高分子材料加工技术专业英语 Basic Theory 04 Mechanical Properties.ppt

Mechanical Properties MFG 355 Forces and Responses Tensile – applied loads “pull” the sample Tensile Forces Forces and Responses Compression – applied loads “squeeze” the sample Forces and Responses Flexural – applied loads “bend” the sample Forces and Responses Shear – applied loads are offset Forces and Responses Torsion – applied loads “twist” the sample Mechanical Behavior Impact (toughness) – applied loads “hit” the sample Impact (charpy, dart) Mechanical Behavior Creep Elastic Solid Stress-strain What happens when force is removed? Recovery Viscous liquid Tensile forces? – cannot exist (like pulling water) Shear forces What happens when force stops? Viscous flow Newtonian and non-Newtonian Measures of Viscosity Equation F/A = τ = ? (dv/dx) Viscometer Viscoelasticity Time/temperature dependant Plastic stress-strain a) start point b) proportional limit c) yield d) recovery e) ultimate failure Mechanical Model of Plastic Behavior Interpretation of Plastic Behavior Time Dependence of Plastics Reinforcements Increase mechanical properties Generally fibers Composites Fillers Reduce cost Can potentially decrease mechanical properties Can improve UV stability Thermal stability Wear resistance Electrical conductivity Flame resistance CTE Toughness Modifiers Increase impact strength Increases the potential for movement within the plastic on impact (creep) Example – ABS Thank You * ? inch ? inch 8 ? inches Failure Zone Gripping Zone Gripping Zone Shear Thickening Shear Thinning Newtonian F/A = ? dv/dx = ?γ Spring Dashpot Permanent Deformation (sandpaper) Intermolecular relationship Intermolecular relationship Stress Strain Increasing shear rate *