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Ph.D. Thesis

Compared Experimental and Theoretical Investigations of Forming Technical Parameters in Shape Rolling with Example of the Hot Rolling of Angle Steels (in German).


To study capability of FEM in describing nonlinear and thermal-coupled deformation process, FEM simulation was carried out for steel processing as steel is rolled between an upper roll and a lower roll. This was done with an existing multi-purpose FEM code MARC. In the first stage, steel deformation process between a pair of flat rolls was performed. On the basis, coupled thermal-mechanical FEM model to roll the steel into angle shape between two grooved rolls was established. Totally 6 passes of the angle steel rolling were simulated. Flow stress, E-modulus and heat transfer coefficients were measured and fed in as function of forming parameters. Steel deformation was assumed as elastic-plastic. Rolls were taken as rigid. FEM meshes and FEM control parameters were optimized to reduce computing time and improve accuracy. To examine and optimize the simulation practice, corresponding experiments were carried out. Before the tests, grids were milled on the surface and cross-section of the samples. In this way, local strain, strain rate and temperature as well as force and power requirements during the rolling were measured. A comparison of the shaping parameters revealed a good level of correlation for the outer contours, grid distortions and strain and strain rate, as well as temperature and normal and shear stresses. In addition, the measured and calculated roll separating forces and rolling torque also corresponded closely (errors normally 5~15%). A FEM model with high performance capability and low computing cost was thus established. By applying the established FEM model, H-beam steel processing and castrolling of thin slab with liquid core were also simulated. After a close study of relative velocity of rolls and stock, a specially simplified 3D upsetting model was developed. The simplified model requires only approximately 0.5% CPU time of a normal model with sufficient accuracy, so it is particularly suitable for industry practice.

Detailed Topics of the Dissertation

Master Thesis

Study on the application of laser alloying technology in metal surface treatment


(Thesis not completed. After one year's Master study I was granted to pursue Ph.D. directly without Master degree)

Bachelor Thesis

Experimental Study of Spray Coating Technology and Influence Factors on Coating Quality

The thesis covers following aspectss

  • Spray coating of a Zn-Al alloy on steel plates was made with various surface conditions (sand hit, machined, acid treated, sand-paper wore, rusted, etc.)
  • Coating quality for every surface condition was evaluated, with photograph, etc.
  • Falling-ball-hitting experiment was made to test the quality of the coat against steel ball hitting in 45 degree direction
  • A special device was designed to measure the sticking strength of the coat against a tensile action perpendicular to the contact surface, while the possible bending effect during measurement can be eliminated.
  • Metallographic analysis for the contact surface was performed.
  • Sticking mechanism was studied and sticking strength was modeled considering major influence factors. A new assumption, under combination of surface alloying (chemical aspect) and multiple-level-gear effect, was proposed to model the sticking strength.


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Bingji (Benjamin) Li 2009. All rights reserved.