Notch Effects, Stress State, and Ductility

1978 ◽  
Vol 100 (4) ◽  
pp. 348-355 ◽  
Author(s):  
Alice M. Agogino
Keyword(s):  
Stress State ◽  
Stress Triaxiality ◽  
Review Of The Literature ◽  
Simple Criterion ◽  
Short Term ◽  
Notched Specimens ◽  
Tension Tests ◽  
Notch Geometry ◽  
Limiting Value ◽  
Triaxiality Factor

A review of the literature on testing of notched specimens is provided with emphasis on short-term notched bar tension tests. The effects of notch geometry, stress state, and smooth-bar tensile properties on notched ductility, notch sensitivity, and mode of fracture are discussed. For design against failure due to notch weakening, a simple criterion based on a limiting value of notched ductility is proposed. Notched ductility for the metals considered in this study, can be approximated by the reduction in and from a smooth tension test divided by a tensile stress triaxiality factor that is proportional to the ratio of hydrostatic to octahedral shearing stresses associated with the notch.

Prediction of Creep Void Growth in Heat-Affected Zone of High Chromium Steel Weldments Considering Multiaxial Stress State

2012 ◽  
Author(s):  
Eiji Murakami ◽  
Masamitsu Hashimoto ◽  
Seiji Kikuhara
Keyword(s):  
Stress State ◽  
Heat Affected Zone ◽  
Void Growth ◽  
Stress Triaxiality ◽  
Chromium Steel ◽  
Growth Behavior ◽  
High Chromium ◽  
Multiaxial Stress State ◽  
The Relationship ◽  
Triaxiality Factor

This paper deals with a method for predicting creep void growth in heat-affected zone (HAZ) of high chromium steel weldments. The method has been proposed by authors based on the relationship between creep void density increasing rate and multiaxial stress state. In this study, internal pressure creep tests of ASME grade 91 (9Cr-1Mo-Nb-V) tubes with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses of the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and void distributions revealed that stress triaxiality factor predominantly affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that there is a proportional relationship between creep void density increasing rate and the parameter to represent stress multiaxiality on the logarithmic graph. To verify proposed prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates were in good agreement with experimental results.

Simplified Prediction of Creep Void Density in Heat-Affected Zone of Grade 122 Steel Considering Multiaxial Stress State

2013 ◽  
Author(s):  
Eiji Murakami ◽  
Masamitsu Hashimoto ◽  
Seiji Kikuhara
Keyword(s):  
Stress State ◽  
Void Growth ◽  
Stress Triaxiality ◽  
Prediction Method ◽  
Growth Behavior ◽  
Multiaxial Stress State ◽  
Grade 91 ◽  
The Relationship ◽  
Tubular Specimens ◽  
Triaxiality Factor

This paper deals with a simplified method for approximately predicting creep void growth in heat-affected zone (HAZ) of ASME grade 122 (11Cr-2W-0.4Mo-Cu-Nb-V) steel weldments. Authors have proposed a simplified prediction method based on the relationship between creep void density increasing rate and multiaxial stress state. This method has been applied to prediction of creep void growth behavior for grade 91 (9Cr-1Mo-Nb-V) tubular specimens with longitudinal weldments. In this study, the method has been also applied to grade 122 steel to clarify the applicability of the method. Internal pressure creep tests of grade 122 tubular specimens with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses for the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and creep void distributions revealed that stress triaxiality factor affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that the slope of this relationship for 122 steel has a tendency to be slightly small compared with grade 91 steel. To demonstrate the applicability of the proposed simplified prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates for grade 122 steel were in good agreement with the experimental results.

scholarly journals Effect of Stress Triaxiality on the Strain Concentration Factor

2019 ◽  
Vol 8 (4) ◽  
pp. 3468-3474
Keyword(s):  
Stress State ◽  
Concentration Factor ◽  
Notch Root ◽  
Stress Triaxiality ◽  
Critical Section ◽  
Triaxial Stress ◽  
Triaxial Stress State ◽  
Strain Concentration ◽  
Machine Element ◽  
Triaxiality Factor

