The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the ...The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the traffic. In this paper, two methods are developed for predicting the fatigue lives of RC structures strengthened with carbon fiber [aminate （CFL） under random loading based on a residual life and a residual strength model. To discuss the efficiency of the model, 12 RC beams strengthened with CFL are tested under random loading by the MTS810 testing system. The predicted residual strength approximately agrees with test results.展开更多
Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval...Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval could be recognized as a constant by neglecting its randomness.Secondly,the randomness of fatigue damage induced by the distribution of rainflow cycles was analyzed.According to central limit theorem,the fatigue damage could be assumed to follow Gaussian distribution,and the statistical parameters:mean and variance,were derived from Dirlik's solution.Finally,the proposed method was used to a simulate Gaussian random loading and the measured random loading from an aircraft.Comparisons with observed results were carried out extensively.In the first example,the relative errors of the proposed method are 2.29%,3.52%and 1.16%for the mean,standard deviation and variation coefficient of fatigue damage,respectively.In the second example,these relative errors are 11.70%,173.32%and 18.20%,and the larger errors are attributable to non-stationary state of the measured loading to some extent.展开更多
This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulati...This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulation method to present random loading and o-riginal intensity for a missile tank. It can effectively predict intensity reliability for a missile tank in the environment of transport and flight.展开更多
Random loadings(RL)are prevalent in mechanical systems,yet their inherent stochasticity poses significant challenges to structural fatigue reliability assessment.In this study,a three-dimensional fatigue reliability m...Random loadings(RL)are prevalent in mechanical systems,yet their inherent stochasticity poses significant challenges to structural fatigue reliability assessment.In this study,a three-dimensional fatigue reliability model is developed under RL through amplitude modulating and Fourier transformation.The non-Gaussian RL characteristics are accurately characterized by employing power spectral density and loading kurtosis.The equivalent initial crack size distributions are evaluated through three-dimensional fatigue growth theory by joint use of the standard fatigue stress-life(S-N)data and the fatigue crack growth data of the materials.Fatigue life distributions in specimens made of different materials with different geometries and thicknesses are analyzed under RL.It is shown that fatigue life exhibits negative correlations with power spectral density,kurtosis,and initial crack size.Especially,it is found that fatigue life and kurtosis approximately follow a power–law relationship,with both mean and variance decreasing as kurtosis increases.Validations against the experimental data available in the literature show that the present model can provide an efficient prediction of the fatigue life of mechanical systems under RL with limited experiment data.展开更多
Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plasti...Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.展开更多
In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea sta...In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.展开更多
Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on a...Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.展开更多
According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the ...According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.展开更多
A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of str...A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.展开更多
Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra o...Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra of high loads encoun-tered 10 times per 1000 flights. The crack growth life is predicted with an equivalentmodel. Comparing the spectra based on 100 flights with those based on 1000 flights, theformer requires only 10 per cent data for cycles. Experiment results show that the differ-ences between two spectra are less than 10% for crack growth life. A more simply con-densed spectrum is derived, retaining groundtoair cycle during every flight and ar-ranging some constant amplitude cycles according to equivalent damage rule. The dataof this spectrum is 10 per cent less than that based on 100 flights, but the differences oftwo spectra whether the predicted or tested results for crack growth life are less than 15per cent. Accordingly, a complex random spectrum may arbitranly be changed to acondensed spectrum with equivalent damage rule, reducing calculation and test work.展开更多
In this study, systematic physical model tests were performed to investigate the wave forces on the twin-plate breakwater under irregular waves. Based on the experimental results, the effects of the relative plate wid...In this study, systematic physical model tests were performed to investigate the wave forces on the twin-plate breakwater under irregular waves. Based on the experimental results, the effects of the relative plate width B/L,wave height Hs/D and incident angle θ0 on the wave forces were analyzed and discussed. The results showed that:(1) The envelopes of the total wave pressure were generally symmetrical along the direction of plate width under the incident angles(θ0) being 0°, 15°, 30°, 45° and 60°. In particular, the envelopes of wave pressure atθ0=30° were larger than all other cases.(2) The synchronous pressure distribution of the breakwater under oblique wave action was more complicated comparing to the normal incident waves.(3) Based on data analysis, an empirical formula was obtained to estimate the total vertical force of the twin-plate breakwater.This empirical formula can be a good reference for the design basis of engineering applications under specified wave conditions.展开更多
基金supported by the National Natural Science Foundation of China(No.10672060)the Guangdong Provincial Nature Science Foundation of China(No.07006538).
