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Session 2666

Connecting Rod Design Competition–Solid Mechanics Multiple Failur e Mode Design and Testing Pr oject

Wendy Reffeor , Ph.D., David Blekhman, Ph.D. Seymour and Esther Padnos School of Engineer ing Gr and Valley State Univer sity Gr and Rapids, MI 49504

Abstract

Students in Solid Mechanics courses commonly struggle with balancing multiple failure modes in a single part. To improve their understanding of failure modes, stress risers and design, students in the Solid Mechanics course are required to compete in a connecting rod design competition. As an added benefit of the project, students have an opportunity to reinforce their CAD/CAM and dimensioning skills learned in a first-year CAD/CAM design course.

Working in teams of two, students designed, machined and tested a connecting rod. The pin connections in the rod were represented by two 3/8” holes 3” apart. Students were to design the geometry of the part around and between two holes. The part was to have a maximum width of 1”. Students documented their designs through design calculations and a dimensioned CAD model, generated machine codes using CAM software, machined their parts, measured their parts to ensure accuracy and tested the rods to failure using a tensile tester. Grading was based on the strength-to-weight ratio of the connecting rod, accuracy of their failure force estimate, documentation of anticipated failure forces in all possible modes of failure, dimensioned CAD drawings, quality of manufacturing and the poster used to present their designs.

In the first year of the competition, the rods were machined from plastic, chosen for ease of machining. However, using plastic caused inaccuracies in determining the failure load as the stress risers reacted differently than in a less ductile material. Aluminum was chosen as the material for the second year of the project.

More than 30 teams participated in the contest the first year and 29 in the second. Testing results for the failure load were within 45% plastic and 21% for aluminum rods. Student comments were very positive both about the design experience and their understanding of the concepts incorporated in the project. The project quite effectively achieved the primary goal of helping students understand multiple failure modes and stress risers in axially loaded members. It also reinforced student design, CAD/CAM, dimensioning and machining skills.

Introduction

The old saying, "A picture is worth a thousand words," is a contemporary pedagogical reality. While looking at a picture is passive, an experiment would be an active learning exercise worth

Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education

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Reffeor, W., & Blekhman, D. (2004, June), Connecting Rod Design Competition–Solid Mechanics Multiple Failure Mode Design And Testing Project Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--13404