The Visual Stress Transformer: An Animated Computer Graphics Program For Engineering Mechanics Education

Abstract

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I Session 1668

The Visual Stress Transformer: An Animated Computer Graphics Program for Engineering Mechanics Education

Stephen J. Ressler United States Military Academy

State of stress at a point. Stress transformation. Maximum principal stresses. Mohr’s Circle. These topics often strike fear in the hearts of undergraduate engineering students; and teaching these topics effectively is an equally daunting challenge for the engineering mechanics educator. In my experience, the fundamental problem with teaching (and learning) stress transformation is that students just don’t see it. With time and practice, they learn to solve problems. They master the equations, sign conventions, and graphical solution techniques. But, their mastery of these skills notwithstanding, many students do not truly understand and internalize the fundamental concepts:

. that the two-dimensional state of stress at a point is uniquely defined by the normal and shear stresses acting on any two orthogonal planes passed through that point; s that the stresses acting on the x- and y-planes are statically equivalent to the stresses on any other pair of orthogonal planes; . that the maximum principal stresses and their orientations are unique characteristics of a given state of stress.

This paper describes a simple animated computer graphics program developed by the author to address this problem. Called the ~S@/st..i?SS TkW$fOZM&?~ it is designed to help students visualize the state of stress at a point and to understand the nature and effects of stress transformation. The software is written in TM the Microsoft Visual Basic programming language and runs on an IBM-compatible personal computer with Windows 3.1. It requires less than 25 kilobytes of hard disk space and is very easy to use. The program performs the following functions:

q It displays a two-dimensional stress block for any user-supplied state of stress. . On command, it rotates the stress block slowly, through a full 360 degrees, to show the variation in normal and shear stresses with changing orientation. q As an option, the program displays Mohr’s Circle for the same user-supplied state of stress.

I have used flSU#Sf..l?SS rhl%?fO/iWf in an undergraduate mechanics of materials course and found it to be an invaluable aid to classroom instruction on stress transformation and Mohr’s Circle.

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