Machine Design Experiments Using Mechanical Springs to Foster Discovery Learning

This paper describes new experiments that were designed to provide engineering students with opportunities for discovery learning experiences with systems using mechanical springs. A suite of practical experiments was developed presenting students with a range of challenges requiring them to analyze, measure, and design springs. Activities in the experiments include: (1) Identifying spring types (tension, compression, torsion) and appropriate applications (automotive door latches, key fobs, pens). (2) Disassembling and re-assembling padlocks (with design and manufacturing questions related to the springs used in the locks, and measurement of the stiffness of the shackle compression spring). (3) Achieving desired stiffnesses through appropriate series and parallel combinations of springs (requiring stiffness measurements of the given springs, and comparing to manufacturer's supplied data). (4) Experimentally determining shear moduli and stiffnesses of wire and 3D printed springs. Investigating overextension limits of springs. Introduction For the typical undergraduate engineering student the topic of mechanical springs is introduced and discussed in several courses. A first exposure may be in a physics course, where springs are modeled as idealized mechanical energy storage components. Springs store potential energy, complementing masses that store kinetic energy and dampers that are resistive and offer no energy storage capability. In an electrical circuit course, springs are often presented as the analog of either capacitors or inductors, depending on whether a force-voltage or force-current analogy, respectively, is used. For mechanical engineering students, real springs are a core component studied in machine design courses, where the nomenclature and design equations are developed for various types of springs. There may be a rudimentary exposure to physical springs in a mechanical engineering laboratory; more often, springs are passed around in class and used as part of demonstrations.