Masanori Kikuchi

Study on Ductile Fracture Including Shear-Lip Fracture under Mixed Mode Loading Condition

Dimple fracture tests are conducted under mode I and mixed mode lading conditions. Dimple fracture zone and shear-lip fracture zone are observed by scanning electron microscope precisely. It is found that crack growth direction is affected largely by the change of loading condition. It is also found that the differences of fracture pattern between mid-plane and at free surface are very large. Void diameter and crack growth direction are measured. Numerical simulation is conducted to simulate fracture tests in three-dimensional field. Gurson’s constitutive equation is used and large deformation analyses are conducted. It is assumed that void nucleation is controlled by both plastic strain and stress. Numerical results are compared with those of experiments. It is found that results of numerical simulation agree well with those of experiment qualitatively.

Dimple Fracture Simulation under Mixed Mode Loading Condition

Dimple fracture under mixed mode loading condition is studied experimentally and numerically. By the mixed mode loading, it is found that fracture surface becomes much rougher than that of mode I fracture. It is also found that ductile fracture growth direction deviates from the original plane. It becomes clear that there are two factors affecting ductile fracture processes, one is mixed mode ratio and another is thickness effect. Three-dimensional finite element analyses are conducted to study effects of these factors. For the simulation of ductile fracture, Gurson’s constitutive equation is used with large deformation theory. These numerical results agree with experimental observation very well qualitatively.

Study on the Stress Intensity Factor for Mixed Mode Surface Crack under Three Point Bending

In the virtual crack closure method (VCCM), the energy release rate is computed based on the results of finite element calculation, and the stress intensity factor (SIF) is computed from the energy release rate. In this paper, the stress intensity factor of mixed-mode surface cracks under three point bending is studied by using the three dimensional modified virtual crack closure method (MVCCM). The modified virtual crack closure method is required to open one element face area whose shape is arbitrary and finite element widths are unequal across the crack front. The effect of the distance between the location of load and crack face, crack shape and crack depth to the stress intensity factor is also discussed, along with practical results and conclusions.

Fatigue Crack Growth Simulation Using S-Version FEM

Fatigue crack growth under mixed mode loading conditions is simulated using S-FEM. By using S-FEM technique, only local mesh should be remeshed and it becomes easy to simulate crack growth. By combining with re-meshing technique, local mesh is re-meshed automatically, and curved crack path is modeled easily. Plural fatigue crack problem is solved by this technique. For two through crack problems, crack coalescence condition is proposed by JSME standard. By simulating this problem by S-FEM, it is shown that thid criterion depends on initial crack size. Then more than 160 cases are simulated by changing several parameters. Results are summarized by normalized form, and new criterion is proposed.Copyright

Numerical Simulation of Ductile Fracture Process Including Shear-Lip Fracture

Thickness effect is studied experimentally. At free surface of the specimen, shear lip fracture pattern appears, though dimple fracture pattern is observed inside of the specimen. The area of shear-lip fracture changes due to the change of the specimen thickness. In this study, experimental study is conducted by changing specimen thicknesses. Fracture surfaces are precisely observed using SEM, and dimple patterns on them are observed. At the free surface, very narrow no-void area is observed. It is also found that many voids are nucleated in shear-lip fracture area. FEM simulation is carried out using Gurson’s constitutive equation. It is found that shear-lip type fracture is simulated near free surface area by this method. The results show similar tendency with the experimental observation.