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Visualized Photostress Images for Stress Concentration Instruction

Abstract

The ever-increasing demand from industry for more sophisticated structural members and machine components requires a solid understanding of the concepts of different stresses and the behavior of members under loading. The optical method of reflected photoelasticity is utilized to achieve the goals concerning some of the learning outcomes of Strength of Materials and Design of Machine Elements courses. In particular, the paper addresses the use of photoelastic images to enhance the learning of stress concentration factors. Student reaction to the new approach is assessed and presented.

Introduction

Mechanical engineering students are introduced to the concepts of stress and strain in a solid body through the Strength of Materials course. The principles and methods used to meet the learning objectives are drawn from prerequisite courses in statics, physics, and calculus together with the basic concepts of elasticity and properties of engineering materials. Perhaps, an analysis of the effects of stress concentrations is also discussed. In the first Machine Design course, junior mechanical engineering students learn to get a stress concentration factors (SCF), particularly with respect to fatigue, from a chart.

Several papers added an instructional prospective to enhance the teaching of mechanics courses to undergraduate students, the focus of this article. For example, the impact of demonstrations to acquaint students with the Statics concepts in the context of a real artifact was articulated in ref.1. A different approach in regard to teaching mechanics course came from Philpot et. al 2. They presented examples of instructional media developed for the Mechanics of Materials Course utilizing computer in novel ways that offer the potential for improved instruction.

In the field of stress concentrations, the limited established theory does not give an insight for the understanding of the development of stresses in the vicinity of a discontinuity. Thus, experimental work is required to enhance the learning such as stress concentrations3. Strain gages are point measurements and the problems of discrete averaging are well documented4. In this article, photoelastic (photostress) images are proposed for the enhancement of learning stress concentration factor at the edge of a circular hole. The images are used to present the limitations of the theory that are not possible within the confines of textbooks.

Stress Concentration Factor

In the intervals of three decades, a large amount of new material on stress concentration has become available, partly because of the growing capability of modern computer technology. The theory usually deals with infinite members. For example, Kirsch developed the theoretical stress distribution in the vicinity of a circular hole in an infinite elastic isotropic plate5. This theory predicts a stress-concentration factor (SCF) of 3.0 for

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Younis, N. (2010, June), Visualized Photostress Images For Stress Concentration Instruction Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--15946