scholarly journals Establishment of Thermal Ductile Fracture Criterion for As-Cast 42CrMo Steel and Its Application in Hot Ring Rolling Process

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Yuanyuan Chen ◽  
Huiping Qi ◽  
Yongtang Li ◽  
Lin Hua
Keyword(s):  
Ductile Fracture ◽  
Fracture Criterion ◽  
Fracture Strain ◽  
Rolling Process ◽  
Ring Rolling ◽  
Ductile Fracture Criterion ◽  
Forming Process ◽  
42Crmo Steel ◽  
Critical Fracture ◽  
Ring Rolling Process

The casting-rolling compound forming process of ring parts is an advanced plastic forming technology that has been developed due to the merits of high efficiency and energy and material saving. However, cracks often occur during the hot ring rolling process, especially at the edges of the ring parts, which severely affects the forming quality. To predict and try to avoid the occurrence of cracks in the casting-rolling compound forming process of ring parts, the high-temperature fracture behaviors of as-cast 42CrMo steel were investigated by thermodynamic experiment method. The high-temperature tensile tests were carried out using the Gleeble-3500D thermomechanical simulator at various temperatures and strain rates. Stress-strain curves and fracture morphology were examined, through which the sensitivity of stress to temperature and strain rate and the effect of dynamic recrystallization and cavity evolution on fracture were found. The law of critical fracture strains was analyzed, and the model of critical fracture strain as a function of temperature and strain rate was established. Based on Oyane criterion, the thermal ductile fracture criterion was established in conjunction with the model of critical fracture strain. By embedding this thermal damage model into the finite element (FE) model for hot ring rolling of an as-cast 42CrMo ring, the damage prediction for this process was realized, and the thermal ductile fracture criterion was proved to be reliable. From the FE results for hot ring rolling, mechanism of damage and fracture in the hot ring rolling process was analyzed. The damage threshold C f is small, and the damage ratio D is large at the top and bottom edges of the inner surface area of the ring, which have the greatest propensity to cracking in the course of hot ring rolling. This is of great significance in terms of improving the forming quality of ring parts in the casting-rolling compound forming process.

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 Comparison of modified Mohr–Coulomb model and Bai–Wierzbicki model for constructing 3D ductile fracture envelope of AA6063

2021 ◽  
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

Abstract Ductile 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 were 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 Investigation of Slip Occurrence in the Ring Rolling Process

2019 ◽  
Vol 291 ◽  
pp. 02006
Author(s):  
Andrzej Gontarz ◽  
Piotr Surdacki
Keyword(s):  
Wall Thickness ◽  
Failure Modes ◽  
Rolling Process ◽  
Ring Rolling ◽  
Thickness Reduction ◽  
Main Stage ◽  
Forming Process ◽  
Limit Values ◽  
Ring Shape ◽  
Ring Rolling Process

Ring rolling is a hot forming process for producing rings that have large diameters when compared to their cross sections. This process is very dynamic and involves considerable variations in ring shape and size. One of the failure modes in ring rolling processes is slip that occurs when a thickness reduction, exceeds the limit value. The thickness reduction depends on the tool speed and dimensions as well as ring size, and varies over time. This paper reports results of a study investigating the thickness reduction with respect to slip occurrence. In terms of wall thickness reduction, the process can be divided into three distinct stages (excluding the sizing stage): (i) initial stage corresponding to the first revolution of the roll, (ii) main stage, when the proper ring rolling takes place, (iii) final stage, when the main roll does not move in an axial direction but the ring is being formed during one revolution of the tool. It has been found that the most slip-prone moment is the end of the second and the beginning of the third stage of the ring rolling process, when the wall thickness reduction is the highest. Based on a comparison of the calculated thickness reduction and its limit values, it could be predicted whether slip would occur, and if so – in what stage of the rolling process. Numerical results and experimental findings are in good agreement.

