Based on the standpoint to take for the crack size also to be a damage variable like the damage variable, by means of the two-directions coordinate system, several new calculation equations on the small crack gro...Based on the standpoint to take for the crack size also to be a damage variable like the damage variable, by means of the two-directions coordinate system, several new calculation equations on the small crack growth rate are suggested for describing the elastic-plastic behavior of some metallic materials. And the estimation formulas of life are also suggested relative to varied small crack size at each loading history, which is unsymmetric cyclic loading. In the calculation method, as a loaded stress-strain parameter to adopt the ratio with plastic strain range to elastic strain range, and as the material constants using the typical material parameters in damage calculation expression, a new concept of the compositive material constant, which has functional relation with the typical material constants, average stress, average strain, critical loading time is given out. In addition, the fatigue damage of a part of car is put up to calculate as an example, its calculation results are accordant with the Landgraf＇s equation, and calculation precision is more rigorous, so could avoid unnecessary fatigue tests and will be of practical significance on saving times, manpower and capitals, as well as the convenience for engineering applications.展开更多
By using the continuous exploration system with multi-pipeline in the borehole, the failure cracks of cover strata (specially, the small cracks developing) after the combined mining of 16, 17 thin seams of the 4th min...By using the continuous exploration system with multi-pipeline in the borehole, the failure cracks of cover strata (specially, the small cracks developing) after the combined mining of 16, 17 thin seams of the 4th mining block in Zhaopo Mine is explored. After that, the researching result is considered as the output and the testing result of rock mechanics parameters is considered as the verifying data, the back analysis is made with the conception of the point safety degree. The relative height of the crack developing is obtaied. So, the evaluating of the safety of 16, 17 seams combined mining under the gob water with extreme distance is made and the mining has been safety. The scientific basis is provided for the evaluating of the mining safety with the similar conditions.展开更多
Studies on microstructurally small fatigue cracks have illustrated that heterogeneous microstructural features such as inclusions, pores, grain size distribution as well as precipitate size distribution and volume fra...Studies on microstructurally small fatigue cracks have illustrated that heterogeneous microstructural features such as inclusions, pores, grain size distribution as well as precipitate size distribution and volume fraction create stochasticity in their behavior under cyclic loads. Therefore, to enhance safe-life and damage-tolerance approaches, accurate modeling of the influence of these heterogeneous microstructural features on microstructurally small crack formation and growth from stress raisers is necessary. In this work, computational micromechanics was used to predict the high cycle fatigue of microstructurally small crack formation and growth in notched polycrystalline nickel-base superalloys and to quantify the variability in the driving force for formation and growth of microstructurally small crack from notch root in the matrix with non-metallic inclusions. The framework involves computational modeling to obtain three-dimensional perspectives of microstructural features influencing fatigue crack growth in notched nickel-base superalloys, which accounts for the effects of nonlocal notch root plasticity, loading, microstructural variability, and extrinsic defects on local cyclic plasticity at the microstructure-scale level. This approach can be used to explore sensitivity of minimum fatigue lifetime to microstructures. The simulation results obtained from this framework were calibrated to existing experimental results for polycrystalline nickel-base superalloys.展开更多
In this paper,a simplified brittle damage model is proposed according to the Mazars-Lemaitre damage model for concrete.A closed-form solution for a mode Ⅲ crack is obtained based on the simplified model under small s...In this paper,a simplified brittle damage model is proposed according to the Mazars-Lemaitre damage model for concrete.A closed-form solution for a mode Ⅲ crack is obtained based on the simplified model under small scale damage conditions,which allows for discontinuities of displacement-gradient and tangential stress on the damage boundary.It is pointed out that the discontinuities of field variables near the tip region exist for the brittle damaged material induced by the softening effect of the material.展开更多
This paper deals with an infinite slab with a semi-infinite crack,which is subjected to the anti-plane shear k_Ⅲ field at infinity.The slab is made of an elasto-damaged material.Analytical solution is obtained by use...This paper deals with an infinite slab with a semi-infinite crack,which is subjected to the anti-plane shear k_Ⅲ field at infinity.The slab is made of an elasto-damaged material.Analytical solution is obtained by use of conformal mapping.The shape of damaged-zone,the dissipative energy,the shear open- ing displacement on the crack surface and several stress distribution curves are given.The far field condition is checked,The asymptotic behavior near the crack-tip is given.展开更多
[目的]溶洞的注浆处理是地铁隧道工程中的难点,施工时溶洞的不恰当处理极易引发事故,因此有必要对小型溶洞裂隙数量和注浆压强之间的关系进行研究。[方法]针对需注浆填充的城市小型非连通型溶洞(体积不大于8 m 3)的裂隙数量不确定问题,...[目的]溶洞的注浆处理是地铁隧道工程中的难点,施工时溶洞的不恰当处理极易引发事故,因此有必要对小型溶洞裂隙数量和注浆压强之间的关系进行研究。[方法]针对需注浆填充的城市小型非连通型溶洞(体积不大于8 m 3)的裂隙数量不确定问题,采用Fluent数值模拟软件中的多相流Mixture模型进行不同裂隙数量的溶洞注浆数值模拟,计算模拟注浆时,测试区的注浆压强随时间的变化情况,并与实际工程溶洞注浆压强数据进行对比分析。[结果及结论]对于体积不大于8 m 3的小型非连通型溶洞,其模拟注浆时测试区的注浆压强与裂隙数量呈平方反比关系,注浆压强随着裂隙数量的增加而降低;当裂隙面积达到0.048 m 2时,注浆压强不再降低;注浆压强随着裂隙位置的增高而降低。在实际工程中,可通过对比同类型体积不超过8 m 3小型非连通溶洞之间的注浆压强数据,判断溶洞的相对裂隙数量,调整与优化后续的注浆方案。展开更多
文摘Based on the standpoint to take for the crack size also to be a damage variable like the damage variable, by means of the two-directions coordinate system, several new calculation equations on the small crack growth rate are suggested for describing the elastic-plastic behavior of some metallic materials. And the estimation formulas of life are also suggested relative to varied small crack size at each loading history, which is unsymmetric cyclic loading. In the calculation method, as a loaded stress-strain parameter to adopt the ratio with plastic strain range to elastic strain range, and as the material constants using the typical material parameters in damage calculation expression, a new concept of the compositive material constant, which has functional relation with the typical material constants, average stress, average strain, critical loading time is given out. In addition, the fatigue damage of a part of car is put up to calculate as an example, its calculation results are accordant with the Landgraf＇s equation, and calculation precision is more rigorous, so could avoid unnecessary fatigue tests and will be of practical significance on saving times, manpower and capitals, as well as the convenience for engineering applications.
