Thermo-elasto-plastic uncoupling model of width variation for online application in automotive cold rolling process

Abstract : In order to save material yields in cold rolling process, the thesis aims at developing a predictive width variation model accurate and fast enough to be used online. Many efforts began in the 1960s in developing empirical formula. Afterward, the Upper Bound Method (UBM ) became more common. [Oh 1975]'s model with 3D "simple" velocity field estimates well the width variation for finishing mill rolling conditions. [Komori 2002] proposed a combination of fundamental ones to obtain a computer program depending minimally on the assumed velocity fields. However, only two fundamental fields were introduced and formed a subset of the "simple" family. [Serek 2008] studied a quadratic velocity family that includes the "simple" one and leads to better results with a higher computing time. Focusing on UBM , the first result of the thesis is a 2D model with an oscillating velocity field family. The model results to an optimum velocity that oscillates spatially throughout the roll-bite. The optimum power and the velocity field are closer to Lam3-Tec3 results than the "simple" one. For 3D modelling, we chose the 3D "simple" UBM and carried a comparison to the experiments performed at Arcelor Mittal using narrow strips [64]. A very good agreement is obtained. Further, a new UBM model is developed for a crowned strip with cylindrical work-rolls. It shows that the width variation decreases as a function of the strip crown and the results match well those of Lam3-Tec3 . However, the UBM considers only a rigid-plastic behaviour while in large strip rolling, the elastic and thermal deformations have important impacts on the plastic one. There exist some models considering these phenomena [23,64] but they are all time-consuming. Thus, the idea is to decompose the plastic width variation into three terms : total, elastic and thermal width variations through the plastic zone that are determined by three new models. The simplified roll-bite entry & exit models allow estimating the elastic and plastic width variations before and after the roll-bite. They give equally the longitudinal stresses defining the boundary conditions for the roll-bite model which is indeed the 3D "simple" UBM approximating the total width variation term. Moreover, with the plastic deformation and friction dissipation powers given by the same model, the thermal width variation term is also obtained. The width variation model, called UBM-Slab combined is very fast (0.05s) and predicts accurately the width variation in comparison with Lam3-Tec3 (<6%)
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Quang Tien Ngo. Thermo-elasto-plastic uncoupling model of width variation for online application in automotive cold rolling process. Mechanics of materials [physics.class-ph]. Université Paris-Est, 2015. English. ⟨NNT : 2015PESC1063⟩. ⟨tel-01220524⟩

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