Wide Range Of Stress Triaxiality Research Articles

On fracture locus in the equivalent strain and stress triaxiality space

The stress triaxiality is, besides the strain intensity, the most important factor that controls initiation of ductile fracture. In this study, a series of tests including upsetting tests, shear tests and tensile tests on 2024-T351 aluminum alloy providing clues to fracture ductility for a wide range of stress triaxiality was carried out. Numerical simulations of each test was performed using commercial finite element code ABAQUS. Good correlation of experiments and numerical simulations was achieved. Based on the experimental and numerical results, the relation between the equivalent strain to fracture versus the stress triaxiality was quantified and it was shown that there are three distinct branches of this function with possible slope discontinuities in the transition regime. For negative stress triaxialities, fracture is governed by shear mode. For large triaxialities void growth is the dominant failure mode, while at low stress triaxialities between above two regimes, fracture may develop as a combination of shear and void growth modes.

フェライト基地球状黒鉛鋳鉄のディンプル破断面の統計的評価(G03-2 き裂・破壊,G03 材料力学)

A statistical analysis of ductile fracture surface was performed on JIS FCD400 spheroidal graphite cast iron with feritic matrix. Both the notched specimens with different notch acuity and the unnotched specimens were employed to obtain a wide range of stress triaxiality. All specimens were loaded to break under tensile loading at room temperature. The maximum nominal stress to break the specimen increased slightly with stress triaxiality, compared with structural steels. However, the extreme value probability of the maximum dimple size in a given unit area showed a clear dependence on the maximum nominal stress. In addition, the lateral growth factor of the maximum dimple against the graphite size increased due to an increased level of transverse stress with stress triaxiality. Thus, the extreme value analysis of the maximum dimple size and the lateral growth factor of the maximum dimple should be expected for providing a positive and quantitative information regarding the fracture behavior of the ductile cast iron.

A Statistical Analysis of Ductile Fracture Surface for Structural Steel

A statistical analysis of ductile fracture surface has been made on a structural steel. Both the notched specimens with different notch acuity and the unnotched specimens were employed to obtain a wide range of stress triaxiality. A large number of dimples were examined to clarify the statistics of dimple size distribution. The ductile fracture surface was compased of variously sized dimples, and the dimple size distributions were expressed approximately by the composite Weibull distribution. Whereas, the extreme value plots of the maximum dimple size has been applied to characterize the statistical variation on the extensive ductile fracture surfaces. A clearly defined change in the ductile fracture surfaces associated with fracture strain was well expressed by plotting the distributions of the maximum dimple size in a given unit area on the extreme probability paper. Then, it should be noted that the extreme value analysis would be quite useful for quantitative fractographic analysis of ductile fracture surfaces.

Extreme Value Analysis of Dimple Size on Ductile Fracture Surface Associated with Fracture Behavior of Tensile Specimens

Extreme value analysis has been applied to clarify the statistical nature of the ductile fracture surface associated with the fracture behavior of JIS SS 490 steel. Both the notched tensile specimens with different notch acuity and the unnotched specimens were employed to obtain a wide range of stress triaxiality. The ductile fracture surfaces were composed of variously sized dimples. The dimple size distributions were well expressed by the composite type of Weibull distributions. Whereas, the extreme value probability plots of the maximum dimple sizes in a given unit area were performed to correlate the dominant feature of the ductile fracture surface with the mechanical test results. As a consequence, the parameters that define the maximum dimple size distribution showed a clear dependence on the maximum stress and the fracture strains of the tensile specimens with stress triaxiality varied in four levels. Then, the extreme value analysis of the ductile fracture surface should be recommended as a powerful and effective tool for providing a quantitative information regarding the fracture behavior of the mechanical components.

Ductile Crack Initiation Behavior of Structural Materials under Low Stress Triaxiality

Significance of investigation of ductile crack initiation characteristics in the evaluation of structure of integrity is on the increase. It is significant to predict ductile crack initiation in plastic forming of metal materials. A lot of examinations about ductile crack initiation behavior under high stress triaxiality for structural steels have been conducted using notched round bar tensile specimens. Satisfactory examination under low stress triaxiality, however, has not necessary been conducted thus far.Ductile crack initiation characteristics of aluminum alloy A 5083-O and high strength steel HT 950 under low stress triaxiality have been investigated using plate tensile specimens in this study. The critical equivalent plastic strain as a function of the stress triaxiality at ductile crack initiation has been estimated using FE analyses.The ductile crack initiation is triggered by secondary void nucleation under low stress triaxiality, and it is controlled by initial void growth under high stress triaxiality for A 5083-O. The ductile crack initiation is triggered by void nucleation under the wide range of stress triaxiality. The critical diameter of void at ductile crack initiation varies with stress triaxiality for both materials. The critical equivalent plastic strain at ductile crack initiation under low stress triaxiality is seemed to be overestimated by extrapolation using curve fitted to test results under high stress triaxiality on the assumption that critical void diameter would be constant.