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A modified Johnson-Cook model for ferritic-pearlitic steel in dynamic strain aging regime
University West, Department of Engineering Science, Research Enviroment Production Technology West. R&D Turning, Sandvik Coromant AB, Sandviken, 811 81, Sweden. (PTW)ORCID iD: 0000-0003-3877-9067
R&D, Sandvik Materials Technology AB, Sandviken, 811 81, Sweden.
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-0976-9820
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-9331-7354
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2019 (English)In: Metals, ISSN 2075-4701, Vol. 9, no 5, article id 528Article in journal (Refereed) Published
Abstract [en]

In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s-1, 5 s-1, and 60 s-1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

Place, publisher, year, edition, pages
MDPI AG , 2019. Vol. 9, no 5, article id 528
Keywords [en]
flow stress; modified Johnson-Cook model; dynamic strain aging
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-13989DOI: 10.3390/met9050528ISI: :000478818700046Scopus ID: 2-s2.0-85066741813OAI: oai:DiVA.org:hv-13989DiVA, id: diva2:1328119
Funder
Swedish Research Council, 20110263, 20140130Available from: 2019-06-20 Created: 2019-06-20 Last updated: 2020-02-19Bibliographically approved
In thesis
1. Improved finite element modelingfor chip morphology prediction inmachining of C45E steel
Open this publication in new window or tab >>Improved finite element modelingfor chip morphology prediction inmachining of C45E steel
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Within the manufacturing of metallic components, machining plays an important role and is of vital significance to ensure process reliability. From a cutting tool design perspective, physics-based numerical modeling that can predict chip morphology is highly necessary to design tool macro geometry. The chip morphology describes the chip shape geometry and the chip curl geometry. Improved chip morphology prediction increases process reliability by improved chip breakability and effective chip evacuation.

To this end, in this work, a platform is developed to compare a numerical model'schip morphology prediction with experimental results. The investigated cuttingprocesses are orthogonal cutting process and nose turning process. Numerical models that simulate the chip formation process are used to predict the chip morphology accompanied by machining experiments. Computed tomography isused to scan the chips obtained from machining experiments evaluating its ability to capture the chip morphology variation. For the nose turning process, chip curl parameters need to be calculated during the cutting process. Kharkevich model is utilized in this regard for calculating the 'chip in process' chip curl parameters. High-speed videography is used to measure the chip side-flow angle during thecutting process experiments enabling comparison with physics-based model predictions.

With regards to chip shape predictability, the numerical models that simulate the chip formation process are improved by improving the flow stress models and evaluating advanced damage models. The workpiece material, C45E steel, arecharacterized using Gleeble thermo-mechanical simulator. The obtained flow stress is modeled using phenomenological flow stress models. Existing phenomenological flow stress models are modified to improve their accuracy. The fracture initiation strain component of damage models' influence on the prediction of transition from continuous chip to segmented chip is studied. The flow stress models and the damage models are implemented in the numerical models through FORTRAN subroutines. The prediction of continuous to segmented chip transitions are evaluated for varying rake angles and feed rate ata constant cutting velocity.

The results from the numerical model evaluation platform show that the methodology provides the framework where an advance in numerical models is evaluated reliably from a 'chip morphology prediction capability' viewpoint forthe nose turning process. The numerical modeling results show that the chip curl variation for varying cutting conditions is predicted qualitatively. The flow stress curves obtained through Gleeble thermo-mechanical simulator show dynamic strain aging presence in specific temperature -strain rate ranges. The results of the phenomenological model modification show their ability to incorporate the dynamic strain aging influence. The modified phenomenological model improvesthe accuracy of the numerical models' prediction accuracy. The flow stress models combined with advanced damage model can predict the transition from continuous to segmented chip. Within damage model, the fracture initiation strain component is observed to influence the continuous chip to segmented chip transition and chip segmentation intensity for varying rake angle and feed rate and at a constant cutting velocity.

Abstract [sv]

Populärvetenskaplig Sammanfattning

Bearbetning är en 150-årig tillverkningsprocess som återfinns antingen direkt eller indirekt i nästan allt som tillverkas. I dagsläget med den snabba omställning motmer digitala arbetssätt riskerar allt som inte digitaliseras med stor sannolikhet att bli kvarlämnat. Två aspekter mot digitaliseringen av skärande bearbetningsprocesser har genomförts i detta arbete. Den första var en utvärdering av befintliga metoder och utvecklingen av nya metoder för att digitalisera komplexa spångeometrier som återfinns i bearbetningsprocessen, vilket inte tidigare gjorts. Nästa steg är att fånga fysiken som är involverad i en skärprocess för att kunna simulera denna med högre noggrannhet. I denna del av arbetet har inriktats till att urskilja små förändringar i ingångsförhållandena i dess relation till spånformning.

En spånans ytstruktur kan vara antingen slät eller korrugerad. Att veta vilken spånform som kommer att skapas ger oss förmågan att bättre kontrollera bearbetningsprocessen. I det genomförda arbetet har det skapats förbättrande materialmodeller som möjliggör en ökad noggrannhet vad gäller möjligheten att simulera spånformen vid skärande bearbetning. En stor del av arbetet här harägnats åt en ökad förståelse av ett materials uppträdande, i detta fall stål, vid skärande bearbetning. Detta har skett genom omfattande materialtestning där testresultaten har presenterats i form av matematiska ekvationer i de numeriska modellerna. Övriga metoder som har används för att skapa dessa digitala spånor inkluderar datortomografi, höghastighetsvideografi och matematiska modeller. När dessa kombineras med datorgrafik kan man erhålla numeriska modeller för att simulera skärande bearbetning.

Resultatet av denna förbättring av befintliga numeriska modeller är förmågan att se påverkan av hur små förändringar i skärverktygets geometri kan påverka formen på den av skärprocessen skapade spånan. Sammantaget kan resultatet av den genomförda forskningen bidra till att skapa ett obrutet virtuellt arbetssätt vidproduktutveckling av skärande verktyg.

Place, publisher, year, edition, pages
Trollhättan: University West, 2020. p. 93
Series
PhD Thesis: University West ; 34
Keywords
Chip curl, Chip flow, Chip segmentation, Computed Tomography, Damage modeling, Flow stress modeling, Machining, Spånkrökning; Spånflöde; Spånsegmentering; Datortomografi; Skademodelleringen; Modellering av Flytspänning; Bearbetning
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14979 (URN)978-91-88847-52-2 (ISBN)978-91-88847-51-5 (ISBN)
Public defence
2020-02-12, Albertssalen, 10:00 (English)
Opponent
Supervisors
Available from: 2020-02-19 Created: 2020-02-19 Last updated: 2020-02-19Bibliographically approved

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Devotta, Ashwin MorisBeno, TomasEynian, MahdiHurtig, Kjell

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