The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack grow...The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.展开更多
The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate...The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate their applicability for differentstress ratios and in the presence of residual stresses. Total fatigue life using the two-phase model consists of crack initiationphase, calculated by strain-life approach, and crack propagation phase, calculated by fracture mechanic’s approach. Calibrationof the fatigue parameters is performed for each phase by fitting numerical to the experimental results. Comparative analysisof calculated and measured fatigue lives is then conducted for different stress ratios, in both stress-relieved and as-weldedconditions. Given that calculation parameters are calibrated for the basic case, uncertainty of predictions is large, showingthat application of the method for real-life complex marine structures is challenging.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
基金China Scholarship Council(CSC)The University of Queensland for a Ph D fellowship。
文摘The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.
文摘The study aims to calibrate parameters of two-phase fatigue prediction model based on the results of the small-scale fatiguetest experiments for zero stress ratio and without residual stresses, and then to investigate their applicability for differentstress ratios and in the presence of residual stresses. Total fatigue life using the two-phase model consists of crack initiationphase, calculated by strain-life approach, and crack propagation phase, calculated by fracture mechanic’s approach. Calibrationof the fatigue parameters is performed for each phase by fitting numerical to the experimental results. Comparative analysisof calculated and measured fatigue lives is then conducted for different stress ratios, in both stress-relieved and as-weldedconditions. Given that calculation parameters are calibrated for the basic case, uncertainty of predictions is large, showingthat application of the method for real-life complex marine structures is challenging.
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.
