To reveal the water inrush mechanics of underground deep rock mass subjected to dynamic disturbance such as blasting, compression-shear rock crack initiation rule and the evolution of crack tip stress intensity factor...To reveal the water inrush mechanics of underground deep rock mass subjected to dynamic disturbance such as blasting, compression-shear rock crack initiation rule and the evolution of crack tip stress intensity factor are analyzed under static-dynamic loading and seepage water pressure on the basis of theoretical deduction and experimental research. It is shown that the major influence factors of the crack tip stress intensity factor are seepage pressure, dynamic load, static stress and crack angle. The existence of seepage water pressure aggravates propagation of branch cracks. With the seepage pressure increasing, the branch crack experiences unstable extension from stable propagation. The dynamic load in the direction of maximum main stress increases type I crack tip stress intensity factor and its influence on type II crack intensity factor is related with crack angle and material property. Crack initiation angle changes with the dynamic load. The initial crack initiation angle of type I dynamic crack fracture is 70.5°. The compression-shear crack initial strength is related to seepage pressure, confining pressure, and dynamic load. Experimental results verify that the initial crack strength increases with the confining pressure increasing, and decreases with the seepage pressure increasing.展开更多
In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safe...In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation, the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.展开更多
This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction.The temperature field and the associated thermal stresses are solved by the dual integral equation technique.Both th...This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction.The temperature field and the associated thermal stresses are solved by the dual integral equation technique.Both thermally insulated crack and heated crack are considered.It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form.Numerical results show that the crack considerably amplifies the local thermal stresses,confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.展开更多
Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field re...Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven jointly by both the singular and non-singular terms of the crack-tip electric field. Combining a full field solution with an energy based switching criterion, we obtain the switching zone by the large scale model around the tip of a stationary impermeable crack. It is observed that the switching zone by the large scale model is significantly different from that by the small scale model. According to the large scale switching zone, the switch-induced stress intensity factor (SIF) and the transverse stress (T-stress) are evaluated numerically. Via the SIF and T-stress induced by the combined loading and corresponding criteria, we address the crack initiation and crack growth stability simultaneously. The two theoretical predictions roughly coincide with the experimental observations.展开更多
基金Projects(51174228,51174088,51204068,51274097)supported by the National Natural Science Foundation of China
文摘To reveal the water inrush mechanics of underground deep rock mass subjected to dynamic disturbance such as blasting, compression-shear rock crack initiation rule and the evolution of crack tip stress intensity factor are analyzed under static-dynamic loading and seepage water pressure on the basis of theoretical deduction and experimental research. It is shown that the major influence factors of the crack tip stress intensity factor are seepage pressure, dynamic load, static stress and crack angle. The existence of seepage water pressure aggravates propagation of branch cracks. With the seepage pressure increasing, the branch crack experiences unstable extension from stable propagation. The dynamic load in the direction of maximum main stress increases type I crack tip stress intensity factor and its influence on type II crack intensity factor is related with crack angle and material property. Crack initiation angle changes with the dynamic load. The initial crack initiation angle of type I dynamic crack fracture is 70.5°. The compression-shear crack initial strength is related to seepage pressure, confining pressure, and dynamic load. Experimental results verify that the initial crack strength increases with the confining pressure increasing, and decreases with the seepage pressure increasing.
基金supported by the National Natural Science Foundation of China (Grant No. 51079109)
文摘In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation, the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10972067 and 11172081)
文摘This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction.The temperature field and the associated thermal stresses are solved by the dual integral equation technique.Both thermally insulated crack and heated crack are considered.It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form.Numerical results show that the crack considerably amplifies the local thermal stresses,confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.
基金supported by the "Sino-German Center for Research Promotion" under a project of "Crack Growth in Ferroelectrics Driven by Cyclic Electric Loading", the National Natural Science Foundation of China (Grant No. 10702071)the China Postdoctoral Science Foundation (Grant No. 201003281)the Shanghai Postdoctoral Scientific Program (Grant No. 10R21415800)
文摘Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven jointly by both the singular and non-singular terms of the crack-tip electric field. Combining a full field solution with an energy based switching criterion, we obtain the switching zone by the large scale model around the tip of a stationary impermeable crack. It is observed that the switching zone by the large scale model is significantly different from that by the small scale model. According to the large scale switching zone, the switch-induced stress intensity factor (SIF) and the transverse stress (T-stress) are evaluated numerically. Via the SIF and T-stress induced by the combined loading and corresponding criteria, we address the crack initiation and crack growth stability simultaneously. The two theoretical predictions roughly coincide with the experimental observations.
