scholarly journals A Fracture Criterion for Prediction of Fracture Initiation of Metal Materials at Various Stress States for Nuclear Waste Storage

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Zhihui Li ◽  
Xue Yang ◽  
Anmin Tang
Keyword(s):  
Fracture Criterion ◽  
Shear Fracture ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Initiation Site ◽  
Fracture Mechanisms ◽  
Nuclear Waste Storage ◽  
Maximal Shear Stress ◽  
Stress States ◽  
New Criterion

A fracture criterion is newly proposed to evaluate fracture behavior and predict fracture initiation of metal materials in different complicated stress states for four different fracture mechanisms including quasicleavage fracture, normal fracture with void, shear fracture with void, and shear fracture without void. The dominant factors of these four different mechanisms are distinct, so it is impossible to capture all features of fracture initiation under different stress states with a single criterion, and different functions are necessary to predict fracture initiation of different mechanisms. In the new fracture criterion, different branches of the fracture criterion have been proposed corresponding to different fracture mechanisms. Quasicleavage fracture and normal fracture with void are described as a function of the principal stress, shear fracture with void is a function of the stress triaxiality and maximal shear stress, and shear fracture without void is only controlled by the maximal shear stress. The new fracture criterion is applied to predict the fracture initiation site and the fracture direction of nodular cast iron QT400-15 in combined tension-torsion tests. Predicted results are compared with experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 0 and 1/3. The new criterion is also applied to predict the crack initiation site and the direction of crack initiation of LY12 aluminium alloy and HY130 mild steel in mixed mode fracture tests to validate the performance of the new criterion in the high stress triaxiality. The new fracture criterion gives consistent results for these materials in a wide stress triaxiality range. It is shown that the new fracture criterion is a better supplement to the deficiency of fracture mechanics and also a better amendment to traditional strength theory in complicated stress states. Therefore, the new fracture criterion is recommended to be utilized to evaluate the fracture initiation of metal structures in nuclear waste storage and other engineering applications.

Shear Constraint and Macroscopic Fracture Criteria for Ductile Metals

1975 ◽  
Vol 42 (1) ◽  
pp. 15-24 ◽  
Author(s):  
M. A. Kaplan ◽  
G. A. Rowell
Keyword(s):  
Internal Pressure ◽  
Shear Fracture ◽  
Maximum Shear Stress ◽  
Fracture Initiation ◽  
Tensile Tests ◽  
Initiation Site ◽  
The Body ◽  
Fracture Criteria ◽  
Ductile Metals ◽  
Stress States

The role of material constraint in the shear fracture of ductile metals is investigated by means of a series of torsion and internal pressure tests on aluminum alloy tubing combined with analytical descriptions of the stress states at fracture. These descriptions include work hardening and, in the case of a tube under internal pressure, account for the nonaxisymmetric deformations that always precede fracture. The results, which indicate that shear fracture initiation depends on conditions at points far removed from the initiation site when the maximum shear stress vector there is directed through the interior of the body, are supported by the results of tensile tests on plates with shallow notches. These latter experiments are also used to show that tensile and shear fracture are governed by independent fracture criteria. A continuum fracture theory for ductile metals, based on the concepts of material constraint and independent fracture criteria, is proposed. The theory predicts fracture in terms of the stress state. A critical analysis of the theory is provided along with examples of fracture phenomena which the theory predicts, but which are not explained by existing theories.

Evaluation of prediction error resulting from using average state variables in the calibration of ductile fracture criterion

2017 ◽  
Vol 27 (8) ◽  
pp. 1231-1251 ◽  
Author(s):  
Xincun Zhuang ◽  
Yehui Meng ◽  
Zhen Zhao
Keyword(s):  
Ductile Fracture ◽  
Prediction Error ◽  
Fracture Criterion ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Equivalent Strain ◽  
State Variables ◽  
Ductile Fracture Criterion ◽  
Series Of Experiments ◽  
Relationship Of

