Development and experimental validation of a simplified Finite Element methodology to simulate the response of steel beams subjected to flame straightening

The most important factor in achieving a successful result in the application of the flame straightening procedure on structural steel parts is, as of today, the operator's skill and experience. In many cases, it is necessary to undertake a trial and error process until the desired final geometry is obtained. A simplified methodology, based on the Finite Element technique, is proposed in this paper, allowing the final geometry and the residual stress state in components subjected to flame straightening to be determined. The behavior of three structural profiles -HEA 300, HEM 340 and IPE 450- manufactured in three widely used steel grades -S235 JR, S355 J2 and S460 ML- has been investigated. The research can be broken down into the following stages. First, the thermal properties have been obtained from the scientific literature and the mechanical behavior of the materials has been experimentally determined by means of tensile tests carried out in the range 20-1000 °C. Second, a thermal Finite Element model was developed to characterize the properties of the propane flame employed in this research. This thermal numerical model was validated by comparing its predictions with the records provided by a set of thermocouples attached to a plate subjected to flame straightening. Next, a thermo-mechanical numerical model was prepared and experimentally validated subjecting a second instrumented steel plate to flame heating. Finally, a simplified approach has been developed and contrasted experimentally to allow the response of a large beam subjected to flame heating to be simulated by means of conventional computational resources. The method proposed is based on breaking down the original beam into a set of short beams, one for each of the heated regions in the original beam. Under very general conditions, one thermal simulation and two mechanical simulations suffice to estimate the whole deformation of a beam, resulting in a great simplification of the problem.