Ductile Fracture Evaluation Research Articles

A new machine learning-based evaluation of ductile fracture

Ductile fracture occurs with large plastic deformation prior to fracture and is primarily characterized by voids of varying sizes. In this work, a new approach based on machine learning is proposed for the characterization of ductile fractures. The method is based on the application of a pre-processing of the fractographies, followed by a processing that includes the generation of a mask through a mathematical morphology, a classification is made according to their size in micrometers to later make a histogram of the size of the cavity in relation respect to its frequency of repetition in each fractography. Besides, the histogram is then normalized to generate a Probability Density Function (PDF). Based on the PDF, a third-order statistical metric known as Fractography Skewness (FS) is used to evaluate fracture susceptibility and is related to the Degree of Fracture Susceptibility (DFS). If the FS is negative (indicating a left-skewed PDF), the fractography is characterized by large voids and is assigned a DFS of 1, indicating low susceptibility. Conversely, a positive FS (indicating a right-skewed PDF) indicates the presence of small voids, resulting in a DFS of 3, indicating high susceptibility. The proposed quantitative methodology demonstrates a higher accuracy than the most advanced current techniques based on deep learning and the subjectivity of the specialist.

Experimental Evaluation of Ductile Fracture of Sheet Metals under Plane Stress States

Experimental Evaluation of Ductile Fracture of Sheet Metals under Plane Stress States

High temperature strain measurement by digital image correlation and ductile fracture evaluation of Ni-based superalloy

Tensile and compression tests at 850℃ were conducted by using 6 types of specimen for ductile fracture evaluation of Ni-based superalloy. The digital image correlation method was applied to measure the strain during the tensile tests. Fracture strain, Lode angle parameter and stress triaxiality were obtained by the finite element analysis of the tensile and compression tests. These parameters were used to calibrate the material parameters of the modified Mohr-Coulomb (MMC) ductile fracture model.

Study on Fracture Assessment for BWR Reactor Pressure Vessel Steel by GTN model

In the JSME fitness-for service code, fracture evaluation methodology based on linear elastic fracture mechanics is provided for reactor pressure vessel (RPV) components by considering brittle fracture due to neutron irradiation in the RPV beltline region. However, in order to make a rational fracture evaluation for the RPV component such as bottom head component of boiling water reactor (BWR), where irradiation embrittlement is not concerned, it is necessary to consider the applicability of the ductile fracture evaluation methodology consistent with material fracture behavior. In this study, the applicability of the damage mechanics analysis method using Gurson-Tvergaard-Needleman (GTN) model, which is a numerical analysis method for ductile failure, was investigated for RPV bottom head component. Mechanical properties tests and fracture tests with plate specimens were performed using RPV law alloy steel (LAS) material. GTN model parameters of RPV LAS material that can reproduce stress-strain curve and load-displacement curve were determined. Fracture analyses of the plate specimens were performed using determined parameters as well. The load-Crack Mouth Opening Displacement (CMOD) curves and fracture behavior of the fracture tests were compared with the analyses results. The analyses predicted the maximum loads of the tests within an error of 4% and the fracture behavior between the tests and analyses was consistent. The results in this study clearly supported the applicability of the GTN model to RPV bottom head ring component.

Evaluation of ductile fracture in welded tubes with tensile, hardness, flaring tests

A continuum damage model (CDM) based on local hardness in welds is developed to predict fracture of welded tubes. A regression function of hardness distribution in the welds is proposed to establish hardness continuously through hardness mapping method in the finite element model. A constitutive model of the weld zone is determined by the rule of mixture, which estimates the flow stress of the welds from the hardness ratio. Coefficients of the flow stress model in the welds are validated by comparing finite element analysis (FEA) solution and experimental load - displacement data of tensile specimens. Softening after necking is considered by Lemaitre CDM. A damage parameter is newly given as a function of hardness ratio varying with angular position. Coefficients of damage parameter are obtained by the inverse FEA of tensile and flaring tests. The proposed method finely predicts the ductile fracture of welded tubes by considering local plastic properties and damage evolution.

Experimental investigation on cumulative damage indices for steel members under ultra-low-cycle loading

Notched bending specimens and axial load specimens were tested under different ultra-low cycle loadings to investigate the plastic deformation capacity and plastic energy capacity of steel members. A total of 53 experiments were performed in cyclic axial and bending configurations. The effect of notch shape, the order of mixed amplitudes, the average deformation of the amplitude, and the environmental temperature on plastic deformation capacity of steel members are studied. Four cumulative damage indices, including the ductility damage index, the normalized plastic energy damage index, the max-side ductility damage index, and the max-side normalized plastic energy damage index were compared for ductile fracture evaluation of these specimens under different ultra-low cycle loadings. The results indicated that the standard deviation of the normalized plastic energy damage index is the smallest among the four damage indices, which shows the lowest data dispersity. The max-side ductility damage index is larger than the ductility damage index, and the max-side normalized plastic energy damage index is larger than the normalized plastic energy damage index, both achieving a safety evaluation. Among the four damage indices, the max-side normalized plastic energy damage index achieves the maximum reliability.

