Numerical modeling of the bimetallic reinforcement bar rolling process. Authors: P. Szota and H. Dyia

1. Numerical modeling of the bimetallic reinforcement bar rolling process.Authors: P. Szota and H. Dyia Presentation by: Daniel Kinder September 8,2010

2. Introduction: • Create a model on the manufacturing of a bimetallic corrosion-resistant re-bar. • Correctly design the finish rolling process to assure uniform thickness in the cladding layer, and prevent breaking. • Determine a method to correctly choose the width-to-height ratio of the pre-finished oval pass to uniformly fill the grooves in the roll during the finish pass to obtain equal thickness. • Numerical model created in two steps. First, the rolling of the bimetallic band in the flat oval pre-finished pass. Second, the rolling of the bimetallic band in the round ribbed finish pass. • From the models created a substantial reduction un cladding layer thickness at the rib base has been found, which is asymmetrical in relation to the rib axis , and is dependent on the rolling direction

3. Experimental Design • Modeling of the plastic processing processes based on the FEM method will be carried out using theFORGE2005® computer software. • The model will be carried out in two steps. • In the first stage, the rolling of round bimetallic band in the flat oval pre-finished pass was modeled. As seen in Fig. 1. • The next stage of the studies was the numerical modeling of the obtained oval bimetallic band in the round ribbed pass. As seen in Fig. 2. Fig. 1 Dimensions can be seen in Table 1. Fig. 2 Dimensions are also contained in Table 1

4. Mathematical Model. For a description of the object being deformed, the Norton-Hoff law was used, which can be expressed with the following equation (1): Friction conditions taking place between the metal and rollers are described by the Coulomb friction model and by the Tresca friction model. Equation 2: The values of coefficientsA0,m1-m4 for both steels are shown in Table 2. The coefficients shown in Table 2 are taken from the material database of the program Forge2005®. The following initial parameters were adopted for simulation: a roll diameter of 350 mm; the temperature of rolled bimetallic band was assumed to be uniform and equal to 1000C; the rolling speed was taken equal to 3 m/s, friction coefficient 0.3, and friction factor 0.7. Assumptions: • The join between the core and cladding layer adhered closely. • Thermal conductivity between rolls and material is the same. • Nodes of material are not shared. See handout for definition of variables in equations 1and 2.

5. Results of Numerical Model.Stage 1. • The described computer simulation of the first stage of rolling created an oval band as shown below. • The dimensions of the oval bimetallic band after rolling in the pre-finished pass were 24.13 x 11.41 mm. The width-to-height ratio of the bimetallic oval amounted to 2.1 [1-6]. The cross-sectional area of the oval bimetallic band was 251.7 mm2, of which the cladding layer area was 49.5 mm2. The initial share of the cladding layer was 19.8% and it did not change after rolling in the oval pass. The elongation factor was equal to 1.13. The initial cladding layer thickness on the perimeter was uniform and equal to 1 mm, whereas after rolling this thickness changed. The thickness of the layer in the locations of band contact with the rolls was 0.72 mm on the average, while on the lateral surfaces in the band widening direction it was equal to 0.9 mm. No surface defects were found to be caused by high magnitudes of stress and strain. When analyzing the computer simulation results, consideration was given to the Cocroft-Latham criterion that allows the determination of the conditions for the occurrence of a crack in the material based on the main stresses and strain intensities occurring during deformation[14]. The value of this criterion during rolling in the pre- finished pass did not exceed 0.2, which indicates that there are no conditions favoring the cracking of the cladding layer (cracks might occur at .6 depending on deformation) [15].

6. Results of Numerical Model.Stage 2. It can be found that the obtained bimetallic ribbed bar model is characterized by correct outer dimensions and a correct rib height of 1.1 mm. The bar width was equal to 16.4 mm. The thickness of the cladding layer between the ribs was equal to 0.61 mm on the average, with a deviation of ±0.07 mm. At the rib top, this layer reached the thickness ranging from 0.9 mm to 1.0 mm. On the cross-section A and B (Fig. 5) it is shown how the cladding layer thickness varies on the core surface. The thickness of the clad surface depends on the rolling direction. At the rib base on the side opposite to the rolling direction, the cladding layer thickness is averagely 0.55 mm. On the other side of the rib, this thickness is much smaller, amounting to 0.22 mm on the average. The cause of such a large difference in cladding layer thickness is the mode of rib formation in the ribs bite region.

7. Conclusions. • Computer modeling drastically reduced cladding layer thickness. • Model will allow for optimal layer of corrosion resistant material to reduce cost while maintaining desired properties. • Bimetallic re-bar is used in high corrosion environments. • Higher corrosion resistant re-bar will allow engineers to maintain material properties in harsh environments.

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