The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural ...The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural members with a uniform stress field, where stresses or strains are approximately the same under loading. A mathematical ap- proach of producing a series of random variables of the ultimate tensile strain in concrete is proposed to describe the randomness ofconcrete deformation. With reinforced concrete finite elements a real model calculation method is found for the randomness of initial cracks determined by a minimum tension strain within the uniform stress fields of concrete members. The proposed methods in our paper have as aim to improve the existing method used by FEM and other rela- tive approaches, which normally pay less attention to randomness with consequences that may possibly differ from testing or practice. The method and sample computation as indicated is meaningful and comply with testing and engi- neering practice.展开更多
A so-called 'local probabilistic Paris relation method' was presented for measuring the random thresholds of long fatigue crack propagation. A check was made to the conventional method, in which the thresholds...A so-called 'local probabilistic Paris relation method' was presented for measuring the random thresholds of long fatigue crack propagation. A check was made to the conventional method, in which the thresholds were measured statistically and directly by the test data. It was revealed that this method was not reasonable because the test data have seldom a unified level of crack growth rates. Differently,in the presented method the Paris-Erdogan equation was applied to model the local test data around the thresholds. Local probabilistic relations with both the survival probability and the confidence were established on a lognormal distribution of the stress density factors. And then, the probabilistic thresholds were derived from the probabilistic factors with a given critical level of growth rate. An analysis on the test data of LZ50 axle steel for the Chinese railway vehicles verifies that the present method is feasible and available.展开更多
Random fatigue of welded K-type tubular joints subjected to axial or out-of-plane bending load is analyzed. By considering the sizes of initial surface cracks and material constants as random variables with some proba...Random fatigue of welded K-type tubular joints subjected to axial or out-of-plane bending load is analyzed. By considering the sizes of initial surface cracks and material constants as random variables with some probabilistic distributions, incorporating the effect of the weld, five hundred random samples are generated. Statistical computational results of life of crack propagation and effect of change of crack shape are finally obtained and compared with experimental data available based on a regression analysis. Meanwhile, crack propagation behaviors are also investigated.展开更多
Two stochastic models of fatigue crack growth under constant amplitude cyclic loading are proposed and studied by using the stochastic averaging method and total probability theorem to account for high frequency compo...Two stochastic models of fatigue crack growth under constant amplitude cyclic loading are proposed and studied by using the stochastic averaging method and total probability theorem to account for high frequency component and low frequency component, respectively, of the irregular nature of fatigue crack growth observed in Virkler's experiment. Particular attention is paid to the prediction performance of the models under a change in the initial crack length. It is shown that the models proposed in the present paper yields better agreement with experimental data than other models available in literature.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
Reliability analysis of the inspected and repaired structure requires dealing with a large number of complex random events. Considering many kinds of random factors, a probability of these random events existing possi...Reliability analysis of the inspected and repaired structure requires dealing with a large number of complex random events. Considering many kinds of random factors, a probability of these random events existing possibly in the inspection and repair process and reliability analysis methodologies are proposed. A systematic dynamic reliability model is given for structures in service under the scheduled inspection and repair.展开更多
The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic co...The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic component parts. In order to have a more reasonable use of testing data, samples from population were stratified suggested by the stratified random sample model (SRAM). The data in each stratum corresponded to the same experiment conditions. A suitable weight was assigned to each stratified sample according to the actual working states of the pressure vessel, so that the estimation of fatigue crack growth rate equation was more accurate for practice. An empirical study shows that the SRAM estimation by using fatigue crack growth rate data from different stoves is obviously better than the estimation from simple random sample model.展开更多
A simple probabilistic model for predicting crack growth behavior under random loading is presented. In the model, the parameters c and m in the Paris-Erdogan Equation are taken as random variables, and their stochast...A simple probabilistic model for predicting crack growth behavior under random loading is presented. In the model, the parameters c and m in the Paris-Erdogan Equation are taken as random variables, and their stochastic characteristic values are obtained through fatigue crack propagation tests on an offshore structural steel under constant amplitude loading. Furthermore, by using the Monte Carlo simulation technique, the fatigue crack propagation life to reach a given crack length is predicted. The tests are conducted to verify the applicability of the theoretical prediction of the fatigue crack propagation.展开更多
To investigate the low temperature fatigue crack propagation behavior of offshore structural steel A131 under random ice loading, three ice failure modes that are commonly present in the Bohai Gulf are simulated accor...To investigate the low temperature fatigue crack propagation behavior of offshore structural steel A131 under random ice loading, three ice failure modes that are commonly present in the Bohai Gulf are simulated according to the vibration stress responses induced by real ice loading. The test data are processed by a universal software FCPUSL developed on the basis of the theory of fatigue crack propagation and statistics. The fundamental parameter controlling the fatigue crack propagation induced by random ice loading is determined to be the amplitude root mean square stress intensity factor K-arm. The test results are presented on the crack propagation diagram where the crack growth rate da/dN is described as the function of K-arm. It is evident that the ice failure modes have great influence on the fatigue crack propagation behavior of the steel in ice-induced vibration. However, some of the experimental phenomena and test results are hard to be physically explained at present. The work in this paper is an initial attempt to investigate the cause of collapse of offshore structures due to ice loading.展开更多
应用M on te-C arlo随机模拟法,分析了白噪声扰动下裂纹转子系统的非线性特性。着重研究了当随机扰动存在时,裂纹转子中刚度变化比、转速比等参数对系统分叉及混沌行为的影响。数值模拟表明,在拟周期与混沌解及其临近的分叉参数区间,随...应用M on te-C arlo随机模拟法,分析了白噪声扰动下裂纹转子系统的非线性特性。着重研究了当随机扰动存在时,裂纹转子中刚度变化比、转速比等参数对系统分叉及混沌行为的影响。数值模拟表明,在拟周期与混沌解及其临近的分叉参数区间,随机扰动对系统的响应有比较显著的影响,且随机扰动的幅值越大,其影响也越明显;而在周期解处,随机扰动对系统响应的影响比较小。展开更多
文摘The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural members with a uniform stress field, where stresses or strains are approximately the same under loading. A mathematical ap- proach of producing a series of random variables of the ultimate tensile strain in concrete is proposed to describe the randomness ofconcrete deformation. With reinforced concrete finite elements a real model calculation method is found for the randomness of initial cracks determined by a minimum tension strain within the uniform stress fields of concrete members. The proposed methods in our paper have as aim to improve the existing method used by FEM and other rela- tive approaches, which normally pay less attention to randomness with consequences that may possibly differ from testing or practice. The method and sample computation as indicated is meaningful and comply with testing and engi- neering practice.
