In project-based learning, the quality of group interaction is one of the key factors influencing instructional effectiveness. This article addresses the prominent issues associated with project-based learning activities within the context of material mechanics courses and proposes an instructional method for teaching materials mechanics using features from the process role theory, an aspect of the field of social psychology. In this model, students are assigned engineering roles according to the characteristics of engineering projects and wear engineer bracelets, enabling them to engage in authentic conflicts and collaborations within and among groups, contributing to the advancement of the project. A teaching practice demonstrates that this method effectively stimulates students' enthusiasm for participation, enhances the quality of project interaction, fosters a sense of responsibility and pride in students as engineers and yields favourable instructional outcomes.