Mechanical Properties

Mechanical Properties MFG 355

Forces and Responses • Tensile – applied loads “pull” the sample

Tensile Forces Gripping Zone Gripping Zone Failure Zone ¾ inch ½ inch 8 ½ inches

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

F/A = ŋ dv/dx = ŋγ Shear Thickening Shear Thinning Newtonian 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 = ŋ (dv/dx) • Viscometer

Viscoelasticity • Time/temperature dependant • Plastic stress-strain • a) start point • b) proportional limit • c) yield • d) recovery • e) ultimate failure

Dashpot Permanent Deformation (sandpaper) Spring Mechanical Model of Plastic Behavior

Intermolecular relationship Intermolecular relationship Interpretation of Plastic Behavior

Time Dependence of Plastics Increasing shear rate Stress Strain

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

Mechanical Properties