In order to evaluate the prediction error resulting from using average state variables in the calibration procedure of the ductile fracture criterion, a series of experiments and corresponding simulations were performed to extract the evolution of fracture-related state variables such as stress triaxiality (η), Lode parameter, and equivalent strain to fracture at the fracture initiation points. The average stress triaxiality, average Lode parameter, and equivalent strain to fracture were used to calibrate the Lou-Huh (L-H) ductile fracture criterion. The average induced prediction error was evaluated by comparing the accumulated damage value, which was computed with the calibrated L-H ductile fracture criterion at the fracture initiation point, with the critical threshold value. Comparisons based on a series of experiments covering a wide range of values for stress triaxiality indicated the existence of an average induced prediction error for the compression tests, and demonstrated that different values of embedded-constants C1 and C2 of L-H ductile fracture criterion resulted in entirely different average induced prediction errors. Thus, a parameter study was performed to investigate the influences of C1, C2, the relationship of η and equivalent plastic strain ([Formula: see text]), and the internal function of the integral formula on the average induced relative error. The influence of the relationship of [Formula: see text] could be represented by the influence of the exponent a, the intercept for the stress triaxiality, and the allocation of equivalent strain for the segmented function. Among these influence factors, the value of C2, the value of the exponent a, and the value of the negative intercept for stress triaxiality contributed significantly to an increase in relative error.

Studies of Size Effect on the Formability of a Domed Part in Incremental Forming

2008 ◽  
Author(s):  
Y. Huang ◽  
J. Cao ◽  
S. Smith ◽  
B. Woody ◽  
J. Ziegert ◽  
...  
Keyword(s):  
Size Effect ◽  
Fracture Criterion ◽  
Incremental Forming ◽  
Single Point ◽  
Sheet Thickness ◽  
Fracture Initiation ◽  
Initiation Site ◽  
Forming Limit ◽  
Sheet Formability ◽  
Tool Diameter

The failure strain level in a single point incremental forming (SPIF) process is found to be much higher than that in the traditional stamping process. Based on the assumption that forming limits in SPIF are dominated by fracture failure, the Oyane ductile fracture criterion is introduced in this paper to predict the fracture initiation site, and hence the forming limit, given the stress and strain values obtained from finite element simulations. The predicted results compare well with those obtained from the SPIF experiments. Furthermore, this fracture criterion is used to study the size effects in SPIF. Analytical equations are derived to comprehensively consider the effects of design and process parameters on sheet formability including sheet thickness, tool diameter, and incremental depth. Previously published experimental data is used to verify the feasibility of the proposed size effect equation.

A Comparative Study on Various Ductile Crack Formation Criteria

2004 ◽  
Vol 126 (3) ◽  
pp. 314-324 ◽  
Author(s):  
Yingbin Bao ◽  
Tomasz Wierzbicki
Keyword(s):  
Crack Formation ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Equivalent Strain ◽  
Fracture Mechanisms ◽  
Ductile Crack ◽  
Fracture Criteria ◽  
Wide Range ◽  
Mechanical Models ◽  
Stress States

Various fracture criteria, based on different assumptions and different mechanical models, have been proposed in the past to predict ductile fracture. The objective of this study is to assess their effectiveness and accuracy in a wide range of process parameters. A series of tests on 2024-T351 aluminum alloy, including upsetting tests and tensile tests is carried out. It is found that none of the existing fracture criteria give consistent results. Two totally different fracture mechanisms are clearly observed from microfractographs of upsetting and tensile specimens. This observation confirms that it is impossible to capture all features of ductile crack formation in different stress states with a single criterion. It is shown that different functions are necessary to predict crack formation for different ranges of stress triaxiality. Weighting functions in a wide range of stress states can be obtained by determining the fracture locus in the space of equivalent strain to fracture and stress triaxiality.

