Effect of friction on uniaxial compression of bread dough

Abstract

The mechanical and frictional properties of foods have received considerable attention in recent years as accurate material data are needed for the simulation of large scale processing operations as well as providing a basis for product quality and development. In this study, uniaxial compression tests were performed on bread flour/water dough. Cylindrical samples of various heights and diameters were tested under both lubricated and non lubricated conditions. The stress-strain data showed a dependency on sample dimensions when no lubricant was used due to surface friction effects. This dependency was eliminated when silicon oil of 500 centistokes viscosity was used as a lubricant and the true stress-strain data were obtained experimentally. A theoretical expression derived from an equilibrium analysis of a compressed disc under frictional conditions was used to determine the coefficient of friction and the true stress-strain curve from unlubricated data. The true stress-strain data were also determined by an empirical extrapolation procedure. Finally, an iterative numerical procedure based on Finite Element Analysis confirmed the calculated values for both the coefficient friction and the true stress-strain curve.