基金Project supported by the National Natural Science Foundation of China (Nos. 50375130 and 50323003)the Special Foundation for the Authors of National Excellent Doctoral Disserta tions (No. 200234)the Outstanding Young Teachers Program of State Education Ministry (No. 2101)
文摘A so-called 'local probabilistic Paris relation method' was presented for measuring the random thresholds of long fatigue crack propagation. A check was made to the conventional method, in which the thresholds were measured statistically and directly by the test data. It was revealed that this method was not reasonable because the test data have seldom a unified level of crack growth rates. Differently,in the presented method the Paris-Erdogan equation was applied to model the local test data around the thresholds. Local probabilistic relations with both the survival probability and the confidence were established on a lognormal distribution of the stress density factors. And then, the probabilistic thresholds were derived from the probabilistic factors with a given critical level of growth rate. An analysis on the test data of LZ50 axle steel for the Chinese railway vehicles verifies that the present method is feasible and available.
文摘Random fatigue of welded K-type tubular joints subjected to axial or out-of-plane bending load is analyzed. By considering the sizes of initial surface cracks and material constants as random variables with some probabilistic distributions, incorporating the effect of the weld, five hundred random samples are generated. Statistical computational results of life of crack propagation and effect of change of crack shape are finally obtained and compared with experimental data available based on a regression analysis. Meanwhile, crack propagation behaviors are also investigated.
文摘Two stochastic models of fatigue crack growth under constant amplitude cyclic loading are proposed and studied by using the stochastic averaging method and total probability theorem to account for high frequency component and low frequency component, respectively, of the irregular nature of fatigue crack growth observed in Virkler's experiment. Particular attention is paid to the prediction performance of the models under a change in the initial crack length. It is shown that the models proposed in the present paper yields better agreement with experimental data than other models available in literature.
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.
文摘Reliability analysis of the inspected and repaired structure requires dealing with a large number of complex random events. Considering many kinds of random factors, a probability of these random events existing possibly in the inspection and repair process and reliability analysis methodologies are proposed. A systematic dynamic reliability model is given for structures in service under the scheduled inspection and repair.
文摘The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic component parts. In order to have a more reasonable use of testing data, samples from population were stratified suggested by the stratified random sample model (SRAM). The data in each stratum corresponded to the same experiment conditions. A suitable weight was assigned to each stratified sample according to the actual working states of the pressure vessel, so that the estimation of fatigue crack growth rate equation was more accurate for practice. An empirical study shows that the SRAM estimation by using fatigue crack growth rate data from different stoves is obviously better than the estimation from simple random sample model.
文摘A simple probabilistic model for predicting crack growth behavior under random loading is presented. In the model, the parameters c and m in the Paris-Erdogan Equation are taken as random variables, and their stochastic characteristic values are obtained through fatigue crack propagation tests on an offshore structural steel under constant amplitude loading. Furthermore, by using the Monte Carlo simulation technique, the fatigue crack propagation life to reach a given crack length is predicted. The tests are conducted to verify the applicability of the theoretical prediction of the fatigue crack propagation.
文摘To investigate the low temperature fatigue crack propagation behavior of offshore structural steel A131 under random ice loading, three ice failure modes that are commonly present in the Bohai Gulf are simulated according to the vibration stress responses induced by real ice loading. The test data are processed by a universal software FCPUSL developed on the basis of the theory of fatigue crack propagation and statistics. The fundamental parameter controlling the fatigue crack propagation induced by random ice loading is determined to be the amplitude root mean square stress intensity factor K-arm. The test results are presented on the crack propagation diagram where the crack growth rate da/dN is described as the function of K-arm. It is evident that the ice failure modes have great influence on the fatigue crack propagation behavior of the steel in ice-induced vibration. However, some of the experimental phenomena and test results are hard to be physically explained at present. The work in this paper is an initial attempt to investigate the cause of collapse of offshore structures due to ice loading.
文摘应用M on te-C arlo随机模拟法,分析了白噪声扰动下裂纹转子系统的非线性特性。着重研究了当随机扰动存在时,裂纹转子中刚度变化比、转速比等参数对系统分叉及混沌行为的影响。数值模拟表明,在拟周期与混沌解及其临近的分叉参数区间,随机扰动对系统的响应有比较显著的影响,且随机扰动的幅值越大,其影响也越明显;而在周期解处,随机扰动对系统响应的影响比较小。