A new ductile fracture criterion considering both shear and tension mechanisms on void coalescence

2020 ◽  
pp. 105678952096283
Author(s):  
Xifeng Li ◽  
Wenbing Yang ◽  
Dongkai Xu ◽  
Ke Ju ◽  
Jun Chen
Keyword(s):  
Aluminum Alloy ◽  
Ductile Fracture ◽  
Prediction Accuracy ◽  
Fracture Criterion ◽  
Fracture Strain ◽  
Stress Triaxiality ◽  
Void Coalescence ◽  
Ductile Fracture Criterion ◽  
New Criterion ◽  
1045 Steel

A new ductile fracture criterion is proposed based on three stages of ductile fracture: void nucleation, growth and coalescence from the microscopic viewpoint. Based on the observation of SEM fracture surfaces of AA2024-T351 aluminum alloy sheet and bar samples under different stress states, it is assumed that the void aggregation is controlled by shear or shear-tension fracture mechanism according to the stress state. And the stress triaxiality is deemed as the only influence factor for controlling the void growth. The new ductile fracture criterion applied to a wide range of stress triaxiality is built. By fitting the available testing data of AA2024-T351 aluminum alloy and AISI 1045 steel, the fracture loci in the stress triaxiality, Lode parameter and equivalent fracture strain space ([Formula: see text]) built by the new criterion are compared with those by DF2014, Hu criterion, modified Mohr-Coulomb criterion (MMC) and Hosford- Coulomb (H-C) criterion. The fitting results prove better prediction accuracy for the new criterion. To further compare the stability of these criteria, the fracture loci in the space of ([Formula: see text]) for AA2024-T351 alloy are established by only fitting five tests. The new criterion can still well predict the equivalent fracture strain ([Formula: see text]). Compared with DF2014, Hu criterion, MMC and H-C criterion, the average errors of the new criterion are reduced by 26.72%, 20.07%, 31.78% and 34.62%, respectively. Furthermore, the maximum errors are reduced by 49.62%, 27.31%, 33.76% and 29.91%, separately. Therefore, the new fracture criterion has higher prediction accuracy and better prediction stability. Last but certainly not least, the new criterion can predict more accurately under high stress triaxiality conditions.

scholarly journals Correlation of Macroscopic Fracture Behavior with Microscopic Fracture Mechanism for AHSS Sheet

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 900 ◽  
Author(s):  
Lingyun Qian ◽  
Xiaocan Wang ◽  
Chaoyang Sun ◽  
Anyi Dai
Keyword(s):  
Fracture Mechanism ◽  
Fracture Behavior ◽  
Pure Shear ◽  
Stress Triaxiality ◽  
High Strength ◽  
Numerical Approach ◽  
Fracture Mechanisms ◽  
Macroscopic Fracture ◽  
Shear Slip ◽  
Stress States

This research aims to correlate the macroscopic fracture phenomenon with its microscopic fracture mechanism for an advanced high-strength steel (AHSS) TRIP 780 sheet by applying a combined experimental-numerical approach. Six specimens with different shapes were tensioned to fracture and the main deformation areas of specimens were subjected to stress states ranging from lower to higher stress triaxiality. The final fracture surface feature for each specimen was obtained to characterize the macroscopic fracture modes at different stress states. The scanning electron microscope (SEM) fractographies of fracture surfaces were detected to reveal the microscopic fracture mechanisms. The stress triaxiality evolution was applied to correlate of fracture mode and fracture mechanism by comparing the macroscopic fracture features as well as micro-defect changes. An increase of stress triaxiality leads to voids extension and then results in a voids-dominant fracture. The micro-shear-slip tends to appear in the stress triaxiality level lower than that of pure shear stress state. The fracture behavior of a practice deformation process was the result of interplay between shear-slip fracture and void-dominant fracture. The unified relationship between average void sizes and stress triaxiality was obtained. The void growth was predicted by the Rice–Tracey model with higher precision.

scholarly journals Mechanical properties, deformation and fracture mechanisms of bimodal Cu under tensile test

2021 ◽  
Vol 60 (1) ◽  
pp. 15-24
Author(s):  
Silu Liu ◽  
Yonghao Zhao
Keyword(s):  
Yield Strength ◽  
Grain Refinement ◽  
Volume Fraction ◽  
Shear Fracture ◽  
High Strength ◽  
Tensile Specimen ◽  
Deformation Mechanisms ◽  
Fracture Mechanisms ◽  
Fracture Angle ◽  
Area Reduction

