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Slip line model for forces estimation in the radial-axial ring rolling process
Quagliato, Luca,Berti, Guido A.,Kim, Dongwook,Kim, Naksoo Elsevier 2018 International journal of mechanical sciences Vol.138 No.-
<P><B>Abstract</B></P> <P>In the research presented in this paper, a slip line-based model is proposed for the estimation of both radial and axial force in the radial-axial ring rolling (RARR) process. Based on the shape of the contact arcs between ring and tools in the two deformation gaps present in the ring rolling process, a recursive algorithm for the calculation of the two slip line fields starting from the two pairs of opposite tools is derived and implemented in a commercial spreadsheet software (MS Excel). By considering the stress boundary conditions applied to the portion of material undergoing the deformation, both for the radial and axial deformation gaps, the pressure factors those make the two slip line fields starting from the two opposite tools to intersect are calculated and utilized for the estimation of radial and axial forces, for each round of the process. The developed model has been validated by cross-comparing its results with those of laboratory experiment and numerical simulation. For the validation study case, the average deviations, in comparison to the experimental results, are calculated in 1.86% and 4.55% for the slip line force model whereas in 6.86% and 0.88% for the numerical simulation, for the radial and axial forces respectively. The proposed slip line model has been also utilized for the estimation of radial and axial forming forces of nine different study cases of flat rings having the outer diameter ranging from 800 mm to 2000 mm, observing a maximum deviation, in comparison to the relevant FEM simulation, of 4.92% (radial force) and 5.88% (axial force). The developed slip line force model allows estimating almost in real time and with a reasonable accuracy the process forces and, for this reason, it may be of interest for both industrial and academic researchers dealing with the set-up and control of the radial-axial ring rolling process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Development of analytical slip line field construction algorithm. </LI> <LI> Slip line algorithm implementation and boundary conditions calculation procedure. </LI> <LI> Radial and axial force calculation in the ring rolling process. </LI> <LI> Model validation by comparison with experimental and numerical results. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Quagliato, L.,Kim, D.,Lee, N.,Hwang, S.,Domblesky, J.,Kim, N. Pergamon Press 2017 International journal of mechanical sciences Vol.130 No.-
Surface wear and spalling phenomena are the most important factors affecting roller bearing performance and operational lifetime, in terms of number of cycles the bearing can operate. Although bearing life has been traditionally defined by the onset of spalling, as specified by international standard ISO 281, this definition does not always reflect the real operational conditions, since bearing wear can also represent a failure criterion when excessive run-out occurs. In such cases, bearing life needs to be predicted according to the amount of bearing run-out resulting from wear due to load and number of cycles. In the current study, the wear phenomenon has been modeled using the Archard wear and Lemaitre damage models, both included in a numerical simulation of a roller bearing assembly. Wear and damage models, along with the results of accelerated life experiments, have been used to develop a reliable method enabling bearing life prediction with a minimal number of material characterization tests. Accelerated life testing experiments on real bearings have been performed to confirm the reliability of the methodology, showing good correlation with numerical simulation results and proving that the developed model can be utilized for prediction of the lifetime of bearings.
Kim, Dongwook,Quagliato, Luca,Park, Donghwi,Kim, Naksoo Elsevier 2019 Wear: An international journal on the science and Vol.420 No.-
<P><B>Abstract</B></P> <P>The research presented in this paper deals with the development of an integrated numerical model for the estimation of the incremental surface wear and damage accumulation in linear slide rails. The target is the estimation of the progressive increment of the end-point deflection of the last member of the slide rail during the operational lifetime. The surface abrasion is accounted for by utilizing a modified Archard equation with the aim of estimating the amount of wear along the vertical direction of the slide rails members. In addition to that, the Lemaitre damage model is utilized for the estimation rolling contact fatigue (pitting), considering the total strain and not only the plastic strain. Experiments have been carried out on a small-scale slide rail testing machine in order to define the wear increment on the slide rail inner groove for increasing number of cycles and, accordingly, estimate the modified Archard model constants. In addition to that, the wear parameters for the Lemaitre damage model have been inversely calibrated from the results of tensile tests. A numerical model has been implemented in ABAQUS/Explicit and an external geometry-update subroutine has been employed to update the geometry of the slide rail groove for increasing number of cycles as a consequence of wear and roll contact fatigue. The comparison between numerical and experimental results on real rails have shown a maximum deviation equal to 12.9%, supporting the reliability of the proposed approach.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Modified Archard wear model to estimate the vertical wear. </LI> <LI> Modified Lemeitre damage model to include the elastic strain contribution. </LI> <LI> Numerical model to estimate the rail members deflection due to wear and RCF. </LI> <LI> Reduction of the computational time due to external program. </LI> <LI> Reliable experimental-numerical approach for the slide rail lifetime prediction. </LI> </UL> </P>
Some Manifestations of Antioxidation Coating for Hot Precision Forging Gears
Li, Dongcheng,Han, Nana,Quagliato, Luca,Kim, Naksoo,Yu, Ge Hindawi Publishing Corporation 2019 Advances In Materials Science And Engineering Vol.2019 No.-
<P>A high temperature protective coating was prepared onto the surface of 20CrMnTi steel by brushing technique, and the heated billet was subjected to hot forging. Compared with an uncoated sample, the effect of coating on high-temperature oxidation behavior of steel was investigated by scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction. Before hot forging, an oxide layer of 153 <I>μ</I>m was formed on the surface of the uncoated sample; however, no oxide layer was formed on the surface of the coated sample. After hot forging, the thickness of scale on the surface of uncoated gear forging is 89 <I>μ</I>m while the thickness of coating on the surface of coated gear forging is 39 <I>μ</I>m. It is concluded that such a coating material not only enhances the dimensional accuracy but also improves the surface quality of the gear.</P>
Change of the yield stress in roll formed ERW pipes considering the Bauschinger effect
Lee, Joonmin,Kim, Dongwook,Quagliato, Luca,Kang, Soochang,Kim, Naksoo Elsevier 2017 Journal of materials processing technology Vol.244 No.-
<P>The growth of the sizing effect ratio has shown to cause the increase of the yield stress, which becomes more uniform along the circumferential direction. (C) 2017 Elsevier B.V. All rights reserved.</P>