A study on central crack formation in cross wedge rolling

Zhou, Xiaochen; Shao, Zhutao; Pruncu, Catalin I.; Hua, Lin; Balint, Daniel S.; Lin, Jianguo; Jiang, Jun

doi:10.1016/j.jmatprotec.2019.116549

Cited by 41 publications

(27 citation statements)

References 27 publications

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“…It was found that the criteria which take into account, at least indirectly, the effect of shear stresses yield better results. Similar observations were made by Zhou et al [ 20 ]. In-depth analyses of the stress state in the rotary compression tests and CWR [ 21 ] revealed that the stresses are not identical, which may affect the accuracy of modelling material fracture in CWR.…”

Section: Introductionsupporting

confidence: 91%

Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

et al. 2021

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This study investigates the problem of material fracture in cross wedge rolling (CWR). It was found that this problem could be analysed by means of well-known phenomenological criteria of fracture that are implemented in commercial FEM (Finite Element Method) simulation programs for forming processes. The accuracy of predicting material fracture depends on the critical damage value that is determined by calibration tests in which the modelled and real stresses must be in good agreement. To improve this accuracy, a new calibration test is proposed. The test is based on the CWR process. Owing to the shape of the tools and test piece used in CWR, the forming conditions in this process deteriorate with the distance from the centre of the test piece, which at a certain moment leads to fracture initiation. Knowing the location of axial crack initiation in the specimen, it is possible to determine the critical value of material damage via numerical simulation. The new calibration test is used to determine the critical damage of 42CrMo4 steel subjected to forming in the temperature range of 900–1100 °C. In addition, 12 criteria of ductile fracture are employed in the study. The results show that the critical damage significantly increases with the temperature.

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Section: Introductionsupporting

confidence: 91%

Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

et al. 2021

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“…Furthermore, in industry, the loading condition on the workpiece is much more complex, as studied in the previous work [5], being subjected to triaxial stress state, cyclic loading, and large plastic strain. This complex loading condition accelerates the decohesion between the inclusion and steel matrix.…”

Section: Fracture Mechanisms In Cwrmentioning

confidence: 99%

“…Yang et al [4] studied central crack formation on a microstructural scale and revealed the ductile fracture mechanism of steels at high temperature. Zhou et al [5] considered the combined effects of the shear and normal stress and proposed a novel fracture criterion, which was validated quantitively. However, there is not an agreement on the fracture mechanisms of central crack formation due to the complex mechanical and microstructural behaviours during CWR.…”

Section: Introductionmentioning

confidence: 99%

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

et al. 2020

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Central cracking in cross-wedge-rolled workpieces results in high wastage and economic loss. Recent cross-wedge rolling tests on two batches of steel showed that one batch formed central cracks, while the other was crack-free. The batches were both nominally of the same chemical composition and thermomechanical treatment history. In addition, both batches had passed all the standard quality assessments set for conventional forging processes. It was suspected that the different cracking behaviours were due to differences in microstructure between the two as-received steel billets, and the material in cross-wedge rolling (CWR) was more sensitive to the initial microstructure compared with other forging processes due to its specific loading condition including ostensibly compression and large plastic strain. Nevertheless, no previous study of this important problem could be identified. The aim of this study is, therefore, to identify the key microstructural features determining the central crack formation behaviour in CWR. The hot workability of the as-received billets was studied under uniaxial tensile conditions using a Gleeble 3800 test machine. Scanning electron microscope with energy-dispersive X-ray spectroscopy and electron backscatter diffraction was applied to characterise, quantitatively analyse, and compare the chemical composition, phase, grain, and inclusions in these two billets, both at room temperature and also at the CWR temperature (1080°C). Non-metallic inclusions (oxides, sulphides, and silicates) in the billets were determined to be the main cause of the reported central cracking problem. The ductility of the steels at both room and elevated temperatures deteriorated markedly in the presence of the large volumes of inclusions. Grain boundary embrittlement occurred at the CWR temperature due to the aggregation of inclusions along the grain boundaries. It is suggested that a standard on specifying the inclusion quantity and size in CWR billets be established to produce crack-free products.

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“…In this equation, A and B are material constants, presenting the contribution ratios of the maximum shear stress τ m and the rst principal stress σ 1 to central crack formation. Zhou et al [17,22] has validated this criterion by low ductility materials, including 27 groups of pure aluminium (highly strained) CWR tests and 16 groups of CWR tests with plasticine/ our composites. When the material is at high ductility, an energy-based fracture criterion will be employed considering the severe plastic deformation occurs before nal fracture, as presented in Eq.…”

Section: Proposal Of a New Central Crack Criterionmentioning

confidence: 99%

“…Recently, Pater et al [16] proposed a damage model considering the fracture mechanisms, void formation and shear fracture, achieving high accuracy in C45 steel at the elevated temperature. Zhou et al [22] proposed a physics-based fracture criterion capable of predicting the central cracks in 27 groups of CWR tests on pure aluminium AA1100 with different die geometries. However, these models have never been validated by different materials, which exhibit different fracture mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Investigation and prediction of central cracking in cross wedge rolling

Zhou¹,

Sun²,

Wang³

et al. 2022

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Central cracking refers to the formation of internal cavities in cross wedge rolling (CWR) products. It occurs in various materials such as aluminium/titanium alloys, steels and plasticine at room or elevated temperatures, driven by different central cracking mechanisms. However, these mechanisms are still elusive, and a unified central cracking predictive model is absent due to the complex stress states within the workpiece, including triaxial stress states, cyclic loading and severe shear effects. In this study, the underlying fracture mechanisms were revealed, and a robust unified damage model with sound physical meanings was developed using a lab-scale CWR physical model and finite element models. The physical model with the plasticine billets was built, allowing the CWR dies with different geometries rapidly 3D printed and the billets with various ductility efficiently manufactured. The central cracking transiting from brittle to ductile fracture was experimentally observed for the first time using specifically designed plasticine/flour composite samples at varying ductility. The corresponding physics-based central cracking predictive model was proposed and validated quantitatively with 60 groups of CWR tests and compared with ten existing damage models/fracture criteria. This study effectively solves the long-lasting central cracking problem in the CWR industry and enhances the scientific understanding of fracture mechanics in complex engineering applications.

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A study on central crack formation in cross wedge rolling

Cited by 41 publications

References 27 publications

Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

Determination of the Critical Value of Material Damage in a Cross Wedge Rolling Test

Microstructural effects on central crack formation in hot cross-wedge-rolled high-strength steel parts

Investigation and prediction of central cracking in cross wedge rolling

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