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R. Comesaña, A. Badaoui, R. Cancelos

University of Vigo, Materials Engineering, Applied Mechanics and Construction Department (SPAIN)
In order to achieve in depth learning approach, a variety of innovations have been applied to high education during last years. Traditional learning methodologies based on theoretical lessons have been substituted by new educational strategies; the increased presence of latest technologies and practical experiences became an important tool to implement the student based learning. Moreover, the reforms applied to European high education system within the framework of the Bologna process modified the teaching role towards concept guiding, and reduced the available time at the lecture theatre. As a result, more attention has been paid to the development of quasi-individual practical learning. Indeed, these learning actions gained importance as learning activator and motivating tool. The work presented here is a case of practice development to improve concept learning in the field of mechanical engineering and particularly in stress analysis. In this field, traditional lessons addressed the study of equilibrium conditions and compatibility conditions to determine strains, displacements and deflections in loaded structures. Nevertheless, this classical approach hardly considers the stress field as a whole and its representative lines that, in fact, are experimentally accessible properties.

The importance of the elastic state and its characteristic lines understanding is evident. For instance, the design of high performance structural and machinery parts often contains a time consuming stage to determine the stress field and to eliminate possible points of stress concentration. Fracture analysis and dramatic failure prediction is a broad discipline where the stress distribution plays a main role. Moreover, all manufacturing techniques involving plastic deformation require a detailed knowledge of the stress distribution in the processed material. The manufactured part strength and working performance can be compromised by an uncontrolled stress distribution. Thus, the stress field understanding has key implications for the mechanical engineer acquired competences. Therefore, we propose the practical implementation of laboratory experiences based on photo-elasticity and focused on the load and geometry dependences of the stress field for continuous and discrete media. This method, complemented by computer simulations and mediated by information technology, is exposed as motivating element and trigger for the student internalization of the stress field, its isoclinics, isochromatics and other characteristic lines. The theoretical introduction, experimental set-up and practice development is presented and discussed in this work.