In the construction of water conservancy and hydropower project,young concrete lining structure is often affected by blasting load. Young concrete has a lot of micro-fractures with random distribution,which are easier...In the construction of water conservancy and hydropower project,young concrete lining structure is often affected by blasting load. Young concrete has a lot of micro-fractures with random distribution,which are easier to propagate and connect under blasting load. This paper focuses on the calculation on dynamic stress intensity factors of bond interface crack of concrete-rock according to concrete age. Result shows that different incidence angles of stress wave lead to different crack propagation mechanisms. Under the normal incidence of impact load,the bonding interface crack propagation of the concrete lining is mainly caused by reflection tensile stress,which forms from the free surface. With horizontal incidence of stress wave,the bond interface crack propagation of concrete lining is affected by concrete age. With the increase of concrete age,the elasticity modulus margin between concrete and rock decreases gradually,and the crack propagation form changes from shear failure to tensile damage.展开更多
When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not suffic...When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not sufficient to distinguish the difference between a micro- and macro-crack by using the length parameter. Microcracks in high strength metal alloys have been known to be sev- eral centimeters or longer. Considered in this work is a dual scale fatigue crack growth model where the main crack can be mi- cro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the micro- structure. This region is referred to as the ＂micro-tip＂ and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions. The combination is sufficient to model microscopic entities in the form of voids, inclusions, precipitations, interfaces, in addition to subgrain imperfections, or cluster of dislocations. This is accomplished by using the method of ＂singularity representation＂ such that closed form asymptotic solutions can be obtained for the development of fa- tigue crack growth rate relations with three parameters. They include： （1） the crack surface tightness o-＊ represented by Cro/Cr~ = 0.3-0.5 for short cracks in region I, and 0.1-0.2 for long cracks in region II, （2） the micro/macro material properties reflected by the shear modulus ratio/1＂ （=,L/micro/]-/macro varying between 2 and 5） and （3） the most sensitive parameter d＊ being the micro-tip characteristic length d＊ （=d/do） whose magnitude decreases in the direction of region I ---~II. The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter da/dN=C（AK）n relation where AK has now been re-derived for a microcrack with surfaces tightly in contact. The contact force will depend on the mean stress ~m or mean stress ratio R as the primary parameter and on the stress amplitude era as the secondary parameter.展开更多
基金The National Natural Science Foundation of China(No.50774056)Scientific Research Fund of Wuhan University of Science and Technology(No.080068)
文摘In the construction of water conservancy and hydropower project,young concrete lining structure is often affected by blasting load. Young concrete has a lot of micro-fractures with random distribution,which are easier to propagate and connect under blasting load. This paper focuses on the calculation on dynamic stress intensity factors of bond interface crack of concrete-rock according to concrete age. Result shows that different incidence angles of stress wave lead to different crack propagation mechanisms. Under the normal incidence of impact load,the bonding interface crack propagation of the concrete lining is mainly caused by reflection tensile stress,which forms from the free surface. With horizontal incidence of stress wave,the bond interface crack propagation of concrete lining is affected by concrete age. With the increase of concrete age,the elasticity modulus margin between concrete and rock decreases gradually,and the crack propagation form changes from shear failure to tensile damage.
文摘When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not sufficient to distinguish the difference between a micro- and macro-crack by using the length parameter. Microcracks in high strength metal alloys have been known to be sev- eral centimeters or longer. Considered in this work is a dual scale fatigue crack growth model where the main crack can be mi- cro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the micro- structure. This region is referred to as the ＂micro-tip＂ and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions. The combination is sufficient to model microscopic entities in the form of voids, inclusions, precipitations, interfaces, in addition to subgrain imperfections, or cluster of dislocations. This is accomplished by using the method of ＂singularity representation＂ such that closed form asymptotic solutions can be obtained for the development of fa- tigue crack growth rate relations with three parameters. They include： （1） the crack surface tightness o-＊ represented by Cro/Cr~ = 0.3-0.5 for short cracks in region I, and 0.1-0.2 for long cracks in region II, （2） the micro/macro material properties reflected by the shear modulus ratio/1＂ （=,L/micro/]-/macro varying between 2 and 5） and （3） the most sensitive parameter d＊ being the micro-tip characteristic length d＊ （=d/do） whose magnitude decreases in the direction of region I ---~II. The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter da/dN=C（AK）n relation where AK has now been re-derived for a microcrack with surfaces tightly in contact. The contact force will depend on the mean stress ~m or mean stress ratio R as the primary parameter and on the stress amplitude era as the secondary parameter.
