By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far ...By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length lcq of wing crack, two terms make up the stress intensity factor K1 at wing crack tip： one is the component K（1） for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K1^（2） due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method （FEM）. In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.展开更多
In this paper, by means of the maximum circle tensile stress on curve of constant ω and stress intensity factors by a path independent contour integral method, trajectories of maxed mode crack propagation are simulat...In this paper, by means of the maximum circle tensile stress on curve of constant ω and stress intensity factors by a path independent contour integral method, trajectories of maxed mode crack propagation are simulated through numerical manifold method. The crack propagation is traced dynamically by modifying the neighboring connection between the crack-top and nodes within elements in the calculating process. This method has the advantages such as less modified area, easiness of programming, high realizability and so on. Then a single sharp nicked specimen is used to verified the numerical result. It is shown that the provided method is reasonable and effective.展开更多
Blanking is a major process and has a wide range of usage in manufacturing industry. The general concept of blanking seems a simple one but governing parameters are many and have a complex relationship which directly ...Blanking is a major process and has a wide range of usage in manufacturing industry. The general concept of blanking seems a simple one but governing parameters are many and have a complex relationship which directly affect the quality of the produced parts （blanks） and also the energy efficiency of the process. The main problem is the lack of prediction capabilities of the effect of these parameters that lead to time, money and labor consuming trial and error procedures in experimental studies. Usage of FEM based programs to simulate blanking to obtain numerical results and observe the shearing mechanism is a cheap and a detailed way for industrial applications. In this study five different clearances （1%, 3%, 5%, 10% and 20%） and three different thicknesses （t = 2 mm, t = 3 mm and t = 4 mm） were used for simulation and experimental studies of the blanking process. Simulations were executed by using the FEM program, Deform 2-D. Investigations were made on the parameters related to crack progression like crack initiation and crack propagation angles, indentation angle, rollover angle and depth and also the related blanking energy values. The results of the present paper are in agreement with the results of experimental studies.展开更多
Based on the framework of the extended finite element method (XFEM), the enriched exponent discontinuous function is modified properly by introducing the rigidity ratio of two sides materials of interface crack, and t...Based on the framework of the extended finite element method (XFEM), the enriched exponent discontinuous function is modified properly by introducing the rigidity ratio of two sides materials of interface crack, and the portion integral scheme is adopted for interface elements containing two materials. To embody the singularity of the crack tip, the triangle function is introduced directly. What’s more, the maximum loop stress fracture criterion is adopted to determine the extension direction in extended material domains, and the true extension distance for each load step is determined by reducing or increasing half the current trial extension distance until the equivalent stress intensity factor reaches the type I fracture toughness of material. Finally, with the improved XFEM, the interface crack propagation in a cantilever deep beam and concrete gravity dam are simulated without re-meshing respectively and their failure modes are also analyzed.展开更多
Molecular dynamics simulation was performed to investigate the influence of twin boundary （TB） spacing on crack propaga- tion of AI. This study reveals the orientation of initial crack may affect the mechanism of cr...Molecular dynamics simulation was performed to investigate the influence of twin boundary （TB） spacing on crack propaga- tion of AI. This study reveals the orientation of initial crack may affect the mechanism of crack growth obviously. TB strengthens A1 when the crack orientation is parallel with TB because of the hinderance of TB to the emission of the disloca- tions. The results indicate that there is an optimal TB spacing for mechanical properties of the A1, exhibiting reverse HP （Hall-Petch） and HP effect when the TB spacing is near the critical TB spacing. Furthermore, we find that there is a yield strength hardening effect in nanotwinned A1 when the crack orientation is perpendicular to the TB, and the Young＇s modulus is smaller in the nanotwinned A1 than that of twin free A1. The studies also demonstrate that this distinctive deformation behavior is related to nucleation of dislocations and the repulsive force of TB to the dislocations and crack propagation, as well as the distance between the crack tip and the TB.展开更多
In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept o...In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness varia- tion and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the 'equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum en- ergy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.展开更多
基金Projects(10972238,51074071,50974059)supported by the National Natural Science Foundation of ChinaProject(10JJ3007)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(11C0539)supported by Scientific Research Fund of Hunan Provincial Education Department,ChinaProject(200905)supported by Open Research Fund of Hunan Provincial Key of Safe Mining Techniques of Coal Mines,China
文摘By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length lcq of wing crack, two terms make up the stress intensity factor K1 at wing crack tip： one is the component K（1） for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K1^（2） due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method （FEM）. In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.