高圧ガスパイプラインの高速延性破壊特性評価の現状と課題

高圧ガスパイプラインの高速延性破壊特性評価の現状と課題

楕円空孔モデルによる据込み加工時の延性破壊評価

楕円空孔モデルによる据込み加工時の延性破壊評価

AE法による高圧水素容器用A6061-T651合金の延性破壊評価

AE法による高圧水素容器用A6061-T651合金の延性破壊評価

019 楕円空孔モデルによる引張試験における延性破壊評価

019 楕円空孔モデルによる引張試験における延性破壊評価

An ellipsoidal void model for the evaluation of ductile fracture in sheet metal forming

A void model that can be used for the evaluation of ductile fracture in the simulation of sheet metal-forming processes is proposed. This void model is an extension of the Thomason model of void coalescence, which is based on the internal necking of the matrix between voids. In sheet metal-forming processes, the material is subjected to a complex strain path. Hence, the prestrain should be considered for the evaluation of ductile fracture in the simulation of sheet metal-forming processes. In the present paper, the prestrain is first introduced in the proposed void model. The simulation of the hole expansion test, which is a fundamental material test in sheet metal forming, is performed while paying special attention to the void configuration and the void shape. Finally, the validity of the proposed void model is confirmed by comparing the simulation results with the experimental results.

손상역학에 근거한 원자력 재료의 평면크기 영향 분석

The influences of stress triaxiality on ductile fracture have been investigated for various specimens and structures. With respect to a transferability issue, recently, the interests on local approaches reflecting micro-mechanical specifics are increased again due to rapid progress of computational environments. In this paper, the applicability of the local approaches has been examined through a series of finite element analyses incorporating modified GTN and Rousselier models as well as fracture toughness tests. The ductile crack growth of nuclear carbon steels is assessed to verify the transferability among compact tension (CT) specimens with different in-plane size. At first, the basic material constants were calibrated for standard CT specimens and used to predict fracture resistance (J-R) curves of larger CT specimens. Then, the in-plane size effects were examined by comparing the numerically estimated J-R curves with the experimentally determined ones. The assessment results showed that the in-plane size effect should be considered for realistic engineering application and the damage models might be used as useful tool for ductile fracture evaluation.

Evaluation of Ductile Fracture in Plastic Forming of Metal Sheet

It is significant to predict ductile fracture initiation in plastic forming of metal materials. Tube hidroforming (THF) is attracting general attention.THFprocess requires the control of internal liquid pressure and axial compression. In this case a ductile fracture may occur under stress triaxiality lower than that for uniaxial tension loading. In this report, combined longitudinal tensile and compression to thickness direction tests using thin plate specimens inA5083-Oaluminum alloy to obtain low stress triaxiality were carried out. On the basis of observations of ductile fracture processes it was founded that ductile fracture was shear type fracture controlled by a nucleation of micro-voids in this test. It is seemed that the local inclusion-matrix interfacial stress was constant independently of any stress ratio of tension and compression. Additionally, THFtests for SPFH590 tubes were performed. It was confirmed that the critical interfacial stress obtained using FE analysis forTHFtest was constant.

P23-02 非線形破壊力学によるステンレス鋼溶接部の延性破壊評価

P23-02 非線形破壊力学によるステンレス鋼溶接部の延性破壊評価

非線形破壊力学による金属キャスクの延性破壊評価手法

非線形破壊力学による金属キャスクの延性破壊評価手法

Evaluation of Ductile Fracture of Structural Steels by Microvoid Model.

In the present work, the ductile fracture of structural steels and the effect of plastic pre-strain on ductility have been investigated by tensile test. The fracture process consisting of void nucleation, growth and coalescence was observed by scanning electron microscopy (SEM). The nucleation strain of microvoid was measured experimentally. The critical interfacial strength of particle/matrix interface was calculated by dislocation model and continuum analysis, and the void growth was evaluated by Rice-Tracey model. It was found that longitudinal void coalescence does not affect fracture even though large cracks exist, but particle position affects void nucleation. Thomason's plastic limit-load model was used to predict void growth strain. Through the analysis of ductile fracture process, the influence of plastic pre-strain on ductility was discussed.

Strength Evaluation Method for Ductile Fracture at Structural Discontinuous Parts in the Ship Hull Structure under Collision

In ship collision the absorbed energy of the hull structures by the plastic deformation is limited by the ductile fracture initiated from structural discontinuous parts, so it is very important to clarify the stress and strain state at the location where ductile crack initiates. To develop a ductile fracture evaluation method with the aid of FEM analysis, tensile breaking tests of plate specimens with structural discontinuities such as small holes or weldments were performed followed by inelastic FEM analyses considering large deformation.It was found that ductile fracture strength can be evaluated by the ductile damage parameter considering the equivalent plastic strain and the stress triaxiality, and the critical value of the damage parameter for crack initiation was estimated as 0.5 for SS 400 steel plate by the FEM analyses used in this paper.