Speed Idle Roll Law Optimization in a Ring Rolling Process

2015 ◽  
Vol 651-653 ◽  
pp. 248-253 ◽  
Author(s):  
Luca Giorleo ◽  
Elisabetta Ceretti ◽  
Claudio Giardini
Keyword(s):  
Rolling Process ◽  
The Other ◽  
Ring Rolling ◽  
Hot Forming ◽  
External Diameter ◽  
Roll Speed ◽  
Forming Process ◽  
Industrial Environment ◽  
Ring Rolling Process

Ring Rolling is a complex hot forming process where different rolls are involved in the production of seamless rings characterized by extreme dimensions (i.e. external diameter higher more than 1m). Because each roll can be independently controlled from the other ones different speed laws must be set; usually, in the industrial environment, a milling curve is introduced to monitor the shape of the workpiece during the deformation in order to ensure a correct ring production. In former works the authors focused their attention on the influence of different milling curves for an industrial case and the results underlined that a ring produced with a good quality and lower loads and energy could be obtained imposing a linearly descending trend to the Idle roll speed law. However different approaches could be used in order to evaluate the mentioned speed law.In this work the authors enhanced the knowledge about the optimization of the Idle roll speed law: different Idle roll speed laws were designed and simulated and the results were compared in order to identify the best speed law that guarantees a good quality ring with lower loads and energy required for manufacturing.

Application of a Material Model to Predict Rolling Forces and Microstructure during a Hot Ring Rolling Process

2013 ◽  
Vol 762 ◽  
pp. 354-359 ◽  
Author(s):  
Thomas Henke ◽  
Gerhard Hirt ◽  
Markus Bambach
Keyword(s):  
Grain Size ◽  
Microstructure Evolution ◽  
Rolling Force ◽  
Flow Behavior ◽  
Rolling Process ◽  
Ring Rolling ◽  
Experimental Investigations ◽  
Forming Process ◽  
Ring Geometry ◽  
Ring Rolling Process

Ring rolling is an incremental bulk forming process. Hence, the process consists of a large number of alternating deformations and dwell steps. For accurate calculations of material flow and thus ring geometry and rolling forces in hot ring rolling processes, it seems necessary to consider material softening due to static and post dynamic recrystallization which could occur between two deformation steps. In addition, due to the large number of cycles, the modeling results, especially the prediction of grain size, can easily be affected by uncertainties in the input data. However, for small rings and ring material with slow recrystallization kinetics, the interpass times can be short compared to the softening kinetics and the effect of softening can be so small, that microstructure evolution and the description of the materials flow behavior can be de-coupled. In this paper, a semi-empirical JMAK-based model for a stainless steel (1.4301/ X5CrNi18-9/ AISI304) is presented and evaluated by the use of experiments and other investigations published in [1],[2]. Finite Element (FE) simulations of a ring rolling process with a high number of ring revolutions and thus multiple, incremental forming steps were conducted based on ring rolling experiments. The FE simulation results were validated with the experimentally derived rolling force and evolution of ring diameter. The microstructure evolution was calculated in a post processing step considering the investigated evolution of strain and temperature. In this calculation the interrelations between the fraction of dynamically recrystallized microstructure, the evolution of post-dynamically recrystallized microstructure and the final grain size have been considered. Both, the calculated final microstructure and the evolution of rolling force and ring geometry calculated stand in good agreement with the experimental investigations.