基金Funded by the National Natural Science Foundation of China (No. 10272033) and Guangdong Provincial Natural Science Foundation(Nos.04105386,5300090 and 05001844).
文摘In this paper, by means of the maximum circle tensile stress on curve of constant ω and stress intensity factors by a path independent contour integral method, trajectories of maxed mode crack propagation are simulated through numerical manifold method. The crack propagation is traced dynamically by modifying the neighboring connection between the crack-top and nodes within elements in the calculating process. This method has the advantages such as less modified area, easiness of programming, high realizability and so on. Then a single sharp nicked specimen is used to verified the numerical result. It is shown that the provided method is reasonable and effective.
文摘Blanking is a major process and has a wide range of usage in manufacturing industry. The general concept of blanking seems a simple one but governing parameters are many and have a complex relationship which directly affect the quality of the produced parts （blanks） and also the energy efficiency of the process. The main problem is the lack of prediction capabilities of the effect of these parameters that lead to time, money and labor consuming trial and error procedures in experimental studies. Usage of FEM based programs to simulate blanking to obtain numerical results and observe the shearing mechanism is a cheap and a detailed way for industrial applications. In this study five different clearances （1%, 3%, 5%, 10% and 20%） and three different thicknesses （t = 2 mm, t = 3 mm and t = 4 mm） were used for simulation and experimental studies of the blanking process. Simulations were executed by using the FEM program, Deform 2-D. Investigations were made on the parameters related to crack progression like crack initiation and crack propagation angles, indentation angle, rollover angle and depth and also the related blanking energy values. The results of the present paper are in agreement with the results of experimental studies.
基金supported by the National Natural Science Foundation of China (Grant No. 10972072)the National Basic Research Program of China ("973" Project) (Grant No. 2007CB714104)the Special Fund of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering at Hohai University (Grant No. 2009585912)
文摘Based on the framework of the extended finite element method (XFEM), the enriched exponent discontinuous function is modified properly by introducing the rigidity ratio of two sides materials of interface crack, and the portion integral scheme is adopted for interface elements containing two materials. To embody the singularity of the crack tip, the triangle function is introduced directly. What’s more, the maximum loop stress fracture criterion is adopted to determine the extension direction in extended material domains, and the true extension distance for each load step is determined by reducing or increasing half the current trial extension distance until the equivalent stress intensity factor reaches the type I fracture toughness of material. Finally, with the improved XFEM, the interface crack propagation in a cantilever deep beam and concrete gravity dam are simulated without re-meshing respectively and their failure modes are also analyzed.
基金supported by the National Natural Science Foundation of China(Grant No.10902083)the Program for New Century Excellent Talents in University(Grant No.NCET-12-1046)the Program for New Scientific and Technological Star of Shaanxi Province(Grant No.2012KJXX-39)
文摘Molecular dynamics simulation was performed to investigate the influence of twin boundary （TB） spacing on crack propaga- tion of AI. This study reveals the orientation of initial crack may affect the mechanism of crack growth obviously. TB strengthens A1 when the crack orientation is parallel with TB because of the hinderance of TB to the emission of the disloca- tions. The results indicate that there is an optimal TB spacing for mechanical properties of the A1, exhibiting reverse HP （Hall-Petch） and HP effect when the TB spacing is near the critical TB spacing. Furthermore, we find that there is a yield strength hardening effect in nanotwinned A1 when the crack orientation is perpendicular to the TB, and the Young＇s modulus is smaller in the nanotwinned A1 than that of twin free A1. The studies also demonstrate that this distinctive deformation behavior is related to nucleation of dislocations and the repulsive force of TB to the dislocations and crack propagation, as well as the distance between the crack tip and the TB.
基金supported by the National Natural Science Foundation of China (Grant No. 11011140335)
文摘In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness varia- tion and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the 'equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum en- ergy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.
