Rheology ·Rheology TXUTO [Greek rheos -"to flow"]is the study of deformation and flow of matter ·Name was coined by Dr. Marcus reiner instead of the more obscure “continuum mechanics' Motto of the Society of Rheology:“Panta Rhei'”or l “everything flows'” after Heraclitus
Rheology • Rheology [Greek rheos - “to flow”] is the study of deformation and flow of matter • Name was coined by Dr. Marcus Reiner instead of the more obscure “continuum mechanics” • Motto of the Society of Rheology:“Panta Rhei” or “everything flows” - after Heraclitus
Solid and Liquids Solids Elastic:Materials that can support a applied stress Liquids -Viscous:Materials that can not support an applied stress (that is they flow under stress)
Solid and Liquids • Solids - Elastic: Materials that can support a applied stress • Liquids - Viscous: Materials that can not support an applied stress (that is they flow under stress)
Pie Liquid Semi-Solid Solid
Pie Liquid Semi-Solid Solid
Units of Measure ·Force (Newton) ·Distance(meter) 。Time(second or derived measures Stress (N/m2 or Pascals) ·Velocity(m/s)
Units of Measure • Force (Newton) • Distance (meter) • Time (second) or derived measures • Stress (N/m2 or Pascals) • Velocity (m/s)
Forces and Stresses Compression Tensile Shear
Forces and Stresses Compression Tensile Shear
Table 2.6 Forces Exerted Between Teeth (in Pounds) Male Female Subject Mean Maximum Mean Maximum Eskimo 270 348 200 326 American(natural teeth) 120 200 85 165 American(dentures） -60 Data taken from Waugh(1937)and Klatsky(1942) 1 pound=0.45 Kg
Table 1.7 Relations Between Textural Parameters and Popular Nomenclature Mechanical characteristics Primary parameters Secondary parameters Popular terms Hardness Soft->firm->hard Cohesiveness Brittleness Crumbly->crunchy->brittle Chewiness Tender->chewy->tough Gumminess Short->mealy->pasty->gummy Viscosity Thin->viscous Elasticity Plastic->elastic Adhesiveness Sticky-tacky→gooey Geometrical characteristics Class Examples Particle size and shape Gritty,grainy,coarse,etc. Particle shape and Fibrous,cellular,crystalline,etc orientation Other characteristics Primary parameters Secondary parameters Popular terms Moisture content Dry->moist->wet->watery Fat content Oiliness Oily Greasiness Greasy
Table 2.3 Size Threshold Between Smooth and Grainy Texture Food Particle size (um) Chocolate 13 Chocolate 20 Chocolate 25 Fondant(sugar crystals) 20-25 Ice cream(ice crystals) 55 Margarine(fat crystals) 22 Sweetened condensed milk(lactose crystals) 10-12 Tofu(soy particles) 24
Stress Compression Stress Force /Area
Stress Compression Stress = Force / Area
Deformation Strain Compression y y Strain=△yly
Deformation - Strain Compression y Dy Strain = Dy/y
