REISH, NATHANIEL E. and GIRTY, GARY H.
San Diego State University, San Diego, CA

Abstract: Visualizing Stress and Strain

Stress and strain, core and essential concepts in structural geology, are conceptually difficult to the beginning geologist. Part of the difficulty is that the description of stress and strain is inherently mathematical and thus to many students non-intuitive. Moreover, 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 cut down on the amount of "busy work" needed to perform a stress and strain analysis, an interactive software program termed Visualizing Stress and Strain was written in Visual Basic 5.0. Visualizing Stress and Strain functions much the same as other more familiar Windows based programs and will run on any PC using Windows 95, 98, or NT 4. In addition, detailed help files on the mathematics of stress and strain along with a tutorial on how to use Visualizing Stress and Strain to solve basic problems in stress and strain analysis was written to accompany dissemination of the program. It is the authors' intentions that the program and tutorial will be made available free of charge to the academic community.

Essential topics covered in the 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.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas