (<I>n</I> = 291) by convenience sampling. Data were collected at 4‐ to 8‐week follow‐up visits after childbirth in 2006, using a self‐report questionnaire. The proposed fatigue theory incorporated postpartum fatigue, postpartum depression, sleep quality, childcare stress, unsatisfactory feeding, social support, infant difficulty and satisfaction with <I>Sanhujori</I>, the Korean traditional postpartum care provided for 3 weeks following delivery by non‐professional caregivers. Structural equation modelling was used to test the explanatory theory of postpartum fatigue.</P><P><B>Results. </B> The modified fatigue theory showed good fit and high compatibility with the empirical data. In the final explanatory theory, postpartum depression and sleep quality directly affected postpartum fatigue, while childcare stress and the cultural phenomenon of <I>Sanhujori</I> had indirect effects on postpartum fatigue, via postpartum depression and sleep quality respectively.</P><P><B>Conclusion. </B> These findings suggest the potential role of comprehensive nursing focused on decreasing postpartum depression and improving sleep quality as a way to decrease postpartum fatigue. Also, nursing strategies for decreasing childcare stress and enhancing <I>Sanhujori</I> satisfaction may be helpful in reducing postpartum fatigue in Korean mothers.</P>

윙게이트 검사에서 무산소능력 및 피로도 산출의 타당성 검출

진영수,박준영,김태욱,김명화,김용권,이혁종,한구석 대한스포츠의학회 1998 대한스포츠의학회지 Vol.16 No.1

Wingate test is the worldwide anaerobic performance test to determine the anaerobic power and anaerobic capacity. Recently, a number of computerized Wingate test system was developed and used to accurate problems with determine fatigue index on this system. The purpose of this study, therefore, was to compare the results of computerized wingate test with isokientic power test of knee extension/flexion, and the establish whether or not a correlation exists between fatigue index in the wingate test(WFI) and endurance ratio in isokinetic high speed test(IED). Forteen health professional baseball players(Age:24.08±2.64(yr); Height:177.79±3.59(cm); Weight:77.71±8.37(kg)) were evaluated by use of Cybex 770 for isokinetic knee Ex/Fx test(IEX, IFX), and Cardio∼key training system for 30s wingate tests. The test speed of isokinetic test was 240deg/sec for 25reps, and the leg force equation was designed to produce 4.4J/kg/rev, in the Wingate test. In addition, we applied four equations to test a validity of fatigue index calculated by the Wingae test system. The test results represented that there were significant correlations between Wingate Peak Power(WPP) and isokinetic knee test(r=.787 for WPPvsIEX(p<.01); r=.676 for WPPvs.IFX(p<.05)). There was correlations between WPPvs WFI(r=5.38(p<.05)). Also, there was significant correlations between endurance ratio at isokinetic knee test(IER) vs three of four calculated fatigue index (IERvs. T1-T2: r=-.726: IERvs.FI-LI: r=-.777: IERvs.MI1-LI: r=-.646) but not with WFI. It was suggested that the computerized Wingate test are meaningful to evaluate anaerobic power and high correlation with isokinetic high speed test. However, to evaluate the anaerobic capacity and fatigue index, it is better to be calculated the fatigue index with work(J) instead of with peak point(W).

Investigation of Fatigue Characteristics of Roller-Compacted Concrete Pavement based on Full-Scale Fatigue Test and Accelerated Pavement Test

Young Kyu Kim,Jun Young Park,Seung Hwan Han,Seung Woo Lee 한국도로학회 2018 한국도로학회 학술대회 발표논문 초록집 Vol.2018 No.05

Roller-compacted concrete (RCC) has been widely used for construction of pavements [1]. The strength of RCCP can be obtained from not only hydration of binder but also the aggregate interlock resulted from roller-compaction [2]. For this reason, RCCP normally achieves higher strength compared to conventional concrete pavement with similar cement content. Even though RCCP can be provided a good structural performance, it has been difficult to verify the long-term performance though actual field construction. Therefore, this study aimed to investigate the fatigue characteristics and crack development in RCCP based on full-scale fatigue test and accelerated pavement test. In case of full-scale fatigue tests, fatigue behavior was evaluated by using 1 m × 1 m dimensional RCC slab specimens obtained from the field in order to consider the field variability. Fatigue equation derived from this study shows that the number of load repetitions which causes fatigue failure at the same stress level is slightly larger than that of PCA fatigue equation. In order to evaluate the performance of RCCP, two phases of accelerated pavement test (APT) were conducted. In phase one, the performance of RCCP at two different strengths (35.6 and 30.4 MPa) was evaluated. In phase two, the performance of RCCP with different thickness (5, 7.5 and 10 cm) was investigated. The number of load repetition of fatigue crack occurrence in each section was compared to the estimated fatigue failure determined from fatigue equation of RCCP. The crack development in each section was compared to the AASHTO crack model for JPCP. Overall, it was confirmed that RCCP has equal or better performance compared to JPCP the estimation in term of fatigue cracking. The fatigue equation from PCA and cracking model from AAHTO can be used on RCCP at certain design thickness range.

실제 차량 주행과 휠 내구 시험이 휠에 미치는 영향에 관한 연구

민윤상(Yoonsang Min),심경석(Kyungseok Sim),정성필(Sungpil Jung),김현일(Hyunil Kim) 한국자동차공학회 2017 한국자동차공학회 학술대회 및 전시회 Vol.2017 No.11

Wheels and tires are parts that are directly connected to the safety of passengers when driving vehicle. Wheels and tires are parts that are directly connected to the safety of passengers when driving. Especially, The expected life of a wheel part is generally 300,000 km, which is equal to the expected life of the vehicle. Therefore, from the development stage, the wheel is an important of impact performance and fatigue endurance performance . currently, fatigue endurance test methods for vehicle wheels include single-axis tests(Conering Fatigue Test, Radial Fatigue Test) and multi-axis test(Bi-axial Wheel Fatigue test). in Korea, only the single-axis test is applied, but the multi-axis test is used as an evaluation index of endurance performance of wheels in European and American carmaker companies because of it reflects the vehicle driving situation well In this paper, we will introduce the effect of the Wheel Fatigue tests and vehicle driving by comparing the severity of the test through the stress and relative damage calculation by each stress test.

Experimental Method for Durability Evaluation of a Chisel Mounted on a Composite Working Implement

( Jeongwoo Han ),( Sanggon Moon ),( Geunho Lee ),( Daesik Kang ) 한국농업기계학회 2017 바이오시스템공학 Vol.42 No.4

Purpose: A chisel mounted on working implement, such as agricultural machinery used in irregular farming conditions, is subjected to highly variable fatigue loading during work. To ensure the safety of the chisel on a working implement for the duration of its service life, fatigue testing must be performed with the proper fatigue test load conditions. In this study, working loads for a chisel were developed by reconstructing loads from strain gage data collected during field tests and used to conduct fatigue tests on the chisel component. Methods: FE analysis with nCode software was utilized to select the proper quantity and locations of strain gages for load measurements. A fatigue test was performed to experimentally verify the fatigue strength of the chisel and to evaluate the validity of the load history developed with the load reconstruction technique. Results: A strain history for the chisel was obtained from data collected during field tests. The data was filtered for the 14-16 km/h speed range, connected, and merged. The chisel load history was developed using the load reconstruction technique. The resulting load history was expressed as a load spectrum using the rain-flow counting method. Conclusions: A fatigue test was conducted on a chisel under a constant load condition with an equivalent load amplitude and number of cycles, as calculated by Miner’s Rule for linear damage accumulation. During the fatigue test, there were no cracks at any position. It is concluded that the fatigue test method proposed in this study can be utilized successfully as a durability evaluation method for the chisel.