Dual-Scale Porosity Effects on Crack Growth in Additively Manufactured Metals: 3D Ductile Fracture Models

In order to investigate the effects of hydrogen on the fatigue crack growth behavior of low carbon steel JIS S10C, bending fatigue tests were carried out using a specimen with a small blind artificial hole in a low pressure pure hydrogen gas atmosphere. The results show that the fatigue crack growth rate in hydrogen gas is higher than that in nitrogen gas, moreover, the degree of acceleration is greater in the high strain range. In fractography, intergranular facets mixed with ductile fracture and quasi-cleavage fracture with brittle striations appear in a hydrogen gas environment, while only ductile fracture mainly appears in nitrogen gas. In the low growth rate range, many intergranular facets are seen on the ductile fracture surface, and in the higher growth rate range, quasi-cleavage facets increase as the growth rate increases. The growth rate of a small crack in nitrogen gas can be expressed by dl/dN ∝ Δεpnl in the wide range of applied total strain range Δεt. The same type equation is also satisfied in hydrogen gas, but in the narrow range roughly from Δεt = 0.25% to Δεt = 0.37%. The fracture surface in this range shows only intergranular facets and a ductile morphology, but no quasi-cleavage fracture. Although the crack growth mechanism in hydrogen is different from that in nitrogen, observation of the mechanism of intergranular facet formation shows a similarity to the mechanism in nitrogen in which the slip-off mechanism of crack growth is valid. The formation of intergranular facets is also closely related to the slip behavior influenced by hydrogen. This means that there exists a high possibility for the application of the small crack growth law inhydrogen to not only S10C, but also to other carbon steels in which the intergranular facet appears.

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Forming limit analysis of Mg-2Zn-1.2Al-0.2Ca-0.2RE alloy sheet using ductile fracture models

International Journal of Damage Mechanics ◽

10.1177/1056789519855763 ◽

2019 ◽

Vol 29 (8) ◽

pp. 1181-1198 ◽

Cited By ~ 1

Author(s):

Fei-Fan Li ◽

Gang Fang ◽

Ling-Yun Qian

Keyword(s):

Magnesium Alloy ◽

Ductile Fracture ◽

Stress Triaxiality ◽

Forming Limit Diagram ◽

Alloy Sheet ◽

Image Correlation ◽

Forming Limit ◽

Correlation Technique ◽

Forming Limits ◽

Fracture Models

This work was aimed to experimentally and theoretically investigate the formability of a new magnesium alloy sheet at room temperature. The fracture forming limit diagram was predicted by MMC3 and DF2014 models, where the non-linear strain path effect was taken into account by means of damage accumulation law. In order to obtain the instantaneous values of the stress triaxiality and the Lode parameter during the deformation process, strains tracked by digital image correlation technique were transformed into stresses based on the constitutive equations. The fracture forming limit diagram predicted by the fracture models was compared with the forming limits obtained by ball punch deformation tests. The prediction errors were evaluated by the accumulative damage values, which verified the advantages of ductile fracture models in predicting the forming limits of the magnesium alloy sheets.

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Edge Fracture Prediction Using Uncoupled Ductile Fracture Models for DP780 Sheet

Journal of Failure Analysis and Prevention ◽

10.1007/s11668-017-0245-z ◽

2017 ◽

Vol 17 (2) ◽

pp. 321-329 ◽

Cited By ~ 8

Author(s):

Lei Mu ◽

Yuan Wang ◽

Yong Zang ◽

Pedro Malaquias Araujo Stemler

Keyword(s):

Ductile Fracture ◽

Fracture Prediction ◽

Edge Fracture ◽

Fracture Models

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Measurement on Fracture Roughness Values of the Cast Steel for Chinese Railway Rolling Wagon Bogie Frames

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.118-120.100 ◽

2010 ◽

Vol 118-120 ◽

pp. 100-104 ◽

Cited By ~ 1

Author(s):

Wen Dong Shao ◽

Yong Xiang Zhao

Keyword(s):

Ductile Fracture ◽

Crack Growth ◽

Cast Steel ◽

Measuring Method ◽

Growth Increment ◽

Roughness Measurement ◽

Present Material ◽

Fracture Roughness ◽

Bogie Frame ◽

Growth Increments

Measurement on fracture roughness values is investigated to the grade B cast steel for China railway rolling wagon bogie frames. Due to be limited by production bogie frame geometry, a ductile fracture roughness measuring method is employed for the present study. Experiments reveal that, when crack growth increments are very scattered, the code based measurement of 0.2 mm crack growth increment for gauge ductile fracture roughness may be not reasonable. And a measurement of 90 % maximum ductile fracture roughness should be suggested to be an appropriate measurement. The new suggested 90 % maximum fracture roughness measurement is verified to be effective for the fracture roughness values of the present material.

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Comparison of MMC and BW fracture models for constructing 3D ductile fracture envelope of AA6063 during cold forming

10.21203/rs.3.rs-48534/v1 ◽

2020 ◽

Author(s):

Jianye Gao ◽

Tao He ◽

Yuanming Huo ◽

Miao Song ◽

Tingting Yao ◽

...

Keyword(s):

Ductile Fracture ◽

Damage Model ◽

Stress Triaxiality ◽

Compression Tests ◽

Cold Forming ◽

Tension Tests ◽

Wide Range ◽

Round Bar ◽

Fracture Models ◽

Fracture Envelope

Abstract The 3D ductile fracture envelopes of AA6063-T6 was developed to predict and prevent its fracture. Smooth round bar (SRB) tension tests were carried out to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar (NR) 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 and Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, a new ductile damage model was proposed based on the 3D fracture envelope of AA6063. The final results show that the predicted results from the proposed ductile fracture model showed good agreement with experimental results.

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On the micromechanism of inclusion driven ductile fracture and its implications on fracture toughness

10.31224/osf.io/s6epj ◽

2020 ◽

Author(s):

Yu Liu ◽

Xinzhu Zheng ◽

shmuel osovski ◽

Ankit Srivastava

Keyword(s):

Fracture Toughness ◽

Ductile Fracture ◽

Crack Growth ◽

Volume Fraction ◽

Void Nucleation ◽

Small Scale ◽

Crack Advance ◽

Crack Growth Behavior ◽

Ductile Crack ◽

Material Parameters

The objective is to identify the micromechanism(s) of ductile crack advance, and isolatethe key microstructural and material parameters that a?ect these micromechanisms andfracture toughness of ductile structural materials. Three dimensional, ?nite element, ?nitedeformation, small scale yielding calculations of mode I crack growth are carried out forductile material matrix containing two populations of void nucleating particles using anelasto-viscoplastic constitutive framework for progressively cavitating solid. The larger par-ticles or inclusions that result in void nucleation at an early stage are modeled discretelywhile smaller particles that require large strains to nucleate voids are homogeneously dis-tributed. The size, spacing and volume fraction of inclusions introduce microstructure-basedlength-scales. In the calculations, ductile crack growth is computed and fracture toughness ischaracterized. Several features of crack growth behavior and dependence of fracture tough-ness on microstructural and material parameters observed in experiments, naturally emergein our calculations. The extent to which the microstructural and material parameters a?ectthe micromechanisms of ductile crack advance and, hence, the macroscopic fracture tough-ness of the material is discussed. The results presented provide guidelines for microstructuralengineering to increase ductile fracture toughness, for example, the results show that for amaterial with small inclusions, increasing the mean inclusion spacing has a greater e?ect onfracture toughness than for a material with large inclusions.

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