Axisymmetric machine element with irregularities such as notches encountered with effects of stress triaxiality on the strain concentration factor (SNCF) at the reduced section. The effect of notch geometries on the triaxial stress state development in the critical section of a notched cylindrical bar is studied here using FEM. In addition, the effect of triaxial stress state (TSS) on the SNCF is evaluated. To this end, a notched cylindrical bars with notch depths from extremely deep notch (do/Do = 0.2) shallow notch (do/Do = 0.95) has been employed. The results show that the notches introduce a TSS at the critical section, which strongly affected by the notch depth as well as the notch radii. In this paper, a new concentration factor is introduced as the ratio of the stress triaxiality factor at the notch root (TFNR) to the average triaxiality on the critical section (), i.e. the triaxiality concentration factor KTF. The numerical results reveal that the variation of the average triaxiality factor with total strain shows the same trend as that of the SNCF. The variation of the elastic values of TFCN, , , and SNCF with do/Do and show that the minimum TFNR leads to the maximum elastic SNCF. It is prominent that elastic TFNR is less that elastic TFCN for 0.2 ≤ do/Do ≤ 0.85, while it is greater for shallow notches. The current results indicate a strong compatibility between the newly defined triaxiality concentration factor and the SNCF up to general yielding.

Hydrogen Diffusion in Metals Assisted by Stress: 2D Numerical Modelling and Analysis of Directionality

2014 ◽  
Vol 225 ◽  
pp. 33-38 ◽  
Author(s):  
Jesús Toribio ◽  
Viktor Kharin ◽  
Diego Vergara ◽  
Miguel Lorenzo
Keyword(s):  
Stress State ◽  
Hydrogen Diffusion ◽  
Loading Rate ◽  
Hydrostatic Stress ◽  
Additional Term ◽  
One Dimensional ◽  
Loading Rates ◽  
Notched Specimens ◽  
Notch Geometry ◽  
Numerical Modelling And Analysis

Hydrogen diffusion within a metal or alloy is conditioned by the stress-strain state therein. For that reason it is feasible to consider that hydrogen diffuses in the material obeying a Fick type diffusion law including an additional term to account for the effect of the stress state represented by the hydrostatic stress. In this paper the hydrogen transport by diffusion in metals is modelled in notched specimens where loading generates a triaxiality stress state. To this end, two different approaches of stress-assisted hydrogen diffusion, one-dimensional (1D) and two-dimensional (2D), were compared in the vicinity of the notch tip in four notched specimens with diverse triaxiality level at two different loading rates. The obtained results show that the 2D approach predicts lower values of hydrogen concentration than the 1D approach, so that a loss of directionality of hydrogen diffusion, depending on both notch geometry parameters (radius and depth) and loading rate, appears when a 2D approach is considered.

Creep Damage Evaluation for Fine Grained HAZ of Mod. 9Cr Steels Under Multi-Axial Stress Conditions

2013 ◽  
Author(s):  
Kimiaki Yoshida ◽  
Masataka Yatomi ◽  
Masaaki Tabuchi ◽  
Ken-ichi Kobayashi
Keyword(s):  
Axial Stress ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Creep Rupture ◽  
Stress Conditions ◽  
Damage Evaluation ◽  
Metallographic Examination ◽  
Fine Grained ◽  
Notched Specimens ◽  
Triaxiality Factor

This study is concerned with the creep damage evaluation for the fine grained heat affected zone (HAZ) of modified 9Cr steels under multi-axial stress conditions. Circumferentially notched bar creep rupture and interrupted tests have been conducted on the simulated HAZ specimens of modified 9Cr Steels. A metallographic examination has been carried out to quantify creep damage accumulation in the specimens. It has been found from void observation that growth of creep void correlates with maximum principle stress and stress triaxiality factor. Finite element predictions based on ductility exhaustion approach have also been performed to predict the creep rupture time and creep damage in notched specimens. It has been concluded that a ductility exhaustion approach with empirical model provides reasonable life predictability almost in a scatter band of a factor of 2.

scholarly journals Comparison of Modified Mohr–Coulomb Model and Bai–Wierzbicki Model for Constructing 3D Ductile Fracture Envelope of AA6063

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Jianye Gao ◽  
Tao He ◽  
Yuanming Huo ◽  
Miao Song ◽  
Tingting Yao ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Fracture Criterion ◽  
Fracture Strain ◽  
Stress Triaxiality ◽  
Ductile Fracture Criterion ◽  
Forming Process ◽  
Tension Tests ◽  
Wide Range ◽  
Round Bar ◽  
Fracture Envelope