Abstract Metals with a bimodal grain size distribution have been found to have both high strength and good ductility. However, the coordinated deformation mechanisms underneath the ultrafine-grains (UFGs) and coarse grains (CGs) still remain undiscovered yet. In present work, a bimodal Cu with 80% volume fraction of recrystallized micro-grains was prepared by the annealing of equal-channel angular pressing (ECAP) processed ultrafine grained Cu at 473 K for 40 min. The bimodal Cu has an optimal strength-ductility combination (yield strength of 220 MPa and ductility of 34%), a larger shear fracture angle of 83∘ and a larger area reduction of 78% compared with the as-ECAPed UFG Cu (yield strength of 410 MPa, ductility of 16%, shear fracture angle of 70∘, area reduction of 69%). Grain refinement of recrystallized micro-grains and detwinning of annealing growth twins were observed in the fractured bimodal Cu tensile specimen. The underlying deformation mechanisms for grain refinement and detwinning were analyzed and discussed.

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.

Experimental and Numerical Investigation on the Influence of Process Speed on the Blanking Process

2002 ◽  
Vol 124 (2) ◽  
pp. 416-419 ◽  
Author(s):  
A. M. Goijaerts ◽  
L. E. Govaert ◽  
F. P. T. Baaijens
Keyword(s):  
Stainless Steel ◽  
Constitutive Model ◽  
Numerical Simulations ◽  
Ferritic Stainless Steel ◽  
Fracture Criterion ◽  
Fracture Initiation ◽  
Rate Dependence ◽  
Numerical Predictions ◽  
Punch Velocity ◽  
Blanking Process

In a previous work a numerical tool was presented which accurately predicted both process force and fracture initiation for blanking of a ferritic stainless steel in various blanking geometries. This approach was based on the finite element method, employing a rate-independent elasto-plastic constitutive model combined with a fracture criterion which accounts for the complete loading history. In the present investigation this work is extended with respect to rate-dependence by employing an elasto-viscoplastic constitutive model in combination with the previously postulated fracture criterion for ferritic stainless steel. Numerical predictions are compared to experimental data over a large range of process speeds. The rate-dependence of the process force is significant and accurately captured by the numerical simulations at speeds ranging from 0.001 to 10 mm/s. Both experiments and numerical simulations show no influence of punch velocity on fracture initiation.

scholarly journals Molecular and Functional Differences between Heart mKv1.7 Channel Isoforms

2006 ◽  
Vol 128 (1) ◽  
pp. 133-145 ◽  
Author(s):  
Rocio K. Finol-Urdaneta ◽  
Nina Strüver ◽  
Heinrich Terlau
Keyword(s):  
Translation Initiation ◽  
Cell Function ◽  
Functional Divergence ◽  
Initiation Site ◽  
Translation Initiation Site ◽  
Inactivation Kinetics ◽  
Mouse Heart ◽  
Redox Stress ◽  
Redox Modulation ◽  
Stress States

Ion channels are membrane-spanning proteins that allow ions to permeate at high rates. The kinetic characteristics of the channels present in a cell determine the cell signaling profile and therefore cell function in many different physiological processes. We found that Kv1.7 channels from mouse heart muscle have two putative translation initiation start sites that generate two channel isoforms with different functional characteristics, mKv1.7L (489 aa) and a shorter mKv1.7S (457 aa). The electrophysiological analysis of mKv1.7L and mKv1.7S channels revealed that the two channel isoforms have different inactivation kinetics. The channel resulting from the longer protein (L) inactivates faster than the shorter channels (S). Our data supports the hypothesis that mKv1.7L channels inactivate predominantly due to an N-type related mechanism, which is impaired in the mKv1.7S form. Furthermore, only the longer version mKv1.7L is regulated by the cell redox state, whereas the shorter form mKv1.7S is not. Thus, expression starting at each translation initiation site results in significant functional divergence. Our data suggest that the redox modulation of mKv1.7L may occur through a site in the cytoplasmic N-terminal domain that seems to encompass a metal coordination motif resembling those found in many redox-sensitive proteins. The mRNA expression profile and redox modulation of mKv1.7 kinetics identify these channels as molecular entities of potential importance in cellular redox-stress states such as hypoxia.

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