Effects of Stress Triaxiality on Fracture Strain of Aluminum Alloy plates

The effect of stress triaxiality on mechanical properties of 6061 aluminium alloy extruded profiles with different specimens was studied. Macroscopic mechanical property of the various specimen was got through universal testing machine. At the same time, stress triaxiality of different specimens was obtained using the method of finite element simulation. And then the fracture strain of each specimen was outputted by DIC. Fracture modes of 6061 aluminium alloy with different stress triaxiality were studied by SEM. The results show that taking tensile samples as comparison, the cross-sectional area of some notched specimens decreases and the peak load increases. Among them, the minimum cross-sectional area of the R5 central hole specimen is 20% smaller than that of the tensile sample, and the peak load is 28% larger. The fracture strain of the alloy increased with the decrease of stress triaxiality. For the same notch specimens, along the path direction, stress triaxiality of R5 notch specimens, R5 Center-hole specimens and R20 Arc notched specimens increased 47%, 17.8%, 25% respectively. According to the analysis of fracture morphology, the main fracture of 6061 aluminium alloy was ductile fracture. When the stress triaxiality is large, the dimples are small and sparsely distributed, and when the stress triaxiality is small, the dimple is large and evenly distributed. Finally, the Johnson-Cook model material parameters of 6061 aluminum alloy are fitted based on the tensile test results of different shapes of specimens, which can accurately simulate the elastic-plastic deformation and fracture instability of 6061 aluminum alloy under different stress states.

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

International Journal of Damage Mechanics ◽

10.1177/1056789520962831 ◽

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.

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

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-021-00549-4 ◽

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.

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Study of Influence of Width to Thickness Ratio in Sheet Metals on Bendability under Ambient and Superimposed Hydrostatic Pressure

Applied Mechanics ◽

10.3390/applmech2030030 ◽

2021 ◽

Vol 2 (3) ◽

pp. 542-558

Author(s):

Mohammadmehdi Shahzamanian ◽

David Lloyd ◽

Amir Partovi ◽

Peidong Wu

Keyword(s):

Hydrostatic Pressure ◽

Stress Ratio ◽

Fracture Strain ◽

Stress Triaxiality ◽

Volumetric Strain ◽

Thickness Ratio ◽

Sheet Metals ◽

The Finite Element Method ◽

Bending Strain ◽

Good Agreement

The effect of the width to thickness ratio on the bendability of sheet metal is investigated using the finite element method (FEM) employing the Gurson–Tvergaard–Needleman (GTN) model. Strain path changes in the sheet with change in the width/thickness ratio. It is shown that bendability and fracture strain increase significantly by decrease in the width/thickness ratio. The stress state is almost uniaxial when the stress ratio (α) is close to zero for narrow sheets. Stress ratio is nothing but the major stress to minor stress ratio. This delays the growth and coalescence of micro-voids as the volumetric strain and stress triaxiality (pressure/effective stress) decrease. On the other hand, ductility decreases with increase in α for wider sheets. Fracture bending strain is calculated and, as expected, it increases with decrease in the width/thickness ratio. Furthermore, a brief study is performed to understand the effect of superimposed hydrostatic pressure on fracture strain for various sheet metals with different width/thickness ratios. It is found that the superimposed hydrostatic pressure increases the ductility, and that the effect of the width/thickness ratio in metals on ductility is as significant as the effect of superimposed hydrostatic pressure. Numerical results are found to be in good agreement with experimental observations.

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Effects of stress triaxiality and strain rate on the fracture of a CuCrZr alloy

Journal of Nuclear Materials ◽

10.1016/j.jnucmat.2020.152546 ◽

2021 ◽

Vol 543 ◽

pp. 152546

Author(s):

Yiqiang Wang ◽

Omar Mohamed ◽

Keren Dunn ◽

Tan Sui ◽

Mutaz Bashir ◽

...

Keyword(s):

Strain Rate ◽

Stress Triaxiality ◽

Effects Of Stress

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Mesh Size Effect on Numerical Fracture Strain of Aluminum Alloy plate A 2024-T3

The Proceedings of Conference of Tokai Branch ◽

10.1299/jsmetokai.2019.68.116 ◽

2019 ◽

Vol 2019.68 (0) ◽

pp. 116

Author(s):

Slim DJEBIEN ◽

Masahiro NISHIDA ◽

Toru TSUDA

Keyword(s):

Aluminum Alloy ◽

Size Effect ◽

Fracture Strain ◽

Mesh Size ◽

Alloy Plate ◽

Aluminum Alloy Plate

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Stress-Strain Behavior of an Aluminum Alloy Under Transient Strain-Rates

Journal of Pressure Vessel Technology ◽

10.1115/1.4003470 ◽

2011 ◽

Vol 133 (4) ◽

Cited By ~ 2

Author(s):

Y. W. Kwon ◽

Y. Esmaeili ◽

C. M. Park

Keyword(s):

Aluminum Alloy ◽

Strain Rate ◽

Fracture Strain ◽

Strain Curve ◽

Strain Rates ◽

Stress Strain Curve ◽

Stress Strain ◽

Single Strain ◽

Transient Strain ◽

Strain Rate Loading

Because most structures are subjected to transient strain-rate loading, an experimental study was conducted to investigate the stress-strain behaviors of an aluminum alloy undergoing varying strain-rate loading. To this end, uniaxial tensile loading was applied to coupons of dog-bone shape such that each coupon underwent two or three different strain-rates, i.e., one rate after another. As a basis, a series of single-strain-rate tests was also conducted with strain-rates of 0.1–10.0 s−1. When the material experienced multistrain-rate loading, the stress-strain curves were significantly different from any single-strain-rate stress-strain curve. The strain-rate history affected the stress-strain curves under multistrain-rate loading. As a result, some simple averaging of single-strain-rate curves did not predict the actual multistrain-rate stress-strain curve properly. Furthermore, the fracture strain under multistrain-rate loading was significantly different from that under any single-strain-rate case. Depending on the applied strain-rates and their sequences, the former was much greater or less than the latter. A technique was proposed based on the residual plastic strain and plastic energy density in order to predict the fracture strain under multistrain-rate loading. The predicted fracture strains generally agreed well with the experimental data. Another observation that was made was that the unloading stress-strain curve was not affected by the previous strain-rate history.

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