AbstractDuctile fracture of metal often occurs in the plastic forming process of parts. The establishment of ductile fracture criterion can effectively guide the selection of process parameters and avoid ductile fracture of parts during machining. The 3D ductile fracture envelope of AA6063-T6 was developed to predict and prevent its fracture. Smooth round bar tension tests were performed to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar tension tests, compression tests and torsion tests. These tests cover a wide range of stress triaxiality (ST) and Lode parameter (LP) to calibrate the ductile fracture criterion. Plasticity modeling was performed, and the predicted results were compared with corresponding experimental data to verify the plasticity model after these experiments. Then the relationship between ductile fracture strain and ST with LP was constructed using the modified Mohr–Coulomb (MMC) model and Bai-Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, two ductile damage models were proposed based on the 3D fracture envelope of AA6063. Through the comparison of the two models, it was found that BW model had better fitting effect, and the sum of squares of residual error of BW model was 0.9901. The two models had relatively large errors in predicting the fracture strain of SRB tensile test and torsion test, but both of the predicting error of both two models were within the acceptable range of 15%. In the process of finite element simulation, the evolution process of ductile fracture can be well simulated by the two models. However, BW model can predict the location of fracture more accurately than MMC model.

scholarly journals Actinomyces meyeriEmpyema: A Case Report and Review of the Literature

2015 ◽  
Vol 2015 ◽  
pp. 1-4 ◽  
Author(s):  
Hae Won Jung ◽  
Chong Rae Cho ◽  
Ji Yoon Ryoo ◽  
Hyun Kyo Lee ◽  
So Young Ha ◽  
...  
Keyword(s):  
Pleural Fluid ◽  
Response To Treatment ◽  
Penicillin G ◽  
Review Of The Literature ◽  
Short Term ◽  
Oral Amoxicillin ◽  
History Of ◽  
Multiple Lung Nodules ◽  
The Right ◽  
Radiological Studies

Actinomyces meyeriis an uncommon cause of human actinomycosis. Here, we report a rare case of empyema caused byA. meyeri. A 49-year-old male presented with a history of 10 days of dyspnea and chest pain. A large amount of loculated pleural effusion was present on the right side and multiple lung nodules were documented on radiological studies. A chest tube was inserted and purulent pleural fluid was drained.A. meyeriwas isolated in anaerobic cultures of the pleural fluid. The infection was alleviated in response to treatment with intravenous penicillin G (20 million IU daily) and oral amoxicillin (500 mg every 8 hours) for 4 months, demonstrating that short-term antibiotic treatment was effective.

Failure Strain Criterion Accounting for the Effect of Material Strength

2021 ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Failure Criterion ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength Steels ◽  
Local Failure ◽  
Material Strength ◽  
Lode Parameter ◽  
Steel Grades

Abstract The objective of this study is to investigate the effect of the Lode parameter on different material strengths. Recent work has shown that ductile failure highly depends on the stress state characterized by both the stress triaxiality T and the Lode parameter L, which is related to the third deviatoric stress invariant. Thus, for six different steel grades, two different specimen geometries were manufactured to account for two different Lode parameters (L = −1 and L = 0), whereas T is controlled by introducing different sized notches at the center of the specimens. By performing tensile experiments and running finite element simulations, the ductile failure loci of the six materials showed variations between the two specimen geometries, indicating that the failure highly depends on the stress state characterized by both T and L. This indicates the need to reassess the ductile local failure criterion in the ASME codes that only accounts for T as a stress state measure. A Lode sensitivity parameter LS is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels.

scholarly journals Stress Triaxiality and Lode Angle Parameter Characterization of Flat Metal Specimen with Inclined Notch

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1627
Author(s):  
Jian Peng ◽  
Peishuang Zhou ◽  
Ying Wang ◽  
Qiao Dai ◽  
David Knowles ◽  
...  
Keyword(s):  
Stress State ◽  
Notch Root ◽  
Stress Triaxiality ◽  
Image Correlation ◽  
Notch Angle ◽  
Strain Evolution ◽  
Metal Specimen ◽  
Lode Angle ◽  
Stress States ◽  
Angle Parameter

The stress state has an important effect on the deformation and failure of metals. While the stress states of the axisymmetric notched bars specimens are studied in the literature, the studies on the flat metal specimen with inclined notch are very limited and the stress state is not clearly characterized in them. In this paper, digital image correlation and finite element simulations are used to study the distribution of strain and stress state, that is stress triaxiality and Lode angle parameter. Flat specimen with inclined notch was tested to extract the full field strain evolution and calculate stress state parameters at three locations: specimen centre, notch root and failure starting point. It is found that compared with the centre point and the notch root, the failure initiation point can better characterize the influence of the notch angle on the strain evolution. Conversely, the centre point can more clearly characterize the effect of the notch angle on stress state, since the stress states at the failure point and the notch root change greatly during the plastic deformation. Then the calculated stress state parameters of the flat metal specimen with inclined notch at the centre point are used in Wierzbicki stress state diagram to establish a relationship between failure mode and stress state.

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