DEFORMATION OF CHARLESTON CHEW CANDY BARS AS A RHEOLOGY ANALOGUE IN THE STRUCTURAL GEOLOGY CLASSROOM

The relationship between stress and strain and the concept of rheology are often very difficult for undergraduate structural geology students to grasp. In order to introduce these concepts in an intuitive and thought provoking way, a relatively simple in-class, experiment-based exercise has been developed. This hands-on exercise allows students to discover how temperature, pressure and strain rate affect the way in which material responds to an applied stress field. The exercise is performed during the first two lectures on rheology and is designed for a sophomore-level structural geology class for geology majors. As preparation the students should have an understanding of stress and strain, and should have been exposed to the ideas of elastic, plastic and viscous behavior.

The goals of the exercise are for students to gain their own conceptualization of what rheology is, and experience firsthand observations of the complex relationship between stress and strain. Higher order thinking concepts for the students include: the use of analogue models and their advantages and disadvantages, an understanding of experimental assumptions, and extrapolation of model observations to real world conditions. The actual exercise involves making and recording observations and constructing empirical graphs of the relationship between stress and strain as a function of 1) temperature, 2) strain rate, and 3) confining pressure. The strain rate and temperature dependent behavior of Charleston Chew candy bars make them an ideal analogue for these experiments. The addition of an in-house triaxial compression apparatus (designed specifically for the dimensions of a Charleston Chew) rounds off the exercise. In class, students receive a short handout that introduces the exercise, several candy bars (one is frozen and one is heated), and the triaxial compression apparatus. The students perform two experiments for each environmental variable (i.e. temperature) by modeling two extremes conditions (i.e., cold and hot) and comparing and recording the results. After the experiments are completed a table is created of rheologic behavior as a function of environmental parameters (e.g., increases or decreases in material strength, ductility, ability to fracture, etc.). Finally, the students' observations are compared to experimental rheology data from the literature.