The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, includin...The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, including Kagome and triangular lattices, are estimated by analyzing their effective yield loci. The normalized in-plane yield loci of these two lattices are almost identical convex curves enclosed by 4 straight lines, which is almost independent of the relative density but is highly sensitive to the principal stress directions. Therefore, the plastic zones around the crack tip of Kagome and triangular are estimated to be quite different to those of the continuum solid and also hexagonal lattice. The plastic zones predictions by convex yield surfaces of both lattices are validated by FE calculations, although the shear lag region caused by non-local bending effect in the Kagome lattice enlarges the plastic zone in cases of small ratio of rp/l.展开更多
The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plan...The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plane-stress crack-tip for both thecases of β=2 and β>2 .展开更多
In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life predic...In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only−0.621%;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is−11.29%.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.展开更多
Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., ...Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., Burns, S. J. have discussed the problem of the plastic zone at a crack tip in isotropic elastic medium. We know that the hard second phase, which neither causes very large stress concentration nor leads to micrographic split, can improve the bearing capacity of the materials. Therefore, it is necessary to discuss the problem of the plastic zone at a crack tip while the hard second phase exists.展开更多
Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-ha...Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-hard ening material is obtained using RKPM. Ramberg-Osgood stress-strain relation is assumed and the crack-tip stress intensity factor （SIF） before and after formation of the plastic zone are examined. To impose the essential boundary conditions, penalty method is used. To construct the shape functions in the vicinity of the crack and crack-tip, both the diffraction and visibility criteria are employed. A comparison between two conventional treatments, visibility and diffraction, to crack discontinuity is conducted. The effects of different dilation parameters on SIF under plane-stress and plane-strain conditions are ~tudied. Results including plastic zone shape are compared with finite element method （FEM） to show the accuracy of RKPM. The main objective is to study the effects of different dilation parameters on SIF under plane stress and plane strain conditions and to obtain the mode I plastic zone shape at the crack-tip in a work hardening material using RKPM.展开更多
The independent influence of microstructural features on fracture toughness of TC21alloy with lamellar microstructure was investigated.Triple heat treatments were designed to obtain lamellar microstructures with diffe...The independent influence of microstructural features on fracture toughness of TC21alloy with lamellar microstructure was investigated.Triple heat treatments were designed to obtain lamellar microstructures with different parameters,which were characterized by OM and SEM.The size and content ofαplates were mainly determined by cooling rate from singleβphase field and solution temperature in two-phase field;while the precipitation behavior of secondaryαplatelets was dominantly controlled by aging temperature in two-phase field.The content and thickness ofαplates and the thickness of secondaryαplatelets were important microstructural features influencing the fracture toughness.Both increasing the content ofαplates and thickeningαplates(or secondaryαplatelets)could enhance the fracture toughness of TC21alloy.Based on energy consumption by the plastic zone of crack tip inαplates,a toughening mechanism for titanium alloys was proposed.展开更多
基金supported by the National Natural Science Foundation of China (No.10502027)the National Fundamental Research Program of China (No.G2006CB601202)
文摘The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, including Kagome and triangular lattices, are estimated by analyzing their effective yield loci. The normalized in-plane yield loci of these two lattices are almost identical convex curves enclosed by 4 straight lines, which is almost independent of the relative density but is highly sensitive to the principal stress directions. Therefore, the plastic zones around the crack tip of Kagome and triangular are estimated to be quite different to those of the continuum solid and also hexagonal lattice. The plastic zones predictions by convex yield surfaces of both lattices are validated by FE calculations, although the shear lag region caused by non-local bending effect in the Kagome lattice enlarges the plastic zone in cases of small ratio of rp/l.
文摘The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plane-stress crack-tip for both thecases of β=2 and β>2 .
基金Supported by National Natural Science Foundation of China(Grant No.51675446)Independent Research Project of State Key Laboratory of Traction Power(Grant No.2019TPL-T13).
文摘In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only−0.621%;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is−11.29%.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.
文摘Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., Burns, S. J. have discussed the problem of the plastic zone at a crack tip in isotropic elastic medium. We know that the hard second phase, which neither causes very large stress concentration nor leads to micrographic split, can improve the bearing capacity of the materials. Therefore, it is necessary to discuss the problem of the plastic zone at a crack tip while the hard second phase exists.
文摘Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-hard ening material is obtained using RKPM. Ramberg-Osgood stress-strain relation is assumed and the crack-tip stress intensity factor （SIF） before and after formation of the plastic zone are examined. To impose the essential boundary conditions, penalty method is used. To construct the shape functions in the vicinity of the crack and crack-tip, both the diffraction and visibility criteria are employed. A comparison between two conventional treatments, visibility and diffraction, to crack discontinuity is conducted. The effects of different dilation parameters on SIF under plane-stress and plane-strain conditions are ~tudied. Results including plastic zone shape are compared with finite element method （FEM） to show the accuracy of RKPM. The main objective is to study the effects of different dilation parameters on SIF under plane stress and plane strain conditions and to obtain the mode I plastic zone shape at the crack-tip in a work hardening material using RKPM.
文摘The independent influence of microstructural features on fracture toughness of TC21alloy with lamellar microstructure was investigated.Triple heat treatments were designed to obtain lamellar microstructures with different parameters,which were characterized by OM and SEM.The size and content ofαplates were mainly determined by cooling rate from singleβphase field and solution temperature in two-phase field;while the precipitation behavior of secondaryαplatelets was dominantly controlled by aging temperature in two-phase field.The content and thickness ofαplates and the thickness of secondaryαplatelets were important microstructural features influencing the fracture toughness.Both increasing the content ofαplates and thickeningαplates(or secondaryαplatelets)could enhance the fracture toughness of TC21alloy.Based on energy consumption by the plastic zone of crack tip inαplates,a toughening mechanism for titanium alloys was proposed.