文摘The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the traffic. In this paper, two methods are developed for predicting the fatigue lives of RC structures strengthened with carbon fiber [aminate （CFL） under random loading based on a residual life and a residual strength model. To discuss the efficiency of the model, 12 RC beams strengthened with CFL are tested under random loading by the MTS810 testing system. The predicted residual strength approximately agrees with test results.
文摘Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval could be recognized as a constant by neglecting its randomness.Secondly,the randomness of fatigue damage induced by the distribution of rainflow cycles was analyzed.According to central limit theorem,the fatigue damage could be assumed to follow Gaussian distribution,and the statistical parameters:mean and variance,were derived from Dirlik's solution.Finally,the proposed method was used to a simulate Gaussian random loading and the measured random loading from an aircraft.Comparisons with observed results were carried out extensively.In the first example,the relative errors of the proposed method are 2.29%,3.52%and 1.16%for the mean,standard deviation and variation coefficient of fatigue damage,respectively.In the second example,these relative errors are 11.70%,173.32%and 18.20%,and the larger errors are attributable to non-stationary state of the measured loading to some extent.
文摘This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulation method to present random loading and o-riginal intensity for a missile tank. It can effectively predict intensity reliability for a missile tank in the environment of transport and flight.
基金supported by the National and Jiangsu Province NSF(T2293691,BK20212008)of ChinaNational Key Research and Development Program of China(2019YFA0705400)+2 种基金the Research Fund of State Key Laboratory of Mechanics and Control for Aerospace Structures(MCMS-I-0422K01)the Fundamental Research Funds for the Central Universities(NC2023001,NJ2023002,NJ2022002)the Fund of Prospective Layout of Scientific Research for Nanjing University of Aeronautics and Astronautics(NUAA).
文摘Random loadings(RL)are prevalent in mechanical systems,yet their inherent stochasticity poses significant challenges to structural fatigue reliability assessment.In this study,a three-dimensional fatigue reliability model is developed under RL through amplitude modulating and Fourier transformation.The non-Gaussian RL characteristics are accurately characterized by employing power spectral density and loading kurtosis.The equivalent initial crack size distributions are evaluated through three-dimensional fatigue growth theory by joint use of the standard fatigue stress-life(S-N)data and the fatigue crack growth data of the materials.Fatigue life distributions in specimens made of different materials with different geometries and thicknesses are analyzed under RL.It is shown that fatigue life exhibits negative correlations with power spectral density,kurtosis,and initial crack size.Especially,it is found that fatigue life and kurtosis approximately follow a power–law relationship,with both mean and variance decreasing as kurtosis increases.Validations against the experimental data available in the literature show that the present model can provide an efficient prediction of the fatigue life of mechanical systems under RL with limited experiment data.
文摘Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.
文摘In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.
文摘Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.
基金This project is supported by National Natural Science Foundation of China (No.59775030).
文摘According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.
文摘A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.
文摘Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra of high loads encoun-tered 10 times per 1000 flights. The crack growth life is predicted with an equivalentmodel. Comparing the spectra based on 100 flights with those based on 1000 flights, theformer requires only 10 per cent data for cycles. Experiment results show that the differ-ences between two spectra are less than 10% for crack growth life. A more simply con-densed spectrum is derived, retaining groundtoair cycle during every flight and ar-ranging some constant amplitude cycles according to equivalent damage rule. The dataof this spectrum is 10 per cent less than that based on 100 flights, but the differences oftwo spectra whether the predicted or tested results for crack growth life are less than 15per cent. Accordingly, a complex random spectrum may arbitranly be changed to acondensed spectrum with equivalent damage rule, reducing calculation and test work.
基金The National Natural Science Foundation of China under contract Nos 51079025 and 11272079the Research Funds from State Key Laboratory of Coastal and Offshore Engineering under contract No.LY1602
文摘In this study, systematic physical model tests were performed to investigate the wave forces on the twin-plate breakwater under irregular waves. Based on the experimental results, the effects of the relative plate width B/L,wave height Hs/D and incident angle θ0 on the wave forces were analyzed and discussed. The results showed that:(1) The envelopes of the total wave pressure were generally symmetrical along the direction of plate width under the incident angles(θ0) being 0°, 15°, 30°, 45° and 60°. In particular, the envelopes of wave pressure atθ0=30° were larger than all other cases.(2) The synchronous pressure distribution of the breakwater under oblique wave action was more complicated comparing to the normal incident waves.(3) Based on data analysis, an empirical formula was obtained to estimate the total vertical force of the twin-plate breakwater.This empirical formula can be a good reference for the design basis of engineering applications under specified wave conditions.
