Design project for advanced mechanics of materials

Abstract

Advanced mechanics of materials is a broad subject encompassing many topics. However, often there is only room in the curriculum for a single course. Thus, there is a tendency to pack the course full of topics, in which case sufficient depth of coverage can be lost. Furthermore, design is at the heart of engineering and demands attention. Advanced mechanics of materials is a major part of many design problems. In this paper we describe the implementation of a team design project into an advanced mechanics of materials course. The project has been developed such that it can be initiated at the beginning of the course, but it builds on itself and students progressively apply principles learned in class. The design of a crank arm for a bicycle was chosen as the project because of the familiarity that students have with it, its simple function, it poses interesting and common design dilemmas, and because the analysis can range from being very simple to being very complicated. The project contains many parts: development of design specifications, material selection, analysis of a straight crank having a circular cross-section, design of a straight crank, validation of analysis with experimental results, design of an elliptical cross-section and a rectangular cross-section, and comparison of results from simple circular, elliptical, and rectangular cross-sections with finite element results from actual crank arms. The primary topics that this project covers are: design, combined stresses, prediction of yielding, fatigue, torsion of noncircular cross-sections, and finite element analysis. Student teams from a separate finite element class conducted the actual finite element analyses. A website is under development to assist students performing design in this and other mechanics courses. It was clear to the instructor that the project increased the students' level of interest during the course.