FE Analysis of Microstructure Evolution during Ring Rolling Process of a Large-Scale Ti-6Al-4V Alloy Ring

2010 ◽  
Vol 638-642 ◽  
pp. 223-228 ◽  
Author(s):  
Jong Taek Yeom ◽  
Jeoung Han Kim ◽  
Jae Keun Hong ◽  
Nho Kwang Park ◽  
Chong Soo Lee
Keyword(s):  
Grain Size ◽  
Prediction Model ◽  
Microstructure Evolution ◽  
Large Scale ◽  
Volume Fraction ◽  
Rolling Process ◽  
Ring Rolling ◽  
Forming Process ◽  
Microstructure Prediction ◽  
Ring Rolling Process

Microstructure evolution during ring rolling process of a large-scale Ti-6Al-4V ring was investigated with the combined approaches of three dimensional finite element method (FEM) simulation and microstructure prediction model. A microstructure prediction model was established by considering the volume fractions and grain size of  and  phases varying with process variables, and grain growth. In order to perform FE simulation for ring rolling process of Ti-6Al-4V alloy, a constitutive equation was generated by utilizing the flow stress data obtained from hot compression tests at different temperature and strain rate conditions. The volume fraction and grain size of  and  phases during ring rolling were calculated by de-coupled approach between FEM analysis and microstructure prediction model. The prediction results were compared with the experimental ones. Our proposed microstructure simulation module was useful for designing hot forming process of Ti-6Al-4V alloy

Research on Edge Cracks of the Ring Part During Ring Rolling Based on Cast Blank

2015 ◽  
Author(s):  
Huiping Qi ◽  
Yongtang Li ◽  
Xiaojian Wei ◽  
Li Ju ◽  
Dongsheng Qian
Keyword(s):  
Rolling Process ◽  
Ring Rolling ◽  
Feed Speed ◽  
Forming Process ◽  
The Core ◽  
Initial Stage ◽  
Initiation And Propagation ◽  
New Process ◽  
Edge Cracks ◽  
Ring Rolling Process

The casting-rolling compound forming process is a new process to produce seamless ring shaped components. In the new process, the input blank for the new process is a ring shaped casting blank. Edge crack affects severely the quality of rolled ring parts in ring rolling process based on cast blank. Theoretical analysis, numerical simulation and experiments were combined to study the edge crack and its prevention methods during ring rolling. Conclusions are obtained that: (1) for casting blank, the initial stage of ring rolling is crucial to prevent the initiation and propagation of the edge cracks. (2) in the ring rolling process, the occurrence of cracks were influenced mainly by rolling temperature and feed speed of the core-roller. Cracks could be avoided by controlling above two rolling parameters. (3) in the initial stage of ring rolling, higher rolling temperature and lower feed speed of the core-roller are beneficial to improve the plasticity of the materials and restrain effectively the initiation and propagation of cracks. The work is a part of the research of the new casting-rolling compound forming process. It will promote the development of the new process.

Speed Roll Laws Influence in a Ring Rolling Process

2013 ◽  
Vol 554-557 ◽  
pp. 337-344 ◽  
Author(s):  
Luca Giorleo ◽  
Elisabetta Ceretti ◽  
Claudio Giardini
Keyword(s):  
Numerical Approach ◽  
Rolling Process ◽  
Ring Rolling ◽  
Roll Speed ◽  
Forming Process ◽  
Industrial Case Study ◽  
Ring Shape ◽  
Deformation Processes ◽  
Ring Rolling Process

Ring Rolling is a complex hot forming process used for the production of shaped rings, seamless and axis symmetrical workpieces. The main advantage of workpieces produced by ring rolling, compared to other technological processes, is given by the size and orientation of grains, especially on the worked surface which give to the final product excellent mechanical properties. In this process different rolls (Idle, Axial, Guide and Driver) are involved in generating the desired ring shape. Because each roll is characterized by a speed law that could be set independently by the speed law imposed to the other rolls an optimization is more critical compared with other deformation processes. Usually in industrial environment a milling curve is introduced in order to correlate the Idle and Axial roll displacement, however it must be underlined that different milling curves lead to different loads and energy for ring realization.In this work an industrial case study was modeled by a numerical approach: different milling curves characterized by different Idle and Axial roll speeds laws (constant, linear and quadratic) were designed and simulated. The results were compared in order to identify the best set of Idle and Axial roll speed laws that guarantee a good quality produced ring (lower fishtail) with lower manufacturing loads and energy.

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.

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