Approach to plastic deformation in the development of a semi-physical based model of the FSW process
By Elizabeth Hoyos (Universidad EIA), Yesid Montoya (Universidad EIA), Ricardo Fernández (CENIM, C.S.I.C.), Alberto Martín (CENIM, C.S.I.C.), Gaspar González-doncel (CENIM, C.S.I.C.)

Modeling plastic deformation during the Friction Stir Welding (FSW) process is one of the most complex and important aspects since it is believed that this phenomenon involves a large fraction of the energy needed for the solid-state union to take place. High deformation rates, added to the required process temperatures, demand that any model looking to predict the quality of the joints, develops constitutive equations. The technical literature shows various models and expressions for both normal and shear stresses, which involve the deformation rate and process temperatures. However, these models become dependent on non-functional parameters that are not always easy to obtain or measure.
A simple equation is proposed to calculate the process deformation rate associated with basic parameters: rotational and travel speed. By using it and employing fitting parameters, it is possible to identify deformation rates, which can in turn be used to define experimental conditions in conventional uniaxial tests conducted at high strain rates and temperatures. The area under the deformation stress curves obtained in these tests would serve for the development of the constitutive equations for the term of the deformation energy, required in the model.
With the deformation rates calculated using the aforementioned expression, conventional uniaxial tests have been carried out at high deformation rates (up to 40 s-1) and high temperatures (up to 500 ° C) in aluminum alloys AA6060-T1 and AA2024-T1, conditions which are considered close to those expected in the FSW process in order to estimate the deformation energy. An expression has been developed that estimates the energy of deformation per unit volume as a function of the operating parameters, temperature and unit deformation, associated with high deformation rates.