Visualizing Stress and Strain: Using Visual Basic 6.0 to Provide a Dynamic Learning Environment
 Nathaniel E. Reish and Dr. Gary H. Girty
San Diego State University Department of Geological Sciences

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Introduction

Structural geology is a fundamental course in a geology students' academic career. Subsequent courses often require an intuitive understanding of the subject. In my own college career, it wasn't until several semesters after I completed a structural geology class that I fully understood everything that I was supposed to carry with me into subsequent courses. In an attempt to prevent another student from following the same painful path to discovery and understanding I developed both a program and a web site for visualizing the key types of structures and concepts encountered in an introductory structural geology class. The resulting program is called Visualizing Structural Geology and will run on any PC using Windows 95, 98, 2000, or NT 4. Visualizing Structural Geology was written in Microsoft Visual Basic Version 6.0 and is broken down into two separate programs and tutorials Visualizing Stress and Visualizing Strain. The programs and tutorials are available through a site published on the World Wide Web (www.geology.sdsu.edu/visualstructure/).

Geology is a dynamic science, which requires an understanding of how to quantify and visualize the change of two and three-dimensional forms through time. It is my hope that the program and tutorial will leave a student with a better foundation with which to build a better understanding of this complex subject. During the development of the program and web site I adhered to the philosophy that learning should be dynamic rather than static.

Visualizing Structural Geology was developed primarily for stress and strain analysis. Stress and strain are core and essential concepts in structural geology. However they are conceptually difficult to the beginning geologist. Part of the difficulty is that the description of stress and strain is inherently mathematical and to many students non-intuitive. Moreover, the traditional methods for visualizing stress and strain lack the dynamic character of the concepts they attempt to represent. Graphing and/or calculating strain and various units of stress is a time consuming task that many students view as "busy work" or "mundane." In an attempt to better illustrate and understand the dynamic character of a stress and strain analysis without the "busy work," Visualizing Structural Geology was developed to allow the student to create and view detailed illustrations and animations of the mathematics of stress and strain.

The tutorial that accompanies the program guides the student through a step-by-step instruction on how to use Visualizing Structural Geology to solve basic problems in stress and strain analysis. Topics covered in the interactive tutorial for stress include (1) lithostatic stress, (2) a graphical approach to understanding the stress tensor and how it relates to the definition of s1, s2, and s3, (3) the Mohr Circle of stress, (4) pore pressure effects on stress, and (5) plastic versus elastic stress-strain relationships. Topics covered in the tutorial for strain include: (1) a graphical approach to understanding the strain transformation matrix for pure and simple shear, (2) strain animations as a way of understanding vorticity and the principle strain directions, (3) incremental versus finite strains, (4) progressive simple and pure shear, (5) strain path dependencies, (6) tools for calculating the various strain parameters such as stretch, elongation, quadratic elongation, and natural strain.

The primary purpose for developing Visualizing Structural Geology was to provide to the academic community an easy to use and cost effective tool for teaching and learning the basic principles of structural geology. Both the program and interactive tutorial are accessible through the web site at no cost to the user. A complete listing of the VB code is provided as Appendix A (Visualizing Stress) and B (Visualizing Strain). Use of this code is strictly prohibited without written authorization from the author or Dr. G. H. Girty. It is provided here only as reference to topics discussed in the following chapters.

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