文摘By using the continuous exploration system with multi-pipeline in the borehole, the failure cracks of cover strata (specially, the small cracks developing) after the combined mining of 16, 17 thin seams of the 4th mining block in Zhaopo Mine is explored. After that, the researching result is considered as the output and the testing result of rock mechanics parameters is considered as the verifying data, the back analysis is made with the conception of the point safety degree. The relative height of the crack developing is obtaied. So, the evaluating of the safety of 16, 17 seams combined mining under the gob water with extreme distance is made and the mining has been safety. The scientific basis is provided for the evaluating of the mining safety with the similar conditions.
基金the funding provided by the Department of Defense (DoD) through the research and educational program for HBCU/MI (Contract No. # W911NF-11-1014) monitored by Dr. Larry Russell (Program Manager, ARO) and Dr. David Stargel (Program Manager, AFOSR)
文摘Studies on microstructurally small fatigue cracks have illustrated that heterogeneous microstructural features such as inclusions, pores, grain size distribution as well as precipitate size distribution and volume fraction create stochasticity in their behavior under cyclic loads. Therefore, to enhance safe-life and damage-tolerance approaches, accurate modeling of the influence of these heterogeneous microstructural features on microstructurally small crack formation and growth from stress raisers is necessary. In this work, computational micromechanics was used to predict the high cycle fatigue of microstructurally small crack formation and growth in notched polycrystalline nickel-base superalloys and to quantify the variability in the driving force for formation and growth of microstructurally small crack from notch root in the matrix with non-metallic inclusions. The framework involves computational modeling to obtain three-dimensional perspectives of microstructural features influencing fatigue crack growth in notched nickel-base superalloys, which accounts for the effects of nonlocal notch root plasticity, loading, microstructural variability, and extrinsic defects on local cyclic plasticity at the microstructure-scale level. This approach can be used to explore sensitivity of minimum fatigue lifetime to microstructures. The simulation results obtained from this framework were calibrated to existing experimental results for polycrystalline nickel-base superalloys.
基金The preoject supported by the National Natural Science Foundation of China.
文摘In this paper,a simplified brittle damage model is proposed according to the Mazars-Lemaitre damage model for concrete.A closed-form solution for a mode Ⅲ crack is obtained based on the simplified model under small scale damage conditions,which allows for discontinuities of displacement-gradient and tangential stress on the damage boundary.It is pointed out that the discontinuities of field variables near the tip region exist for the brittle damaged material induced by the softening effect of the material.
基金The project supported by National Natural Science Foundation of China
文摘This paper deals with an infinite slab with a semi-infinite crack,which is subjected to the anti-plane shear k_Ⅲ field at infinity.The slab is made of an elasto-damaged material.Analytical solution is obtained by use of conformal mapping.The shape of damaged-zone,the dissipative energy,the shear open- ing displacement on the crack surface and several stress distribution curves are given.The far field condition is checked,The asymptotic behavior near the crack-tip is given.
文摘[目的]溶洞的注浆处理是地铁隧道工程中的难点,施工时溶洞的不恰当处理极易引发事故,因此有必要对小型溶洞裂隙数量和注浆压强之间的关系进行研究。[方法]针对需注浆填充的城市小型非连通型溶洞(体积不大于8 m 3)的裂隙数量不确定问题,采用Fluent数值模拟软件中的多相流Mixture模型进行不同裂隙数量的溶洞注浆数值模拟,计算模拟注浆时,测试区的注浆压强随时间的变化情况,并与实际工程溶洞注浆压强数据进行对比分析。[结果及结论]对于体积不大于8 m 3的小型非连通型溶洞,其模拟注浆时测试区的注浆压强与裂隙数量呈平方反比关系,注浆压强随着裂隙数量的增加而降低;当裂隙面积达到0.048 m 2时,注浆压强不再降低;注浆压强随着裂隙位置的增高而降低。在实际工程中,可通过对比同类型体积不超过8 m 3小型非连通溶洞之间的注浆压强数据,判断溶洞的相对裂隙数量,调整与优化后续的注浆方案。
