RHEOLOGY OF PLAY DOH: SIMPLE EXPERIMENTS TO DEMONSTRATE THE EFFECT OF VISCOSITY CONTRAST ON STRAIN ANALYSIS RESULTS

The rate at which ductile materials deform under stress is a function of the effective viscosity of the material. To better understand this relationship experiments were conducted utilizing simple materials to quantify the relationship between measured strain and viscosity. Experiments were designed to be easily reproducible and accessible as a teaching tool for understanding rheology and strain-viscosity relationships. Five sets of Play Doh with different viscosities were used in these experiments. The viscosity of each sample of Play Doh varied due to age and relative desiccation. The older Play Doh was drier and therefore more viscous. The rheology of each was quantified by determining the strain rate dependence on stress. This data was then graphically analyzed for trends and to calculate the effective viscosity. Strain was then calculated after running experiments using four different age Play Doh strain markers within the fifth as a matrix. Experiments were compared by calculating the ratio of the strain (Rf) recorded in the marker to the strain recorded within the matrix for various viscosity contrasts. The matrix vs. marker Rf ratio was plotted versus the ratio of the effective viscosity of the marker to that of the matrix. The four data points show a clear linear relationship with an R2 value of 0.89, indicating that markers with higher viscosities record lower strain. The experimental results where the marker viscosity was almost equal to the matrix viscosity is the point that deviates most from linear trend. We interpret this to be an expression of the experimental precision of the effective viscosity and strain measurements. These simple experiments can be used as a teaching tool in the context of a structural geology class to help students understand: (1) the methods for quantitatively determining the rheology of ductile materials; and (2) the potential effect of marker vs. matrix heterogeneity on strain analysis results.